Introduction to Genetics

Introduction to Genetics The Work of Gregor Mendel Honors Biology Chapter 11 Section 1

Gregor Mendel and his Peas!!! • Genetics is the scientific study of heredity • Gregor Mendel (born in 1822 Czech Republic) studied genetics using pea plants. • He worked at a monastery and one of his duties was to take care of the garden

Gregor Mendel and his Peas!!! • Noticed that the pollen was the male part and the stigma is the female part • During fertilization, the male and female reproductive cells join and create a new cell that produces the embryo • Pea plants self pollinate – which means the sperm fertilizes the egg from the same flower • The seeds inherit all of the characteristics from the single plant that produced them – In essence they have a single parent • These pea plants are true-breeding, meaning that if they self-pollinate, they produce offspring identical to themselves

Gregor Mendel and his Peas!!! • One group of plants only produces tall plants, one group makes short plants, one produces yellow seeds and one makes green seeds • Mendel wanted to chose the male and female traits so he prevented the pea plants from self pollinating by cutting away the pollen and using pollen from another plant. This is called cross-pollination and it produces plants with two different parents

Genes and Dominance • Mendel studied different pea plant traits – specific characteristic that varies (seed color or plant height) • Each trait that Mendel studied had 2 contrasting characteristics (ex: yellow or green seed, round or wrinkled seed, tall or short plant)

Genes and Dominance • Each original pair of plants are called the p generation (parental) • The first round of offspring are called the F1 generation (first filial – filius and filia means son or daughter in Latin) • The offspring of the crosses between the parents with different traits are called hybrids

Genes and Dominance • To Mendel’s surprise, the F1 generation had characteristics of only one of the parents • In each cross, the characteristic of the other parent seemed to disappear

Medel’s Seven F1 Crosses on Pea Plants Section 11-1 Seed Shape Seed Color Seed Coat Color Pod Shape Pod Color Flower Position Plant Height Round Yellow Gray Smooth Green Axial Tall Wrinkled Green White Constricted Yellow Terminal Short Round Yellow Gray Smooth Green Axial Tall

Genes and Dominance • Mendel drew 2 conclusions 1. Biological inheritance is determined by factors that are passed on. We call them genes. Each trait was controlled by 1 gene that occurs in 2 contrasting forms, each produce different characteristics. The different forms of the genes are called alleles. 2. Some alleles are dominant and some are recessive. An organism that contains a dominant allele for a gene will always exhibit that form of the trait. If an organism has a recessive allele, it will only exhibit this trait if the dominant allele is not present. DOMINANT MASKS RECESSIVE. WHICH TRAITS WERE DOMINANT?

Segregation • Had the recessive alleles disappeared? • Mendel allowed the seven hybrid F1 plants to produce another generation by self-pollination, which he called F2 (second filial) • To his surprise, the recessive traits reappeared in the F2 generation

The F2 Generation Results P Generation F1 Generation F2 Generation Tall Short Tall Tall Tall Tall Tall Short What proportion of the F2 generation had a trait controlled by the dominant allele???

The F1 Cross • The recessive traits reappeared • ¼ of the F2 plants showed the trait controlled by the recessive allele • ¾ of the F2 plants still showed the trait controlled by the dominant allele

The F1 Cross • Segregation, or separation of the recessive alleles must have occurred during formation of the sex cells or gametes (MEIOSIS!). • The F1 would get one allele for tallness and one allele for shortness. The plant would be tall because tall is dominant and dominant masks recessive

The F1 Cross • When the F1 self-pollinates and produces gametes, the 2 alleles separate from each other so that each gamete contains only a single copy of the gene (MEIOSIS!) • Therefore, each F1 plant produces 2 types of gametes- those with the allele for tallness and those with the allele for shortness

The F1 Self-Pollination F1 Tt Tt T t gametes T t F2 tt Tt Tt TT short tall tall tall

Frayer Model

Frayer Model Assignment Create a Frayer Model for each of the following words • Trait • Phenotype • Genotype

Introduction to Genetics