genetics unit 3

discontinous/discrete traits

only a few possible phenotypes that fall inot discrete clases, phenotypoes is controlled by one or few genes, environment usually doesn’t affect trait expression

continuous/quantitative traits

can take numerous values, controlled by multiple genes, each obeys Mendel’s laws, can be affected by environment to varying degrees

polygenic traits

characteristics controlled by 2 or more genes that interact to form a range of phenotypes

mendelian model

one allel is dominat and other allele is recessive

additive model

each allele contributes some amount to phenotype and heterozygote is average of homozygotes

number of genotypes formula

4^n

number of phenotypes formula

2n+1

common garden experiment

two diffferent populations of species raised in same environment and any differences between them must be a result of their genetics

mendel’s 2nd law

law of independent assortment and alternative arrangement of pairs of homologs

phenotypic ratio for dihybrid cross independent assortment

9:3:3:1

when crossing over happens

alleles on the same chromosome will always be inherited together

crossing over during meiosis 1 results in

genetic variation

what recombines in crossing over

non-sister chromatids

dihybrid of two linked genes produce

two nonrecombinant(parental) and two recombinant

frequency of recombinants depends on

physical distance between two genes

phased genotype

linked genes have slash for alleles on separate homologs

coupling(cis) configuration

dominant alleles of two linked genes are present on the same homolog (AB/ab)

repulsion(trans) configuration

dominant alleles of two linked genes are present on the different homologs (aB/Ab)

recombinant offspring will make up

less than 50% of the total offspring

if crossing over occurs between the two loci we are observing

50% parental and 50% recombinant

if crossing over occurs outside the two loci we are observing

100% parental and 0% recombinant

recombinatinon frequency

(# recombinant progeny)/(# progeny score)

map distance

recombinaiton frequency * 100

frequency of crossing over between genes farther apart is higher/lower/equal than frequency of crossing over between genes that are close together

higher

maximum proportion of recombinant gametes that can be produced from a dihybrid

50%

50% recombination frequency usually indicates

loci that are either on separate chromosomes(unlinked genes) or are located very far apart on the same chromosome

intervening loci is used to

map two loci greater than 50 mu apart on the same chromosome

double crossovers between two loci appear

parental

how many loci can be observed in a double crossover

3 or more

recombinant chromosomes resulting from doubble crossover only have which gene altered

middle gene

when do you use mapping

when wanting to know the underlying genes for a genetic disorder or adaptive phenotype

forward genetics

starting with observable trait(phenotype) and work backward to identify genes responsible for it

linkage map

shows relative positions of gene markers(loci) on chromosomes

genes and markers close together on chromosome tend to be inherited together because

recombination is less likely to separate them

what must the individuals have to map genes

have variation in the trait and genetic differences at the markers being studied

what two things are needed to identify recombinants

double heterozygote parents and scorable gamete genotypes in offspring