In pea plants, the allele for green pod color (G) is completely dominant over the allele f… — JAMB UTME

In pea plants, the allele for green pod color ( $G$ ) is completely dominant over the allele for yellow pod color ( $g$ ). What is the expected genotypic ratio of the offspring when two heterozygous green-podded plants ( $Gg$ ) are crossed?

$1 : 2 : 1$ Answer
B
$3 : 1$
C
$1 : 1$
D
$9 : 3 : 3 : 1$

Answer

The expected genotypic ratio of the offspring is

1 : 2 : 1

(

1\ GG : 2\ Gg : 1\ gg

In a monohybrid cross between two heterozygous individuals (

Gg \times Gg

), the Law of Segregation dictates that gametes carry either allele

G

g

with equal probability. Combining these gametes produces offspring with genotypes

1/4\ GG

2/4\ Gg

, and

1/4\ gg

, resulting in a genotypic ratio of

1 : 2 : 1

Step-by-Step Solution

Identify parental genotypes

Both parent plants are heterozygous green-podded (

Gg \times Gg

The stem specifies crossing two heterozygous green-podded plants.

Determine gamete formation according to Mendel's Law of Segregation

Each parent produces two types of gametes:

G

and

g

in equal proportions (

50\%

G

50\%

g

Alleles separate during gamete formation so each gamete carries only one allele for the trait.

Perform the monohybrid cross using a Punnett square

Genotype combinations are

1/4\ GG

2/4\ Gg

, and

1/4\ gg

Random fertilization yields

1\ GG

2\ Gg

, and

1\ gg

among four equal outcomes.

State the genotypic ratio

The genotypic ratio is

1 : 2 : 1

The ratio compares homozygous dominant (

GG

), heterozygous (

Gg

), and homozygous recessive (

gg

) combinations.

Key Concept

Monohybrid Cross Genotypic Ratio

Estimated Time:45s

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