Mendelian Genetics Flashcards
(104 cards)
Law of Segregation (Mendel’s 1st Law)
Each trait is controlled by particulate factors that occur in pairs.
These factors (alleles) seperate from one another during gamete formation (in meiosis) : each gamete receives only 1 of each pair.
The double number is restored upon fertilization.
gene
name for one of Mendel’s factors
allele
alternate forms of a gene
gamete
sex cell; sperm & egg or pollen & ovum
zygote
formed by fusion of 2 gametes.
2 types: homozygotes (identical alleles), heterozygotes (different alleles)
genotype
genetics makeup-description of alleles carried by individual
phenotype
character determined by genotype (oversimplication for first part of course)
“Law” of Independent Assortment (Mendel’s 2nd Law)
Segregation of each gene pair is independent of all other gene pairs.
Summarize extensions of Mendel’s Laws
1) Dominance not general (not always seen)
2) Multiple alleles are possible
3) Several genes can affect the same character
4) One gene can affect multiple phenotypes
5) Some alleles are lethal when homozygous
6) Alleles may not have constant effects on phenotype
epistasis
masking of the effects of one gene by an allele of another
Gene whose allele is epistatic must function ______ in the biochemical pathway?
upstream
What does it mean for a gene to be “essential”?
It is necessary to complete normal development, and when mutated can result in a lethal phenotype
penetrance
% of carriers of an allele that are affected by it
expressivity
degree to which the phenotype is altered in the carriers that are affected
How much do the sperm and egg contribute to inheritance?
Although they differ greatly in size, each contributes about the same to inheritance.
What does the sperm contribute to the zygote?
Its nucleus, and little else
What type of cells give rise to gametes and what are the cells that don’t called?
germ cells give rise to gametes; somatic cells make up the rest of the cells in the body.
Although a gene may have multiple alleles in a given population of individuals…..
a single diploid individual can have only a maximum of two of these alleles, one on each of the two homologous chromosomes caring the gene locus.
The number of possible genotypes in a MULTIPLE allelic series depends on the number of alleles involved. What is the general formula for n alleles?
n(n+1)2 possible genetopes; n are homozygotes and n(n-1)/2 are heterozygotes.
What happens in the case of complete recessiveness? Complete dominance?
The recessive allele is phenotypically expressed only when it is homozygous. Complete dominance is the phenomenon in which one allele is dominant to another, so that the phenotype of the heterozygote is the same as that of the homozygous dominant.
What does incomplete (partial) dominance mean?
With incomplete dominance, the phenotype of
the heterozygote lies in the range between the phenotypes of individuals that are homozygous for
either allele involved. The phenotype of the heterozygote is typically referred to as an INTERMEDIATE phenotype, even though it may not be exactly in the middle between the phenotypes of the two homozygotes.
What is codominance and how is it different from incomplete dominance?
Another modification of the dominance relationship is codominance. In codominance, the heterozygote exhibits the phenotypes of BOTH homozygotes. By contrast, in incomplete dominance, the heterozygote exhibits a phenotype intermediate between the two homozygotes.
If n is the number of independently assorting, heterozygous gene pairs, how many phenotypic classes are in F2 assuming that a true dominant-recessive relationship holds for each of the gene pairs?
2^n
If n is the number of independently assorting, heterozygous gene pairs, how many genotypic classes are in F2 assuming that a true dominant-recessive relationship holds for each of the gene pairs?
3^n