Mendelian+genetics

deduced that hereditary information is stored in discrete units called

particulate factors

(genes)

each trait is controlled by

two genes

one from male & one from female

Mendel’s postulates

1. unit factors in pairs

2. dominance and recessive

3. segregation

   1. independent assortment

law of segregation 

each gamete carries one allele

alleles segregate from each other in the formation of

gametes

law of independent assortment or

law of dominance

genes for different traits assort independently of one another

law of segregation 

genes are transmitted as pairs 

particulate theory 

zygote

fertilized egg

dominant

allele masking the effect of the other allele when present

recessive 

allele masked at the locus   

test cross

unknown parent crossed with homozygous recessive parent

epistasis

masking of the phenotypic effect of one pair of alleles at one locus by those at another locus

types of gene 

no dominance 

complete dominance 

codominance 

partial dominance (incomplete)

genes segregate into

gametes equally and randomly so one gene per trait and one allele in each gamete

gametes combine at random to form

zygote

BB or Bb 

black 

bb

red

PP or Pp

polled

pp 

horned 

WW or Ww

belted

ww

solid

RR 

red 

Rr

roan

rr

white

no dominance 

same as codominance 

heterozygote is phenotypically intermediate or half-way between the homozygous type 

partial dominance

same as incomplete dominance

heterozygote is between the two homozygotes but is not exactly half-way

W

white

w 

colored 

B

black

b

brown

sex limited gene expression 

autosomal chromosomes 

one sex is uniform in expression of a trait but they don’t transfer genes that produce no expression of the trait in opposite sex

milk production