Question

Three plant genes, A, B, and C, are linked and occur in the following order. Genetic distances are given as map units (m.u.):

A________10 m.u.______B_____0 m.u.__C

The genes underlie the following phenotypes:

A/_ = blue flowers, a/a = white flowers

B/_ = tall stems, b/b = short stems

C/_ = green leaves, c/c = red leaves

You cross two individuals with the following genotypes:

AbC/AbC x aBc/aBc

You testcross the resulting F1. The proportion of offspring that will have blue flowers is _

Answer 1

Answer:

AbC/AbC x aBc/aBc---Parents

AbC / aBc ----------------F1

AbC / aBc (F1) x abc/abc----Test cross

Expectec double crossover frequency = (Single crossover frequency (SCO) b/w a&b) x (Single crossover frequency (SCO) b/w b&c)

= 10% x 0% = 0

Class of gametes	Phenotype	Frequency of reciprocal pair	Numbers	Frequency of each class	Number of progeny frequency * 100 = %
Parental	AbC	1- all recombinant progeny	1- 0.1 = 0.9	0.45	45% (AbC/abc) = blue, short, green
	aBc			0.45	45% (aBc/abc) = white, tall, red
SCO 1	ABc	RF in region 1 = SCO1 - DCO	SCO1 = 0.1 – 0 = 0.1	0.05	5% (ABc/abc) = blue, tall, red
	abC			0.05	5% (abC/abc) = white, short, green
SCO 2	Abc	RF in region 2 = SCO2 - DCO	SCO2 = 0-0 = 0	0	0% (Abc/abc)
	aBC			0	0%(aBC/abc)
DCO	ABC	(RF in region 1) * (RF in region 2)	0	0	0 (ABC/abc)
	abc			0	0(abc/abc)

The proportion of offspring that will have blue flowers is 45% + 5% = 50%