Chapter 15 q &a
In cats, black fur color is caused by an X-linked allele; the other allele at this locus causes orange color. The heterozygote is tortoiseshell. What kinds of offspring would you expect from the cross of a black female and an orange male?
tortoiseshell females; black males
Calico cats are female because
a male inherits only one of the two X-linked genes controlling hair color.
Women (and all female mammals) have one active X chromosome per cell instead of two. What causes this?
modification of the XIST gene so that it is active only on one X chromosome, which then becomes inactive
Which of the following statements is true of linkage?
The closer two genes are on a chromosome, the lower the probability that a crossover will occur between them.
What does a frequency of recombination of 50% indicate?
The two genes are likely to be located on different chromosomes.
What is the reason that linked genes are inherited together?
They are located close together on the same chromosome.
Recombination between linked genes comes about for what reason?
Crossovers between these genes result in chromosomal exchange.
Why does recombination between linked genes continue to occur?
New allele combinations are acted upon by natural selection.
If nondisjunction occurs in meiosis II during gametogenesis, what will be the result at the completion of meiosis?
1/4 of the gametes will be n + 1, 1/4 will be n - 1, and 1/2 will be n.
Of the following human aneuploidies, which is the one that generally has the most severe impact on the health of the individual?
What is the source of the extra chromosome 21
nondisjunction or translocation in either parent
At which phase(s) is it preferable to obtain chromosomes to prepare a karyotype
late prophase or metaphase
Which of the following produces a Mendelian pattern of inheritance?
a trait acted upon by many genes