PCB3063 Exam 1 Latest Update
Autosomal Dominant - Answer -Appear in every generation
-Males & females equally affected
-All affected individuals have an affected parent
-Most affected individuals are heterozygotes
Autosomal Recessive - Answer -Skips generations
-Males & females equally affected
-All affected individuals are homozygous recessive
-Unaffected parents of affected offspring are obligate heterozygotes
-Occurs more often in consanguineous matings
law of independent assortment - Answer the law that states that genes separate
independently of one another in meiosis
What is independent assortment?
a. That in diploids, two alleles exist on independent chromosomes
b. That the two homologous chromosomes separate and become independent of each
other during meiosis
c. That the two alleles for a single gene can be crossed over during prophase 1
independently of one another
d. That nonhomologous chromosomes move independently of one another in meiosis
e. That the two stages of meiosis are independent of one another - Answer d. That
nonhomologous chromosomes move independently of one another in meiosis
As seen in the figure, how one homologous pair separates does not influence how a
different homologous pair separates. For unlinked genes, this leads to variations in
alleles in the gametes
What is the probability that two parents who are heterozygous for the recessive trait of
albinism will have two albino offspring?
a. 1/2
b. 1/4
,c. 1/8
d. 1/16
e. 1/32 - Answer d. 1/16
For each birth, the probability that the couple will have a homozygous recessive child is
1/4. Using the product law, the probability of having two such offspring is 1/4 x 1/4 =
1/16.
Law of Segregation - Answer Mendel's law that states that the pairs of homologous
chromosomes separate in meiosis so that only one chromosome from each pair is
present in each gamete
Law of Dominance - Answer In many traits one allele is dominant over the other allele.
The "weaker (recessive" allele is only expressed when it is paired with another
recessive allele
Mendel's third postulate is "During the formation of gametes, the paired unit factors
separate, or segregate, randomly so that each gamete receives one or the other with
equal likelihood." When does this segregation occur?
a. in G1
b. in mitotic anaphase
c. in meiotic anaphase I
d. in meiotic anaphase II
e. in both meiotic anaphase I and anaphase II - Answer c. in meiotic anaphase I
The alleles separate ("segregate") from one another when the homologs are separated.
The two homologs migrate to opposite poles at anaphase I.
How many different types of gametes can be formed by the genotype AaBbCc?
a. 3
b. 4
c. 8
d. 16
e. 32 - Answer c. 8
First, you must determine the number of different heterozygous gene pairs (n) involved.
Once n is determined, 2n is the number of different gametes that can be formed. Here,
there are three heterozygous genes, so the correct formula is 2^3 = 8.
,The possible gametes are as follows.
P genotype: AaBbCc
Gametes: ABC, ABc, AbC, Abc, aBC, aBc, abC, abc
X-linked dominant - Answer -disorders caused by mutations in genes on the X
chromosome,
-In females (who have two X chromosomes), a mutation in one of the two copies of the
gene in each cell is sufficient to cause the disorder.
-In males (who have only one X chromosome), a mutation in the only copy of the gene in
each cell causes the disorder.
-males experience more severe symptoms of the disorder than females
-No male to male transmission
X-linked recessive - Answer -disorders caused by mutations in genes on the X
chromosome.
-In males (who have only one X chromosome), one altered copy of the gene in each cell
is sufficient to cause the condition.
-In females (who have two X chromosomes), a mutation would have to occur in both
copies of the gene to cause the disorder.
-affect males more frequently
-no male-to-male transmission
Mitochondrial inheritance - Answer -no transmission from M
-maternal inheritance
-potential for the disease to affect both sons and daughters of affected F
Homozygote - Answer An individual with 2 identical alleles for a gene
Heterozygote - Answer An individual with 2 different alleles for a gene
Mendel's first postulate is "Genetic characters are controlled by unit factors existing in
pairs in an individual." What is a modern term for "unit factors?"
a. genes
b. chromosomes
c. D N A
d. phenotypes
, e. alleles - Answer a. genes
If the green pea pod allele (G) is dominant to the yellow allele (g), a cross between two
heterozygous plants would be expected to produce _____.
a. all green
b. 1/4 green and 3/4 yellow
c. 1/2 green and 1/2 yellow
d. 3/4 green and 1/4 yellow
e. all yellow - Answer c. 3/4 green and 1/4 yellow
The cross is expected to produce offspring in the genotypic proportions of 1/4 GG, 2/4
Gg, and 1/4 gg. Since G is dominant to g, 1/4 GG and 2/4 Gg = 3/4 green and 1/4 gg is
yellow.
Hemizygote - Answer a male positive for an x-linked mutation
Sex-linked gene - Answer -All sons of an affected mother are affected
-All daughters of an affected male are carriers
-No male-to-male transmission of trait
-Males more often affected than females
Sex-limited traits - Answer a characteristic controlled by autosomal genes that is
phenotypically exhibited in only one gender
sex-influenced traits - Answer an autosomal trait that is influenced by the presence of
male or female sex hormones (ex.baldness)
Duchenne muscular dystrophy is caused by a recessive X-linked allele. A man with this
disorder _____
a. could have inherited it from either parent
b. must have inherited it from his mother
c. must have inherited it from both parents
d. can pass it along to all of his children
e. can pass it along to only his sons - Answer b. must have inherited it from his mother
The man must carry only one copy of the allele on his X chromosome, which he must
have inherited from his mother. He would have inherited a Y chromosome from his
father. He would pass that X chromosome on to only his daughters.
Autosomal Dominant - Answer -Appear in every generation
-Males & females equally affected
-All affected individuals have an affected parent
-Most affected individuals are heterozygotes
Autosomal Recessive - Answer -Skips generations
-Males & females equally affected
-All affected individuals are homozygous recessive
-Unaffected parents of affected offspring are obligate heterozygotes
-Occurs more often in consanguineous matings
law of independent assortment - Answer the law that states that genes separate
independently of one another in meiosis
What is independent assortment?
a. That in diploids, two alleles exist on independent chromosomes
b. That the two homologous chromosomes separate and become independent of each
other during meiosis
c. That the two alleles for a single gene can be crossed over during prophase 1
independently of one another
d. That nonhomologous chromosomes move independently of one another in meiosis
e. That the two stages of meiosis are independent of one another - Answer d. That
nonhomologous chromosomes move independently of one another in meiosis
As seen in the figure, how one homologous pair separates does not influence how a
different homologous pair separates. For unlinked genes, this leads to variations in
alleles in the gametes
What is the probability that two parents who are heterozygous for the recessive trait of
albinism will have two albino offspring?
a. 1/2
b. 1/4
,c. 1/8
d. 1/16
e. 1/32 - Answer d. 1/16
For each birth, the probability that the couple will have a homozygous recessive child is
1/4. Using the product law, the probability of having two such offspring is 1/4 x 1/4 =
1/16.
Law of Segregation - Answer Mendel's law that states that the pairs of homologous
chromosomes separate in meiosis so that only one chromosome from each pair is
present in each gamete
Law of Dominance - Answer In many traits one allele is dominant over the other allele.
The "weaker (recessive" allele is only expressed when it is paired with another
recessive allele
Mendel's third postulate is "During the formation of gametes, the paired unit factors
separate, or segregate, randomly so that each gamete receives one or the other with
equal likelihood." When does this segregation occur?
a. in G1
b. in mitotic anaphase
c. in meiotic anaphase I
d. in meiotic anaphase II
e. in both meiotic anaphase I and anaphase II - Answer c. in meiotic anaphase I
The alleles separate ("segregate") from one another when the homologs are separated.
The two homologs migrate to opposite poles at anaphase I.
How many different types of gametes can be formed by the genotype AaBbCc?
a. 3
b. 4
c. 8
d. 16
e. 32 - Answer c. 8
First, you must determine the number of different heterozygous gene pairs (n) involved.
Once n is determined, 2n is the number of different gametes that can be formed. Here,
there are three heterozygous genes, so the correct formula is 2^3 = 8.
,The possible gametes are as follows.
P genotype: AaBbCc
Gametes: ABC, ABc, AbC, Abc, aBC, aBc, abC, abc
X-linked dominant - Answer -disorders caused by mutations in genes on the X
chromosome,
-In females (who have two X chromosomes), a mutation in one of the two copies of the
gene in each cell is sufficient to cause the disorder.
-In males (who have only one X chromosome), a mutation in the only copy of the gene in
each cell causes the disorder.
-males experience more severe symptoms of the disorder than females
-No male to male transmission
X-linked recessive - Answer -disorders caused by mutations in genes on the X
chromosome.
-In males (who have only one X chromosome), one altered copy of the gene in each cell
is sufficient to cause the condition.
-In females (who have two X chromosomes), a mutation would have to occur in both
copies of the gene to cause the disorder.
-affect males more frequently
-no male-to-male transmission
Mitochondrial inheritance - Answer -no transmission from M
-maternal inheritance
-potential for the disease to affect both sons and daughters of affected F
Homozygote - Answer An individual with 2 identical alleles for a gene
Heterozygote - Answer An individual with 2 different alleles for a gene
Mendel's first postulate is "Genetic characters are controlled by unit factors existing in
pairs in an individual." What is a modern term for "unit factors?"
a. genes
b. chromosomes
c. D N A
d. phenotypes
, e. alleles - Answer a. genes
If the green pea pod allele (G) is dominant to the yellow allele (g), a cross between two
heterozygous plants would be expected to produce _____.
a. all green
b. 1/4 green and 3/4 yellow
c. 1/2 green and 1/2 yellow
d. 3/4 green and 1/4 yellow
e. all yellow - Answer c. 3/4 green and 1/4 yellow
The cross is expected to produce offspring in the genotypic proportions of 1/4 GG, 2/4
Gg, and 1/4 gg. Since G is dominant to g, 1/4 GG and 2/4 Gg = 3/4 green and 1/4 gg is
yellow.
Hemizygote - Answer a male positive for an x-linked mutation
Sex-linked gene - Answer -All sons of an affected mother are affected
-All daughters of an affected male are carriers
-No male-to-male transmission of trait
-Males more often affected than females
Sex-limited traits - Answer a characteristic controlled by autosomal genes that is
phenotypically exhibited in only one gender
sex-influenced traits - Answer an autosomal trait that is influenced by the presence of
male or female sex hormones (ex.baldness)
Duchenne muscular dystrophy is caused by a recessive X-linked allele. A man with this
disorder _____
a. could have inherited it from either parent
b. must have inherited it from his mother
c. must have inherited it from both parents
d. can pass it along to all of his children
e. can pass it along to only his sons - Answer b. must have inherited it from his mother
The man must carry only one copy of the allele on his X chromosome, which he must
have inherited from his mother. He would have inherited a Y chromosome from his
father. He would pass that X chromosome on to only his daughters.
