Exam 2: Concept Checks Flashcards
Autosomal recessive traits often appear in pedigrees in which there have been consanguine matings, because these traits……..
It might skip generations when a new mutation arises or the trait has reduced penetrance.
How can you distinguish between an autosomal recessive trait with higher penetrance in males and an X-linked recessive trait?
If X-linked recessive, the trait will not be passed from father to son.
A male affected with an X-linked dominant trait will have what pro- portion of offspring affected with the trait?
All daughters and no sons
What features of a pedigree would distinguish between a y-linked trait and a trait that is rare, autosomal dominant, and sex-limited to males?
If the trait were Y linked, an affected male would pass it on to all his sons, whereas, if the trait were autosomal and sex- limited, affected heterozygous males would pass it on to only half of their sons on average.
Why are monozygotic twins genetically identical, whereas dizygotic twins have only 1/2 of their genes in common on average?
Monozygotic twins develop from a single embryo, whereas dizygotic twins develop from two embryos.
A trait exhibits 100% concordance for both monozygotic and dizygotic twins. What conclusion can you draw about the role of genetic factors in determining differences in the trait?
Genetic factors are unimportant.
What assumptions underlie the use of adoption studies in genetics? a. Adoptees have no contact with their biological parents after birth. b. The foster parents and biological parents are not related. c. The environments of biological and adopted parents are independent. d. All of the above.
All the above
For single crossovers, the frequency of recombinant gametes is half the frequency of crossing over because
each crossover takes place between only two of the four chromatids of a homologous pair.
The following testcross produces the progeny shown: Aa Bb × aa bb → 10 Aa Bb, 40 Aa bb, 40 aa Bb, 10 aa bb. Were the genes in the Aa Bb parent in coupling or in repulsion?
Repulsion
How does a genetic map differ from a physical map?
Genetic maps are based on rates of recombination; physical
maps are based on physical distances.
Write the genotypes of all recombinant and nonrecombinant progeny expected from the following three-point cross:
4
The c locus
In analyzing the results of a three-point testcross, a student deter- mines that the interference is −0.23. What does this negative interfer- ence value indicate?
a) Fewer double crossovers took place than expected on the basis of single-crossover frequencies.
b) More double crossovers took place than expected on the basis of single-crossover frequencies.
c) Fewer single crossovers took place than expected.
d) A crossover in one region interferes with additional crossovers in the same region.
More double crossovers took place than expected on the basis of single-crossover frequencies.
Chromosome duplications often result in abnormal phenotypes
because
a) developmental processes depend on the relative amounts of proteins encoded by different genes.
B) extra copies of the genes within the duplicated region do not pair in meiosis.
c) the chromosome is more likely to break when it loops in meiosis.
d) extra DNA must be replicated, which slows down cell division.
A) developmental processes depend on the relative amounts of proteins encoded by different genes.
What is pseudodominance and how is it produced by a chromosome deletion?
Pseudodominance is the expression of a recessive mutation. It is produced when the dominant wild-type allele in a heterozygous individual is absent due to a deletion on one chromosome.
