Mendelian Inheritance II

Question 1

Four Mendel concepts from the monohybrid cross

Answer 1

alleles account for variation of inherited characters
an organisms inherits two alleles of a gene, one from each parent
if two alleles differ, one will be dominant and one will be recessive
law of segregation

Question 2

Incomplete Dominance

Answer 2

situation where phenotype of heterozygotes is intermediate between the phenotypes of individuals homozygous for either allele

white + red flowers makes pink flowers in F1, can have red & white in F2

Question 3

Codominance

Answer 3

phenotypes of both alleles are exhibited in the heterozygote because both alleles affect the phenotype in separate, distinguishable ways
ex: Lm and Ln allele; both M and N molecules are present on heterozygotes (LmLn)

Question 4

Tay-Sachs Disease

Answer 4

organismal: recessive: need 2 copies of alleles
biochemical: incomplete dominant: in heterozygotes, there is an intermediate level relative to homozygotes
molecular: codominant: heterozygotes produce equal amounts of normal and defective protein

Question 5

Huntington Disease

Answer 5

involuntary movement, emotional disturbance (3-7/10000)
disorder attributable to a single dominant gene

Question 6

Multiple Alleles

Answer 6

Populations typically contain multiple alleles for most genes
The four phenotypes of the ABO blood group in humans are determined by 3 alleles (Ia, Ib, i)

Question 7

Pleiotropy

Answer 7

The ability of a single gene to have multiple effects
ex: sickle cell disease results in multiple phenotypes

Question 8

Quantitative Characters

Answer 8

heritable feature that varies continuously over a range rather than in an either-or fashion (height). Usually indicates polygenic inheritance

Question 9

Polygenic Inheritance

Answer 9

an additive effect of two or more genes on a single phenotypic character (opposite of pleiotropy)
ex: 3 genes with alleles additively controlling the amount of melanin on the skin

Question 10

Epistasis

Answer 10

a type of gene interaction in which the phenotypic expression of one gene alters that of another independently inherited gene
ex: dog coat color dependent on two genes: one gene determines black or brown pigment and another determines if pigment is presented on hair (if not, golden). The E/e gene is epistatic to the B/b gene

Question 11

Overall Key Concepts

Answer 11

Mendel used the scientific approach to identify two laws of inheritance
The laws of probability govern Mendelian inheritance
Inheritance patters are often more complex than predicted by simple Mendelian genetics