BIO 210 Genetics Exam #2
Genes that have a Mendelian inheritance pattern conform to four rules - answer
Expression of the genes in the offspring directly influences their traits
Genes are passed unaltered from generation to generation (except when rare mutations
occur)
Genes obey Mendel's law of segregation
When crosses involve more than one gene, the genes obey Mendel's law of
independent assortment
Maternal effect - answer genotype of the mother directly determines the phenotype of
her offspring
Surprisingly, for maternal effect genes, the genotypes of the father and of the offspring
themselves - answerdo not affect the phenotype of the offspring
Maternal effect inheritance is explained by - answerthe accumulation of gene products
that the mother provides to her developing oocytes (immature eggs)
Example of maternal effect - answermorphological features of the water snail, Linnaean
peregra
In linnaean peregra, the - answershell and internal organs can be arranged in one of
two directions
Dominant: Right-handed (dextral)
Recessive:Left-handed (sinistral)
Maternal Effect- Snail Coiling: F1 Generation - answerWhen a dextral female (DD) was
crossed to a sinistral male (dd), all F1 offspring were dextral.
However, in the reciprocal cross, where a sinistral female (dd) was crossed to a dextral
male (DD), all F1 offspring were sinistral.
Taken together, these results contradict a Mendelian pattern of inheritance.
Maternal Effect- Snail Coiling: F2 Generation - answerthe predicted genotypic ratio for
the F2 generation was 1 DD : 2 Dd : 1 dd.
,Instead of a 3:1 phenotypic ratio of dextral to sinistral snails, the predicted phenotypic
ratio of the F2 generation was composed of all dextral snails.
The F1 mothers were Dd. The D allele in the mothers is dominant to the d allele and
caused the offspring to be dextral, even when the offspring's genotype was dd!
Maternal Effect- Snail Coiling: F3 Generation - answerThe F3 generation exhibited a 3:1
ratio of dextral to sinistral snails. This ratio corresponds to the genotypes of the F2
females, which were the mothers of the F3 generation.
The ratio of F2 females was 1 DD : 2 Dd : 1 dd. The DD and Dd females produced
dextral offspring, whereas the dd females produced sinistral offspring.
Explain why all of the offspring in the F2 generation are dextral even though some of
them are dd. - answerThe F2 offspring are all dextral because all of the F1 mothers are
Dd, and the genotype of the mother determines the phenotype of the offspring.
Maternal effect genes encode RNA and proteins that play important roles - answerin the
early steps of embryogenesis
A female snail that coils to the left (sinistral) has offspring that coil to the right (dextral).
What are the genotypes of this mother and of the maternal grandmother of the offspring
respectively? - answerD/d, d/d
Epigenetic - answerstudy of modifications that occur to a gene or chromosome that
alters gene expression, but is not permanent over the course of many generations
reversible and does not change the DNA sequence
Epigenetic changes are caused by - answerDNA (e.g., methylation - CH3) and
chromosomal modifications
epigenetic occurs - answerduring oogenesis, spermatogenesis or early embryonic
development or throughout life
Dosage Compensation - answerMechanism in which X chromosome inactivation
equalizes gene expression between males and females.
Barr body - answera structure in the interphase nuclei of somatic cells of female
mammals that is a highly condensed X chromosome
Barr Body: Calico Cat - answerThe pattern of black and orange fur on this cat is due to
random X-chromosome inactivation during embryonic development.
, The orange patches of fur are due to the inactivation of the X chromosome that carries
a black allele; the black patches are due to the inactivation of the X chromosome that
carries the orange allele.
In general, only heterozygous female cats can be calico. A rare exception would be a
male cat that has an abnormal composition of sex chromosomes (XXY).
Example of Dosage Compensation - answerA white and black variegated coat color
found in certain strains of mice
A female mouse has inherited two X chromosomes:
One from its mother that carries an allele conferring white coat color (Xb)
One from its father that carries an allele conferring black coat color (XB)
A calico cat...99% of calico cats are female...why? - answerMales only have one X
X-chromosome inactivation occur in .... - answerearly in development
Lyon hypothesis - answera hypothesis to explain the pattern of X-chromosome
inactivation seen in mammals. Initially, both X chromosomes are active. However, at an
early stage of embryonic development, one of the two X chromosomes is randomly
inactivated in each somatic cell
According to the Lyon hypothesis, each somatic cell of female mammals expresses the
genes on one of the X chromosomes, but not - answerboth
Example of Lyon Hypothesis - answerglucose-6-phosphate dehydrogenase (G-6-PD),
an enzyme used in sugar metabolism
G-6-PD gel electrophoresis - answerOne G-6-PD allele encodes a G-6-PD enzyme that
migrates very quickly during gel electrophoresis (closer to botton), whereas another G-
6-PD allele produces an enzyme that migrates more slowly.
When multiple skin samples are collected from a heterozygous adult female and mixed
together, both types of enzymes are observed on a gel. In contrast, a hemizygous male
produces either the fast or slow type, but not both.
Why do these two forms of G-6-PD migrate differently? - answerThey migrate differently
because their amino acid sequences are slightly different
According to the Lyon hypothesis, an adult female who is heterozygous for the fast and
slow G-6-PD alleles should express.... - answeronly one of the two alleles in any
particular somatic cell and its descendants, but not both
Genes that have a Mendelian inheritance pattern conform to four rules - answer
Expression of the genes in the offspring directly influences their traits
Genes are passed unaltered from generation to generation (except when rare mutations
occur)
Genes obey Mendel's law of segregation
When crosses involve more than one gene, the genes obey Mendel's law of
independent assortment
Maternal effect - answer genotype of the mother directly determines the phenotype of
her offspring
Surprisingly, for maternal effect genes, the genotypes of the father and of the offspring
themselves - answerdo not affect the phenotype of the offspring
Maternal effect inheritance is explained by - answerthe accumulation of gene products
that the mother provides to her developing oocytes (immature eggs)
Example of maternal effect - answermorphological features of the water snail, Linnaean
peregra
In linnaean peregra, the - answershell and internal organs can be arranged in one of
two directions
Dominant: Right-handed (dextral)
Recessive:Left-handed (sinistral)
Maternal Effect- Snail Coiling: F1 Generation - answerWhen a dextral female (DD) was
crossed to a sinistral male (dd), all F1 offspring were dextral.
However, in the reciprocal cross, where a sinistral female (dd) was crossed to a dextral
male (DD), all F1 offspring were sinistral.
Taken together, these results contradict a Mendelian pattern of inheritance.
Maternal Effect- Snail Coiling: F2 Generation - answerthe predicted genotypic ratio for
the F2 generation was 1 DD : 2 Dd : 1 dd.
,Instead of a 3:1 phenotypic ratio of dextral to sinistral snails, the predicted phenotypic
ratio of the F2 generation was composed of all dextral snails.
The F1 mothers were Dd. The D allele in the mothers is dominant to the d allele and
caused the offspring to be dextral, even when the offspring's genotype was dd!
Maternal Effect- Snail Coiling: F3 Generation - answerThe F3 generation exhibited a 3:1
ratio of dextral to sinistral snails. This ratio corresponds to the genotypes of the F2
females, which were the mothers of the F3 generation.
The ratio of F2 females was 1 DD : 2 Dd : 1 dd. The DD and Dd females produced
dextral offspring, whereas the dd females produced sinistral offspring.
Explain why all of the offspring in the F2 generation are dextral even though some of
them are dd. - answerThe F2 offspring are all dextral because all of the F1 mothers are
Dd, and the genotype of the mother determines the phenotype of the offspring.
Maternal effect genes encode RNA and proteins that play important roles - answerin the
early steps of embryogenesis
A female snail that coils to the left (sinistral) has offspring that coil to the right (dextral).
What are the genotypes of this mother and of the maternal grandmother of the offspring
respectively? - answerD/d, d/d
Epigenetic - answerstudy of modifications that occur to a gene or chromosome that
alters gene expression, but is not permanent over the course of many generations
reversible and does not change the DNA sequence
Epigenetic changes are caused by - answerDNA (e.g., methylation - CH3) and
chromosomal modifications
epigenetic occurs - answerduring oogenesis, spermatogenesis or early embryonic
development or throughout life
Dosage Compensation - answerMechanism in which X chromosome inactivation
equalizes gene expression between males and females.
Barr body - answera structure in the interphase nuclei of somatic cells of female
mammals that is a highly condensed X chromosome
Barr Body: Calico Cat - answerThe pattern of black and orange fur on this cat is due to
random X-chromosome inactivation during embryonic development.
, The orange patches of fur are due to the inactivation of the X chromosome that carries
a black allele; the black patches are due to the inactivation of the X chromosome that
carries the orange allele.
In general, only heterozygous female cats can be calico. A rare exception would be a
male cat that has an abnormal composition of sex chromosomes (XXY).
Example of Dosage Compensation - answerA white and black variegated coat color
found in certain strains of mice
A female mouse has inherited two X chromosomes:
One from its mother that carries an allele conferring white coat color (Xb)
One from its father that carries an allele conferring black coat color (XB)
A calico cat...99% of calico cats are female...why? - answerMales only have one X
X-chromosome inactivation occur in .... - answerearly in development
Lyon hypothesis - answera hypothesis to explain the pattern of X-chromosome
inactivation seen in mammals. Initially, both X chromosomes are active. However, at an
early stage of embryonic development, one of the two X chromosomes is randomly
inactivated in each somatic cell
According to the Lyon hypothesis, each somatic cell of female mammals expresses the
genes on one of the X chromosomes, but not - answerboth
Example of Lyon Hypothesis - answerglucose-6-phosphate dehydrogenase (G-6-PD),
an enzyme used in sugar metabolism
G-6-PD gel electrophoresis - answerOne G-6-PD allele encodes a G-6-PD enzyme that
migrates very quickly during gel electrophoresis (closer to botton), whereas another G-
6-PD allele produces an enzyme that migrates more slowly.
When multiple skin samples are collected from a heterozygous adult female and mixed
together, both types of enzymes are observed on a gel. In contrast, a hemizygous male
produces either the fast or slow type, but not both.
Why do these two forms of G-6-PD migrate differently? - answerThey migrate differently
because their amino acid sequences are slightly different
According to the Lyon hypothesis, an adult female who is heterozygous for the fast and
slow G-6-PD alleles should express.... - answeronly one of the two alleles in any
particular somatic cell and its descendants, but not both
