Pattern of inheritance

Question 1

What is mendels Principle of dominance?

Answer 1

n a heterozygote, one dominant allele completely masks the effects of a
the presence of recessive allele

Question 2

What is mendels principle of segregation?

Answer 2

Each diploid organism possess 2 alleles for each trait; the alleles segregate
(separate) from each other during the formation of gametes.

Question 3

What is Mendels principle of independent assortment?

Answer 3

The alleles on different chromosomes are distributed randomly (OR
independently assorted) of each other to individual gametes.

Question 4

Give 2 examples of autosomal dominant diseases

Answer 4

Hypercholesterolemia
(chromosome 19): Missing protein that removes
cholesterol from the blood; heart attack by age 50

Huntington disease
(chromosome 4): Progressive mental and neurological damage; neurologic
disorders by ages 40 - 70

Question 5

Give 2 examples of Autosomal Recessive Diseases

Answer 5

Phenylketonuria (PKU)
(chromosome 12): Missing enzyme; mental deficiency

Thalassemia (chromosome 16 or 11): Reduced amounts of hemoglobin; anemia, bone, and spleen enlargement

Sickle-cell anemia (chromosome 11): Abnormal hemoglobin; sickle-shaped
red cells, anemia, blocked circulation;
increased resistance to malaria

Cystic fibrosis
(chromosome 7): Defective cell membrane protein;
excessive mucus production; digestive
and respiratory failure

Tay-Sachs disease
(chromosome 15): Missing enzyme; buildup of fatty
deposit in brain; buildup disrupts
mental development

Question 6

Who discovered Sex linked inheritence?

Answer 6

Thomas Hunt Morgan (1910)

Question 7

What is the product rule?

Answer 7

The probability of simultaneous independent events equals the product of the
probabilities of the individual events.

Question 8

What is the sum rule?

Answer 8

The probability of either of two mutually exclusive events occurring is the
sum of their individual probabilities.

Question 9

What are lethal Alleles?

Answer 9

Allele(s) that causes an organism to die or to have reduced life expectancy before the individual can reproduce.

Question 10

What happens if 2 lethal alleles are present?

Answer 10

Lethal allele combinations
remove an expected
progeny class from the
population, leaving the
heterozygous and either
homozygous dominant or
recessive.

Question 11

What is Incomplete dominance?

Answer 11

a form of Gene interaction in which both alleles of a gene at a locus are partially expressed, often resulting in an intermediate or different phenotype. It is also known as partial dominance.

Question 12

What is codominance?

Answer 12

This is when neither allele is dominant and both are expressed in a heterozygous individual

Question 13

How does Familial hypercholesterolemia show incomplete dominance?

Answer 13

Heterozygote (with 1 LDL-R mutant allele) has only ~50% the normal
number of receptors in the liver for LDL cholesterol, thus showing
moderate increase in plasma cholesterol level.
 Homozygous for the mutant alleles totally lacks the receptor, resulting
in very high plasma cholesterol level.

Question 14

How does huntington disease show penetrance?

Answer 14

The defective gene causes increased number of CAG repeat (number of 
CAG repeats ↑; severity of symptoms ↑)  but the age of onset cannot 
be predicted (varies from teens to late 60s)

HD gene with > 40 repeat counts has a lifetime penetrance of 100% for HD
 a.k.a ________ % of individuals with the genotype (>40 repeat counts) will develop the HD
in their lifetime
 but HD has an age-related penetrance  incidence increase by age, and the
age of onset for the disease cannot be predicted

Question 15

How does Familial hypercholesterolemia show incomplete dominance?

Answer 15

Heterozygote (with 1 LDL-R mutant allele) has only ~50% the normal
number of receptors in the liver for LDL cholesterol, thus showing
moderate increase in plasma cholesterol level.
Homozygous for the mutant alleles totally lacks the receptor, resulting
in very high plasma cholesterol level.

Question 16

What is epistasis?

Answer 16

This is when a gene at one locus affects the expression of a gene in a different locus and 2 or more pairs of alleles affect a single trait. It is common during zygote development. Example includes inheritence of coat colour in dogs

Question 17

What is penetrance?

Answer 17

the proportion of individuals carrying a particular variant of a gene that also express an associated trait

Question 18

What is expressivity?

Answer 18

expressivity is the degree to which a phenotype is expressed by individuals having a particular genotype. Expressivity is related to the intensity of a given phenotype; it differs from penetrance, which refers to the proportion of individuals with a particular genotype that actually express the phenotype

Question 19

Define gene

Answer 19

A segment of the DNA that codes for a protein that is used to express a trait

Question 20

What is pleiotropy?

Answer 20

the phenomenon in which a single locus affects two or more apparently unrelated phenotypic traits and is often identified as a single mutation that affects two or more wild-type traits

Question 21

What is a phenotype?

Answer 21

This describes the physical appearance of an individual

Question 22

What is genotype?

Answer 22

This is the genetic makeup of an individual and the type of genes found on them

Question 23

What are sex influenced traits?

Answer 23

Sex-influenced traits are autosomal traits that are influenced by sex. If a male has one recessive allele, he will show that trait, but it will take two recessive for the female to show that same trait. One such gene is baldness.

Question 24

What are sex limited traits?

Answer 24

Sex-limited traits are determined by genes located on autosomes and express only in one sex. While these traits are responsible considerably for sexual dimorphism, sex-influenced traits do not show distinctive expression between women and men.