adriencleme/openstax_sciq_noformula_split · Datasets at Hugging Face

text stringlengths 2 3.56k	source stringclasses 725 values
chiasmata : (singular,chiasma) the structure that forms at the crossover points after genetic material is exchanged	https://openstax.org/books/biology/pages/11-key-terms
cohesin : proteins that form a complex that seals sister chromatids together at their centromeres until anaphase II of meiosis	https://openstax.org/books/biology/pages/11-key-terms
crossover : exchange of genetic material between non-sister chromatids resulting in chromosomes that incorporate genes from both parents of the organism	https://openstax.org/books/biology/pages/11-key-terms
diploid-dominant : life-cycle type in which the multicellular diploid stage is prevalent	https://openstax.org/books/biology/pages/11-key-terms
fertilization : union of two haploid cells from two individual organisms	https://openstax.org/books/biology/pages/11-key-terms
gametophyte : a multicellular haploid life-cycle stage that produces gametes	https://openstax.org/books/biology/pages/11-key-terms
germ cells : specialized cell line that produces gametes, such as eggs or sperm	https://openstax.org/books/biology/pages/11-key-terms
haploid-dominant : life-cycle type in which the multicellular haploid stage is prevalent	https://openstax.org/books/biology/pages/11-key-terms
interkinesis : (also,interphase II) brief period of rest between meiosis I and meiosis II	https://openstax.org/books/biology/pages/11-key-terms
life cycle : the sequence of events in the development of an organism and the production of cells that produce offspring	https://openstax.org/books/biology/pages/11-key-terms
meiosis : a nuclear division process that results in four haploid cells	https://openstax.org/books/biology/pages/11-key-terms
meiosis I : first round of meiotic cell division; referred to as reduction division because the ploidy level is reduced from diploid to haploid	https://openstax.org/books/biology/pages/11-key-terms
meiosis II : second round of meiotic cell division following meiosis I; sister chromatids are separated into individual chromosomes, and the result is four unique haploid cells	https://openstax.org/books/biology/pages/11-key-terms
recombination nodules : protein assemblies formed on the synaptonemal complex that mark the points of crossover events and mediate the multistep process of genetic recombination between non-sister chromatids	https://openstax.org/books/biology/pages/11-key-terms
reduction division : nuclear division that produces daughter nuclei each having one-half as many chromosome sets as the parental nucleus; meiosis I is a reduction division	https://openstax.org/books/biology/pages/11-key-terms
somatic cell : all the cells of a multicellular organism except the gametes or reproductive cells	https://openstax.org/books/biology/pages/11-key-terms
spore : haploid cell that can produce a haploid multicellular organism or can fuse with another spore to form a diploid cell	https://openstax.org/books/biology/pages/11-key-terms
sporophyte : a multicellular diploid life-cycle stage that produces haploid spores by meiosis	https://openstax.org/books/biology/pages/11-key-terms
synapsis : formation of a close association between homologous chromosomes during prophase I	https://openstax.org/books/biology/pages/11-key-terms
synaptonemal complex : protein lattice that forms between homologous chromosomes during prophase I, supporting crossover	https://openstax.org/books/biology/pages/11-key-terms
tetrad : two duplicated homologous chromosomes (four chromatids) bound together by chiasmata during prophase I	https://openstax.org/books/biology/pages/11-key-terms
Working with garden pea plants, Mendel found that crosses between parents that differed by one trait produced F1offspring that all expressed the traits of one parent. Observable traits are referred to as dominant, and non-expressed traits are described as recessive. When the offspring in Mendelâs experiment were self-crossed, the F2offspring exhibited the dominant trait or the recessive trait in a 3:1 ratio, confirming that the recessive trait had been transmitted faithfully from the original P0parent. Reciprocal crosses generated identical F1and F2offspring ratios. By examining sample sizes, Mendel showed that his crosses behaved reproducibly according to the laws of probability, and that the traits were inherited as independent events.	https://openstax.org/books/biology/pages/12-chapter-summary
Two rules in probability can be used to find the expected proportions of offspring of different traits from different crosses. To find the probability of two or more independent events occurring together, apply the product rule and multiply the probabilities of the individual events. The use of the word âandâ suggests the appropriate application of the product rule. To find the probability of two or more events occurring in combination, apply the sum rule and add their individual probabilities together. The use of the word âorâ suggests the appropriate application of the sum rule.	https://openstax.org/books/biology/pages/12-chapter-summary
When true-breeding or homozygous individuals that differ for a certain trait are crossed, all of the offspring will be heterozygotes for that trait. If the traits are inherited as dominant and recessive, the F1offspring will all exhibit the same phenotype as the parent homozygous for the dominant trait. If these heterozygous offspring are self-crossed, the resulting F2offspring will be equally likely to inherit gametes carrying the dominant or recessive trait, giving rise to offspring of which one quarter are homozygous dominant, half are heterozygous, and one quarter are homozygous recessive. Because homozygous dominant and heterozygous individuals are phenotypically identical, the observed traits in the F2offspring will exhibit a ratio of three dominant to one recessive.	https://openstax.org/books/biology/pages/12-chapter-summary
Alleles do not always behave in dominant and recessive patterns. Incomplete dominance describes situations in which the heterozygote exhibits a phenotype that is intermediate between the homozygous phenotypes. Codominance describes the simultaneous expression of both of the alleles in the heterozygote. Although diploid organisms can only have two alleles for any given gene, it is common for more than two alleles of a gene to exist in a population. In humans, as in many animals and some plants, females have two X chromosomes and males have one X and one Y chromosome. Genes that are present on the X but not the Y chromosome are said to be X-linked, such that males only inherit one allele for the gene, and females inherit two. Finally, some alleles can be lethal. Recessive lethal alleles are only lethal in homozygotes, but dominant lethal alleles are fatal in heterozygotes as well.	https://openstax.org/books/biology/pages/12-chapter-summary
Mendel postulated that genes (characteristics) are inherited as pairs of alleles (traits) that behave in a dominant and recessive pattern. Alleles segregate into gametes such that each gamete is equally likely to receive either one of the two alleles present in a diploid individual. In addition, genes are assorted into gametes independently of one another. That is, alleles are generally not more likely to segregate into a gamete with a particular allele of another gene. A dihybrid cross demonstrates independent assortment when the genes in question are on different chromosomes or distant from each other on the same chromosome. For crosses involving more than two genes, use the forked line or probability methods to predict offspring genotypes and phenotypes rather than a Punnett square.	https://openstax.org/books/biology/pages/12-chapter-summary
Although chromosomes sort independently into gametes during meiosis, Mendelâs law of independent assortment refers to genes, not chromosomes, and a single chromosome may carry more than 1,000 genes. When genes are located in close proximity on the same chromosome, their alleles tend to be inherited together. This results in offspring ratios that violate Mendel's law of independent assortment. However, recombination serves to exchange genetic material on homologous chromosomes such that maternal and paternal alleles may be recombined on the same chromosome. This is why alleles on a given chromosome are not always inherited together. Recombination is a random event occurring anywhere on a chromosome. Therefore, genes that are far apart on the same chromosome are likely to still assort independently because of recombination events that occurred in the intervening chromosomal space.	https://openstax.org/books/biology/pages/12-chapter-summary
Whether or not they are sorting independently, genes may interact at the level of gene products such that the expression of an allele for one gene masks or modifies the expression of an allele for a different gene. This is called epistasis.	https://openstax.org/books/biology/pages/12-chapter-summary
allele : gene variations that arise by mutation and exist at the same relative locations on homologous chromosomes	https://openstax.org/books/biology/pages/12-key-terms
autosomes : any of the non-sex chromosomes	https://openstax.org/books/biology/pages/12-key-terms
blending theory of inheritance : hypothetical inheritance pattern in which parental traits are blended together in the offspring to produce an intermediate physical appearance	https://openstax.org/books/biology/pages/12-key-terms
codominance : in a heterozygote, complete and simultaneous expression of both alleles for the same characteristic	https://openstax.org/books/biology/pages/12-key-terms
continuous variation : inheritance pattern in which a character shows a range of trait values with small gradations rather than large gaps between them	https://openstax.org/books/biology/pages/12-key-terms
dihybrid : result of a cross between two true-breeding parents that express different traits for two characteristics	https://openstax.org/books/biology/pages/12-key-terms
discontinuous variation : inheritance pattern in which traits are distinct and are transmitted independently of one another	https://openstax.org/books/biology/pages/12-key-terms
dominant : trait which confers the same physical appearance whether an individual has two copies of the trait or one copy of the dominant trait and one copy of the recessive trait	https://openstax.org/books/biology/pages/12-key-terms
dominant lethal : inheritance pattern in which an allele is lethal both in the homozygote and the heterozygote; this allele can only be transmitted if the lethality phenotype occurs after reproductive age	https://openstax.org/books/biology/pages/12-key-terms
epistasis : antagonistic interaction between genes such that one gene masks or interferes with the expression of another	https://openstax.org/books/biology/pages/12-key-terms
F1 : first filial generation in a cross; the offspring of the parental generation	https://openstax.org/books/biology/pages/12-key-terms
F2 : second filial generation produced when F1individuals are self-crossed or fertilized with each other	https://openstax.org/books/biology/pages/12-key-terms
genotype : underlying genetic makeup, consisting of both physically visible and non-expressed alleles, of an organism	https://openstax.org/books/biology/pages/12-key-terms
hemizygous : presence of only one allele for a characteristic, as in X-linkage; hemizygosity makes descriptions of dominance and recessiveness irrelevant	https://openstax.org/books/biology/pages/12-key-terms
heterozygous : having two different alleles for a given gene on the homologous chromosome	https://openstax.org/books/biology/pages/12-key-terms
homozygous : having two identical alleles for a given gene on the homologous chromosome	https://openstax.org/books/biology/pages/12-key-terms
hybridization : process of mating two individuals that differ with the goal of achieving a certain characteristic in their offspring	https://openstax.org/books/biology/pages/12-key-terms
incomplete dominance : in a heterozygote, expression of two contrasting alleles such that the individual displays an intermediate phenotype	https://openstax.org/books/biology/pages/12-key-terms
law of dominance : in a heterozygote, one trait will conceal the presence of another trait for the same characteristic	https://openstax.org/books/biology/pages/12-key-terms
law of independent assortment : genes do not influence each other with regard to sorting of alleles into gametes; every possible combination of alleles is equally likely to occur	https://openstax.org/books/biology/pages/12-key-terms
law of segregation : paired unit factors (i.e., genes) segregate equally into gametes such that offspring have an equal likelihood of inheriting any combination of factors	https://openstax.org/books/biology/pages/12-key-terms
linkage : phenomenon in which alleles that are located in close proximity to each other on the same chromosome are more likely to be inherited together	https://openstax.org/books/biology/pages/12-key-terms
model system : species or biological system used to study a specific biological phenomenon to be applied to other different species	https://openstax.org/books/biology/pages/12-key-terms
monohybrid : result of a cross between two true-breeding parents that express different traits for only one characteristic	https://openstax.org/books/biology/pages/12-key-terms
P0 : parental generation in a cross	https://openstax.org/books/biology/pages/12-key-terms
phenotype : observable traits expressed by an organism	https://openstax.org/books/biology/pages/12-key-terms
product rule : probability of two independent events occurring simultaneously can be calculated by multiplying the individual probabilities of each event occurring alone	https://openstax.org/books/biology/pages/12-key-terms
Punnett square : visual representation of a cross between two individuals in which the gametes of each individual are denoted along the top and side of a grid, respectively, and the possible zygotic genotypes are recombined at each box in the grid	https://openstax.org/books/biology/pages/12-key-terms
recessive : trait that appears âlatentâ or non-expressed when the individual also carries a dominant trait for that same characteristic; when present as two identical copies, the recessive trait is expressed	https://openstax.org/books/biology/pages/12-key-terms
recessive lethal : inheritance pattern in which an allele is only lethal in the homozygous form; the heterozygote may be normal or have some altered, non-lethal phenotype	https://openstax.org/books/biology/pages/12-key-terms
reciprocal cross : paired cross in which the respective traits of the male and female in one cross become the respective traits of the female and male in the other cross	https://openstax.org/books/biology/pages/12-key-terms
sex-linked : any gene on a sex chromosome	https://openstax.org/books/biology/pages/12-key-terms
sum rule : probability of the occurrence of at least one of two mutually exclusive events is the sum of their individual probabilities	https://openstax.org/books/biology/pages/12-key-terms
test cross : cross between a dominant expressing individual with an unknown genotype and a homozygous recessive individual; the offspring phenotypes indicate whether the unknown parent is heterozygous or homozygous for the dominant trait	https://openstax.org/books/biology/pages/12-key-terms
trait : variation in the physical appearance of a heritable characteristic	https://openstax.org/books/biology/pages/12-key-terms
X-linked : gene present on the X, but not the Y chromosome	https://openstax.org/books/biology/pages/12-key-terms
The Chromosomal Theory of inheritance, proposed by Sutton and Boveri, states that chromosomes are the vehicles of genetic heredity. Neither Mendelian genetics nor gene linkage is perfectly accurate; instead, chromosome behavior involves segregation, independent assortment, and occasionally, linkage. Sturtevant devised a method to assess recombination frequency and infer the relative positions and distances of linked genes on a chromosome on the basis of the average number of crossovers in the intervening region between the genes. Sturtevant correctly presumed that genes are arranged in serial order on chromosomes and that recombination between homologs can occur anywhere on a chromosome with equal likelihood. Whereas linkage causes alleles on the same chromosome to be inherited together, homologous recombination biases alleles toward an inheritance pattern of independent assortment.	https://openstax.org/books/biology/pages/13-chapter-summary
The number, size, shape, and banding pattern of chromosomes make them easily identifiable in a karyogram and allows for the assessment of many chromosomal abnormalities. Disorders in chromosome number, or aneuploidies, are typically lethal to the embryo, although a few trisomic genotypes are viable. Because of X inactivation, aberrations in sex chromosomes typically have milder phenotypic effects. Aneuploidies also include instances in which segments of a chromosome are duplicated or deleted. Chromosome structures may also be rearranged, for example by inversion or translocation. Both of these aberrations can result in problematic phenotypic effects. Because they force chromosomes to assume unnatural topologies during meiosis, inversions and translocations are often associated with reduced fertility because of the likelihood of nondisjunction.	https://openstax.org/books/biology/pages/13-chapter-summary
aneuploid : individual with an error in chromosome number; includes deletions and duplications of chromosome segments	https://openstax.org/books/biology/pages/13-key-terms
autosome : any of the non-sex chromosomes	https://openstax.org/books/biology/pages/13-key-terms
centimorgan (cM) : (also, map unit) relative distance that corresponds to a recombination frequency of 0.01	https://openstax.org/books/biology/pages/13-key-terms
Chromosomal Theory of Inheritance : theory proposing that chromosomes are the vehicles of genes and that their behavior during meiosis is the physical basis of the inheritance patterns that Mendel observed	https://openstax.org/books/biology/pages/13-key-terms
chromosome inversion : detachment, 180Â° rotation, and reinsertion of a chromosome arm	https://openstax.org/books/biology/pages/13-key-terms
euploid : individual with the appropriate number of chromosomes for their species	https://openstax.org/books/biology/pages/13-key-terms
homologous recombination : process by which homologous chromosomes undergo reciprocal physical exchanges at their arms, also known as crossing over	https://openstax.org/books/biology/pages/13-key-terms
karyogram : photographic image of a karyotype	https://openstax.org/books/biology/pages/13-key-terms
karyotype : number and appearance of an individuals chromosomes; includes the size, banding patterns, and centromere position	https://openstax.org/books/biology/pages/13-key-terms
monosomy : otherwise diploid genotype in which one chromosome is missing	https://openstax.org/books/biology/pages/13-key-terms
nondisjunction : failure of synapsed homologs to completely separate and migrate to separate poles during the first cell division of meiosis	https://openstax.org/books/biology/pages/13-key-terms
nonparental (recombinant) type : progeny resulting from homologous recombination that exhibits a different allele combination compared with its parents	https://openstax.org/books/biology/pages/13-key-terms
paracentric : inversion that occurs outside of the centromere	https://openstax.org/books/biology/pages/13-key-terms
parental types : progeny that exhibits the same allelic combination as its parents	https://openstax.org/books/biology/pages/13-key-terms
pericentric : inversion that involves the centromere	https://openstax.org/books/biology/pages/13-key-terms
polyploid : individual with an incorrect number of chromosome sets	https://openstax.org/books/biology/pages/13-key-terms
recombination frequency : average number of crossovers between two alleles; observed as the number of nonparental types in a population of progeny	https://openstax.org/books/biology/pages/13-key-terms
translocation : process by which one segment of a chromosome dissociates and reattaches to a different, nonhomologous chromosome	https://openstax.org/books/biology/pages/13-key-terms
trisomy : otherwise diploid genotype in which one entire chromosome is duplicated	https://openstax.org/books/biology/pages/13-key-terms
X inactivation : condensation of X chromosomes into Barr bodies during embryonic development in females to compensate for the double genetic dose	https://openstax.org/books/biology/pages/13-key-terms
DNA was first isolated from white blood cells by Friedrich Miescher, who called it nuclein because it was isolated from nuclei. Frederick Griffith's experiments with strains ofStreptococcus pneumoniaeprovided the first hint that DNA may be the transforming principle. Avery, MacLeod, and McCarty proved that DNA is required for the transformation of bacteria. Later experiments by Hershey and Chase using bacteriophage T2 proved that DNA is the genetic material. Chargaff found that the ratio of A = T and C = G, and that the percentage content of A, T, G, and C is different for different species.	https://openstax.org/books/biology/pages/14-chapter-summary
The currently accepted model of the double-helix structure of DNA was proposed by Watson and Crick. Some of the salient features are that the two strands that make up the double helix are complementary and anti-parallel in nature. Deoxyribose sugars and phosphates form the backbone of the structure, and the nitrogenous bases are stacked inside. The diameter of the double helix, 2 nm, is uniform throughout. A purine always pairs with a pyrimidine; A pairs with T, and G pairs with C. One turn of the helix has ten base pairs. During cell division, each daughter cell receives a copy of the DNA by a process known as DNA replication. Prokaryotes are much simpler than eukaryotes in many of their features. Most prokaryotes contain a single, circular chromosome. In general, eukaryotic chromosomes contain a linear DNA molecule packaged into nucleosomes, and have two distinct regions that can be distinguished by staining, reflecting different states of packaging and compaction.	https://openstax.org/books/biology/pages/14-chapter-summary
The model for DNA replication suggests that the two strands of the double helix separate during replication, and each strand serves as a template from which the new complementary strand is copied. In conservative replication, the parental DNA is conserved, and the daughter DNA is newly synthesized. The semi-conservative method suggests that each of the two parental DNA strands acts as template for new DNA to be synthesized; after replication, each double-stranded DNA includes one parental or âoldâ strand and one ânewâ strand. The dispersive mode suggested that the two copies of the DNA would have segments of parental DNA and newly synthesized DNA.	https://openstax.org/books/biology/pages/14-chapter-summary
Replication in prokaryotes starts from a sequence found on the chromosome called the origin of replicationâthe point at which the DNA opens up. Helicase opens up the DNA double helix, resulting in the formation of the replication fork. Single-strand binding proteins bind to the single-stranded DNA near the replication fork to keep the fork open. Primase synthesizes an RNA primer to initiate synthesis by DNA polymerase, which can add nucleotides only in the 5' to 3' direction. One strand is synthesized continuously in the direction of the replication fork; this is called the leading strand. The other strand is synthesized in a direction away from the replication fork, in short stretches of DNA known as Okazaki fragments. This strand is known as the lagging strand. Once replication is completed, the RNA primers are replaced by DNA nucleotides and the DNA is sealed with DNA ligase, which creates phosphodiester bonds between the 3'-OH of one end and the 5' phosphate of the other strand.	https://openstax.org/books/biology/pages/14-chapter-summary
Replication in eukaryotes starts at multiple origins of replication. The mechanism is quite similar to prokaryotes. A primer is required to initiate synthesis, which is then extended by DNA polymerase as it adds nucleotides one by one to the growing chain. The leading strand is synthesized continuously, whereas the lagging strand is synthesized in short stretches called Okazaki fragments. The RNA primers are replaced with DNA nucleotides; the DNA remains one continuous strand by linking the DNA fragments with DNA ligase. The ends of the chromosomes pose a problem as polymerase is unable to extend them without a primer. Telomerase, an enzyme with an inbuilt RNA template, extends the ends by copying the RNA template and extending one end of the chromosome. DNA polymerase can then extend the DNA using the primer. In this way, the ends of the chromosomes are protected.	https://openstax.org/books/biology/pages/14-chapter-summary
DNA polymerase can make mistakes while adding nucleotides. It edits the DNA by proofreading every newly added base. Incorrect bases are removed and replaced by the correct base, and then a new base is added. Most mistakes are corrected during replication, although when this does not happen, the mismatch repair mechanism is employed. Mismatch repair enzymes recognize the wrongly incorporated base and excise it from the DNA, replacing it with the correct base. In yet another type of repair, nucleotide excision repair, the incorrect base is removed along with a few bases on the 5' and 3' end, and these are replaced by copying the template with the help of DNA polymerase. The ends of the newly synthesized fragment are attached to the rest of the DNA using DNA ligase, which creates a phosphodiester bond.	https://openstax.org/books/biology/pages/14-chapter-summary
Most mistakes are corrected, and if they are not, they may result in a mutation defined as a permanent change in the DNA sequence. Mutations can be of many types, such as substitution, deletion, insertion, and translocation. Mutations in repair genes may lead to serious consequences such as cancer. Mutations can be induced or may occur spontaneously.	https://openstax.org/books/biology/pages/14-chapter-summary
electrophoresis : technique used to separate DNA fragments according to size	https://openstax.org/books/biology/pages/14-key-terms
helicase : during replication, this enzyme helps to open up the DNA helix by breaking the hydrogen bonds	https://openstax.org/books/biology/pages/14-key-terms
induced mutation : mutation that results from exposure to chemicals or environmental agents	https://openstax.org/books/biology/pages/14-key-terms
lagging strand : during replication, the strand that is replicated in short fragments and away from the replication fork	https://openstax.org/books/biology/pages/14-key-terms
leading strand : strand that is synthesized continuously in the 5'-3' direction which is synthesized in the direction of the replication fork	https://openstax.org/books/biology/pages/14-key-terms
ligase : enzyme that catalyzes the formation of a phosphodiester linkage between the 3' OH and 5' phosphate ends of the DNA	https://openstax.org/books/biology/pages/14-key-terms
mismatch repair : type of repair mechanism in which mismatched bases are removed after replication	https://openstax.org/books/biology/pages/14-key-terms

chiasmata : (singular,chiasma) the structure that forms at the crossover points after genetic material is exchanged

https://openstax.org/books/biology/pages/11-key-terms

cohesin : proteins that form a complex that seals sister chromatids together at their centromeres until anaphase II of meiosis

https://openstax.org/books/biology/pages/11-key-terms

crossover : exchange of genetic material between non-sister chromatids resulting in chromosomes that incorporate genes from both parents of the organism

https://openstax.org/books/biology/pages/11-key-terms

diploid-dominant : life-cycle type in which the multicellular diploid stage is prevalent

https://openstax.org/books/biology/pages/11-key-terms

fertilization : union of two haploid cells from two individual organisms

https://openstax.org/books/biology/pages/11-key-terms

gametophyte : a multicellular haploid life-cycle stage that produces gametes

https://openstax.org/books/biology/pages/11-key-terms

germ cells : specialized cell line that produces gametes, such as eggs or sperm

https://openstax.org/books/biology/pages/11-key-terms

haploid-dominant : life-cycle type in which the multicellular haploid stage is prevalent

https://openstax.org/books/biology/pages/11-key-terms

interkinesis : (also,interphase II) brief period of rest between meiosis I and meiosis II

https://openstax.org/books/biology/pages/11-key-terms

life cycle : the sequence of events in the development of an organism and the production of cells that produce offspring

https://openstax.org/books/biology/pages/11-key-terms

meiosis : a nuclear division process that results in four haploid cells

https://openstax.org/books/biology/pages/11-key-terms

meiosis I : first round of meiotic cell division; referred to as reduction division because the ploidy level is reduced from diploid to haploid

https://openstax.org/books/biology/pages/11-key-terms

meiosis II : second round of meiotic cell division following meiosis I; sister chromatids are separated into individual chromosomes, and the result is four unique haploid cells

https://openstax.org/books/biology/pages/11-key-terms

recombination nodules : protein assemblies formed on the synaptonemal complex that mark the points of crossover events and mediate the multistep process of genetic recombination between non-sister chromatids

https://openstax.org/books/biology/pages/11-key-terms

reduction division : nuclear division that produces daughter nuclei each having one-half as many chromosome sets as the parental nucleus; meiosis I is a reduction division

https://openstax.org/books/biology/pages/11-key-terms

somatic cell : all the cells of a multicellular organism except the gametes or reproductive cells

https://openstax.org/books/biology/pages/11-key-terms

spore : haploid cell that can produce a haploid multicellular organism or can fuse with another spore to form a diploid cell

https://openstax.org/books/biology/pages/11-key-terms

sporophyte : a multicellular diploid life-cycle stage that produces haploid spores by meiosis

https://openstax.org/books/biology/pages/11-key-terms

synapsis : formation of a close association between homologous chromosomes during prophase I

https://openstax.org/books/biology/pages/11-key-terms

synaptonemal complex : protein lattice that forms between homologous chromosomes during prophase I, supporting crossover

https://openstax.org/books/biology/pages/11-key-terms

tetrad : two duplicated homologous chromosomes (four chromatids) bound together by chiasmata during prophase I

https://openstax.org/books/biology/pages/11-key-terms

Working with garden pea plants, Mendel found that crosses between parents that differed by one trait produced F1offspring that all expressed the traits of one parent. Observable traits are referred to as dominant, and non-expressed traits are described as recessive. When the offspring in Mendelâs experiment were self-crossed, the F2offspring exhibited the dominant trait or the recessive trait in a 3:1 ratio, confirming that the recessive trait had been transmitted faithfully from the original P0parent. Reciprocal crosses generated identical F1and F2offspring ratios. By examining sample sizes, Mendel showed that his crosses behaved reproducibly according to the laws of probability, and that the traits were inherited as independent events.

https://openstax.org/books/biology/pages/12-chapter-summary

Two rules in probability can be used to find the expected proportions of offspring of different traits from different crosses. To find the probability of two or more independent events occurring together, apply the product rule and multiply the probabilities of the individual events. The use of the word âandâ suggests the appropriate application of the product rule. To find the probability of two or more events occurring in combination, apply the sum rule and add their individual probabilities together. The use of the word âorâ suggests the appropriate application of the sum rule.

https://openstax.org/books/biology/pages/12-chapter-summary

When true-breeding or homozygous individuals that differ for a certain trait are crossed, all of the offspring will be heterozygotes for that trait. If the traits are inherited as dominant and recessive, the F1offspring will all exhibit the same phenotype as the parent homozygous for the dominant trait. If these heterozygous offspring are self-crossed, the resulting F2offspring will be equally likely to inherit gametes carrying the dominant or recessive trait, giving rise to offspring of which one quarter are homozygous dominant, half are heterozygous, and one quarter are homozygous recessive. Because homozygous dominant and heterozygous individuals are phenotypically identical, the observed traits in the F2offspring will exhibit a ratio of three dominant to one recessive.

https://openstax.org/books/biology/pages/12-chapter-summary

Alleles do not always behave in dominant and recessive patterns. Incomplete dominance describes situations in which the heterozygote exhibits a phenotype that is intermediate between the homozygous phenotypes. Codominance describes the simultaneous expression of both of the alleles in the heterozygote. Although diploid organisms can only have two alleles for any given gene, it is common for more than two alleles of a gene to exist in a population. In humans, as in many animals and some plants, females have two X chromosomes and males have one X and one Y chromosome. Genes that are present on the X but not the Y chromosome are said to be X-linked, such that males only inherit one allele for the gene, and females inherit two. Finally, some alleles can be lethal. Recessive lethal alleles are only lethal in homozygotes, but dominant lethal alleles are fatal in heterozygotes as well.

https://openstax.org/books/biology/pages/12-chapter-summary

Mendel postulated that genes (characteristics) are inherited as pairs of alleles (traits) that behave in a dominant and recessive pattern. Alleles segregate into gametes such that each gamete is equally likely to receive either one of the two alleles present in a diploid individual. In addition, genes are assorted into gametes independently of one another. That is, alleles are generally not more likely to segregate into a gamete with a particular allele of another gene. A dihybrid cross demonstrates independent assortment when the genes in question are on different chromosomes or distant from each other on the same chromosome. For crosses involving more than two genes, use the forked line or probability methods to predict offspring genotypes and phenotypes rather than a Punnett square.

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Although chromosomes sort independently into gametes during meiosis, Mendelâs law of independent assortment refers to genes, not chromosomes, and a single chromosome may carry more than 1,000 genes. When genes are located in close proximity on the same chromosome, their alleles tend to be inherited together. This results in offspring ratios that violate Mendel's law of independent assortment. However, recombination serves to exchange genetic material on homologous chromosomes such that maternal and paternal alleles may be recombined on the same chromosome. This is why alleles on a given chromosome are not always inherited together. Recombination is a random event occurring anywhere on a chromosome. Therefore, genes that are far apart on the same chromosome are likely to still assort independently because of recombination events that occurred in the intervening chromosomal space.

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Whether or not they are sorting independently, genes may interact at the level of gene products such that the expression of an allele for one gene masks or modifies the expression of an allele for a different gene. This is called epistasis.

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allele : gene variations that arise by mutation and exist at the same relative locations on homologous chromosomes