1
A
A
a
a
B
B
b
b
A a
B b
Meiosis
25% AB
25% Ab
25% aB
25% ab
Independent Assortment and Meiosis
A
Ba
ba
b
A
B
a
b
A
B
50% AB
50% ab
0% aB
0% Ab
Meiosis
Linkage and Meiosis
Crossingover and Recombinantion
Which are the Parental types and which the recombinant types?
A
Ba
ba
b
A
B
A
b
a
B
?% AB
?% ab
?% aB
?% Ab
Meiosis
Partial Linkage and Meiosis
Genetic Distance
• The likelihood of recombination is roughly
proportional to the distance two genes are apart.
• If two genes are close together on a
chromosome there will be few recombinants.
• If two genes are farther apart on a chromosome
there will be more recombinants.
Genetic Distance
Genetic
Distance =Frequency of
Recombination (Rf)==
# of Recombinants
total # of progeny
In a Testcross
•Units for genetic distance – centimorgans = map units
1 map unit = 1%Rf
An underestimate
of true Rf!!!
