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Chapter 11

BIOL 1000 Chapter 11 - Mendel, Genes, & Inheritance.docx

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York University
BIOL 1000
Jennifer Steeves

Chapter 11 – Genes, Chromosomes, & Human Genetics 11.1 – Genetic Linkage and Recombination • Genes consist of sequences of nucleotides in DNA and are arranged linearly in chromosomes • Linked Genes – Genes on the same chromosome  Linked together in their transmission from parent to offspring  Inherited in patterns similar to single genes - excluding recombination • Linkage – The phenomenon of genes being located on the same chromosome  Can be changed during recombination during Prophase I in Meiosis Recombination • Mixes up the order of a particular collection of alleles linked on any given chromosome  Results due to exchanging of corresponding alleles between homologues • Likelihood of recombination btwn 2 genes on the same chromosome reflects their distance  ↑ Distance = ↑ Chance of Exchanging Segments = ↑ freq. of recombinant gametes • Linkage Map – Map of chromosome showing the relative locations of genes based on recombination frequencies • Testcrosses (AaBb x aabb) can be used to detect linkage  If all progeny are equally frequent, then the genes are not linked • Gene carried on the same chromosome may not show genetic linkage if they are quite far apart  i.e. crossover almost always occurs between them; their linkage cannot be determined  However linkage can be established by noting linkage to another gene(s) between them 11.2 – Sex-Linked Genes • Autosomes – Chromosomes other than the Sex Chromosomes • Sex Chromosomes – Chromosomes that are diff, in the male & female individuals of a species  Causes sex linkage – pattern of inheritance produced by genes on these chromosomes  Females have 2 copies of the X chromosomes; two alleles for each gene  Females must have 2 copies of a recessive allele to develop the trait  Males have 1 copy of the X chromosome; one allele for each gene – more vulnerable  Only males have an allele for genes carried on the Y chromosome – SRY gene  Males only need to have 1 copy of a recessive allele to develop the trait • Comparing the X and Y chromosomes:  Short pseudoautosomal (homologous) regions interact during meiosis; same genes  Includes cross-over  Non-Homologous (differential) regions; genes are not the same • Sex Linkage is suggested by a particular Non-Mendelian patter of inheritance  The progeny of reciprocal crosses are different • Pedigree – Chart that shows all parents and offspring for as many generations as possible, the sex of individuals in the different generations, and the presence or absence o
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