In maize plants (*Zea mays*), the allele for purple kernels (P) is completely dominant to … — JAMB UTME

In maize plants (*Zea mays*), the allele for purple kernels ( $P$ ) is completely dominant to the allele for yellow kernels ( $p$ ). A true-breeding purple-kernel plant is crossed with a true-breeding yellow-kernel plant. If the $F_1$ plants are self-pollinated, what is the expected genotypic ratio in the $F_2$ generation?

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

Answer

The expected genotypic ratio in the

F_2

generation is

1 : 2 : 1

(

1\ PP : 2\ Pp : 1\ pp

Crossing two heterozygous

F_1

plants (

Pp \times Pp

) yields genotypes

PP

Pp

, and

pp

in the proportions

1/4\ PP

1/2\ Pp

, and

1/4\ pp

. This corresponds to a genotypic ratio of

1 : 2 : 1

Step-by-Step Solution

Determine parental genotypes and

F_1

genotype

True-breeding parents are

PP

and

pp

; all

F_1

offspring are

Pp

Homozygous dominant (

PP

) crossed with homozygous recessive (

pp

) produces offspring that all inherit one

P

and one

p

allele.

Perform the

F_1

self-cross (

Pp \times Pp

)

Gametes

P

and

p

combine to produce

PP

Pp

pP

, and

pp

According to Mendel's Law of Segregation, alleles segregate into gametes with equal probability.

Calculate the genotypic ratio of the

F_2

offspring

Genotypic ratio is

1\ PP : 2\ Pp : 1\ pp

, or

1 : 2 : 1

Grouping offspring by genetic constitution yields 1 homozygous dominant (

PP

), 2 heterozygous (

Pp

), and 1 homozygous recessive (

pp

Key Concept

Monohybrid Cross Genotypic Ratio under Mendel's First Law

Estimated Time:1m 0s

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