Extensions and Modifications of Mendelian Genetics

Question 1

Dominance

Answer 1

Phenotype of the homozygote is the same as the phenotype of the heterozygote

Question 2

Codominance

Answer 2

Phenotype of the heterozygote includes the phenotype of both homozygotes (e.g. mottled flowers)

Question 3

Incomplete Dominance

Answer 3

Phenotype of the heterozygote is intermediate between the phenotypes of the two homozygotes

Question 4

Penetrance

Answer 4

Percentage of individuals with a certain genotype that express the phenotype

Question 5

Expressivity

Answer 5

The degree or severity to which the phenotype is expressed

Question 6

Lethal alleles

Answer 6

Cause death at an early stage of development so some genotypes do not appear among the progeny

Question 7

Multiple alleles

Answer 7

More than two alleles present within a group of individuals (e.g. ABO blood group)

Question 8

Gene interaction

Answer 8

Effects of genes at one locus depend on the presence of genes at other loci producing novel phenotypes

Question 9

Epistasis

Answer 9

One gene masks the effect of another gene

Question 10

Recessive epistasis

Answer 10

ABO blood groups - recessive Bombay phenotype controls expression of ABO

Question 11

Dominant epistasis

Answer 11

e.g. Squash pigmentation - Dominant allele inhibits the conversion of Enzyme A into Enzyme B

Question 12

Duplicate recessive epistasis

Answer 12

Two enzymes must be recessive in order to display the phenotype

Question 13

Genetic complementation

Answer 13

Multiple genes complement each other to produce a given phenotype (e.g. coat color in dogs)

Question 14

Sex-influenced characteristics

Answer 14

Same genotype expressed differently in males vs. females

Question 15

Sex-limited characteristics

Answer 15

Same genotype only expressed in one sex vs. another

Question 16

Mitochondrial characteristics

Answer 16

Vary wildly based on population frequency of randomly assorted mitochondria

Question 17

Genomic imprinting

Answer 17

Differential expression of genetic material depending on whether it is inherited from the male or female parent

Question 18

Epigenetics

Answer 18

Phenomena due to alterations to DNA that do not include changes to DNA sequence which often affect the way DNA is expressed, e.g. methylation

Question 19

Genetic maternal effect

Answer 19

The genotype of the maternal parent determines the phenotype of the offspring

Question 20

Genetic anticipation

Answer 20

A genetic trait becomes more strongly expressed or expressed at an earlier stage as it is passed from generation to generation (e.g. Fragile X Syndrome)

Question 21

Temperature-sensitive allele

Answer 21

An allele whose product is functional only at a certain temperature