Post on 21-Jul-2016
description
Chapter 12Chromosomal Basis of Inheritance
Copyright © 2010 Pearson Education Inc.
X
male female
males and females X brother-sister
mate
males females
50% of offspring25%
25%
unexpected resultsexual dimorphism
a a b b
c
d d
a a b b
c cc
d
two copies of eachdifferent gene
only one copy of eachdifferent gene on the Xchromosome
autosomes: chromosomes that are the same in number andmorphology in the two sexes
sex chromosomes: chromosomes that differ in number ormorphology in the two sexes
X and Ychromosome pair although they do not fit the definition of homologous chromosomes
X
male female
brother-sistermate
males
females
50% of offspring25%
25%
Xw
Y Xw+X
w+
Xw
Xw+
Y Xw+
X
Xw+
Xw+
Y
X weggs
sperm
Xw X
w+
Xw+
Xw
Y Y
Xw+
Xw+
red red
redwhite
X-chromosomelinked genes
Xw+
Xw
Y
eggs
spermX X
w+
Xw+
Y Y
Xw
Xw
red red
redred
Xw+
w+
Xw+
parental
F1
X
male female
brother-sistermate
males
females
50% of offspring25%
25%
Xw
Y Xw+X
w+
Xw
Xw+
Y Xw+
X
Xw+
Xw+
Y
X weggs
sperm
Xw X
w+
Xw+
Xw
Y Y
Xw+
Xw+
red red
redwhite
X-chromosomelinked genes
Xw+
Xw
Y
eggs
spermX X
w+
Xw+
Y Y
Xw
Xw
red red
redred
Xw+
w+
Xw+
parental
F1
Xw+
Xw
Xw+X
w+Xw+
Xw
Y
Y
12
X
red eyed male white eyed female
5000 white eyed males 5000 red eyed female
2 red eyed males 2 white eyed females
expected
exceptionaloffspring
Xw+ Y X
w Xw
X
red eyed male white eyed female
5000 white eyed males 5000 red eyed female
2 red eyed males 2 white eyed females
expected
exceptionaloffspring
Xw+ Y X
wX
w
XwY X
w+X
w
Xw+ X
wX
w Yo
Calvin Bridges explanation for the appearance of exceptions nondisjunction of X chromosome
X
red eyed male white eyed female
5000 white eyed males 5000 red eyed female
2 red eyed males 2 white eyed females
expected
exceptionaloffspring
Xw+ Y X
wX
w
XwY X
w+X
w
Xw+ X
wX
w Yo
Calvin Bridges explanation for the appearance of exceptions nondisjunction of X chromosome
nondisjunction: failure of homologues to segregate to opposite poles during anaphase of meiosis I or meiosis II
possible pairingof X and Y chromosomes
sperm
eggs
if the white eyedfemale is normalone would expectall white eyed male and all red eyedfemale offspring
dies
whitefemale
redmale
dies
redfemale
whitemale
redfemale
whitemale