Week 8 Flashcards
(8 cards)
Q1: What is codominance?
Codominance occurs when both alleles in a heterozygous organism are fully expressed, resulting in a phenotype that shows both traits equally.
Example: In blood types, the A and B alleles are codominant. An individual with genotype AB will express both A and B antigens on their red blood cells.
Q2: What is incomplete dominance?
Incomplete dominance is when neither allele is completely dominant, and the heterozygous phenotype is a blend of both traits.
Example: In snapdragons, crossing a red-flowered (RR) plant with a white-flowered (WW) plant results in pink flowers (RW) in the F1 generation.
Q3: What are multiple alleles?
Multiple alleles refers to the existence of more than two alleles for a particular gene, though an individual still only has two alleles.
Example: The ABO blood type is controlled by three alleles: A, B, and O. An individual can have any two of these, such as AA, AO, BB, or BO, leading to four possible blood types: A, B, AB, and O.
Q4: What is pleiotropy?
Pleiotropy occurs when one gene influences multiple, unrelated phenotypic traits.
Example: The sickle cell disease gene (S) not only affects red blood cell shape but also influences susceptibility to malaria, pain episodes, and organ damage.
Q5: What is epistasis?
Epistasis is when the expression of one gene is affected by the presence of one or more other genes.
Example: In labrador retrievers, the gene for coat color (B for black, b for brown) can be influenced by a separate epistatic gene (E for pigment production, e for no pigment). A dog with the ee genotype will be yellow, regardless of the coat color alleles.
Q6: What are lethal alleles?
Lethal alleles are alleles that cause death in an organism, usually when present in a homozygous state.
Example: The yellow coat color allele (Y) in mice is lethal in the homozygous condition (YY), but heterozygous (Yy) mice will be yellow.
Q7: What are sex-linked traits?
Sex-linked traits are traits carried on the X or Y chromosomes. Most commonly, traits are X-linked and are more commonly expressed in males, who only have one X chromosome.
Example: Colorblindness is a recessive, X-linked trait. A male with the genotype XcY will be colorblind, while a female needs two copies of the allele (XcXc) to express the trait.
