Agricultural breeders often apply Mendelian genetics to select desirable traits in farm an… — JAMB UTME

Agricultural breeders often apply Mendelian genetics to select desirable traits in farm animals. A livestock breeder crosses two cattle that are both heterozygous for high milk production ( $Mm$ ) and disease resistance ( $Rr$ ). Assuming independent assortment of these dominant autosomal traits, what proportion of the offspring is expected to display both high milk production and disease resistance?

$\frac{9}{16}$ Answer
B
$\frac{3}{4}$
C
$\frac{3}{16}$
D
$\frac{1}{16}$

Answer

\frac{9}{16}

of the offspring will display both dominant traits (high milk production and disease resistance).

Crossing two dihybrid individuals (

MmRr \times MmRr

) produces offspring with a phenotypic ratio of 9 (both dominant) : 3 (dominant/recessive) : 3 (recessive/dominant) : 1 (both recessive). Therefore,

\frac{9}{16}

of the offspring inherit both high milk production and disease resistance.

Step-by-Step Solution

Determine the probability of expressing the dominant phenotype for the first trait (milk production).

From

Mm \times Mm

, the probability of high milk yield (

M\_

) is

\frac{3}{4}

Genotypes

MM

Mm

, and

Mm

out of

MM, Mm, Mm, mm

express the dominant phenotype.

Determine the probability of expressing the dominant phenotype for the second trait (disease resistance).

From

Rr \times Rr

, the probability of disease resistance (

R\_

) is

\frac{3}{4}

Genotypes

RR

Rr

, and

Rr

out of

RR, Rr, Rr, rr

express the dominant phenotype.

Apply the product rule of probability for independent assortment.

\frac{3}{4} \times \frac{3}{4} = \frac{9}{16}

The inheritance of milk yield and disease resistance assort independently during gamete formation.

Key Concept

Selective breeding using Mendelian dihybrid inheritance principles to combine desirable agricultural traits.

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