BIOL 114
Biology Dept
Kenyon College

Mechanisms of Inheritance Quiz

After your response, look above for reply.


1 A boy is born with an extra finger on one hand. Extra digits are known to be common in members of the father's extended family, but not the mother's. The boy's two sisters have normal fingers. What is the most likely explanation?
X-linked inheritance, since only males are affected.
Y-linked inheritance: Males inherit from their fathers.
The extra finger trait is autosomal dominant.
A spontaneous mutation occurred.

2 In the father's family, both men and women show extra digits, sometimes an extra finger on both hands, sometimes just one hand, sometimes extra fingers and toes. What do we call this phenomenon?
Multiple gene loci combining to produce the trait.
Variable expressivity of the trait, though all affected individuals carry the same allele.
Gene product interaction.
Different mutations in the same family.

3 Suppose the boy's aunt and her husband have no extra fingers--yet their child has an extra finger! How do we explain this, if the trait is dominant?
The professor made a mistake in the test.
The allele changed from recessive to dominant.
The aunt's husband has a recessive allele for a different gene locus that results in the same phenotype.
The gene for extra finger shows partial penetrance.

4 Explain the inheritance of this rare trait in the pedigree.Ped11.gif
The trait is X-linked recessive, inherited through the mothers.
The trait is autosomal recessive.
X-linked recessive.
The trait is autosomal dominant.

5 Explain the inheritance of this rare disease in the pedigree.
The trait is X-linked dominant.
Imprinting must cause it to be inherited only through the female.
The disease is inherited on the mitochondrial DNA.
Penetrance or expressivity.

6 In a family, mildly retarded girls have children with more profound retardation. The X-chromosome shows a multiple triplet repeat. What is the explanation?
The condition is double-recessive; the father also carries the allele.
The condition is caused by expansion of the triplet repeat region in each generation, a non-random form of mutation. The expanded non-coding DNA region turns off expression of a nearby essential gene.
X-linked inheritance.
Variable expressivity.

7 A pair of yellow mice produce a litter of five yellow mice and one white. One mouse of indeterminate color is stillborn. Suggest an explanation.
Yellow trait is codominant; two "yellow" alleles cause lethality.
This "five to one to one" ratio must be explained by multiple gene loci.
The mice have different fathers.
Multiple alleles cause three different phenotypes.

8 When the yellow mice are examined physiologically, the yellow color is determined to result from jaundice; the trait causes a liver defect. Multiple effects of one gene illustrates:
Multiple alleles.
Multiple gene loci.
Partial penetrance.

9 A father with type A blood and a mother with type B blood have three children with blood of type AB and type O. Explain.
Three different gene loci cause A, B, and O type.
There are multiple alleles for A, B, and O. The parents are genotype AO and BO.
O blood type shows partial penetrance.
O blood type shows partial expressivity.

10 Two red-eyed flies are crossed, producing 94 red-eyed, 31 orange-eyed, 36 brown-eyed, and 11 white-eyed flies. Explain.
Multiple alleles, like A B O blood type.
Partial expressivity of color.
Two gene loci. One double-null leaves orange pigment; the other double-null leaves only brown. If both double-nulls are present, zero pigment--white.
I don't know!