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10 C
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K
1. The best definition of a true-breeding plant is one that ______.
cannot be cross-fertilized
self-fertilizes to produce offspring identical to the parent
produces sterile offspring when cross-fertilized
self-fertilizes to produce hybrid offspring
becomes sterile after three generations
2. Alleles are described as ______.
homologous chromosomes
environmental factors that affect gene expression
alternate forms of a gene
heterologous chromosomes
alternate phenotypes
3. ______ genes violate Mendel's principle of independent assortment.
Codominant
Dominant
Linked
Epistatic
Pleiotropic
4. Which of the following human genetic disorders is NOT caused by nondisjunction?
Down's syndrome
Turner's syndrome
Klinefelter syndrome
Fragile X syndrome
5. Which refers to the addition of an extra segment of a chromosome?
inversion
translocation
deletion
duplication
monosomy
6. In chromosome mapping, one map unit represents
the distance between one gene and the next on a chromosome.
1% crossing over between two sites on a chromosome.
1% of the length of the chromosome.
10% crossing over between two sites on a chromosome.
10% of the length of the chromosome.
C
According to Mendel's principle of segregation, ______.
a. The movement of maternal and paternal chromosomes is a random process.
b. homologous chromosomes move to the same gamete.
c. more individuals express the dominant allele than the recessive allele.
d. gametes have one copy of each allele.
e. each pair of alleles for a trait segregates into gametes.
To determine the phenotype of an individual who expresses a dominant trait, you would cross that
individual with an individual who ______.
expresses the dominant trait
is homozygous recessive for that trait
has the genotype Aa
is homozygous dominant for that trait
is heterozygous for that trait
An individual heterozygous for cystic fibrosis ______.
cannot have children with cystic fibrosis
is a carrier
will have children who are all carriers of cystic fibrosis
cannot reproduce
has cystic fibrosis
An individual with the genotype AaBb produces four different gametes in equal proportions. This is a
demonstration of ______.
the chromosomal theory of inheritance
Mendel's law of independent assortment
linkage
crossing over
Mendel's principle of segregation
An individual with (naturally) curly hair and an individual with (naturally) straight hair mate; all of their
offspring have (naturally) wavy hair. What is the relationship between the alleles for hair texture?
pleiotropy
incomplete dominance
straight hair and curly hair are sex-linked, but wavy hair is not
wavy hair is dominant to both straight and curly hair
codominance
Which statement is NOT true about X-linked characteristics?
More males than females are affected.
If a female has the characteristic, all her sons will show it.
Females can be carriers of the gene without showing it.
The characteristic often skips a generation, from a woman's father to her son.
Males can have two copies of the alleles for the trait, but females can have only one.
Which term best describes a gamete’s chromosome number?
Euploid
Aneuploid
Monosomy
Polyploidy
Two of the above are correct.
Males can’t be carriers of X-linked disorders because they…
only have one copy of the Y chromosome
have a single allele for the disorder
always have two mutated alleles for the disorder
Two of the above answers are correct
None of these answers are correct
A chromosomal translocation results in…
A net loss of the amount of genomic material
No change in the amount of genomic material
A change in a gene’s location
A net gain in the amount of genomic material
Two of the above answers are correct
If a woman is a carrier for the color-blind recessive allele and her husband is normal, what are their
chances that a son will be color-blind?
None since the father is normal.
50% since the mother is the only carrier.
100% because the mother has the gene.
25% because the mother is a hybrid.
None since he will also be just a carrier.
A dihybrid cross produces 30 recombinant offspring out of a total of 1,000 offspring. What is the
recombination frequency of the two gene pairs?
6%
3%
30%
1.5%
0.5%
H
Considering that males are produced by Klinefelter (XXY) syndrome, XYY and normal XY chromosome
combinations, and females are produced by Turner (XO) syndrome, triple-X (XXX) and normal XX
combinations, it is obvious that
A. maleness is caused by the presence of only one X chromosome.
B. femaleness is caused by the presence of two or more X chromosomes.
C. maleness is caused by the minimal presence of one Y chromosome.
D. maleness occurs in the absence of two or more X chromosomes.
E. sex determination is a delicate balance between X and Y chromosomes.
A genetic disorder (not counting disjunctions) is more likely to be common in the population if it
A. does not manifest itself until after reproductive age has passed.
B. is recessive.
C. bestows some benefit in a heterozygous state.
D. is not sex-linked if recessive.
E. All of the choices would increase the survival of a deleterious gene.
Hypophosphatemia (vitamin D-resistant rickets) is inherited as an X-linked dominant. What is the
expected outcome of a cross between a healthy homozygous recessive woman and a man with
hypophosphatemia?
All of their daughters and none of their sons exhibit hypophosphatemia.
Fifty percent of their daughters and fifty percent of their sons exhibit hypophosphatemia.
Seventy-five percent of their offspring exhibit hypophosphatemia.
All of their sons and none of their daughters exhibit hypophosphatemia.
Twenty-five percent of their offspring exhibit hypophosphatemia.
The parents of a child with unusual disease symptoms took the child to a doctor for help. The doctor was
unsuccessful treating the disease and felt that it might have a genetic basis. He explained that if that was
true, it could have possibly been inherited. He recommended that the child be taken to a specialty clinic
where physicians and staff members were trained to diagnose genetic diseases and counsel parents.
Ultimately, the child was shown to have a rare recessively inherited disease. The parents were tested for
the gene, and both were found to be heterozygous. The parents wanted to have another child but were
afraid this child would also be affected.
What would genetic counselors say is the probability of the second child having the disease?
1/2
1/4
1/8
1/16
1/32
What if children with this disease always have attached earlobes, a recessive trait and a trait that is
independently inherited. If both parents are heterozygous for attached earlobes, what is the probability
that the second child will have the disease?
1/2
1/4
1/8
1/16
1/32