A dihybrid genetic question...?

Question

Two plants having red flowers are mated. When their F1 offspring are studied, it is found that 95 have red flowers and 31 have white flowers. What is the genotype of the parents and diagram a cross to support you answer.

Well, i attempted this problem but i don't know how to approach it. I'd appreciate your help-- thank you so much!

Answer 1

We assume that red flower is dominant and white flower is recessive.

Let R (capital) = red Let r (lower-case) = white

One parent: Rr The other parent: Rr
=> as you can see the both have red flowers because they each have a dominant red allele.

Now you do the cross, there are 4 possibilities:

RR, Rr, rR, rr

The first 3 will give you red flowers, and the last one will give you white flower.

The ratio is 3 : 1. If you look at your question, the numbers are 95 and 31, which is roughly 3 : 1.

Does that help? =)

Answer 2

First you know that both flowers are red, lets call the gene for it R, there is another color in the offspring, white, lets call it r. There are more red flowers than white flowers so you can safely say that red is dominant over white. Now since there was both red and white flower offspring you now that each of the adult flowers are heterozygous, meaning one of each gene. This is because in order to have white, you need a genotype of r,r. This is because in order for a recessive to be expressed you need both recessive copies of the gene. So both parents must be R,r. If you do the punnit square you will see that 1/4 of the offspring have r,r. Which is what you needed. Hope that helped.

Answer 3

95 red:31 white is just about the same as 3 red: 1 white.

If you mate two reds and get any white offspring, then white must be recessive. White didn't show in the parents, but it popped up in the offspring.

So red parents that can pass on a white gene must be Rr.

Parents: Rr x Rr
Gametes: first parent R and r; second parent R and r
Punnett square:
first row of answer boxes: RR and Rr
second row of answer boxes: rR and rr.

Answer 4

dihybrid means there are two traits. in an f1 cross the ratio for the genotype will always be 1:2:1:2:4:2:1:2:1. The phenotype is 9:3:3:1. always. The parents of an F1 are always hybrids (From P1)
ex: RrYy
The p1 parents would be RRYY and rryy
(y is just a random variable)