Biology Unit 2, Part 2: heredity, Mendel, probability

Diploid

contains 2 chromosomes from homologous pair, one from each parent

Haploid

contains only 1 chromosome from homologous pair

Alleles

alternative versions of genes, reside at the same genetic locus

Hemizygous

having only one allele (sex in humans)

When alleles are segregated in Meiosis

Meiosis I, anaphase I

Mendel’s Law of Segregation

If an individual has identical alleles at locus, that allele is present in all gametes. If an individual has two different alleles, half its gametes receive one allele and the other half the other allele.

Punnett square

Used to determine equal frequency of two parent genotype cross, can also use a testcross to determine genotype of parent from its offspring

Dihybrid cross

dependent assortment: 1 allele depends on presence of another

Mendel’s Law of Independent Assortment

Alleles at each locus segregate independently of alleles at other loci

= product of each event happening independently (p x q)

Probability of both events happening (p&q)

Probability of either of two events happening (p or q)

= sum of probability of each event happening individually (p+q)

Tetrad

structure formed by pair of homologous chromosomes during early meiosis (prophase I), formed during synapsis, allows non-sister chromatids to overlap and swap DNA pieces (recombination)

Wild-type

most common phenotype in a population

n

If n alleles, there are _______ homozygotes

[n(n-1)]/2

If n alleles, there are ______ heterozygotes

[n(n+1)]/2

If n alleles, there are ______ genotypes

Pleiotropy

one gene affects multiple traits

Pleiotropy examples

Tyrosinase (albinism), Sry (sex-determining locus in mammals)

Epistasis

an allele at one locus affects the phenotypic effects of an allele at another locus

Epistasis examples

mouse coat color (one locus controls hair color, one controls pigment deposition)

Polygenic inhereitance

most traits controlled by multiple loci, often continuous traits (hair, weight, skin color)

Norm of reaction

given genotype can take on range of phenotypes depending on environment

Genotype by environment interaction

different genotypes may have different norms of reaction

50%

Pr(recomb) = ______ if loci are on different chromosomes

how far apart they are, further apart = higher probability

Loci Pr(recomb) if on same chromosome is determined by

reduce

Double cross-overs ____ the apparent distance between loci

recombination

If non-sister chromatids rejoin, ____ occurs

two, two

One crossover produces ___ recombinant chromosomes and ___ parental chromosomes