In a dihybrid organism with the genotype AaBb, the two gene pairs assort independently dur… — JAMB UTME

In a dihybrid organism with the genotype $AaBb$ , the two gene pairs assort independently during meiosis according to Mendel's Second Law. What is the expected phenotypic or genotypic ratio of the gametes produced by this individual?

$1\ AB : 1\ Ab : 1\ aB : 1\ ab$ Answer
B
$9\ AB : 3\ Ab : 3\ aB : 1\ ab$
C
$3\ AB : 1\ ab$
D
$1\ Aa : 1\ Bb$

Answer

The expected ratio of gametes produced is 1 AB : 1 Ab : 1 aB : 1 ab.

The correct answer states a 1:1:1:1 ratio of

AB

Ab

aB

, and

ab

. A dihybrid organism heterozygous for two unlinked genes (

AaBb

) undergoes independent assortment during meiosis. Allele

A

a

has a 50% chance of combining with allele

B

b

, generating four distinct haploid gametes in equal proportions (25% each).

Step-by-Step Solution

Determine the possible allele combinations for gamete formation from genotype

AaBb

Gene

A

produces alleles

A

and

a

; Gene

B

produces alleles

B

and

b

Meiosis separates homologous chromosomes so each gamete receives one allele per gene.

Apply Mendel's Law of Independent Assortment to combine alleles from both genes.

The four possible gamete combinations are

AB

Ab

aB

, and

ab

Alleles of unlinked genes segregate independently into gametes.

Calculate the probability of each gamete combination.

Each combination has a probability of

\frac{1}{2} \times \frac{1}{2} = \frac{1}{4}

, yielding a ratio of

1 : 1 : 1 : 1

Since segregation of each allele pair is equally likely, all four gamete types occur in equal frequencies.

Key Concept

Mendel's Law of Independent Assortment states that alleles of different genes segregate independently of one another during gamete formation, resulting in equal proportions of all possible haploid allele combinations.

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