Download biology 30•genetics worksheet 1

BIOLOGY 30•GENETICS WORKSHEET 1
1.
In sheep, the gene for white wool is dominant, the gene for black wool is recessive. What
three crosses could result in a black sheep in the family?
2.
In one experiment Mendel crossed a true-breeding pea plant having green pods with a truebreeding pea plant having yellow pods. All of the F1 plants had green pods.
a) Which trait (green or yellow pods) is recessive? Explain how you arrived at your
conclusion.
b) Suppose the F1 plants are self-pollinated (F1 cross) and 135 F2 plants are produced.
What phenotypes should be present in the F2 generation, and how many of the plants in
that generation should show each of those phenotypes?
3.
In a certain animal, one breed is known to always have a hairy tail another breed is
known to always have a naked tail. How would you determine which trait is dominant?
4.
In laboratory mice, the normal gray colour is dominant over the albino (all-white) colour.
Starting with pure-bred albino and pure-bred gray as parents what is the ratio of phenotypes
in the F2 generation?
5.
In man, normal pigmentation is due to a dominant gene, A, albinism to its recessive allele,
a. A normal man marries an albino woman and their first child is albino. What are the
genotypes of these three persons? If they have several other children, what would these
children probably be like?
6.
Could two blue-eyed parents have a brown-eyed child? Could two brown-eyed parents
have a blue-eyed child?
7.
A blue-eyed man, both of whose parents were brown-eyed, marries a brown-eyed woman
whose father was blue-eyed and whose mother is brown-eyed. This man and woman have a
blue-eyed child. What are the genotypes of all of the individuals mentioned?
8.
In the question above, what is the probability that a brother or sister of the blue-eyed child
would have blue eyes, brown eyes?
9.
What does it mean to say that a characteristic skips a generation? Could it skip 2 or 3
generations? Explain.
10.
In guinea pigs short hair is dominant over long hair. A short-haired male and a short-haired
female produce mostly short-haired offspring, but a few were long-haired. Show how you
can determine the genotypes of the parents.
11.
Mendel crossed a true-breeding, tall purple-flowered pea plant with a true-breeding dwarf
(short), white-flowered plant. All of the F1 plants were tall and purple-flowered. If an F1 plant is
now self-pollinated, what is the probability of obtaining an F2 plant heterozygous for the genes
controlling height and flower colour?
12.
One gene has alleles A and a, another gene has alleles B and b. For each of the following
genotypes,
what type(s) of gamates will be produced?
a) AABB
b) AaBB
c) Aabb
d) AaBb
13.
Referring still to the preceding problem, what genotypes will be
present in the
offspring from the following matings? (Indicate the frequencies of each genotype among
the offspring.)
a) AABB X aaBB
b) AaBB X AABb
c) AaBb X aabb
d) AaBb X
AaBb
14.
In addition to the genes mentioned in the problem above, assume you now study a third
gene having alleles C and c. For each of the following genotypes, indicate what type(s) of
gamates will be produced.
a) AABBCC b) AaBBCc
c) AaBBcc
d) AaBbCc
BIOLOGY 30•GENETICS WORKSHEET 2
Incomplete Dominance, Multiple Alleles and Multiple Genes
1.
The shape of radishes may be long, round or oval. The following results were obtained in
the different possible crosses:
long X oval gave: 50% long and 50% oval.
oval X round gave: 50% oval and 50% round.
long X round gave: 100% oval.
oval X oval gave: 25% long, 50% oval and 25% round.
Explain these results.
2.
In shorthorn cattle, the polled condition, H, is dominant over the horned condition, h.
Also the heterozygous condition of red coat, W, and white coat, w, is roan. If a homozygous
polled red animal is bred to a white horned one, what will the F1 and the F2 generations be
like?
3.
Explain the difference between the way in which the ABO blood groups are inherited and
the way in which skin colour is inherited.
4.
A woman having blood type A marries a man having blood type B. They have five
children. Two sons have blood type 0. One daughter has blood type AB, another
daughter type A, and a third type B.
a) Draw a pedigree showing the blood types of the parents and offspring. Use letters in
the pedigree symbols to represent the individuals' blood types.
Figure out the genotypes of the parents and children.
b)
5.
The ABO blood system has often been employed to settle cases of disputed paternity.
Suppose as an expert in genetics you are called to testify in a case where the mother has
type A blood and the child has type 0 blood, and the alleged father has type B blood. How
would you respond to the following statements of the attorneys:
Attorney of the alleged father: "Since the mother has type A blood, the type 0 blood of
the child must have come from the father, and since my client has type B blood, he
obviously could not have fathered this child.''
Attorney of the mother: "Further tests revealed that this man is heterozygous and therefore he
must be the father.''
6.
In Duroc jersey hogs, coat colour is dependent on two pairs of alleles, R and r and S and s.
Any genotype containing at least one R gene and at least one S gene results in red coat
colour. The double recessive genotype results in white coat colour. All other genotypes
result in sandy coat colour. if two hogs, each heterozygous for both pairs of genes, are
mated, what kinds of offspring will be produced in what ratio?
BIOLOGY 30•GENETICS WORKSHEET 3
Sex-linked, Sex-influenced and Sex-limited Traits
1.
What are the differences between a sex-linked, a sex-limited and a sex-influenced trait?
Give an example of each.
2.
Recall that human sex chromosomes are XX for females and XY for males.
a)
b)
c)
d)
Does a male child inherit his X chromosome from his mother or father?
With respect to an X-linked gene how many different types of gamates can a male produce?
If a female is homozygous for an X-linked gene, how many different types of gamates can she
produce with respect to this gene?
If a female is heterozygous for an X-linked gene, how many different types of gamates can
she produce with respect to this gene?
3.
One human gene that may be Y-linked controls the length of hair on mens' ears. One
allele at this gene locus produces non-hairy ears, another allele produces rather long hairs
(hairy pinnae).
a) Why would you not expect females to have hairy pinnae?
b) If a man with hairy pinnae has sons, all of them will have hairy pinnae, if he has
daughters, none of them will. Explain this statement.
4.
In hemophilia A, the body's blood-clotting mechanism is defective. This condition has
been traced to a recessive allele of an X-linked gene. Refer now to figure on page 660.
a)
b)
Why are only the females shown as carriers of the recessive allele?
If Victoria had married a hemophiliac, what phenotypes would have been expected
among their children and with what probabilities?
5.
A woman heterozygous for colour blindness XCXc marries someone with normal colour
vision. What is the probability that their first child will be colour blind? The second child?
If they only have two children, what is the probability that both will be colour blind?
6.
A colour-blind man marries a woman with normal red-green vision. They have two
daughters and one son. The son is colour-blind. One daughter is colour-blind and the
other has normal vision.
a) Draw a pedigree showing the phenotypes of the parents and children. Shade in those
symbols representing colour-blind individuals. Symbols representing people with
normal colour vision should be left blank.
What are the genotypes of the mother and father?
b)
BIOLOGY 30•GENETICS WORKSHEET 4
Nondisjunction
1.
A person afflicted with Turner's syndrome has only a single sex chromosome (X only),
yet may survive. In contrast, a person having a single Y chromosome and no X chromosome
cannot survive. What does this tell you about the genetic contents of the X and the Y
chromosomes?
2.
Fertilization of a normal egg by a sperm that has no sex chromosomes (male
nondisjunction) can lead to Turner's syndrome. Also fertilization of an egg that has no sex
chromosomes (female nondisjunction) by a sperm carrying one X chromosome can lead to
the same disorder. Suppose a hemophilic male and a carrier (heterozygous) female have a
child. The child is nonhemophillic and is afflicted with Turner's syndrome. In which
parent did the nondisjunction occur?
3.
The trisomic XXY condition is also called Klinefelter's syndrome. How could this syndrome
arise if nondisjuction occured in the female parent of an afflicted individual? How could it
arise if nondisjunction occurred in the male parent?
4.
If nondisjunction occurs for X chromosomes during oogenesis, then some eggs having two
X chromosomes and others having no X chromosomes are produced at about equal
frequencies. If normal sperm fertilize these two types of eggs, what karyotypes are
possible?
5.
Expectant parents want to learn whether the fetus the woman is carrying has sickle-cell
disease. Could a genetic counselor determine this by looking at the fetus's karyotype?
Explain.
6.
Individuals afflicted with Down's syndrome typically have an extra chromosome 21, so
their cells have a total of 47 chromosomes. However, in a few cases of Down's syndrome
46 chromosomes are present. Included in this total are two normal-appearing
chromosomes 21, and a longer than normal chromosome 14. Interpret this observation
and indicate how these few individuals can have a normal chromosome number.
7.
Since any pair of chromatids can fail to separate during meiosis, there are theoretically 23
possible kinds of monosomy and trisomy. However, monosomies and trisomies for most of
the 23 chromosome pairs are extremely rare or unheard of in live babies. Why do you
think this is so?
BIOLOGY 30•GENETICS WORKSHEET 5
Population Genetics
1.
In the gene pool for a certain population of rabbits, the gene frequency for brown fur
(B) is 63%. What is the gene frequency of white fur?
2.
Twenty-five homozygous brown rabbits are placed with 75 homozygous white rabbits.
What are the gene frequencies for brown fur (B) and white fur (b)?
3.
Fifty heterozygous brown rabbits are placed with 100 homozygous white rabbits. What are
the gene frequencies for brown (B) and white (b) fur?
a)
b)
c)
4.
If there were an equal distribution of males and females in both colours and random matings
occured, what distribution of white and brown rabbits would your expect to get in the F1
generation?
What distribution of white and brown rabbits would your expect to get with this gene pool?
Is there a difference between your answers in a) and b). If yes explain.
The gene frequency for the dominant allele for tongue rolling in a certain high school is
70%. Construct a cross-multiplication table for this gene.
a)
b)
What percentage of the student population is heterozygous for this trait?
What percentage of the population is homozygous recessive?
5.
Population geneticists have studied a human population in which 9% of the people are
homozygous for a recessive gene that causes red hair. What is the frequency of this gene
in the total population.
6.
Phenylketonuria (PKU) is an autosomal recessive condition. About 1 of every 50 individuals
is heterozygous for the gene but displays no symptoms of the disorder.
a)
b)
c)
If you select a symptom-free male at random from the population, what is the probability that
he will be heterozygous?
If you select a symptom-free female at random from the population, what is the probability
that she will be heterozygous?
If you select a symptom-free male and a symptom-free female at random, what is the
probability that both will be heterozygous? What is the probability that they could have a
child afflicted with PKU?
7.
Laws restricting marriage between close relatives (consanguineous matings) are
widespread, the rationale being that such marriages generally lead to an increase in the
incidence of genetic defects among offspring. Suppose you are a carrier (Heterozygous)
for PKU. If you pick a potential mate at random from the population, what is the
probability that he or she would also be a PKU carrier? If you marry your first cousin, do
you think he or she would have the same probability of being a PKU carrier as your
randomly selected mate? Explain.
8.
A small population of deer becomes geographically isolated from others of the same
species. The isolated deer mate among themselves.
a)
If this situation persists for many years, harmful traits due to mutations may increase. What
genetic principle may explain this?
b)
If this isolation persists for a much longer time period, what is likely to happen to this particular
group of deer. Explain.
Now try these for a challenge:
1.
A man is homozygous dominant for ten different genes, which assort independently. How many
genotypically different types of sperm could he produce? A woman is homozygous recessive for
eight of these ten genes, and she is heterozygous for the other two. How many genotypically
different types of eggs could she produce? (HINT: Look at the first worksheet (#18-20) and see
what can you conclude regarding the relationship between the number of different gamates
possible and the number of heterozygous and homozygous genes that are present.) Try predicting
the number of different types of gamates produced by a man heterozygos for ten different genes.
For a species (or population), what might be the biological benefits, if any, of possessing, a large
number of heterozygotes?
2.
A pure breeding mink with black fur and a white tipped tail was crossed with a pure
breeding brown furred mink without a white tip. The offspring were all black with a white
tip on their tail. A test cross of numerous matings produced:
36 black, white tipped
29 black, no white tips
21 brown, no white tips
32 brown, white tipped
Are the two genes linked? If so what is the percentage of crossover?
3.
What conditions result in the following phenotypic ratios? (HINT: more than 1 locus
may be involved.)
a)
3: 1
e)
b)
1: 2: 1 f)
c)
9: 3: 3: 1
d) 1: 1
3: 6: 3: 1: 2: 1
47: 47: 3: 3
g)
1: 2: 1: 2: 4: 2: 1: 2: 1
4.
In mice colour is controlled by two gene loci, each with two alleles. The B allele produces
black and the b allele produces brown coat depending upon the action of the second
locus. The C allele produces the colour controlled by the first locus and the c allele
produces an absence of colour (white or albino) irregardless of the first locus. It two mice
each heterozygous at both loci mate determine the genotypic and phenotypic ratios.
5.
The manx cat is a tailless or short tailed cat produced by the presence of a dominant
allele M. Normal tailed cats are homozygous mm. The homozygous MM situation is
lethal. Use to explain why, on average, manx X manx breedings produce manx to tailed
cats in a 2 to 1 ratio.