Mendel‘s Law of Segregation

Early Ideas Blending Theory believed that traits from the mother and father were blended together in their offspring. For example If the father was tall and the mother was short. According to the blending theory the children would be medium height This theory was wrong

Gregor Mendel Austrian monk born in 1822 in monastery known for research and teaching after his death (1884) acknowledgment of his discoveries in 1900

Experiments with Pea Plants - Flower color (purple or white) - Seed shape (round or wrinkled) - Seed color (yellow or green) - Pod color (green or yellow) - Flower position (axial or terminal) - Pod shape (inflated or constricted) - Stem length (tall or dwarf)

Genetic crosses To hybridize 2 varieties of pea plants, Mendel used an artist’s brush. He transferred pollen from a true breeding white flower to the carpel of a true breeding purple flower.

What do you think happened? True-breeding Purple flower plant + True breeding White flower plant equals? All purple flower plants He then allowed all of these plants to self pollinate.

What do you think happened? Produced a ratio of 3 purple flower plants to one white flower plant

Mendel’s law of segregation By carrying out these monohybrid crosses, Mendel determined that the 2 alleles for each character segregate during gamete production. Mendel discovered this c.1860. DNA was not discovered until 1953.

Mendel‘s Generalization Alternative versions of genes account for variations in inherited characters - concept of alleles (P=purple, p=white) 2. For each character, an organism inherits two genes, one from each parent - two gametes form somatic cells - one allele comes from the mother, one from the father

Mendel‘s Generalization 3. If the two alleles differ, then: - dominant allele is fully expressed in the organism's appearance (phenotype) - recessive allele has no noticeable effect on the organism's appearance (genotype) 4. The two genes for each character segregate during gamete production - ensures variation

Law of Segregation the pair of alleles of each parent separate and only one allele passes from each parent on to an offspring which allele in a parent's pair of alleles is inherited is a matter of chance  segregation of alleles occurs during the process of gamete formation (meiosis) randomly unite at fertilization

Mendel’s terminology True breeding: When the plants self-pollinate, all their offspring are of the same variety. Hybridization: Mating, or crossing, of two varieties. Monohybrid cross: A cross that tracks the inheritance of a single character. P generation: True breeding parents. F1 generation: (first filial) Hybrid offspring of the P generation. F2 generation: (second filial) Offspring from the self-fertilization of the F1 hybrids.