How Genetics Began

1. Sexual Reproduction and Genetics Section 2 Mendelian Genetics How Genetics Began • The passing of traits to the next generation is called inheritance, or heredity. • Mendel performed cross-pollination in pea plants. • Mendel followed various traits in the pea plants he bred.

2. Sexual Reproduction and Genetics Section 2 Mendelian Genetics How Genetics Began

3. Sexual Reproduction and Genetics Section 2 Mendelian Genetics How Genetics Began

4. Sexual Reproduction and Genetics Section 2 Mendelian Genetics • The parent generation is also known as the P generation. • The offspring of this P cross are called the first filial (F1) generation. • The second filial (F2) generation is the offspring from the F1 cross.

5. Sexual Reproduction and Genetics Section 2

6. Sexual Reproduction and Genetics Section 2 Mendelian Genetics

7. Sexual Reproduction and Genetics Section 2 Mendelian Genetics Genes in Pairs • Allele • An alternative form of a single gene passed from generation to generation • Dominant (Purple flower color) • Expressed form of a trait represented by a capital letter and first letter of the trait (P). • Recessive (White flower color) • Only appears when both alleles are recessive. Represented by a lower case letter of the dominant trait (p)

8. Sexual Reproduction and Genetics Section 2 Mendelian Genetics Dominance • An organism with two of the same alleles for a particular trait is homozygous. • PP or pp • An organism with two different alleles for a particular trait is heterozygous. • Pp

9. Sexual Reproduction and Genetics Section 2 Mendelian Genetics Genotype and Phenotype • An organism’s allele pairs are called its genotype. • Example would be Pp • The observable characteristic or outward expression of an allele pair is called the phenotype. • Example would be purple flower color

10. Sexual Reproduction and Genetics Section 2 Mendelian Genetics Mendel’sLaw of Segregation • The law of segregation, states that the two alleles for a trait segregate (separate) when gametes are formed. • Two alleles for each trait separate during meiosis. • During fertilization, two alleles for that trait unite. • Each offspring receives one allele from each parent resulting in two alleles for each trait.

11. Sexual Reproduction and Genetics Section 2 Mendelian Genetics Mendel’sLaw of Segregation

12. Sexual Reproduction and Genetics Section 2 Mendelian Genetics Mendel’sLaw of Independent Assortment • Mendel found that the inheritance of one trait, such as plant height, did not influence the inheritance of any other trait, such as flower color. • The law of independent assortment states that the alleles of different genes separate independently of one another during gamete formation. • This occurs during meiosis I when the homologous chromosomes line up along the metaphase plate

13. Sexual Reproduction and Genetics Section 2 Mendelian Genetics Mendel’sLaw of Independent Assortment

14. Sexual Reproduction and Genetics Section 2 Mendelian Genetics Mendel’sLaws

15. Sexual Reproduction and Genetics Section 2 Mendelian Genetics Monohybrid Cross • A cross that involves hybrids for a single trait is called a monohybrid cross.

16. Sexual Reproduction and Genetics Section 2 Mendelian Genetics Punnett Squares • Predict the possible offspring of a cross between two known genotypes

17. Sexual Reproduction and Genetics Section 2 Mendelian Genetics

18. Sexual Reproduction and Genetics Section 2 Mendelian Genetics

19. Sexual Reproduction and Genetics Section 2 Mendelian Genetics Dihybrid Cross • The simultaneous inheritance of two or more traits in the same plant is a dihybrid cross. • For example, if you crossed a yellow round pea (YYRR) with a green wrinkled pea (yyrr) • What would be the predicted offspring genotypes and phenotypes?

20. Sexual Reproduction and Genetics Section 2 Mendelian Genetics Punnett Square—Dihybrid Cross • Four types of alleles from the male gametes and four types of alleles from the female gametes can be produced. • The resulting phenotypic ratio is 9:3:3:1.

21. Sexual Reproduction and Genetics Section 3 Complex Patterns of Inheritance Incomplete Dominance • In some organisms, however, an individual displays a trait that is intermediate between the two parents, a condition known asincomplete dominance. • For example, when a snapdragon with red flowers is crossed with a snapdragon with white flowers, a snapdragon with pink flowers is produced.

22. Sexual Reproduction and Genetics Section 3 Complex Patterns of Inheritance Incomplete Dominance

23. Sexual Reproduction and Genetics Section 3 Complex Patterns of Inheritance Codominance • For some traits, two dominant alleles are expressed at the same time. • In this case, both forms of the trait are displayed, a phenomenon called codominance. • Codominance is different from incomplete dominance because both traits are displayed. • Instead of pink you would get a red and white flower • Comparing Dominances

24. Sexual Reproduction and Genetics Section 3 Complex Patterns of Inheritance Codominance

25. Sexual Reproduction and Genetics Section 3 Complex Patterns of Inheritance Polygenic Inheritance • When several genes influence a trait, the trait is said to be a polygenic trait. • The genes for a polygenic trait may be scattered along the same chromosome or located on different chromosomes. • Familiar examples of polygenic traits in humans include eye color, height, weight, and hair and skin color.

26. Sexual Reproduction and Genetics Section 3 Complex Patterns of Inheritance Polygenic Inheritance

27. Sexual Reproduction and Genetics Section 3 Complex Patterns of Inheritance Multiple Alleles • Genes with three or more alleles are said to have multiple alleles. • Example: Blood types A, B, AB, and O • Multiple Alleles

28. Sexual Reproduction and Genetics Section 3 Complex Patterns of Inheritance Multiple Alleles

29. Sexual Reproduction and Genetics Section 3 Complex Patterns of Inheritance Pedigree • Geneticists often prepare a pedigree, a family history that shows how a trait is inherited over several generations. • Pedigrees are particularly helpful if the trait is a genetic disorder and the family members want to know if they are carriers or if their children might get the disorder • Pedigree

30. Sexual Reproduction and Genetics Section 3 Complex Patterns of Inheritance Pedigree

31. Sexual Reproduction and Genetics Section 3 Complex Patterns of Inheritance Pedigree • Scientists can determine several pieces of genetic information from a pedigree: • Autosomal or Sex-Linked? If a trait is autosomal, it will appear in both sexes equally. If a trait is sex-linked, it is usually seen only in males. A sex-linked trait is a trait whose allele is located on the X chromosome. • Dominant or Recessive? If the trait is autosomal dominant, every individual with the trait will have a parent with the trait. If the trait is recessive, an individual with the trait can have one, two, or neither parent exhibit the trait.

32. Sexual Reproduction and Genetics Section 3 Complex Patterns of Inheritance Sex-linked - Hemophilia • Sex-linked traits occur on the X chromosomes • Females have 2 Xs so they must have both defective alleles to have the genetic disorder • Males only have 1 X making sex-linked disorders much more common in males • Sex-linked with Flies • Hemophilia is a sex-linked trait a condition that impairs the blood’s ability to clot. • Hemophilia

33. Sexual Reproduction and Genetics Section 3 Complex Patterns of Inheritance Sex-linked

34. Sexual Reproduction and Genetics Section 3 Complex Patterns of Inheritance Sex-linked - Hemophilia