Law of SegregationTrisha M. Salanatin

• Before Mendel’s time, it was believed that all traits become mixed when they are transmitted from generation to generation, as red and blue paints mix to give a violet color. However, when Mnedel crossed pure-breeding pea plants, the pea plants did not produce offspring with blended or intermediate traits.

• During meiotic division, the genes separate or segregate in the formation of gametes. These factors or genes are located in the chromosomes and transmitted to the offspring through the gametes.

matched pair of chromosome that separate during gametic formation. These factors or the genes also separate in the formation of gametes. Hence, only one member of a pair of genes goes to a gamete.

HOMOLOGOUS

CHROMOSOMES

Mendel used letters to symbolize the characteristic traits. He used capital letters to represent the dominant gene. He used the symbol “R” for round and “r” for wrinkled. PLANT (garden pea) Symbol

Pure breeding P₁ Plant bearing round seeds

RR

Pure breeding P₁ Plant bearing wrinkled seeds

rr

F₁ plant bearing round seeds

Rr

• Mendel was aware of the operation of chance in the transmission of traits from parents to offspring. There is a chance for the determiner (genes) of the recessive trait to combine during reproduction, and appear in the F₂

EXPERIMENTS WITH PEA PLANTES

CROSS-POLLINATION OF PUREBREED PLANTS

• cross-pollination between true breeding green and yellow pods

• all F1 green

F1 GenerationGg = heterozygous

F2 GENERATION

• self-pollination of green F1 plants

• ¾ in F2 green, ¼ yellow• 3 : 1 ratio in pod colour in F2

G = dominant = greeng = recessive = yellowGG,gg=homozygous

SEED COLOUR

• C = dominant = yellow

• c = recessive = green

Mendel hypothesized that:

“The pair of genes segregate or separate from each other during gamete formation.”

TRIVIA

Mendel's studies show that two in four pea plants were hybrid. Between 1856

and 1863, Mendel cultivated and tested some 29,000 pea plants -

amazing!