Advanced Genetics Problems

PURPOSE: To predict and compare the genetic variations that will result from a genetic cross.

Codominance occurs when both alleles contribute to the phenotype, leaving a phenotype that is intermediate of the parents.

Example: Red flowers are fertilized by white flowers. The resulting offspring have pink flowers.

PRACTICE:

1.Sickle cell anemia is a codominant disorder, where N stands for normal red blood cells and n stands for sickle-shaped red blood cells. Heterozygous individuals have a phenotype showing both sickle-celled and normal-shaped red blood cells. Cross two people who are heterozygous for this trait. /

**Remember to express probability inpercentage form.

a. What is the probability their offspring are likely to have sickle cell anemia? ______

b. What is the probability their offspring will have both normal and sickle cell-shaped red blood cells?

c. What is the probability their offspring will be able to pass along the sickle trait to their children?

2.Multiple alleles occur when a trait has more than just a dominant and recessive allele. For example, coat color in rabbits is determined by a single gene with four different alleles: C, cch, ch, c . The combination of two of these alleles determines the rabbit’s phenotype.

a. If a homozygous Himalayan rabbit and an albino rabbit mate, what are the possible phenotypes of their offspring?

3.Blood types are controlled by multiple alleles. Look at the chart below containing blood types for the human population. Type A and B are both dominant, while type O is recessive.

BLOOD TYPE / GENOTYPES
A / IAIA, IAi
B / IBIB, IBi
AB / IAIB
O / ii
a. A man with type O blood marries a woman with type AB blood. What is the probability that they will have a child with type A blood?
(Show your work in a Punnett Square.) /

b. If a child has type A blood and the father has type AB blood, what are the child’s possible genotypes?

______

c. If a child has type AB blood and the mother has type B blood, what blood type does the father have?

______

d. Vincent has type A blood and his mother has type O blood. What is his genotype? ______

e. Christy has type B blood and her father has type O blood. What is her genotype? ______

f. If Vincent from problem 3 and Christy from problem 4 have children, what are the children’s likely genotypes?
______
(Show your work in a Punnett Square.) /

4.Sex-linked genes are so-called because they are located on one of the sex chromosomes, either the X or the Y. Since the X chromosome contains more genes than the smaller Y chromosome, mutations on the X appear more frequently in the population. In addition, sex-linked disorders are found more commonly in males than females because they have only one copy of the X chromosome. The genotypes for sex-linked traits are also written with superscripts: XBY or XbY for males or XBXB, XBXb, or XbXb for females.

Complete the following chart by giving the phenotypes and genders for the following genotypes, XN gene for normal vision and Xn gene for color blindness.

GENOTYPE / PHENOTYPE / GENDER
XNXN
XNY
XNXn
XnY
XnXn
a. What are the possible genotypes and phenotypes resulting from a cross between a carrier female for color blindness and a normal vision male?
______
(Show your work in a Punnett Square.) /
b. Duchenne Muscular Dystrophy is caused by a recessive allele located on the X chromosome. Affected people experience progressive weakening and loss of skeletal muscle. How can two unaffected people can have a child with Duchenne MD?
______
(Show your work in a Punnett Square.) /

a) Is the child with MD a male or female? ______

b) Who did this child inherit the disorder from? Why? ______

c) What is the probability that the couple’s next child will have MD? ______

d) What percentage of the couple’s female children will probably have MD? ______

e) What percentage of the couple’s male children will probably have MD? ______

d. Hemophilia is caused by a recessive allele on the X chromosome that causes abnormal clotting of blood when cut or bruised. How can a mother whose blood clots normally can have a daughter with hemophilia.?
______
(Show your work in a Punnett Square.) /

a) What is the father’s genotype? ______

b) Why is it extremely rare for a female to have hemophilia? ______

c) What is the probability that their offspring will have hemophilia? ______

d) What is the probability that their offspring can pass hemophilia on to their children? ______

e) In this case, what do we call the mother if she is heterozygous for this trait? ______

e.Not all sex-linked genes are recessive. For example, hypophosphatemia, which causes defective bone development is caused by a dominant allele on the X chromosome. Work a cross showing a woman with a genotype of XAXa and a man with a genotype of XaY.
a) What are the phenotypes of the mother and father? ____
______/

b) What is the probability that the children will have hypophosphotemia? ______