v + cv + ct

May 14, 2018 | Author: Anonymous | Category: Science, Biology, Biochemistry, Genetics
Share Embed Donate


Short Description

Download v + cv + ct...

Description

Chapter 4 overview

Fig. 4-1

Genetic recombination: mixing of genes during gametogenesis that produces gametes with combinations of genes that are different from the combinations received from parents.

• Independent assortment of homologous chromosomes (Anaphase I). Genes on nonhomologous chromosomes (unlinked genes) assort independently.

Fig. 4-6

Using a testcross to distinguish gamete genotypes

Fig. 4-7

50% = independent assortment (genes are not linked) Fig. 4-8

Genetic recombination: mixing of genes during gametogenesis that produces gametes with combinations of genes that are different from the combinations received from parents.

• Independent assortment of homologous chromosomes (Anaphase I). Genes on nonhomologous chromosomes (unlinked genes) assort independently. • Crossing over (recombination among linked genes)

cis linked: both dominant alleles on the same homolog trans linked: dominant alleles on different homologs

Fig. 4-2

Fig. 4-3

Crossing over • Physical exchanges among non-sister chromatids; visualized cytologically as chiasmata • Typically, several crossing over events occur within each tetrad in each meiosis (chiasmata physically hold homologous chromosome together and assure proper segregation at Anaphase I)

p. 115

Crossing over occurs at the four-strand stage (pre-meiotic G2 or very early prophase I)

Fig. 4-4

Crossing over can involve 2, 3, or 4 chromatids in a single meiosis

Fig. 4-5

Crossing over • Physical exchanges among non-sister chromatids; visualized cytologically as chiasmata • Typically, several crossing over events occur within each tetrad in each meiosis (chiasmata physically hold homologous chromosome together and assure proper segregation at Anaphase I) • The sites at which crossing over occur are random • The likelihood that a crossover occurs between any two particular sites (genes) is a function of the physical distance between those two sites

Crossing over usually affects a minority of chromatids in a collection of meioses – recombinants are typically a minority of products Fig. 4-9

View more...

Comments

Copyright © 2017 NANOPDF Inc.
SUPPORT NANOPDF