Discussion:
Genetics Problem Set on Patterns of Inheritance
1. G6PD is an enzyme found in human white blood cells. It is made by a gene that has 2 alleles, A and B. In females, cells either make the A type or the B type, but never both.
This is very different from most other enzymes, where all cells in a heterozygote make both types of enzyme. What is the most reasonable explanation for this unusual havior of G6PD?
2. In humans, red-green color blindness is recessive and X-linked, while albinism is recessive and autosomal. What types of children can be produced as the result of marriages between two homozygous parents, a normal-visioned albino woman and a color-blind, normally pigmented man? (Give your answer separately for males and females)
3. Suppose that a mutation occurred in the SRY gene on the human Y chromosome, knocking out its ability to produce the testis-determining factor. Predict the phenotype of an individual who carried this mutation and a normal X chromosome?
4. Sex determination in Gryllus campestris (cricket) is by the XO method. The somatic lls of a cricket are analyzed and found to contain 29 chromosomes.
A. What sex is this individual?
B. What is the diploid number of the opposite sex?
5. Ichthyosis hystrix gravior (a greatly thickened horny condition of the skin) is a rare human condition, but in the single extensive pedigree which has been studied it occurs only in males. All the sons of each affected father have the condition. Females are not only unaffected, but never transmit the gene for this defect. Can you suggest a possible explanation for this curious and unusual type of inheritance?
6. Dosage compensation is only found in organisms that have sex chromosomes. What is ge compensation? Briefly describe how dosage compensation is achieved in Drosophila and humans.