Genetics

1. Genetics Genetics is the scientific study of heredity and variation.

2. Genetics • In asexual reproduction: • Single-celled organisms reproduce by simple cell division • There is no fertilization of an egg by a sperm FUNCTIONS OF CELL DIVISION Asexual Reproduction LM Sea stars African Violet Amoeba

3. Genetics • Sexual reproduction requires fertilization of an egg by a sperm using a special type of cell division called meiosis.

4. Genetics • Gregor Mendel • •Worked in the 1860s • •Was the first person to analyze patterns of inheritance • •Deduced the fundamental principles of genetics

5. Genetics White Removed stamens from purple flower. Stamens Transferred pollen from stamens of white flower to carpel of purple flower. Parents (P) Carpel Purple Pollinated carpel matured into pod. Planted seeds from pod. Offspring (F1) • Mendel studied garden peas because they: • •Easy to grow • • Come in many readily distinguishable varieties • • Easily manipulated • • Can self-fertilize

6. Genetics • A character is a heritable feature that varies among individuals. • A trait is a variant of a character. • Each of the characters Mendel studied occurred in two distinct forms.

8. Genetics *P - parental generation *F1 – first filial generation *F2 – second filial generation -Example: F2 P X Tall Dwarf F1 – all Tall Tall

9. Genetics *genes and alleles Mendel’s hypotheses (to explain his results) 1. Alternative versions of genes (alleles) account for variation in inherited characters. 2. For each character, an organism inherits two alleles, one from each parent.

10. Genetics 4. The two alleles for each character segregate (separate) during gamete production. 3. If two alleles differ, one is dominant, the other recessive P: X DD dd Tall Dwarf F1 – all Tall Tall Dd Mendel’s Law of Segregation

11. Genetics D D D D D D D D d d d d d d d d A Punnett Square predicts the results of a genetic cross between individuals of known genotype Tall Dwarf X P: DD dd Gamete formation: *genotype *phenotype 4/4 are Dd 4/4 are Tall *Homozygous *Heterozygous

12. Genetics

13. Genetics Example: P1 X gw yellow, round green, wrinkled gw GGWW ggww gw F1 gw All yellow, round Dihybrid cross- A genetic cross between two individuals involving two characters GW GW GW GW GgWw

14. F1 F1 X GW All yellow, round All yellow, round Gw GgWw GgWw gW gw 9:3:3:1 Phenotypic ratio; Genotypic ratio as follows: 1/16 GGWW, 2/16 GGWw, 2/16 GgWW, 4/16 GgWw F2 9/16 yellow, round 1/16 GGww, 2/16 Ggww 3/16 yellow, wrinkled 1/16 ggWw, 2/16 ggWw 3/16 green, round 1/16 ggww 1/16 green, wrinkled GW Gw gW gw

15. Genetics F1 Genotypes Bb female Bb male Formation of sperm Formation of eggs F2 Genotypes Male gametes b B 1 1 1 1 B B B 4 4 4 4 b 1 1 1 1 1 1 B 2 2 2 2 2 2 (  ) Female gametes b B b b b Mendelian inheritance is based on probability Example- coin toss *1/2 chance landing heads *Each toss is an independent event *Coin toss, just like the distribution of alleles into gametes *The rule of multiplication – determines the chance that two or more independent events will occur together ½ x ½ = ¼

16. Genetics: Pedigrees First generation (grandparents) ff Ff Ff Ff Second generation (parents, aunts, and uncles) ff Ff FF ff ff Ff or Ff Third generation (brother and sister) ff FF or Ff Female Male Attached Free

17. Human Disorders

18. P Generation White Red RR rr Gametes r R F1 Generation Pink Rr Gametes r R Sperm F2 Generation r R R RR Rr Eggs 1 1 1 1 1 1 r rr Rr 2 2 2 2 2 2 Variations in Mendel’s Laws In incomplete dominance, F1 hybrids have an appearance in between the phenotypes of the two parents.

19. Variations in Mendel’s Laws Hypercholesterolemia • Dangerously high levels of cholesterol in the blood. • Is a human trait that is incompletely dominant. • Heterozygotes have blood cholesterol levels about 2X normal. • Homozygotes have blood cholesterol levels about 5X normal. Hh HH hh Homozygous for ability to make LDL receptors Heterozygous Homozygous for inability to make LDL receptors GENOTYPE LDL LDL receptor PHENOTYPE Cell Normal Mild disease Severe disease

20. Variations in Mendel’s Laws Multiple Alleles Blood Group (Phenotype) Red Blood Cells Genotypes Carbohydrate A IAIA or IAi A Carbohydrate B IBIB or IBi B AB IAIB ii O

21. Variations in Mendel’s Laws • Pleiotropy is the impact of a single gene on more than one character. Pleiotropy Multiple traits (e.g., sickle-cell disease) Single gene

22. Variations in Mendel’s Laws

23. Polygenic inheritance Single trait (e.g., skin color) Multiple genes Variations in Mendel’s Laws • Polygenic inheritance is the additive effects of two or more genes on a single phenotype.

24. P Generation aabbcc (very light) AABBCC (very dark) F1 Generation AaBbCc AaBbCc Sperm F2 Generation 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 Eggs 1 1 20 15 15 6 6 64 64 64 64 64 64 64 Variations in Mendel’s Laws

25. Sex Linkage II III XY IV or XX *1909 Thomas Hunt Morgan *Sex chromosomes *Autosomes Example: In Drosophila and all mammals sex chromosomes designated as X and Y XX=female XY=male

26. Sex Linkage Any gene located on a sex chromosome is called a sex-linked gene. • Most sex-linked genes are found on the X chromosome.