Question

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, pointed 14 red, smooth hape?
What is the recombination frequency between the gene for color and for shape?

Answer 1

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
`$=\frac{\text{total no. of recombination}}{\text{total no. of progeny}}* 100$`

`$=(14+10)/(100) * 100$`

= 24 %

= 24 map units