Dihybrid Cross

Question 1

What is the dominant trait discussed in the text?

Answer 1

Dimples

Dimples are indicated as a dominant trait in genetic crosses.

Question 2

What are the genotypes of the offspring from a heterozygous male and a homozygous dominant female?

Answer 2

AA, Aa

The ratios of the genotypes are 2 AA : 2 Aa : 0 aa.

Question 3

What is the genotype ratio for AA, Aa, and aa in the offspring?

Answer 3

AA: 50%, Aa: 50%, aa: 0%

This translates to 2/4 for AA and 2/4 for Aa.

Question 4

Define a dihybrid cross.

Answer 4

A cross among two traits

‘DI’ means two, and ‘HYBRID’ refers to combination.

Question 5

What are dihybrid Punnett squares used for?

Answer 5

To determine probability for two traits

They serve as prediction tools in genetics.

Question 6

What is the genotype of the male in the dihybrid cross example?

Answer 6

Heterozygous for dimples and freckles (FfDd)

The female is recessive for both traits (ffdd).

Question 7

What method is suggested for determining allelic combinations among gametes?

Answer 7

Foil method

This method helps in organizing parental alleles.

Question 8

How many possible combinations can be formed from FfDd x ffdd?

Answer 8

4 combinations

The allele combinations are FD, Fd, fD, fd.

Question 9

What percentage of offspring is predicted to have freckles (F) AND dimples (D)?

Answer 9

25%

This is equivalent to 4 out of 16 offspring.

Question 10

What percentage of offspring is predicted to have freckles (F) but NO dimples (d)?

Answer 10

25%

This is also equal to 4 out of 16 offspring.

Question 11

What percentage of offspring is predicted to have dimples (D) but NO freckles (f)?

Answer 11

25%

Again, this is 4 out of 16 offspring.

Question 12

What percentage of offspring is predicted to have no freckles (f) nor dimples (d)?

Answer 12

25%

This results in 4 out of 16 offspring.

Question 13

What ratios are seen in Mendelian genetics for monohybrid crosses?

Answer 13

3:1 for dominant:recessive and 1:2:1 for homozygous dominant:heterozygous:homozygous recessive

These ratios are consistent across experiments.

Question 14

What pattern is observed in dihybrid crosses among two heterozygous individuals?

Answer 14

9:3:3:1 ratio

This pattern applies to traits like tail length and fur color in cats.

Question 15

In guinea pigs, what trait is dominant in terms of hair length?

Answer 15

Short hair (S)

Long hair (s) is recessive.

Question 16

What is the parental cross genotype in the guinea pig example?

Answer 16

SsBb x SsBb

Both parents are heterozygous for both traits.