Module 2

Question 1

if dominant allele is present, dominant trait is always expressed

Answer 1

Complete Dominance

Question 2

type of complete dominance

One copy of the gene is enough for the individual to be affected.

Examples of conditions inherited in this manner are:
- Huntington’s disease
- achondroplasia (short-limbed dwarfism)
- polycystic kidney disease
- polydactyly

Answer 2

Autosomal dominant inheritance

Question 3

type of complete dominance

It takes 2 copies of the gene for the trait to be expressed.

Examples of conditions inherited in this manner are:
- Cystic fibrosis
- Tay-Sachs
- Hemochromatosis
- phenylketonuria (PKU)
- Deafness

Answer 3

Autosomal recessive inheritance

Question 4

non-Mendelian inheritance

a dominant allele and a recessive allele but the dominant one cannot completely mask the effect of the recessive allele such that heterozygotes come out with a blended phenotype

both parental phenotypes are not seen

results to new phenotype

Answer 4

Incomplete Dominance or Partial Dominance

Question 5

non-Mendelian inheritance

both alleles involved are equally dominant

phenotypes of both parent flower plants can be seen simultaneously expressed in the same offspring

Answer 5

Codominance

Question 6

is due to a single
base substitution in the DNA sequence of the gene encoding the beta
chain of hemoglobin, the protein that carries oxygen in the blood

Answer 6

Sickle cell anemia

Question 7

heterozygote has a more extreme phenotype than that of either of his parents

also called _________

heterozygous individuals have a higher fitness than homozygous individuals

Answer 7

Overdominance

heterozygote advantage

Question 8

are alleles that cause an organism to die only when present in homozygous condition, where the gene involved must have been an essential gene.

modify the 3:1 phenotypic ratio into 2:1 because 1⁄4 of the offspring die earlier in development

Answer 8

Lethal Alleles

Question 9

usually cause death of the zygote, or later in the embryonic development or even after birth or hatching.

Answer 9

Completely lethal genes

Question 10

in many cases lethal genes become operative at the time the individuals become sexually mature

lethal genes which handicap but do not destroy their possessor

Answer 10

Subvital, sublethal or semi-lethal genes

Question 11

If the mutation is caused by a recessive lethal allele, the homozygote for the allele will have the lethal phenotype. The good thing is that most lethal genes are recessive.

TaySachs disease
cystic fibrosis
sickle cell anemia

Answer 11

Recessive Lethal Genes

Question 12

is due to deficiency of hexosaminidase A, resulting to
inability to break down specific membrane lipids. It progressively
destroys nerve cells (neurons) in the brain and spinal cord. The most common form of this disease becomes apparent in infancy

due to recessive lethal genes

Answer 12

Tay-Sachs disease

Question 13

If the mutation is caused by a dominant lethal allele, the heterozygote for the allele will show the lethal phenotype, the homozygote dominant dies early.

Answer 13

Dominant Lethal Genes

Question 14

Autosomal dominant progressive disorder whose symptoms can develop at any time, but they often first appear when people are in their 30s or 40s. It affects the brain’s basal ganglia, which are associated with a variety of functions, including voluntary and involuntary motor control, procedural learning relating to routine behaviors or “habits,” eye movements, and cognitive, emotional functions.

Answer 14

Huntington’s disease (HD)

Question 15

Some lethal alleles exert their effects only under certain environmental conditions, thus the term conditional. They can be expressed due to specific circumstances, such as temperature.

Answer 15

Conditional Lethal Genes

Question 16

Conditional Lethal Genes example is the case of temperature-sensitive (ts) lethal genes in ____________, which can cause death in a developing larva at 30C. Larvae, however, can survive if grown at lower temperatures like 22C.

Answer 16

Drosophila melanogaster

Question 17

In humans, a condition called ________ is controlled by conditional lethal genes.

is a sex-linked, inherited condition that results from deficiency in an enzyme called glucose-6-phosphate dehydrogenase (G6PD).

The disease was named because when affected individuals eat fava beans (fig. 34) or inhale pollen from fava plants, they develop hemolytic anemia, a condition in which red blood cells break apart and block blood vessels. Blockage can cause kidney failure and result in death. The defective G6PD allele only causes death under certain conditions.

Answer 17

favism

Question 18

These genes kill some individuals in a population, but not all of them. Environmental factors and other genes may help prevent the detrimental effects of semi-lethal genes.

In humans, ______ is a hereditary disease caused by deficiencies in clotting factors, which results in impaired blood clotting and coagulation.

Answer 18

Semi-lethal or sublethal genes

hemophilia

Question 19

2 pairs of genes determine the same phenotype but assorted independently, produce new phenotypes by mutual genetic interaction

9:3:3:1

Answer 19

Non-epistatic inter-allelic genetic interaction

Question 20

Homozygous recessive genotype at one locus masks the expression at second locus.

9:3:4

Answer 20

Recessive epistasis

Question 21

Dominant allele at one locus masks expression at second locus

12:3:1

Answer 21

Dominant epistasis

Question 22

One gene when dominant, is epistatic to the other, and the second gene when homozygous recessive, is epistatic to the first

13:3

Answer 22

Dominant suppression

Question 23

At least one dominant allele from each of two genes needed for phenotype

9:7

Answer 23

Complementary gene action

Question 24

One dominant allele from either of two genes needed
for phenotype

15:1

Answer 24

Duplicate dominant epistasis

Question 25

Two independent dominant genes have similar phenotypic effect when present individually but produce a cumulative or double effect when found together.

9:6:1

Answer 25

Dominant gene interaction

Question 26

It occurs when one gene masks or modifies the effect of another gene pair (epistasis) and alters the phenotype.

best example of gene interactions

Answer 26

Epistasis