Exam 3 Book Questions Flashcards
For single crossovers, the frequency of recombinant gametes is half the frequency of crossing over because
A. testcross between a homozygote and a heterozygote produces 1/2 heterozygous and 1/2 homozygous progeny.
B. the frequency of recombination is always 50%.
C. each crossover takes place between only two of the four chromatids of a homologous pair.
D. crossovers take place in about 50% of meioses.
C. each crossover takes place between only two of the four chromatids of a homologous pair.
The following testcross produces the progeny shown:
AaBb × aabb → 10 AaBb, 40 Aabb, 40 aaBb, 10 aabb. Were the A and B alleles 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:
m+p+s+ / mps x mps / mps
(answer on page 210)
A three-point testcross is carried out between three linked genes. The resulting nonrecombinant progeny are s+r+c+ ands r c, and the double-crossover progeny are s r c+ and s+r+c. Which is the middle locus?
The c locus
In analyzing the results of a three-point testcross, a student determines that the interference is −0.23. What does this negative interference 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.
B) More double crossovers took place than expected on the basis of single-crossover frequencies.
Autosomal recessive traits often appear in pedigrees in which there have been consanguineous matings because these traits
A) tend to skip generations.
B) appear only when both parents carry a copy of the gene for the trait, which is more likely when the parents are related.
C) usually arise in children born to parents who are unaffected.
D) appear equally in males and females.
B) appear only when both parents carry a copy of the gene for the trait, which is more likely when the parents are related.
When might you see an autosomal dominant trait skip generations?
It might skip generations when a new mutation arises or the trait has incomplete penetrance.
How can you distinguish between an autosomal recessive trait with higher penetrance in males and an X-linked recessive trait?
If it is 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 proportion of offspring affected with the trait?
A) 1/2 sons and 1/2 daughters
B) All sons and no daughters
C) All daughters and no sons
D) 3/4 daughters and 1/4 sons
C) 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 share only 50% of their genes on average?
A) Monozygotic twins tend to look more similar.
B) Monozygotic twins develop from two different eggs fertilized by the same sperm, whereas dizygotic twins develop from two eggs fertilized by two different sperm.
C) Monozygotic twins develop from a single egg fertilized by one sperm, whereas dizygotic twins develop from a single egg fertilized by two different sperm.
D) Monozygotic twins develop from a single egg fertilized by a single sperm, whereas dizygotic twins develop from two eggs fertilized by two different sperm.
D) Monozygotic twins develop from a single egg fertilized by a single sperm, whereas dizygotic twins develop from two eggs fertilized by two different sperm.
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?
A) Genetic factors are extremely important.
B) Genetic factors are somewhat important.
C) Genetic factors are unimportant.
D) Both genetic and environmental factors are important.
C) 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 adoptive parents and biological parents are not related.
C) The environments of biological and adoptive parents are independent.
D) All of the above
D) All of the above
How does preimplantation genetic diagnosis differ from prenatal genetic testing?
Preimplantation genetic diagnosis determines the presence of disease-causing genes in an embryo at an early stage, before the embryo is implanted in the uterus and initiates pregnancy. Prenatal genetic testing determines the presence of disease-causing genes or chromosomes in a developing fetus.
