Genetics

Question 1

Mendelian Genetics

Answer 1

complete dominance - dominant alleles completely mask recessive allele

• 2 alleles determine one trait
• 2 recessive alleles express recessive trait
• most human traits are not Mendelian

Question 2

allele expression

Answer 2

Allele expression not always
complete dominance where
the dominant alleles
override recessive ones
• Alleles of a single gene may interact together & create unexpected phenotypes
• This could be caused by:
• Sex-linked traits
• Incomplete dominance
• Codominance
• Multiple alleles

Question 3

Incomplete Dominance

Answer 3

Neither allele dominates
and the heterozygote is
an intermediate phenotype
• Examples color in
snapdragons: white &
red alleles make pink

Question 4

Codominance

Answer 4

Both alleles are independently and equally
expressed in the heterozygote
• Examples:
• Roan (stippled red & white) coat color in cattle
• ABO human blood groups

Question 5

Multiple Alleles in Blood

Answer 5

Humans have 4 blood
group phenotypes: A, B, AB
& O
• The four common blood
groups of the human ABO
blood group system are
determined by three alleles: IA, IB, i
• IA & IB are codominant & i
is recessive

Question 6

Pleiotropy

Answer 6

One gene impacts numerous different phenotypic characters
• Example: albinism in which
the mutation of one gene
affects the production of
melanin which has effects
multiple traits in the
individual

Question 7

Epistasis

Answer 7

• One gene affects the phenotypic expression of
another gene
– Example in mice: one gene determines the color of fur (brown or black) & a separate gene determines if
pigment will be deposited into the fur (color or albino)

Question 8

Polygenic Inheritance

Answer 8

• Multiple genes may interact to create one phenotype creating a continuum in the
phenotype
– Aka: quantitative characters
– Environmental factors create the smooth bell curve
shape

Question 9

Nature & Nurture

Answer 9

• The environment impacts phenotypic expression of genes creating a range of
phenotypes that depend on environmental conditions (aka: the norm of reaction)
– Some traits have an inflexible norm of range
(blood types) while other vary greatly (red
blood cells) based on the environment
– Polygenic traits tend to have the greatest
norms of reactions especially when
considering environmental impacts

Question 10

Law of Independent Assortment

Answer 10

when two or more characteristics are inherited, individual hereditary factors assort independentlyduring gamete production, giving different traits an equal opportunity of occurring together

Question 11

Law of segregation

Answer 11

During gamete formation, the alleles for each genesegregate from each other into separate gametes so that each gamete carries only one allele for each gene.