3-15-10 IN

Explain the purpose of a punnett square. Create your own monohybrid cross

3-15-10 Through

Analysis questions

OUT Study guide Look through your

notes preparing for the test. Begin to think about questions to ask me.

1. Predict the possible phenotypes and genotypes of the offspring from a mating of two beagles. A heterozygous female with the dominant phenotype for droopy ears (D) mates with a male with recessive phenotype for upright ears (d).

Predictions: Phenotypes-- 50% droopy 50% upright Genotypes --- 50% Dd(heterozygous)

50% dd(homozygous)

Dd dd

Dd dd

D d

d

d

2. Describe the role of a Punnett square in predicting the potential ratio of genotypes that may result from a particular cross.

3. Recall that crossing-over causes some genes on the same chromosome to assort independently. What relationship might you expect between the spacing of genes on the chromosome and their frequency of independent assortment?

4. Remember that the gene for eye color in fruit flies is linked to the X chromosome. Predict F1 and F2 results of a initial mating between a homozygous red-eyed female and a white-eyed male.

XRXr XRXr

XRY XRY

XR XR

Xr

Y

F1

Predictions:

Genotypes: 100% males XRY 100% females XRXr

Phenotypes: males are Red-eyed

females are red-eyed

XRXR XRXr

XRY XrY

XR Xr

XR

Y

F2

Predictions:

Genotypes: If male, 50% XRY 50% XrY If female, 50% XRXR 50% XRXr

Phenotypes: Females are red-eyed, 50% males are red-eyed, 50% males are white-eyed

5. Explain why males are more likely than females to display the phenotypes associated with X-linked recessive traits.

6. Use your knowledge of X-linked traits to explain the inheritance of hemophilia in the story A royal tragedy.

7. Consider how tall you are. How tall will you likely be when you are fully grown? How tall might you have been if you were raised in a very different situation? How do your genes and the environment interact to determine how tall you will be?