Study of heredity

1. Study of heredity

2. Heredity: passing of traits from parent to child Patterns of relatedness can help predict offspring characteristics

3. Chromosomes and Genes • Genes are located on chromosomes • Genes inherited from mom and dad • Genes come in several forms called alleles

4. Chromosomes and Genes • Allele: Alternative forms of a gene • Ex: Flower color • White allele or Purple allele

5. Each parent donates one allele for every gene. • Homozygous describes two alleles that are the same at a specific locus. • Heterozygous describes two alleles that are different at a specific locus. • An allele is any alternative form of a gene occurring at a specific locus on a chromosome.

6. Alleles can be represented using letters. Ex: Aa or AA or aa • A dominant allele is expressed as a phenotype when at least one allele is dominant. • A recessive allele is expressed as a phenotype only when two copies are present. • Dominant alleles are represented by UPPERCASE letters • Recessive alleles by lowercase letters.

7. Dominant and Recessive Genes • Gene that prevents the other gene from “showing” – dominant • Gene that does NOT “show” even though it is present – recessive • Symbol – Dominant gene – upper case letter – T • Recessive gene – lower case letter – t Recessive color Dominant color

8. Genotype and Phenotype • Combination of genes an organism has (actual gene makeup) – GENOTYPE • Ex: TT, Tt, tt • Physical appearance resulting from gene make-up – PHENOTYPE • Ex: hitchhiker’s thumb or straight thumb

9. Genetics Vocabulary Review Choices: • YY • Tall • Yy • SS • yY • gg • Smooth • Green • TT • Dwarf Which choice(s) are examples of: Genotypes? 1, 3, 4, 5, 6, 9 Phenotypes? 2, 7, 8, 10 Homozygous genotypes? 1, 4, 6, 9 Heterozygous genotypes? 3, 5 Homozygous recessive genotypes? 6 Homozygous dominant genotypes? 1, 4, 9

10. Dominant vs. Recessive #1 • If Brown eye color is dominant over blue eye color, how would you indicate… • The brown allele? • The blue allele?

11. Dominant vs. Recessive #2 • If dimples in the cheeks are dominant, how would you indicate… • The allele for dimples? • The allele for no dimples?

12. Dominant vs. Recessive #3 • If left thumb over right thumb is dominant, how would you indicate… • Left over right? • Right over left?

13. Mendel laid the groundwork for genetics. • Traits are distinguishing characteristics that are inherited. • Genetics is the study of biological inheritance patterns and variation. • Gregor Mendel showed that traits are inherited as discrete units. • Many in Mendel’s day thought traits were blended.

14. Mendel’s data revealed patterns of inheritance. • Mendel made three key decisions in his experiments. • use of purebred plants • control over breeding • observation of seven“either-or” traits

15. Mendel controlled the fertilization of his pea plants by removing the male parts, or stamens. He then fertilized the female part, or pistil, with pollen from a different pea plant. • Mendel used pollen to fertilize selected pea plants. • P generation crossed to produce F1 generation • interrupted the self-pollination process by removing male flower parts

16. Mendel allowed the resulting plants to self-pollinate. • Among the F1 generation, all plants had purple flowers • F1 plants are all heterozygous • Among the F2 generation, some plants had purple flowers and some had white

17. Genetic Vocabulary • Generations: • P = parental generation • F1 = 1st filial generation, progeny of the P generation • F2 = 2nd filial generation, progeny of the F1 generation (F3 and so on) • Crosses: • Monohybrid cross = cross of two different true-breeding strains (homozygotes) that differ in a single trait. • Dihybrid cross = cross of two different true-breeding strains (homozygotes) that differ in two traits.

18. Each trait had a 3:1 ratio. No way that can be a coincidence!

19. Mendel’s 3 Conclusions 1. Law of Dominance • If the two alleles of a particular gene present in an individual are the same, the individual is said to be homozygous. (dominant or recessive) • If the alleles of a particular gene present in an individual are different, the individual is heterozygous. • In heterozygous individuals, only the dominant allele is expressed; the recessive allele is present but unexpressed.

20. purple white Mendel’s 3 Conclusions • 2. Traits are inherited as discrete units. • Organisms inherit two copies of each gene (allele), one from each parent. • Genes are inherited independently of each other.

21. Mendel’s 3 Conclusions 3. Law of Segregation The two copies of alleles segregate during gamete formation.

22. Punnett Squares • Defined: Tools used to determine genetic probability • Probability = likelihood that a certain event will happen • 2 Steps: • 1) Place parent genotypes on the outside of the box • 2) Fill in the boxes

23. Cross a homozygous dominant yellow (YY) plant with a homozygous recessive green (yy) plant y y y y y y Key Y = yellow y = green Y Y 100% Probability of growing a yellow plant? _____________ 0% Probability of growing a homozygous recessive plant? ____________ 0% Probability of growing a homozygous dominant plant? ____________

24. Cross a heterozygous dominant yellow (Yy) plant with a heterozygous dominant yellow (Yy) plant Y Y Y y y y Y Y Y Key Y = Yellow y = green y y y 50% Probability of growing a heterozygous plant? ________ 25% Probability of growing a green plant? ________ 25% Probability of growing pure yellow? _________

25. Maria is a heterozygous healthy (Hh) female and Jeff suffers from recessive cystic fibrosis (hh). h h h h h h Key H = healthy h = cystic fibrosis H H H h h h Probability of having a healthy child? _________ Probability of having a homozygous dominant child? ________ 50% 0%