Dihybrid Cross (Lecture 6)

Question 1

Let’s look at 2 traits: Seed shape (round or wrinkled) and seed colour (yellow or green). What would the P generation look like for round, yellow seeds and wrinkled, green seeds

Answer 1

Question 2

Given gametes:

RY ry Ry rY

After self-fertilization what would the F2 generation look like? What is the phenotypic ratio?

Answer 2

Phenotypic ratio:

9 round, yellow:

3 round, green:

3 wrinkled, yellow:

1 wrinkled, green

Question 3

In G1 phase we have

R r Y y

Where each cell contains two pairs of homologous chromosomes what happens in S phase after Chromosome replication?

Answer 3

RR rr YY yy

Question 4

In anaphase 1 of meiosis what happens to

RR rr YY yy

Answer 4

In anaphase 1 of meiosis, each pair of homologous chromosomes separates independently

Question 5

After anaphase 1 what happens to the homologous chromosomes?

Answer 5

They go into anaphase II, so genes located on different pairs of chromosomes assort independently, producing different combinations of alleles in the gametes. 8 gametes total, but there are duplicates.

Question 6

8 Gametes total, but there are duplicates, what does this mean?

Answer 6

So essentially, there are 4 possible genotypes or 4 different gametes

Question 7

Given this (round, yellow) X (round, yellow) The dihybrid cross is broken into two monohybrid crosses and the probability of each character is determined. What is the expected proportions for first character (shape)?

Draw punnet square and list the genotype and phenotype for each probability.

(Hint: Rr X Rr)

Answer 7

Genotype:

Probability of being RR = 0.25% (1/4)

Probability of being Rr- 0.50% (1/2)

Probability of being rr = 0.25% (1/4)

Phenotype:

Probability of being round = Probability of being RR OR Rr

Probability of being RR= 1/4; Rr = 1/2

Therefore probability of being round = 1/4 + 1/2 = 3/4

Probability of being wrinkled = 1/4

Question 8

Given this (round, yellow) X (round, yellow) The dihybrid cross is broken into two monohybrid crosses and the probability of each character is determined. What is the expected proportions for the second character (colour)?

Draw punnet square and list the phenotype for each probability.

(Hint: Yy X Yy)

Answer 8

Probability of being yellow = 0.75% (3/4)

Probability of being green = 0.25% (1/4)

Question 9

Given… what is

The probability of being:

Round and yellow?

Round and green?

Wrinkled or Round?

Yellow or green?

Answer 9

Round and yellow = 3/4 x 3/4 = 9/16

Round and green = 3/4 x 1/4 = 3/16

Wrinkled or Round = 3/4 + 1/4 = 4/4

Yellow or green = 3/4 + 1/4 = 4/4