BIO 181: Unity of Life
Study Guide for Chapter 10
1.
Distinguish between the following terms
A. dominant and recessive
B. phenotype and genotype
C. P1, F1 and F2
D. Homozygous and heterozygous
E. Monohybrid and dihybrid crosses
2.
True-breeding plants
A. produce the same offspring when crossed for many generations
B. result from a monohybrid cross
C. result from a dihybrid cross
D. result from crossing over during prophase I of meiosis
A. monohybrid and dihybrid crosses produce heterozygous individuals; truebreeding individuals are always homozygous
3.
What is the probability that a cross between a true-breeding pea plant with
smooth seeds and a tree breeding pea plant with wrinkled seeds will produce
F1 offspring with smooth seeds?
A. ½
B. ¼
C. 0
D. 1
D. This is an example of a monohybrid cross. All of the F1 offspring would
have smooth seeds (Ss).
4.
What is the pattern of inheritance for a sex linked trait?
A. Every affected person has an affected parent
B. Unaffected parents can produce children who are affected
C. Unaffected mothers have affected sons and daughters who are carriers
D. None of the above
C. The most common sex linked alleles are X linked and are passed from a mother to
her son because the mother always donates on of her X chromosomes to her son and
the father always donates his Y chromosome to his son. Daughters can also receive
the X linked allele from their mothers but the father donates the other X
chromosomes so daughters can be carriers
5.
Linked genes are genes that
A. assort independently
B.
C.
D.
E.
segregate equally in the gametes during meiosis
always contribute the same trait to the zygote
are found on the same chromosome
recombine during mitosis
D. linked genes by definition are on the same chromosome and thus do not
assort independently, do not contribute the same trait to the zygote, and do not recombine
during mitosis or segregate equally to the gametes during meiosis.
6.
Draw a pedigree for three generations in which the grandfather has re-green
color blindness and his daughter is a carrier. This daughter has four sons.
Predict how many of the sons will be colorblind.
See figure 10.26, generation II, III and IV. One half of her sons could be colorblind.
7.
You are a genetics counselor who is working with a 23 year old pregnant
woman who has just discovered that her father has Huntington’s chorea, a rare
dominant autosomal trait. This disease usually develops in middle aged
individuals, so people carrying this trait do not find out they have this genetic
disorder until midlife. What are the chances that the child she is carrying will
develop Huntington’s chorea? Assume that her husband’s family has no
history of Huntington’s chorea. What is the chance that she has Huntington’s
chorea?
She has a 50% chance that she will get Hungtinton’s chorea. Since the trait is an
autosomal dominant allele, one half of her father’s gametes will contain the homologous
chromosome carrying that allele and 1/2 of his gametes will contain the homologous
chromosome that carries the wild type allele. If she received the Huntington’s allele, her
child has a 50% chance of receiving this allele from her. To predict the probability that
her child will inherit the Huntinton’s allele: ½ the probability the mother has the gene
times ½ the probability the child will inherit the gene from her = ¼ or 25% chance.
8.
Explain sex determination in humans.
In humans sex is determined by a pair of sex chromosomes. Males are typically XY and
females XX. Sex is determined by which sperm cell (that one carrying the Y or the one
carrying the X) fertilizes the egg.
Secondary sex determination are determined by the actions of hormones.
9.
What is the role of the SRY gene in sex determination?
SRY is the sex determining region of the Y chromosome. The SRY gene codes for a
protein involved in primary sex determination – type of gamete produced and organs
needed to produce them. The SRY gene must be present for testes and sperm to form.
10.
How is it possible to have X, XYY, and XXY individuals?
Monosomies and trisomies are caused by nondisjunction – failure of the
chromosomes to separate in meiosis
11.
A couple have three boys and are expecting their fourth child. What are the
chances that it will be a boy?
Each event is independent of the other. 50%
Be sure to work the 5 genetic problems that will be handed out Wednesday in class.
They will be worth 10 points. They are due Thursday.