In monohybrid crosses obeying Mendel's First Law (Law of Segregation) with complete domina… — JAMB UTME

In monohybrid crosses obeying Mendel's First Law (Law of Segregation) with complete dominance, match each parental genotype combination on the left with its corresponding expected offspring ratio on the right.

Heterozygous $\times$ Heterozygous ( $Aa \times Aa$ )Phenotypic ratio of $3 : 1$ ( $75\%$ dominant : $25\%$ recessive)
Heterozygous $\times$ Homozygous recessive ( $Aa \times aa$ )Phenotypic ratio of $1 : 1$ ( $50\%$ dominant : $50\%$ recessive)
Homozygous dominant $\times$ Homozygous recessive ( $AA \times aa$ ) $100\%$ heterozygous offspring ( $Aa$ ), all exhibiting the dominant phenotype
Homozygous dominant $\times$ Heterozygous ( $AA \times Aa$ ) $100\%$ dominant phenotype with a $1 : 1$ genotypic ratio ( $AA : Aa$ )

Cevap

The correct pairings are:

Aa \times Aa

matches with a phenotypic ratio of

3 : 1

;

Aa \times aa

matches with a phenotypic ratio of

1 : 1

;

AA \times aa

matches with

100\%

heterozygous offspring (

Aa

); and

AA \times Aa

matches with

100\%

dominant phenotype and a

1 : 1

genotypic ratio (

AA : Aa

Each monohybrid cross pair follows Mendel's First Law, where allele segregation determines genetic combinations. A heterozygous cross (

Aa \times Aa

) segregates to produce a

3 : 1

dominant-to-recessive phenotypic ratio. A test cross (

Aa \times aa

) produces a

1 : 1

phenotypic ratio. A pure-line cross (

AA \times aa

) results in

100\%

heterozygous

Aa

offspring. A cross of

AA \times Aa

produces

100\%

dominant phenotype offspring with a

1 : 1

genotypic ratio of

AA : Aa

Adım Adım Çözüm

Determine the gametes and offpsring genotypes for

Aa \times Aa

Gametes:

A

and

a

from each parent. Offspring genotypes:

1\,AA : 2\,Aa : 1\,aa

. Under complete dominance,

3

express dominant phenotype and

1

expresses recessive phenotype (

3 : 1

phenotypic ratio).

Mendel's Law of Segregation states that paired alleles separate during gamete formation so each gamete carries only one allele.

Determine the outcome of the test cross

Aa \times aa

Heterozygous parent produces

A

and

a

gametes; homozygous recessive parent produces only

a

gametes. Offspring are

50\%\,Aa

(dominant) and

50\%\,aa

(recessive), giving a

1 : 1

ratio.

Test crosses determine the genotype of an organism displaying the dominant phenotype by crossing it with a homozygous recessive individual.

Determine the outcome of crossing true-breeding parents

AA \times aa

Homozygous dominant parent contributes

A

to all gametes, and homozygous recessive parent contributes

a

. All F1 offspring are

Aa

(

100\%

heterozygous) and show the dominant phenotype.

True-breeding cross produces uniform offspring in the F1 generation.

Determine the outcome of crossing

AA \times Aa

Gametes

A

from the first parent combine with

A

a

from the second parent to produce

50\%\,AA

and

50\%\,Aa

genotypes (

1 : 1

genotypic ratio). All (

100\%

) present the dominant phenotype.

The presence of the dominant allele

A

in all offspring masks the recessive allele

a

Anahtar Kavram

Mendel's First Law of Segregation and Monohybrid Cross Ratios

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