Mendel and Genetics

1. Mendel and Genetics Mrs. Potz

2. Gregor Mendel • Carried out the first important studies of heredity. • Passing on of characteristics from parents to offspring • Genetics • Branch of biology that studies heredity • Studies inheritance pattern of traits • Characteristics that are inherited

3. Mendel’s experiment • Used pea plants • Reproduce sexually • Have two distinct sex cells • Gametes are sex cells • Male and female gametes are in the same flower • Pollination and fertilization occur in the same flower • Pollination: transfer of male pollen grains to the pistil of a flower • Fertilization: male gamete in the pollen grain meets and fuses with the female gamete in the ovule

4. Careful researcher • Studied one trait at a time • Analyzed data mathematically

5. Monohybrid crosses • Performed controlled crosses • Crossed tall and short pea plants • Created hybrids • Offspring that have different forms of a trait • Two parent plants differed by a single trait: height

6. First Generation • Crossed tall with short pea plants • All offspring were tall • F1 generation

7. Second Generation • First generation allowed to self-pollinate • ¾ of offspring were tall • ¼ of offspring were short • Ratio 3:1 • F2 generation

8. Unit Factors • Mendel’s conclusion • Unit factors control each trait • Alleles: alternative forms of a gene • One from mother and one from father

9. Rule of Dominance • Dominant trait: the observed trait • Uses an uppercase letter • Recessive trait: the trait that disappears • Uses a lowercase letter

10. Law of Segregation • Mendel’s 1st law of heredity • Two alleles for each trait must combine when gametes are formed. • A parent passes only one allele for each trait to offspring

11. Phenotypes and Genotypes • Phenotype • The way an organism looks and behaves • Genotype • The gene combination an organism contains • Homozygous (TT or tt) • Two alleles for the trait are the same • Heterozygous (Tt) • Two alleles for the trait differ from each other

12. Dihybrid Crosses • Organisms differ from each other in two traits rather than one • F1 generation: all traits were dominant • Yellow color (Y) • Round shape (R) • F2 generation • RRYY: round yellow • RRyy: round green • rrYY: wrinkled yellow • rryy: wrinkled green

13. Law of Independent Assortment • Genes for different traits are inherited independently of each other • When a pea plant with the genotype RrYy produces gametes, the alleles R and r will separate from each other (law of segregation) as well as from the alleles Y and y (law of independent assortment). • Alleles recombine in four different ways.