Biology: In a plant, leaf color and leaf shape are controlled by two linked genes Leaves of the wild-type plant are red. A recessive mutation in this gene causes white leaves. Wild-type leaves are pointed, and a recessive mutation in this gene causes them to be smooth. The following crosses were performed Cross 1: pure breeding white, smooth X pure breeding red, pointed gives: all red, pointed Cross 2: red, pointed F1 X pure breeding white, smooth (test cross gives: 40 white, smooth 36 red, pointed 10 white,

In a plant, leaf color and leaf shape are controlled

barboursj

17.03.2021

Solution :

Red is dominant over the white leaves and pointed is dominant over smooth.

Red = R , white = r

Pointed = P , smooth = p

Red, pointed x white,smooth ------ Parents

RRPP rrpp

RP rp ----------------- Gametes

RrPp -------- $F_1$

(red, pointed)

When this $F_1$ is test crossed,

RrPp x rrpp ---- $F_1$ test cross

Gametes → rp

RP ---------- RrPp - red, pointed - 36 parental type

Rp ---------- Rprp - red, smooth - 14 re- combination

rP ----------- rrPp - white pointed - 10 re- combination

rp ----------- rrpp - white, smooth - 40 - parental type

Total = 100

As this ratio is deviating from 1:1:1:1, it indicated the two genes are linked.

Linkage strength = percentage of crossing over = map distance between the genes.

Percentage crossing = recombination frequency = percentage of recombination.

Recombination frequency $=\frac{\text{total no. of recombination}}{\text{total no. of progeny}}\times 100$

$=\frac{14+10}{100} \times 100$

= 24 %

= 24 map units

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