Chapter 2 Flashcards
Incomplete dominance meaning
Incomplete dominance means that neither trait is dominant, so that
an intermediate phenotype exists, which is a blending
ex. flowers in snapdragons Fig 3.3
Codominance meaning
phenotypic detection of both gene products (from both parents)
ex. Lentils (spotted or dotted)
In both cases F2 progeny phenotypic ratios mirror genotypic ratios
Complete dominance meaning
Complete dominance means that Hybrid resembles one of the two parents
How much an individual diploid organism has alleles?
An individual diploid organism has two alleles at each genetic locus, with one allele inherited from
each parent.
What are the kinds of blood types (genotypes/phenotypes)?
What is a wild type allele?
Wildtype alleles is a term used to refer to most
common allele in the population
a. displayed as (+)
What is a mutant allele?
b. Mutant allele is a rare allele (less than 1% of pop.)
Monomorphic gene meaning
Monomorphic gene is the gene that has only one common wild type allele
Ex. Agouti color in mice
Polymorphic gene meaning
Polymorphic gene is the gene that has more than one common allele (not wild type, but rather common variants)
Ex. ABO blood typing
Pleiotrophy meaning
It’s a single gene that determines several distinct and seemingly unrelated characteristics. The gene that has different effects in different tissues
Ex. Marfan syndrome
Lethal allele meaning
It’s an allele that has the potential to cause death of an organism,
because it encodes an essential gene for survival (1/3 of our genes) ????
What are the 3 kinds of lethal alleles?
a. Recessive lethal allele
b. Delayed lethality and
c. Dominant lethal allele
What is a Recessive lethal allele?
an allele that negatively affects the survival of a homozygote.
Ex. Coat color in mice:
•Recall our dominance structure A^Y >A > a^t > a
•Two alleles A^Y A^Y (2 copies) in mouse can not occur —> fatal,
>we need only one allele (1 copy) of yellow coat
What is Delayed lethality?
Delayed lethality- homozygotes (recessive) survive, but die later
from consequences from genetic defect
Ex. Tay Sachs
What is Dominant lethal allele?
It the delayed onset lethal alleles, which kills organism from any point in life (from birth) or delayed
Ex. Huntington’s disease
Additive interaction
yields 4 distinct F2 phenotypes
9 to 3 to 3 to 1 phenotypic/genotypic ratio
Ex. Seed color in lentils
Epistasis meaning
Epistasis is a circumstance where the expression of one gene is modified (e.g., masked) by the expression of one or more other genes.
Hypostasis meaning
A gene interaction in which the effects of one gene hides the effects of another gene
Epistatic vs hypostatic
gene doing the masking vs gene being masked
Recessive (Suppression ) Epistasis meaning?
-Homozygous recessive condition at one locus masks the expression of a second locus.
9:3:4 ratio in F2 progeny of dihybrid
crosses indicates recessive epistasis
Ex. The Bombay phenotype for ABO blood groups,
coat color in Labrador Retrievers
Genotype ee masks the effect of all B genotypes
What is recessive epistasis ratio?
9:3:4 ratio in F2 progeny of dihybrid crosses
indicates recessive epistasis
9/16 black (B— E—)
3/16 brown (bb E—)
3/16 yellow (B— ee)
1/16 yellow ( bb ee)
Genotype ee masks the effect of all B genotypes
What is the precursor to the “A” and “B” antigens (blood type)?
H protein. Without the H substance, neither the A or B can be added
to the cell surface so type O phenotype is expressed.
What is Dominant Epistasis?
Dominant allele of one gene hides effects of
both alleles of the other gene
12:3:1 ratio in F2 progeny of dihybrid crosses
indicates dominant epistasis
b. Ex color in summer squash
What is the genotypic/phenotypic ratio of dominant epistasis?
12:3:1 phenotypic ratio in F2 progeny of dihybrid crosses indicates dominant epistasis 12/16 white (A— B—, aa B—) 3/16 yellow (A— bb) 1/16 green (aa bb)
Reciprocal recessive epistasis meaning?
When homozygous, recessive allele of each gene masks the dominant allele of the other gene
9:7 ratio in F2 progeny of dihybrid crosses indicates
9/16 purple (A—B—)
7/16 white (A— bb, aa B—, aa bb)
Phenotypic variation for some traits can occur because of??
- Effects of modifier genes
- Effects of environment
- Pure chance
Penetrance definition
Penetrance is the percentage of individuals with a particular genotype that
show the expected phenotype
Penetrance is a measure of the proportion of individuals in a population who carry a specific gene and express the related trait.
•Can be complete (100%) or incomplete
Expressivity definition
Expressivity is the degree or intensity with which a particular
genotype is expressed in a phenotype
•Can be variable or unvarying
Expression of phenotype depends on?
the environment and genes
3 Environmental Effects on Phenotype?
- the environment and genes
- product of genotype is a range of phenotypic possibilities
- variation due to environmental differences - Temperature
Phenocopy meaning
Phenocopy - phenotype arising from an environmental agent
that mimics the effect of a mutant gene
•Examples in humans
Genetic predisposition to lung cancer is strongly affected by cigarette smoking
Discontinuous traits vs Continuous traits
Discontinuous traits
a. clear-cut, “either-or” phenotypic differences between
alternative alleles (white or pink)
Continuous traits
2. Also called quantitative traits because the traits vary
over a range that can be measured
3. Usually polygenic
True breeding parent means
Homozygous genotype (one parent dominant and the other parent recessive)
Redundancy meaning
Only one dominant allele of either of two genes is necessary
to produce phenotype
15:1 phenotypic ratio in F2 progeny of dihybrid crosses
indicates dominant epistasis
