Question

heredity
directions study the punnett square shown. read each statement. answer the questions on the lines provided.
r r
r rr rr
r rr rr

1. what genotype do both parents have?
2. what letter represents the recessive gene?
3. what letter represents the dominant gene?
4. what genotypes could an offspring have?
5. if r is a recessive gene, which offspring could exhibit the recessive trait?
6. if r is dominant over r, what is the chance that an offspring will exhibit the dominant trait?
7. is an offspring more likely to have a genotype rr or rr? explain.
8. if r is dominant and represents red flowers, which genotypes will have the phenotype for red flowers?
9. if r is dominant and represents red flowers, what is the chance that the offspring with the genotype rr will have white flowers?
10. what is the chance that an offspring will not receive a dominant gene?
11. which genotype has a 50 percent chance of being inherited?
12. could these parents have three offspring with the genotype rr? explain.

directions draw a punnett square for each of the crosses listed below.

1. rr rr
2. yy yy
3. qq qq

Explanation:

Step1: Analyze Punnett - square for parent genotypes

In a Punnett - square, the alleles of the parents are placed on the top and side. Here, since the top row has R and r, and the left - hand column has R and r, both parents have the genotype Rr.

Step2: Identify recessive gene

By convention, the recessive gene is represented by a lowercase letter. So the letter 'r' represents the recessive gene.

Step3: Identify dominant gene

By convention, the dominant gene is represented by an uppercase letter. So the letter 'R' represents the dominant gene.

Step4: List possible offspring genotypes

From the Punnett - square, the possible genotypes of the offspring are RR, Rr, and rr.

Step5: Determine offspring with recessive trait

An offspring will exhibit the recessive trait when it has the homozygous recessive genotype. So the offspring with genotype rr will exhibit the recessive trait.

Step6: Calculate chance of dominant trait

There are 3 out of 4 genotypes (RR, Rr, Rr) that will exhibit the dominant trait. So the chance is $\frac{3}{4}$ or 75%.

Step7: Compare likelihood of Rr and RR

There are 2 Rr genotypes and 1 RR genotype in the Punnett - square. So an offspring is more likely to have the genotype Rr because there are 2 out of 4 possible genotypes that are Rr compared to 1 out of 4 that is RR.

Step8: Determine genotypes for red flowers

Since R is dominant and represents red flowers, the genotypes RR and Rr will have the phenotype for red flowers.

Step9: Determine chance of white flowers for Rr

Since R is dominant for red flowers, an Rr genotype will have red flowers. So the chance of white flowers for Rr is 0.

Step10: Calculate chance of no dominant gene

The genotype with no dominant gene is rr. There is 1 rr out of 4 possible genotypes. So the chance is $\frac{1}{4}$ or 25%.

Step11: Identify 50 - percent chance genotype

The genotype Rr has a 50 - percent chance of being inherited because 2 out of 4 possible genotypes are Rr.

Step12: Analyze possibility of three rr offspring

Yes, these parents could have three offspring with the genotype rr. Each offspring has a $\frac{1}{4}$ chance of having the genotype rr, and the inheritance of each offspring is an independent event.

Step13: Draw Rr x rr Punnett - square

	R	r
r	Rr	rr

Step14: Draw YY x yy Punnett - square

	Y	Y
y	Yy	Yy

Step15: Draw Qq x Qq Punnett - square

	Q	q
q	Qq	qq

Answer:

1. Rr
2. r
3. R
4. RR, Rr, rr
5. rr
6. $\frac{3}{4}$ or 75%
7. Rr, because there are 2 Rr and 1 RR in the Punnett - square.
8. RR, Rr
9. 0
10. $\frac{1}{4}$ or 25%
11. Rr
12. Yes, each offspring has a $\frac{1}{4}$ chance and they are independent events.
13. See above Punnett - square
14. See above Punnett - square
15. See above Punnett - square