4.4 Flashcards
mutations
creates different versions of the same genes
a gamete with the mutation passes it on to a new organism at fertilization
multiple allelism
a single gene has more than two alleles in a population
each diploid individual carries only 2 alleles at a locus
many genes have multiple alleles
many alleles at a single gene can encode multiple traits for a single character in a population
rabbit coat color
multiple alleles can increase the number of possible phenotypes
multiple alleles often show a hierarchy of dominance
C>chd>Ch>c
codominance
the heterozygotes display the phenotypes of both alleles at a single gene simultaneously
neither allele is dominant or recessive
ABO blood types
determined by 3 alleles of one gene (multiple allelism and codominance)
gene I encodes a glycotransferase that adds a saccharide to a glycoprotein
the three alleles IA, IB, i produces 4 different versions of the enzyme
oligosaccharides can function as antigens
type A
IAIA, IAi
A antigen
anti-B antibody
type B
IBIB, IBi
B antigen
anti-A antibody
type AB
IAIB
AB antigens
no antibodies
universal acceptor
type O
ii
no antigens
AB antibodies
universal donor
incomplete dominance
heterozygotes have an intermediate phenotype
neither of the two alleles of a gene is dominant or recessive to the other
does not show blended alleles
in the F2, the original phenotype appears
pleiotropy
one allele has multiple phenotypic effects
epistasis
the phenotype ptoduced by an allele depends on the action of alleles of other gene(s)
Labrador retrievers
the E gene determines the expression of the B gene
B (black) is dominant over b (brown)
E (pigment) is dominant over e (no pigment)
B and b are not expressed until E is expressed
quantitative variation
for more complex characters, phenotypes are not discrete but vary continuously over a range
produced by the interaction of genes at multiple loci and the environment
polygenic inheritance
polygenic characteristics are controlled by multiple genes
each gene (may have two or more alleles) adds a small amount of value to the phenotype
quantitative trait loci
the chromosomal regions together determine a complex character that exhibits quantitative variation
a quantitative trait locus can contain one or several genes
a locus is a specific position on a chromosome
