Genetics

1. Chapter 6.3 -6.4 and Chp. 7 Genetics

2. What is genetics? • Genetics- The study of heredity • Heredity- the passing of traits from parents to offspring. • Traits- a specific characteristic Ex: eye color, height How are DNA-Genes-Chromosomes related? • DNA – Deoxyribonucleic acid- the genetic code of life • DNA wound tightly makes up a gene • Stacks of genes make up a chromosome • Gene-chemical factors that determine traits C H R O M O S O M E gene

3. Gregor Mendel “Father of Genetics” • Australian monk that worked with pea plants to discover many details of genetics. • Mendel's Experiments • Mendel chose pea plants as his experimental subjects, mainly because they were easy to cross and showed a variety of contrasting traits (purple vs white flowers, tall vs short stems, round vs wrinkled seeds) • Pea plants usually self-pollinate- when pollen fertilizes the egg of the same plant • Mendel would cross pollinate pea plants which he used pollen from one plant to fertilize(pollinate) the egg of another pea plant.

4. Mendel chose true-breeding lines of each plant/trait he studied (true breeding lines always produced offspring of the same type) • He crossed a true breeding plant with a plant of the opposite trait (purple x white). He called this the Parental (P) generation. • He recorded data on the offspring of this cross (First Filial, F1) • He self pollinated the F1 offspring • He recorded data on the offspring of the second generation, calling it the Second Filial generation (F2)

5. Mendel’s Analysis of his Experiments • The F1 generation always displayed one trait (he later called this the dominant trait) • The F1 generation must have within it the trait from the original parents - the white trait • The F2 generation displayed the hidden trait, 1/4 of the F2 generation had it (he later called this hidden trait the recessive trait) • Each individual has two "factors" that determine what external appearance the offspring will have. (We now call these factors genes or alleles)

6. Mendel established three principles (or Laws) from his research • 1. The Principle of Dominance and Recessiveness - one trait is masked or covered up by another trait • 2. Principle of Segregation - the two factors (alleles) for a trait separate during gamete formation • 3. Principle of Independent Assortment - factors of a trait separate independently of one another during gamete formation; another way to look at this is, whether a flower is purple has nothing to do with the length of the plants stems - each trait is independently inherited

7. Modern Genetics~ Punnett Squares • There are 2 alleles(genes) that determine traits. • Alleles are represented by letters. Ex: Bb,bb,BB • Dominant allele- the stronger allele; represented by a capital letter EX: Brown eyes =B • Recessive allele- the weaker allele; represented by a lower case letter Ex: Blues eyes=b • When a Dominant and recessive are paired, the Dominant allele will show in the appearance of the organism the recessive will not. • Example: Bb- the child will have Brown eyes

8. Genotype- genetic make up **when asked for the genotype give the two alleles(letters) Ex: Bb or BB or bb Phenotype- physical characteristics ** When asked for the phenotype look at the alleles(letters) then give what the child would look like: Ex: Brown eye or Blue eyes Homozygous(aka.Pure Bred)- having the same alleles for a trait Ex: BB or bb Heterozygous (aka. Hybrid)- having different alleles for a trait. Ex: Bb

9. Problem: What are the combinations if the mother has BB and father has bb Mom’s alleles B B b b Father’s Alleles • The top alleles drop down into the boxes & side alleles go in the boxes across. • Write the capital letter first.

10. Genetics and Probability • Probability- the likelihood that a particular event will take place. • Ex: when flipping a coin the likelihood that it will land on head is ½. If flipping twice the likely hood is 1/2X1/2=1/4 • Each event is an independent event.

11. Probability of a Punnet Square • It can be expressed as a fraction, percent or ratio. • Punnett Square that have 4 squares the probability is out of 4. Ex: 1 out of 4 = ¼ or 25% ; 2 out of 4 = ½ or 50% Genotype: BB=25% or ¼ Bb=50% or 2/4 bb=25% or ¼ Ratio = 1:2:1 B=Brown eyes b = blue eyes b B B Phenotype: Brown eyes =75% or ¾ Blue eyes = 25% or ¼ Ratio: 3:1 b

12. Punnett Square practice problem: Fill in the square and give the probabilities in percent and the ratios T t • Genotypes: • Heterozygous: • Homozygous: • Phenotypes: T t This cross is a monohybrid cross= crosses 1 trait both parents are hybrids. The Ratio is always 1:2:1 T= Tongue roller t = Non tongue roller

13. 2 Factor Crosses These two factors come from the 4 possible allele pairs of gametes according to the law of independent assortment Mom=RrYy DAD=RrYy Possible Gametes= RY, Ry, rY, ry Ratio: 9:3:3:1 This is a Dihybrid cross- 2 traits are crossed at one time and both parents were hybrid for both traits. Ratio is always 9:3:3:1

14. Incomplete Dominance • Incomplete Dominance- When traits are neither dominant nor recessive. Hybrids produce mixed traits • Ex: Red flower x White flower produces all pink flowers • Codominance- When Both alleles contribute to the phenotype. Example: instead of a mixture being produced both traits are produced • Ex: Brown hair cow x White hair cow produces cows that have both brown & white hairs .

16. Multiple Allele Traits • Multiple Allele Traits- Traits that are controlled by more than two alleles. Blood type in humans is controlled by three alleles: A, B, and O

17. Sample of Multiple Allele Crosses

18. Sex-linked traits • Traits that are on one of the sex chromosomes ( X or Y ) but not the other. • Example: red/green color blindness carried on the X chromosome • If the trait is on the X chromosome then it may be represented by Xc. • X Xc.= (Female)a carrier but not in the phenotype • Xc. Xc. = (Female)trait shows in phenotype • Xc. Y= (male) trait shows in phenotype

19. Sex Linked Punnett Square h- represents balding Xh X Xh Y