Introduction to Genetics Chapter # 11 Introduction to Genetics

Who is Gregor Mendel?

I. The Work of Gregor Mendel Genetics – study of heredity. A. Gregor Mendel’s Peas Gregor Mendel – Austrian monk who experimented with garden pea plants to learn more about inheritance. Is known as the “Father of Genetics”. -Mendel worked with 2 basic types of pea plants : tall & short. The seeds of one were yellow & the seeds of the other were green.

Self vs. Cross Pollination -Mendel’s pea plants reproduced by means of self pollination – process by which a flower on a plant is pollinated by pollen from that same plant. -Self-pollinating plants are sometimes called true-breeding – when permitted to self pollinate, they produce offspring identical to themselves. -Mendel did experiments in which he cross pollinated his pea plants. Cross-pollination – the pollination of a flower by pollen from a completely different plant (involves 2 parents).

B. Genes and Dominance -Mendel studied 7 different traits in pea plants. Trait – a specific characteristic, ex : seed color. -Each trait studied had a contrasting trait, ex : green vs. yellow seed color. -Mendel crossed plants with the 7 contrasting traits & studied their offspring.

P1, F1, & F2 -We call the original pair of plants the P (parental) generation & their offspring the F1 or first filial generation. Filius/filia = Latin for son/daughter. -The offspring of F1 are referred to as the second filial generation (F2). *Offspring of crosses between parents with different traits are called hybrids.

Mendel’s Conclusions Mendel concluded that : 1. Biological inheritance is determined by factors that are passed from one generation to the next. -The chemical factors that determine traits are genes. -Each trait is controlled by one gene that occurs in 2 contrasting forms. The contrasting forms produce different characters of each trait. -Different forms of a gene are alleles. 2. The Principal of Dominance, which states that some alleles are dominant & others are recessive. -Dominant alleles are expressed if in an allele pair. Recessive alleles are expressed if no dominant alleles are present in an allele pair (D = tall/yell).

C. Segregation -Mendel crossed F1 plants with each other to find out what happened to the recessive traits. -Mendel’s F1 cross resulted in a re-appearance of the recessive traits in the F2 plants (about 1 of 4 were short). This is due to segregation – separation of alleles during gamete formation.

Gamete Formation *When gametes are produced, the two alleles segregate from each other so that each gamete carries only a single copy of each gene. So, each F1 plant produces 2 kinds of gametes : ones with alleles for tallness & ones with alleles for shortness. Dominant alleles are represented with capital letters & recessive alleles with lower case letters, ex : T=tall, t=short.