Assignment Task
1. Mitochondrial
a. inheritance is maternal.
b. DNA is linear.
c. function depends on nuclear genes.
d. diseases have minor effects.
e. two of the above
2. Genomic imprinting is an example of
a. pleiotropy.
b. heterogeneity.
c. epistasis.
d. differential gene expression.
e. a phenocopy.
3. In a typical human female child
a. the oocytes have begun, but not completed, meiosis.
b. there are indifferent gonads.
c. the Müllerian ducts have been degraded.
d. the SRY gene has been inactivated.
e. Information from only one X chromosome is required for both survival and proper development.
4. Heritability describes the
a. genetic composition for a trait in a particular population.
b. phenotypic variation of a trait in a particular population.
c. variation in a phenotype caused by the environment.
d. proportion of genetic contribution to a trait in a particular population.
e. none of the above.
5. Heterozygotes may or may not be indistinguishable from a homozygote. Based on the information in Lewis,
a. compare the enzyme (molecular) and whole-body (general) phenotypes of heterozygotes for Tay-Sachs disease to heterozygotes for AB blood type.
b. describe if and how the following terms apply to Tay-Sachs disease and to ABO blood type: pleiotropy, multiple alleles, genetic heterogeneity.
Note: Many students struggle with questions 6-8. Please refer to Appendix C of the study guide for help with these questions
6. Differentiate between parental and recombinant phenotypes and parental and recombinant genotypes, with respect to two traits caused by different genes. Can an offspring have a parental phenotype and a recombinant genotype? Use your own examples (theoretical or actual) to support your answer, referring to dominant and recessive traits, and to allele combinations.
7. Drosophila melanogaster (fruit flies) are excellent animals to use for studying Mendel’s laws of inheritance. Two Mendelian traits that are often used for these experiments are eye colour (encoded for by the ‘W’ gene) and wing shape (encoded for by the ‘Vg’ gene).
The ‘W’ allele is dominant, and gives red eyes, while the ‘w’ allele is recessive and gives white eyes. The ‘Vg’ allele is dominant, and gives normal wings, while the ‘vg’ allele is recessive and gives vestigial wings (which are almost absent and have only a small amount of wing tissue). For interest,
Starting with a cross between a true breeding red-eyed, vestigial-winged fly (WW vgvg) and a true-breeding white-eyed, normal winged fly (ww VgVg):
a. List the genotypes of the F1 flies.
b. List the four types of gametes and their proportions (in percent) that these F1s will produce, assuming the two genes are unlinked, and classify them as parental or recombinant.
c. List the four types of gametes and their proportions (in percent) if these genes had been on the same chromosome, 20 map units apart.
d. Draw a Punnett square representing the cross between the F1 flies, assuming linkage between the Vg and W genes as described in part c. Then list the F2 genotypes and their proportions.
8. A woman is heterozygous for three linked autosomal genes and has the genotype GgHhMm. The three genes are arranged on the chromosomes in the order listed (i.e. G then H then M). Her husband is homozygous recessive for each of the genes. They have eight children with the following genotypes:
Three are GghhMm.
Two are ggHhmm.
One is GgHhmm.
One is Gghhmm.
One is gghhmm.
a. What is the most likely combination of alleles on each of the mother’s chromosomes? Explain.
b. List the genotypes of the recombinant children above. For each of these children, determine the location of the required crossover(s) in the mother’s oocyte to create their recombinant chromosome by identifying the two genes between which the crossover(s) occurred.
c. List the other possible recombinant genotypes that have not appeared in the offspring.
9. A mother is heterozygous for an over-expressed plastin allele on her X chromosome, thus has longer than normal axons. She is also heterozygous for the SMN1 gene on chromosome 5. Her children’s father is normal for plastin and has normal length axons. He too is heterozygous for the SMN1 gene. Both genes influence spinal muscular atrophy type 1 (SMA1); two abnormal copies of the SMN1 gene are required to cause spinal muscular atrophy, but their effect is prevented by high expression of the plastin gene (Lewis 94).
a. Give the genotypes of the mother and the father; provide a legend for your symbols. For each gene, explain why the abnormal alleles are dominant or recessive.
b. List all the possible genotypes and proportions of their offspring for the plastin gene.
c. List all the possible genotypes and proportions of their offspring for the SMN1 gene.
d. Showing your work, determine the probability that this couple will have a daughter with SMA.
e. Showing your work, determine the probability that this couple will have a son with SMA.
10. The pedigree in Figure 5.6 in Lewis shows the inheritance for a mitochondrial gene. If it instead represented an X-linked gene, can you determine whether or not it is dominant or recessive? Why or why not? Make sure to use examples from the pedigree to support your answer.
11. In the following pedigrees, the disorders or traits presented follow simple patterns of Mendelian inheritance. For each pedigree, determine the most probable mode of inheritance of the trait, stating whether the trait is due to an autosomal or X-linked gene and whether it is due to a dominant or recessive allele. Indicate and explain the evidence supporting your choice of pattern, and note evidence that does not support or conclusively eliminate the other patterns. Provide specific examples to defend your statements.
12. Choose a current newspaper article (no older than two years before the start of your course contract) that describes a genetic study.* The article cannot be from a medical/health type of information source (such as Science Daily), or from a scientific publication. Summarize the information presented in the article in paragraph form by addressing the points below. (If you cannot address all or nearly all of these points, choose another article.) Include any other information relevant to your studies in this course, as provided in the article.