Mendelian Inheritance II

Question 1

What can a dihybrid cross determine?

Answer 1

Whether two characters are transmitted to offspring as a package or independently

Question 2

2 Rules of Probability

Answer 2

1. Multiplication
2. Addition

Question 3

Multiplication Rule (probability)

Answer 3

the probability that two or more INDEPENDENT events will occur TOGETHER is the product of their individual probabilities

Question 4

Addition Rule (probability)

Answer 4

the probability that any one of two or more mutually exclusive events will occur is calculated by adding together their individual probabilities

Question 5

Situations where inheritance of characters by a single gene may deviate from simple Mendelian patterns

Answer 5

1. When phenotypes of alleles are not completely dominant or recessive
2. When a gene has more than two alleles
3. When a gene produces multiple phenotypes

Question 6

Incomplete dominance

Answer 6

the phenotype of the heterozygotes is intermediate between two homozygotes
Ex: red flowers + white flowers = pink flowers

Question 7

Codominance

Answer 7

the phenotype of the heterozygotes is the sum of the phenotypes of the two homozygotes
Ex: Calico cats, AB blood type (both carbohydrates are expressed)

Question 8

Tay Sachs and relationship w/ dominance

Answer 8

1. Since only an individual w/ 2 copies of the disease allele manifests the disease, at the ORGANISMAL level the allele is recessive
2. Since the activity of the gene in heterozygotes is intermediate relative to the two homozygotes, at the BIOCHEMICAL level the allele is incomplete dominant
3. Since heterozygotes produce equal amounts of normal and defective protein, at the MOLECULAR level the allele is codominant w/ the normal allele

Question 9

Multiple alleles

Answer 9

Four phenotypes of ABO blood group in humans are determined by three alleles for the enzyme (I) that attaches A or B carbohydrates to RBCs: IA, IB, i

Question 10

Pleiotropic

Answer 10

most genes have multiple phenotypic effects

Question 11

Example of pleiotropy

Answer 11

Sickle Cell Disease: caused by substitution of a single amino acid in the Hgb protein in RBCs, results in multiple phenotypes (normal shape RBCs and sickle-shaped RBCs

Question 12

Quantitative characters

Answer 12

those that vary in the population along a continuum
-usually indicates polygenic inheritance

Question 13

Polygenic inheritance

Answer 13

an additive effect of 2+ genes on a single phenotype

Question 14

Example of polygenic inheritance

Answer 14

Skin color: three genes w/ alleles additively controlling the amount of melanin on the skin

Question 15

Epistasis

Answer 15

a gene at one locus alters the phenotypic expression of a gene at a different locus

Question 16

Example of epistasis

Answer 16

Dog coat color depends on two genes: one gene determines the pigment color (B and b) and the other determines whether the pigment will be deposited in the hair (E and e)
-E/e gene is epistatic to the B/b gene because it determines whether the pigment is even deposited in the fur