Genetics 2

Law of Segregation- The random Assortment of either pair of homologous chromosomes to opposite poles during Meiosis I. Creates different gametes.

Law of Independent Assortment- The movement of one pair of chromosomes odes not affect the movement of another pair. They segregate independently.

Gregor Mendel’s Crosses

Gregor Mendel was an Augustinian Monk. Studied under Physicist Doppler and Botanist Unger. In 1857 began breeding and cross breeding pea plants. Results yielded two previous laws. Nothing was known about genes or DNA.

Gregor Mendel’s Crosses

Mendel experimented with different varieties of pea plants. Observed and counted offspring. Ex. Purple flowered plant x White flowered plant.

Gregor Mendel’s CrossesP = Parental Generation Purple x White

F1= First Filial Generation All purple

F2 = Second Filial Generation 3:1 Purple to white

What is dominant? How do we explain?

Monohybrid Cross

A mating in which just 1 trait is focused on. Ex. Just plant color or just plant height. Letters are used to represent the parent’s genes.

Cross a Homozygous Dominant Purple (PP) flowered plant with a Homozygous recessive White flowered plant(pp)

P P

p Pp Pp

p Pp Pp

Monohybrid Cross

P p

P PP Pp

p Pp pp

The offspring have one gene from each parent but only show purple phenotype.

Now cross the offspring.

Heterozygous Purple Flower x Heterozygous Purple Flower

Monohybrid Cross

P p

P PP Pp

p Pp pp

The offspring show a 3 : 1 phenotype distribution.

1 PP Homo. Dom. Purple

2 Pp Hetero. Purple

1 pp Homo. Rec. White

Genotype Phenotype

Test CrossUsed to determine a genotype that is unknown. Ex. A purple flower of unknown genptype with a white pp flower. Predict outcome for each scenario and compare with actual results.

Dihybrid CrossA mating in which 2 different traits are focused on at the same time. Ex. Both plant color & height (more complex)

Homo. Dom. Purple Tall x Homo. Rec. White Short

PT PT PT PT

pt PpTt

pt

pt

pt16 PpTt purple tall plants

Dihybrid CrossNow try the cross between the offspring. A heterozygous purple tall plant with a heterozygous purple tall plant.

PT Pt pT pt

PT PPTT

Pt

pT

pt

9 Purple Tall

3 Purple Short

3 White Tall

1 White Short