Question

1. What is the probability that for a particular trait, two heterozygous parents will both contribute a recessive allele to their child?
2. For a typical Mendelian trait with complete dominance how many different phenotypes are possible?
3. For alleles that display incomplete dominance, how many phenotypes are possible?
4. Some phenotypes appear to be expressed on a continuum. Several traits in this lab demonstrate this. If most genes have only two alleles, how can some phenotypes be so variable?
5. Chin shape genes are epistatic. Explain what this means in terms of chin traits.
6. For traits where a parent is heterozygous, we flipped a coin in this simulation to determine which allele was passed on. What aspect of meiosis does flipping a coin simulate?
7. If your mother and father both have phenylketonuria (PKU) (a recessive disorder), but you do not, what is the most likely explanation?
8. Speculate on how hairy ears, which are found only in males, could be inherited.

Answer 1

1. Aa × Aa

Gametes	A	a
A	AA normal	Aa normal
a	Aa normal	aa affected

Out of four progenies, one is affected, if both the parents are heterozygous. Therefore there are 25% chances that the progeny will be affected.

2. Only two,

AA, Aa = dominant phenotype

aa = recessive phenotype

3. Thre phenotypes for incomplete dominance,

AA = dominant phenotype

Aa = intermediate phenotype

aa = recessive phenotype

4. Phenotypes can be so variable, like human skin, which ranges from very fair to very dark, because these traits are controlled by more than two genes. For example human skin colour is controlled by 3 genes two alleles for each gene and therefore 6 alleles in total.

5. Epistasis is non allelic interaction between the alleles of different genes. Chin genes are epistatic. It means that this trait is controlled by two genes. Alleles of one locus are epistatic over the alleles of other locus which are hypostatic. The alleles which are epistatic are able to express themselves even in the presence of alleles of other locus.

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