Chapter 9 - Patterns of Inheritance
Chapter 9 - Patterns of Inheritance Biology 110 002
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This 2 page Class Notes was uploaded by Kathleen Maris on Sunday October 11, 2015. The Class Notes belongs to Biology 110 002 at University of South Carolina - Columbia taught by Dr. Dhameja in Fall 2015. Since its upload, it has received 26 views. For similar materials see General Biology in Science at University of South Carolina - Columbia.
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Date Created: 10/11/15
Chapter 9 Patterns of Inheritance 0 Heredity is the way genes are passed down and expressed in an organism O Mendel discovered basic principles of heredity by breeding garden peas in carefully planned experiments He discovered alleles which are variants of a gene His experiments show heredity and alleles for only one set of variations 0 In an experiment via cross pollination Mendel mated two contrasting varieties a process called hybridization When cross contrasting white and purple owered pea plants all of the F1 hybrids the F1 generation were purple When the F1 individuals self pollinated the F2 generation was produced When Mendel crossed the F1 hybrids many of the F2 plants had purple 1F EEI IEKIE HEI I Embrewing 39 r H palm t l Purple White flamr filmslam F1 EaanE rafEian H ri39fi l MI pla rcils had gpu mph TIWEIZIE FE Eainm an 1 E39IE prurl39aaflf rudi 39Il39II39I39IEIEEiEHDHEEEI plants plants Mendel called the purple ower color a dominant trait overpowering the other traits and represented by a capital letter and the white ower color a recessive trait masked by the dominant trait and represented by a lowercase letter 0 An organism with two identical alleles for a gene is said to be homozygous for the gene controlling that characteristic 0 An organism that has two different alleles for a gene is said to be heterozygous for the gene controlling that characteristic Unlike homozygotes heterozygotes are not true breeding 0 Because of the different effects of dominant and recessive alleles an organism s traits do not always reveal its genetic composition A genotype is an organism s genetic makeup I A phenotype is the physical expression of genes I In the ower color example PP and Pp plants have the same phenotype purple but different genotypes Mendel s law of segregation states that the two alleles for a heritable character separate segregate during gamete formation and end up in different gametes I Thus an egg or sperm gets only one of the two alleles that are present in the somatic cells of an organism I Mendel derived the law of segregation by following a single character 0 The F1 offspring produced in this cross were monohybrids individuals that are heterozygous for one character 0 A cross between such heterozygotes is called a monohybrid cross Mendel s law of independent assortment states that each pair of alleles segregates independently of each other pair of alleles during gamete formation I This law re ects the rules of probability like when tossing a coin the outcome of one toss has no impact on the outcome of the next In the same way the alleles of one gene segregates into gametes independently of another gene s alleles I Mendel identified this law by following two characters at the same time I Crossing two true breeding parents differing in two characteristics produced dihybrids in the F1 generation heterozygous for both characteristics Inheritance may deviate from the simple Mendelian patterns when alleles are not completely dominant or recessive incomplete dominance I Complete dominance occurs when phenotypes of the heterozygote and dominant homozygote are identical I In incomplete dominance the phenotype of F1 hybrids is somewhere between the phenotypes of the parents I Example A red ower and a white ower make a pink ower In human sex chromosomes only the ends of the Y chromosome have regions that are homologous with the X chromosome I The SRY gene on the Y chromosome cods for the development of testes I Each egg contains an X chromosome but a sperm may contain either an X or a Y chromosome I Other animals have different methods of sex determination