In pea plants, the peas can be rough or smooth , and soft or hard . You do some
ID: 282572 • Letter: I
Question
In pea plants, the peas can be rough or smooth, and soft or hard.
You do some crosses and obtain the following results:
Cross 1: purebred rough, soft pea X purebred smooth, hard pea
F1: all rough, hard
Cross 2: rough, hard F1 X smooth, soft gives
F2:
?????115 rough soft
?????110 smooth hard
?????8 rough hard
?????12 smooth soft
A. Using sing letters of your own choosing, state the genotypesof the:
- parents,
- the F1,
- and each phenotypic class in the F2.
Write genotypes using cis/trans chromosome nomenclature
B. Which F2 progeny inherited non-recombinant gametes from the F1 parent, and which recombinant?
C. Are the genes for roughness and softness linked? If so, what is the recombination frequency between the genes?
Explanation / Answer
A) Let R = rough (dominant), r = smooth (recessive)
Let H = hard (dominant), h = soft (recessive)
Parents are RRhh x rrHH, It is recommended to write this way:
Rh/Rhx rH/rH
F1 are dihybrids: Rh/rH, which are crossed to the tester strain rh/rh
F2 are:
RH/rh rough hard (the gamete from the F1 is RH) nonparental
rH/rh smooth hard (the gamete from the F1 is rH) parental
Rh/rh rough soft (the gamete from the F1 is Rh) parental
Rh/rh smooth soft (the gamete from the F1 is rh) nonparental
B) (Please refers the labels in a). The parental (non-recombinant) types of gametes are Rh and rH, because these allele combinations match the chromosomes of the parents of the F1. The remaining gametes, RH and rh are recombinant.
C) Parental types > nonparental (recombinant) types, therefore, yes, they are linked.
r.f. = # recombinants / total x100 = 8+12 / 8+12+112+110 x100 = 8.2%
rf = 8.2 cM