Flashcards in Reproduction Deck (54):
what is asexual reproduction? what does it occur in?
production of offspring from just one parent.
It occurs in bacteria and fungi and some plants and animals.
how does asexual reproduction work? what is produced? what can differ?
Asexual reproduction works by mitosis.
Daughter cells receive a copy of every parent cell chromosome.
Offspring are clones- genetically identical.
Appearance may differ: environment etc.
what are ways of asexually reproducing?
fission, budding, fragmentation, spore formation, vegetative reproduction, parthenogenesis
what is fission? how does it work? longitudinal? transverse? strobiliation?
Most common form with uni-cellular.
A single parent cell divides in two.
Fission occurs by binary fission in prokaryotes and mitosis in eukaryotes.
Longitudinal fission: cells splits at longest axis.
Transverse fission: splits at shortest axis.
Strobilation: similar to transverse but happens in multicellular organisms- a segment from and when it matures, it detaches.
what is budding? what organisms do it?
In unicellular organisms such as yeasts.
Like fission but division of cytoplasm is unequal.
New organisms arises from an outgrowth.
Also happens in small multicellular organisms- hydra.
what is fragmentation?
Similar to fission but happens in multicellular organisms.
Body splits and each body part generates a new body.
Common in flatworms, marine worms and echinoderms.
Cuttings of plants.
what is spore formation? how does it happen asexually? what is a sporangium?
In some fungi.
Asexual or sexual.
Asexually: mitospores (produced by mitosis).
Spores have a protective coating that allows them to survive.
Sporangium: cluster of spores in a structure that are dispersed when the case disintegrates.
Lands and grows.
what is vegetative reproduction? what does it? rhizomes? stolons? tubers? bulbs and corms? issues?
Rhizomes: underground stems that become new plants.
Stolons: like rhizomes but above ground.
Tubers: swollen underground stems that become plants.
Bulbs and corms: produce lateral buds that develop into new plants.
Outcomplete: displace other species quickly.
Lack of genetic variation.
what is parthenogenesis? how does it work? what is produced?
Development of an egg in the absence of fertilisation.
Occurs only in females.
No males are present.
Double of chromosomes to make a clone.
Genetic recombination increases genetic variation.
what are advantages of asexual reproduction?
Amount of time and energy is small
Population can increase quickly
No need for a sexual partner
Genetically identical- well suited to the environment.
what are disadvantages of asexual reproduction?
Rapid population growth can lead to overcrowding and competition
lack of genetic variation
Lack of genetic diversity could lead to death.
what is cloning?
Production of individuals that have the same genetics as their parent.
A parent cell divides to produce two cells.
how do cuttings and grafts work? how can itbee good? what is rootstock? what is cultivar?
Grow a plant from a cutting of a plant.
Grafting is taking the cut stem of one plant and attacking it the a brach of another.
Rootstock: the plant that hosts the graft.
Grafting can increase yield, tolerance, disease resistance etc.
what is tissue culture? how does it work? what is micropropagation?
Grows large numbers of plants rapidly.
Cells from the parent are grown in a culture with a sterilising solution.
The culture has nutrients and hormones.
micropropagation: cloning of plants from stock plant material.
what are advantages of cuttings, grafts and tissue culture?
Large number of plants.
Can control growth to get preferred characteristics.
New genes can be introduced.
what are disadvantages of cutting, grafts and tissue culture?
Lack of new traits.
Genetic diversity is reduced and some alleles are permanently removed.
what is embryo splitting? how does it work>
Up until the 16-cells stage, each cell can become an entire organism.
If an embryo splits in the early stage, twins, triplets etc. develop.
IVF is used with livestock.
Eggs are fertilised in a petri dish and they multiply before being put in a surrogate mother.
what is nuclear transfer or somatic cell nuclear transfer? where is it used? how does it work? what is an example?
Used in agriculture.
Most advanced method.
Remove nucleus from unfertilised egg and then put back in the mother or surrogate.
Genetically identical to donor of somatic cell.
Dolly the sheep.
what are issues with cloning?
susceptibility to disease, high failure rate, adverse health affects, premature ageing, cloned food products.
how does susceptibility to disease increase with cloning?
Less genetic variation in populations.
Food shortages etc.
Legal issues with cross-contamination between cloned and non-cloned.
how high is cloning failure rate?
Many stages in development can have issues.
what are adverse health affects of cloning?
Impaired immune systems and organ malfunctions.
what are premature ageing issues with cloning?
As cell ages, telomeres on chromosomes shorten.
Same telomere length as parent.
Genetically old at brith.
what are issues with cloned food products?
Have to label.
No cloned food in Australia.
what is sexual reproduction? what organisms do it?
Union of male and female sex cells to create an individual.
Most multicellular, some unicellular.
what are the two main cells that multicellular organisms have?
Multicellular organisms have two main cell types: somatic (body cells) and germ cells (cells able to become gametes).
what are gametes, male and female? where are they formed?
Gametes: specialised sec cells.
Male gametes (sperm), female gametes (eggs). in gonads (reproductive organs).
are gametes haploid or diploid? does this change?
haploid until they fuse together to make a zygote
what is meiosis? what organisms have it?
Cell division that produces gametes is meiosis.
Happens only in eukaryotes and only in gametes.
comparison between mitosis and meiosis on genetic recombination, number of cells and number of chromosomes
No recombination of alleles
Two genetically identical daughter cells
Daughters are diploid like parents
Rearranges alleles, creating variation
Four genetically identical daughter cells
Daughter cells have haploid number, parents have diploid.
why is meiosis also called reduction division?
reduces number of chromosomes.
how are somatic cells chromosomes arranged?
have two sets of homologous (matching) chromosomes, one from each parent.
what chromosomes do gametes receive?
Gametes receive one copy from each homologous pair, mitosis receives a copy of every chromosome.
what chromosomes do humans have?
Humans have 22 pairs of homologous chromosomes and two sex-determining chromosomes, X and Y.
Y determines male development.
what chromosomes do the gametes have? What happens in female gametes?
After meiosis in males, four haploid gametes (sperm) are made and each has 23 chromosomes (one of each homologous chromosome and an X or Y).
In females, only one haploid gamete results (ovum) and the others degenerate this is because of uneven distribution in cytokinesis, so one is large.
Each ovum has 23 chromosomes (one of each homologous chromosome and one X).
what happens in the first division in meiosis?
Prophase 1: chromosomes condense from fine threads. Each one is composed of two chromatids, connected by a centromere. Crossing over if homologous chromosomes happens late in the phase.
Metaphase 1: members of a chromosome pair align, chromatids become apparent and nuclear membrane breaks down.
Anaphase 1: the spindle draws members of each chromosome pair to opposite poles and the cell membrane begins to pinch.
Telophase 1 and cytokinesis: the cytoplasm divides and nuclear membranes form. Two haploid daughters are created but each chromosome is still in its replicated state.
what happens in the second division of meiosis?
Prophase 2: the nuclear envelope breaks down and the meiotic spindle is recreated.
Metaphase 2: chromosomes at each end of the cell move to a central position. Second division begins.
Anaphase 2: the centromeres split, separating the sister chromatids and the single-stranded chromosomes move to opposite poles.
Telophase 2 and cytokinesis: the cytoplasm divides and nuclear membranes reform. Four haploid daughter cells are made.
summary of the first division?
DNA replication occurs in interphase.
During the first division, each chromosome pairs up at the equator with its match.
The pairing is called synapsis.
Each pair of homologous chromosomes has four chromatids.
summary of second division?
Chromosomes align and the chromatids are separated.
Four cells are formed.
how does crossing over happen?
Homologous chromosomes exchange portions of their genetic information.
DNA is cut at equivalent points and they are swapped.
Chiasma: point of crossing- has temporary molecular scaffold that disappears. Long chromosomes may have several.
what is recombination?
production of a chromosome that has new combinations of genes.
what is another way that genetic variation is produced in meiosis?
Homologous chromosome pairs align along the midline of the cell, randomly, meaning that maternal and parental do not line up on the same side of the midline.
The homologues then separate or segregate to opposite ends.
Each gamete then has a random assortment of paternal and maternal chromosomes.
Forms two daughter cells with full chromosomes.
how else in variation increased?
Variability is increased when different combinations come together at fertilisation.
why do gametes only have half the genetic information from their parent cells?
because they only receive a single set of chromosomes.
how can defective gametes arise?
Defective gametes can form from missing, extra or malformed chromosomes.
what is non-disjunction? when can it happen? what does it result in? what is an example?
When chromosomes do not separate.
Can happen in meiosis 1 if members of a pair don’t move away properly or in meiosis 2, if sister chromatids don’t separate.
Gametes then receive two and the other none.
A zygote will have an abnormal number of chromosomes.
Disorder called aneuploidy eg. Non-familial Down syndrome.
In down syndrome this happens with chromosome 21- slower, less muscle development, shorter.
what are deletions?
chromosome segment is lost
what is duplication?
extra chromosome segment (might be from deletion)
what is inversion?
reverses a segment within a chromosome.
what is translocation?
:moves a segment from one chromosome to another, non-homologous one.
what errors are more common and what effects can they have?
Deletions and duplications are more common- crossing over.
Deletions involve essential genes being missing- lethal often.
duplications, translocations and inversions can result in changes in physical characteristics.
what is polyploidy? what can happen? where is it more common? what can it result in? how is this induced?
Having more than two sets of chromosomes in a genome.
Can come from meiosis: gametes end up diploid.
Zygote can end up being 3n or 4n.
Zygotes like this do not survive but in groups of somatic cells it is ok.
More common in plants, because they can survive by asexual reproduction.
A triploid can reproduce asexually but not sexually.
Can result in larger and more productive plants.
Artificial induction uses chemical, colchicine which prevents microtubule formation.
what are advantages of sexual reproduction?
Long-term evolutionary potential
Unfavourable genetic variation is eliminated from the population more efficiently.
Generates genetic variation and selects for beneficial genetic variation more efficiently.
Populations are better able to adapt to and survive changing environmental conditions.