Three pairs of genes with two alleles each A 1 and A 2 , B 1 and B 2 , and C 1 a

Question

Three pairs of genes with two alleles each A1 and A 2, B1 and B2, and C 1 and C2 control the height of a plant. The alleles of these genes have an additive relationship: each copy of alleles A1, B1, and C 1 contributes 6 cm to plant height, and each copy of alleles A 2, B2, and C2 contributes 3 cm.

A) What is the expected height of plants with the homozygous genotype A1B1C1?

B) What is the expected height of plants with the homozygous genotype A2B2C2?

C) What height is expected in the F1 progeny of a cross between A1A1 B1 B1C1 C1 and A2A2B2B2C2 C2?

D) What is the expected height of a plant with the genotype A1A2 B2B2C1 C2 ?

G) Identify the number of different phenotypes (expected plant heights) that are possible with these three genes.

Explanation / Answer

Let’s consider the copy of allele A1, B1, and C1 as dominant and A2, B2, and C2 as recessive.

A) The three pairs of homozygous dominant alleles are A1A1B1B1C1C1

A1A1B1B1C1C1 = 6 x 6 = 36 cm

B) The three pairs of homozygous recessive alleles are A2A2B2B2C2C2

A2A2B2B2C2C2 = 3 x 6 = 18 cm

C) Progeny of a cross between A1A1B1B1C1C1 and A2A2B2B2C2C2 will result in a F1 hybrid with genotype A1A2B1B2C1C2. So the expected phenotype of the F1will be :-

6 x 3 = 18 cm for the three dominant genes.

3 x 3 = 9 cm for the three recessive genes.

D) The expected phenotype of the plant with genotype A1A2B2B2C1C2

Height contributed byA1C1 = 6 x 2 = 12

Height contributed by A2B2B2C2 = 3 x 4 = 12

12 + 24 = 36.

G) Quantitative inheritance with three pairs of genes will show seven possible phenotypes. One type with all dominant genes, One type with all recessive genes, With five dominant genes, With four dominant genes, With three dominant genes, With two dominant genes, With one dominant gene as given :-

One typewith all dominant genes:- 6 x 6 = 36 cm

One typewith five dominant genes:- 6 x 5 + 3 = 33 cm

One typewith four dominant genes:- 6 x 4 + 3 x 2 = 30 cm

One typewith three dominant genes:- 6 x 3 + 3 x 3 = 27 cm

One typewith two dominant genes:- 6 x 2 + 3 x 4 = 24 cm

One typewith one dominant genes:- 6 + 3 x 5 = 18 cm

One type with all recessive genes:- 3 x 6 = 18 cm

Related Questions

Navigate

• Browse (All)
• Browse T
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.