BIO 210 Genetics Exam #2 Carefully Analyzed
Questions with Correct Answers Graded A+ 2026
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
1
,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 ANSWER>> do not affect the phenotype of the offspring
Maternal effect inheritance is explained by ANSWER>> the accumulation of gene
products that the mother provides to her developing oocytes (immature eggs)
Example of maternal effect ANSWER>> morphological features of the water snail,
Linnaean peregra
In linnaean peregra, the ANSWER>> shell 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 ANSWER>> When 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.
2
,Taken together, these results contradict a Mendelian pattern of inheritance.
Maternal Effect- Snail Coiling: F2 Generation ANSWER>> the 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 ANSWER>> The 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. ANSWER>> The 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 ANSWER>> in
the early steps of embryogenesis
3
, 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? ANSWER>> D/d, d/d
Epigenetic ANSWER>> study 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 ANSWER>> DNA (e.g., methylation - CH3) and
chromosomal modifications
epigenetic occurs ANSWER>> during oogenesis, spermatogenesis or early embryonic
development or throughout life
Dosage Compensation ANSWER>> Mechanism in which X chromosome inactivation
equalizes gene expression between males and females.
Barr body ANSWER>> a structure in the interphase nuclei of somatic cells of female
mammals that is a highly condensed X chromosome
Barr Body: Calico Cat ANSWER>> The 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.
4
Questions with Correct Answers Graded A+ 2026
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
1
,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 ANSWER>> do not affect the phenotype of the offspring
Maternal effect inheritance is explained by ANSWER>> the accumulation of gene
products that the mother provides to her developing oocytes (immature eggs)
Example of maternal effect ANSWER>> morphological features of the water snail,
Linnaean peregra
In linnaean peregra, the ANSWER>> shell 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 ANSWER>> When 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.
2
,Taken together, these results contradict a Mendelian pattern of inheritance.
Maternal Effect- Snail Coiling: F2 Generation ANSWER>> the 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 ANSWER>> The 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. ANSWER>> The 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 ANSWER>> in
the early steps of embryogenesis
3
, 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? ANSWER>> D/d, d/d
Epigenetic ANSWER>> study 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 ANSWER>> DNA (e.g., methylation - CH3) and
chromosomal modifications
epigenetic occurs ANSWER>> during oogenesis, spermatogenesis or early embryonic
development or throughout life
Dosage Compensation ANSWER>> Mechanism in which X chromosome inactivation
equalizes gene expression between males and females.
Barr body ANSWER>> a structure in the interphase nuclei of somatic cells of female
mammals that is a highly condensed X chromosome
Barr Body: Calico Cat ANSWER>> The 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.
4
