8A - Monohybrid crosses

Monohybrid cross

A genetic cross performed to observe the inheritance of alleles and phenotypes for a single gene

• Parental generation = P1

• first generation = F1

Autosomal complete dominace

Widows peak = WW

normal = ww

therefore, Ww = Widows peak

Autosomal codominance

happens when two traits are independently and equally expressed

• there will be 2 dominant alleles (2 capital letters) and no recessive allele (no lower-case letters).

Autosomal dominance - blood types

Both the A and B blood group alleles are dominant (written as IA and IB, respectively) so they will both be expressed. Meanwhile, the O blood group is recessive and written as i.

• I^Ai = type A

• I^A I^A = Type A

• I^B i = Type B

• I^B I^B = type B

• ii = type O

• I^A I^B= Type AB

Sex-linked alleles

Sex linked traits involve alleles on sex chromosomes

Sex-linked when explaining phenotype

With sex-linked traits, it is important to notice for proportions are calculated with respect to sex. So, in the example shown, we would say 50% of female offspring will be red-green colour blind and 50% of male offspring will be red-green colour blind

Test cross

when an individual expressing the dominant phenotype but with an unknown genotype is crossed with a homozygous recessive individual. The results indicate whether the individual with the dominant phenotype is homozygous dominant or heterozygous