Question

1. In cattle, hornless (H) is dominant over horned (h) and black (B) is
dominant over red (b). Consider that these two pairs of genes assort
independently. (i) What proportion of the offspring from the cross,
BbHh X bbhh, would be black and hornless? (ii) From the cross Bbhh X
Bbhh, how many will be (a) black and horned, and (b) red and horned?​

Answer 1

Explanation:

Dear Student,

Dihybrid cross will be performed between the alleles from dominant black hornless cattle and red horned cattle, so as to find the proportion of black hornless cattle offsprings.

Answer 2

i) Proportion of offspring  of the offspring from the cross BbHh X bbhh that would be black and hornless is 25%

                                           $BbHh X bbhh$

Gametes of BbHh are     $BH bH Bh bh$

gametes of bbhh   are     $bh$

By use of punett square

we will get the ratio genotypic and phenotypic ratio of -

$BbHh(Black hornless) : Bbhh(black horned) : bbHh(red hornless) : bbhh(Red horned)$

                                     $1 : 1 : 1 : 1$

Hance 25% of total number of the cattle from the cross will be Black and Hornless

ii) Total black and horned are  3 or 75% of total and Red and Horned would be 1 or 25% of total

here it is how

Parental generation genotype $Bbhh X Bbhh$

Gametes of Bbhh are                $Bh , bh$

By use of punnet square as shown in image 2

we will get

1) genotypic ratio of $BBhh : Bbhh : bbhh$            

                                          $1 : 2 : 1$

2) phenotypic ratio of   $Black horned : Red horned$

                                                   $3 : 1$

hance total no of offspring that would be black and horned are 3 or 75% of total and Red and Horned would be 1 or 25% of total

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