1. Introduction to Genetics Dr. Donna Howell Blacksburg High School 2013-2014

2. What is Genetics? • Have you ever wondered how traits are passed from parents to the children? • Genetics is the study of heredity, or how traits are passed down from generation to generation.

3. Gregor Mendel • Gregor Mendel was a monk who lived in the 1800’s, and he is famous for the work he did with pea plants in the field of genetics.

4. Gregor Mendel • He knew that the eggs of the female plants and the sperm of the male plants joined together in the process of fertilization.

5. Gregor Mendel • Mendel studied 7 traits of the pea plants: • Seed shape • Seed color • Seed coat color • Pod shape • Pod color • Flower position • Plant height

6. Gregor Mendel Trait Alleles Findings of cross

7. Genes and Dominance • The offspring crosses between parents with different traits, like on the previous slide, are called “hybrids.” • He concluded that: • Inheritance is determined by factors that determine traits, called genes. • The different forms of a gene are called alleles.

8. Dominant and Recessive • Mendor concluded that some genes are dominant, meaning they show up in the offspring, and some are recessive, meaning they do not show up in the offspring. • Example: For seed shape, round (R) is dominant, and wrinkled (r) is recessive. • If you cross a R with an r, the seed shape is round.

9. Segregation • Mendel now wanted to know if, since a Rr seed shape is round, what happened to the recessive r gene? • This time, he crossed Rrwith Rr plants, and observed what happened. • He discovered that some of the recessive traits reappeared! • He concluded that the R gene was separate, or segregated, from the r gene.

10. Segregation • Mendel concluded that the R and r gene became segregated during the formation of sex cells, or gametes. • What this means is that each gamete only carries a single copy of each gene (either R or r)

11. Probability • Mendel realized we could use probability to predict what the gene types of crosses between male and female will be. • We do this using a Punnett square.

12. Punnett Squares • A Punnett square is a diagram that shows possible outcoming of mating.

13. Vocabulary Words • If you have two of the same type of allele together, such as RR or rr, they are called homozygous. • If you have two different alleles together, such as Rr, they are called heterozygous.

14. Vocabulary Words • When talking about the outcome of crosses, two other words are used: • Genotype: what the genes of an organism look like – Rr or rr or RR • Phenotype: what you actually see when looking at the organism – round or wrinkled peas.

15. Monohybrid Cross • Let’s do a simple monohybrid cross Punnett square: Genotype: 100% Rr Phenotype: 100% round

16. Monohybrid Cross • Let’s see what happens when we cross two of the Rr offspring: Genotype: 50% Rr, 25% RR and 25% rr Phenotype: 75% round, 25% wrinkled

17. Independent Assortment • Mendel found that the alleles for seed shape segregated independently of those for seed color (they were not attached) • This happens during the formation of gametes

18. Dihybrid Cross

19. Other Types of Dominance • So far we have only looked at alleles that have a dominant and recessive allele. • But there are other types of dominance: • Incomplete dominance • Codominance • Multiple alleles • Polygenic traits

20. Incomplete Dominance • When neither allele is completely dominant over the other. • The offspring are a mixture of each allele.

21. Codominance • In this case, BOTH alleles contribute to the phenotye. • Both alleles are expressed.

22. Multiple Alleles • Many genes have more than two alleles for a trait. • Example: coat color in rabbits.

23. Polygenic Traits • Traits that are controlled by two or more genes. • Example: human skin color

24. Meiosis • Meiosis is the process of reduction division in which the number of chromosomes per cell is cut in half through the separation of like chromosomes in a cell. • Happens in sperm and egg cells • Why might the number of chromosomes need to be cut in half?

25. Meiosis I

26. Meiosis II

27. Mitosis vs. Meiosis

28. The End!