Lecture 7

Question 1

Recessive Epistasis

Answer 1

Genotypes at 2 different loci on a chromosome determine the phenotype; for example, slide 28 discusses the ABO blood type

Question 2

Dominant Epistasis

Answer 2

1 dominant allele can determine what phenotype is present and/or absent; for example, slide 29 discusses pigment in squash; plants with a dominant W allele have no enzyme 1, but plants with a dominant Y and no dominant W produce both enzyme 1 and 2

Question 3

Duplicate Recessive Epistasis

Answer 3

At least one dominant allele at each locus is needed to get the desired phenotype; if either locus is homozygous recessive, the cascade is blocked

Question 4

Pleiotropy

Answer 4

One gene is able to affect multiple phenotypic characters, such as sickle cell disease

Question 5

In a standard dihybrid cross (AaBb x AaBb) produces what phenotypic ratio? Assume the genes segregate independently and do not interact with each other.

Answer 5

9:3:3:1

Question 6

Complementation

Answer 6

Determines whether mutations are at the same locus or at different loci

Question 7

If you cross pure breeding strains that have mutations occurring at a single locus, what phenotype is produced?

Answer 7

Mutant phenotype

Question 8

If you cross pure breeding strains that have mutations occurring at different loci, what phenotype is produced?

Answer 8

Wild-type phenotype

Question 9

Sex Influenced Traits

Answer 9

Controlled by genes present on autosomes, hence such genes are present in both the sexes but their expression is different in males vs females, usually because the expression responds differently to androgens or estrogens; for example, soft facial hair in females vs coarse facial hair in males

Question 10

Sex Limited Characteristics

Answer 10

Autosomal genes whose expression is limited to one sex; for example, precocious puberty in humans, where both males and females can transmit the sex-limited trait, but it is only expressed in males

Question 11

Genomic Imprinting

Answer 11

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

Question 12

Epigenetics

Answer 12

Phenomena due to alterations to DNA that do not include changes in the base sequence; often affect the way in which the DNA sequences are expressed

Question 13

Epigenetic Trait

Answer 13

Stably heritable phenotype resulting from changes in a chromosome without alterations in the DNA sequence

Question 14

Sex Linked Characteristic

Answer 14

Genes located on the sex chromosomes

Question 15

Genetic Maternal Effect

Answer 15

Nuclear genotype of the maternal parent

Question 16

Cytoplasmic Inheritance

Answer 16

Cytoplasmic genes, which are usually inherited from only one parent

Question 17

Anticipation

Answer 17

Genetic trait becomes more strongly expressed or is expressed at an earlier stage as it is passed generation to generation; occurs due to expansion of an unstable region of DNA from generation to generation