1. Introduction to Genetics The Work of Gregor Mendel

2. Genetics Scientific study of heredity Gregor Mendel –Born in 1822 in Czech Republic –Worked in monastery garden while teaching H.S. (math & science) –Worked w/ true-breeding pea plants If allowed to self-pollinate, produce offspring identical to themselves

4. Genes and Dominance Mendel studied 7 traits –Specific characteristic that varies from one individual to another– color, height –Each trait had two contrasting characters – greed seeds vs. yellow –Crossed true-breeding plants of each type to opposing character

5. True-breeding yellow seed X True- breeding green seed Original pair of plants = P (parental) generation Offspring = F1 (first filial) Offspring of crosses between parents w/ different traits = hybrids Genes and Dominance

6. What did the F1 hybrids look like? Did they look like a blend of both parents? No! All F1 offspring only showed the character of one parent.

7. Mendel’s Two Conclusions 1. Biological inheritance is determined by factors that are passed on from one generation to the next –Genes – chemical factors that determine traits

8. Each trait that Mendel studied was controlled by one gene that occurred in two contrasting forms –Ex: Gene for Plant Height = One form for tall one for short Alleles – different forms of a gene

9. 2. Principle of Dominance – some alleles are dominant and others are recessive –If there is a dominant present, that form is shown –If there are two recessive present, the recessive is shown

10. Segregation Did the recessive alleles disappear, or were they still present ? –To find the answer, he allowed F1 generation plants to self-pollinate to create an F2 generation What happened? –Traits reappeared. ¼ of the F2 plants showed the recessive allele

11. Segregation, cont’d Law of Segregation –Two alleles separate from each other so that each gamete carries only a single copy of each gene –Ex: Fig. 11-5

12. Introduction to Genetics Genetics and Probability

13. Probability –The likelihood that a particular event will occur Ex: tossing a quarter –Heads = 1 in 2 –Tails = 1 in 2 –3 tails in a row ½ x ½ x ½ = 1/8 –Principles can be used to predict outcome of genetic crosses

14. Genetic Vocabulary Character –Detectable inheritable feature of an organism Trait –Variant of inheritable character = allele / alleles Dominant –Capital letter (SS) Recessive –Lower case (ss) Two alleles for each character –Mom and dad

15. Genetic Vocabulary Genotype –The genetic makeup of an organism –Written in letter format –PP, pp, Pp Phenotype –The physical traits of an organism

16. Genetic Vocabulary Homozygous –Having two identical alleles for a given trait PP ss Heterozygous –Having two different alleles for a given trait Pp Ss

17. Pea Traits

18. Basic Crosses

19. Recessive/Dominant action items required of you