BIO 311C QUESTIONS AND ANSWERS A+ GRADED
What are the two laws of inheritance?
1. Law of Segregation- Allele pairs segregate during gamete formation and the paired
condition is restored by the random fusion of gametes at fertilization.
Example: **Monohybrid Cross-(pPxpp) 3:1 ratio after crossing pure bred pea varieties
with either spherical seeds or dented seeds. Found that 3/4th of the F2 progenies had
spherical seeds and 1/4th had dented seeds.
2. Law of independent assortment- the segregation of each allele pair is independent of
other allele pairs. The individual allele pairs need to be located on separate loci, far from
each other to allow independent assortment during gamete formation.
Example: Dihybrid cross-if we cross a parent which is homozygous dominant for both
(SSYY) with spherical yellow seeds with another parent which is homozygous recessive
(ssyy) for both alleles with dented green seeds, one can expect a completely
heterozygous condition (SsYy).
Non-Mendelian Patterns of Inheritance
Intermediate inheritance or incomplete dominance, Codominance, Pleiotropy, Epistasis,
Multiple genes, Sex-linked inheritance, Maternal inheritance, Environmental effect on
gene expression
Intermediate inheritance or incomplete dominance
The homozygotes have a particular phenotype, and the heterozygous have an
intermediate phenotype meaning that no single gene is completely dominant.
Codominance
Both phenotypes are expressed at about equal levels by the expression of two types of
proteins by two alleles.
Pleiotropy
One gene or allele codes for more than one phenotype.
Epistasis
One gene interferes with the expression of another gene. Several pairs of alleles may
interact to affect a single phenotype.
Multiple genes
Some genes exist in more than two forms.
Sex-Linked Inheritance
The phenotypes affected by genes located on sex chromosomes are expressed
depending on the sex of the individuals.
Maternal Inheritance
The genes present in mitochondria and chloroplasts are always inherited maternally.
Only nuclear genes are carried on from one gamete to another in males, and the
mitochondria and chloroplasts present in the egg are copied in the zygote and passed
on to the next generation.
Environmental effect on gene expression
The influence of environment on gene expression results in wider variation especially in
traits controlled by multiple genes.
, Ex: skin color in mice is affected by two pairs of alleles, and if one pair of alleles
is homozygous recessive, mice are always albino irrespective of the other locus.
Epistasis
Ex: albino individuals lack pigments in the skin, eye and hair showing the effect
of a single mutation in one locus causing varied effects.
Pleiotropy
Ex: Snapdragon flowers with red (RR) and white (rr) color flowers are crossed the
F1 generation will have all pink flowers(Rr) showing _______?
Intermediate Inheritance
Ex: People with the blood type AB will express both the proteins for types A and
B. The white clover leaf has two patterns which are present in different
homozygous conditions; both the patterns will appear in the heterozygous
condition.
Codominance
Ex: In humans, XX= female, XY=male. Baldness, hemophilia, and muscular
dystrophy
Sex-Linked Inheritance
Ex: Skin color determined by 3 alleles is affected further by sunlight intensifying
the melanin pigmentation. Also, the influence of nutrition and exercise on weight
or height. Hydrangea flowers may be blue if grown in acidic soil or pink in
alkaline soil
Environmental effect on gene expression
Ex: Stem coloration in the 4-o'clock plant is due to the chlorophyll content
determined by chloroplast genes derived from female parent.
Maternal Inheritance
Ex: skin color in humans is determined by three genes (A,B,C). Dominant= dark
skin, Recessive= light skin. Based on combination of three allele pairs, the skin
color varies from light(aa,bb,cc) to dark color (AA,BB,CC). Height, intelligence,
and weight are also determined by multiple genes.
Multiple Genes
A couple that does not have cystic fibrosis have their first child showing
symptoms of cystic fibrosis. What is the probability that their next child will be a
carrier for cystic fibrosis but not show the symptoms?
A. 0%
B. 50%
C. 25%
D. 100%
E. 75%
B
In crossing a homozygous recessive with a heterozygote, what is the chance of
getting an offspring with the homozygous dominant phenotype?
A) 0%
B) 75%
C. 25%
D. 100%
E. 50%
What are the two laws of inheritance?
1. Law of Segregation- Allele pairs segregate during gamete formation and the paired
condition is restored by the random fusion of gametes at fertilization.
Example: **Monohybrid Cross-(pPxpp) 3:1 ratio after crossing pure bred pea varieties
with either spherical seeds or dented seeds. Found that 3/4th of the F2 progenies had
spherical seeds and 1/4th had dented seeds.
2. Law of independent assortment- the segregation of each allele pair is independent of
other allele pairs. The individual allele pairs need to be located on separate loci, far from
each other to allow independent assortment during gamete formation.
Example: Dihybrid cross-if we cross a parent which is homozygous dominant for both
(SSYY) with spherical yellow seeds with another parent which is homozygous recessive
(ssyy) for both alleles with dented green seeds, one can expect a completely
heterozygous condition (SsYy).
Non-Mendelian Patterns of Inheritance
Intermediate inheritance or incomplete dominance, Codominance, Pleiotropy, Epistasis,
Multiple genes, Sex-linked inheritance, Maternal inheritance, Environmental effect on
gene expression
Intermediate inheritance or incomplete dominance
The homozygotes have a particular phenotype, and the heterozygous have an
intermediate phenotype meaning that no single gene is completely dominant.
Codominance
Both phenotypes are expressed at about equal levels by the expression of two types of
proteins by two alleles.
Pleiotropy
One gene or allele codes for more than one phenotype.
Epistasis
One gene interferes with the expression of another gene. Several pairs of alleles may
interact to affect a single phenotype.
Multiple genes
Some genes exist in more than two forms.
Sex-Linked Inheritance
The phenotypes affected by genes located on sex chromosomes are expressed
depending on the sex of the individuals.
Maternal Inheritance
The genes present in mitochondria and chloroplasts are always inherited maternally.
Only nuclear genes are carried on from one gamete to another in males, and the
mitochondria and chloroplasts present in the egg are copied in the zygote and passed
on to the next generation.
Environmental effect on gene expression
The influence of environment on gene expression results in wider variation especially in
traits controlled by multiple genes.
, Ex: skin color in mice is affected by two pairs of alleles, and if one pair of alleles
is homozygous recessive, mice are always albino irrespective of the other locus.
Epistasis
Ex: albino individuals lack pigments in the skin, eye and hair showing the effect
of a single mutation in one locus causing varied effects.
Pleiotropy
Ex: Snapdragon flowers with red (RR) and white (rr) color flowers are crossed the
F1 generation will have all pink flowers(Rr) showing _______?
Intermediate Inheritance
Ex: People with the blood type AB will express both the proteins for types A and
B. The white clover leaf has two patterns which are present in different
homozygous conditions; both the patterns will appear in the heterozygous
condition.
Codominance
Ex: In humans, XX= female, XY=male. Baldness, hemophilia, and muscular
dystrophy
Sex-Linked Inheritance
Ex: Skin color determined by 3 alleles is affected further by sunlight intensifying
the melanin pigmentation. Also, the influence of nutrition and exercise on weight
or height. Hydrangea flowers may be blue if grown in acidic soil or pink in
alkaline soil
Environmental effect on gene expression
Ex: Stem coloration in the 4-o'clock plant is due to the chlorophyll content
determined by chloroplast genes derived from female parent.
Maternal Inheritance
Ex: skin color in humans is determined by three genes (A,B,C). Dominant= dark
skin, Recessive= light skin. Based on combination of three allele pairs, the skin
color varies from light(aa,bb,cc) to dark color (AA,BB,CC). Height, intelligence,
and weight are also determined by multiple genes.
Multiple Genes
A couple that does not have cystic fibrosis have their first child showing
symptoms of cystic fibrosis. What is the probability that their next child will be a
carrier for cystic fibrosis but not show the symptoms?
A. 0%
B. 50%
C. 25%
D. 100%
E. 75%
B
In crossing a homozygous recessive with a heterozygote, what is the chance of
getting an offspring with the homozygous dominant phenotype?
A) 0%
B) 75%
C. 25%
D. 100%
E. 50%
