Modifications to Mendelian Ratios

1)  Conduct the following cross:   Aa   x   Aa

Determine the genotypic and phenotypic ratios if there is:

 - complete dominance
 - Incomplete dominance
 - Codominance
 - Overdominance
- a recessive lethal expressed before birth, that has no phenotypic effect.
- a recessive lethal expressed before birth that is phenotypically dominant (like yellow coat color in mice)

2)  Provide a cellular explanation for complete dominance, intermediate inheritance, codominance, and overdominance. A cellular explanation means to explain, at the protein level, why the heterozygote expresses a given phenotype.... like a "dosage effect" for incomplete dominance (intermediate inheritance).

3)  Consider this cross:

                                        AaBbCc    x    AaBbCC

                     - assume independent assortment of the three genes
                     - There is incomplete dominance at the A locus  (meaning A is incompletely dominant to a).
                     - There is complete dominance at the B locus.
                     - There is overdominance at the C locus.

How many genotypes are possible in the offspring?

How many phenotypes are possible in the offspring?

4) Explain how a continuously variable trait, like skin pigmentation in humans, could be governed by genes.

5) What is an epistatic interaction? Give an example.

6) The "h" allele exerts an epistatic effect over the ABO locus. What is the genotypic and phenotypic ratio you would expect from the following cross: HhAB x hhAO?

7) Although they are often very rare, every population has many lethal alleles... indeed, each of us probably has 7-10 lethal alleles. You would expect lethal alleles to be "weeded out" of a population by selection... after all, dead organisms don't reproduce. However, they can be maintained in populations even though they are lethal. List three different ways that lethal alleles can be maintained in a population (or even in an individual).

8) Provide an example of conditional expression of coat color at different termperatures, explaining WHY the color vaires at differnt temperatures.

9) What is PKU, what causes it, and how can it's effects be interrupted?

10) How can the location of a gene influence its expression? describe an example.

11) Describe the pattern of imprinting for IGF-2 and the competititve receptor. Describe Haig's hypothesis for the adaptive value of this pattern of imprinting for males and females.

12) What is a CpG island, where are they common, and how are they invovled in imprinting?

13) Explain how either Prader-Willi or Angelman's Syndrome are caused.

14) "Maternal Effects" can be caused my maternal proteins placed in the egg that influence the phenotype of the developing embryo. Explain why, in Limnaea snails, an organisms coiling is not depedent on its own genotype. Provide an example (draw a family tree that demonstrates your argument).

15) Another type of maternal effect can be caused by mitochondria or chloroplasts. Why? And why can these effects vary over the organism?

16) The "value" of an allele is often independent of its phenotypic effect. So, an allele might have a given effect on the phenotype, but whether this effect is beneficial or deleterious depends on.... what? describe how the allele that causes malaria is an example of this.