Fundamentals of Genetics

1. Fundamentals of Genetics • Turn in your Karyotype Lab to the alpha sorter! • Pick up Genetics Notes Packet • http://app.discoveryeducation.com/player/view/assetGuid/0C4200E0-0CEC-4A73-8569-A9EF08E03F3F

2. Genetics Notes Who is Gregor Mendel? • Principle of Independent Assortment– genes for different traits can segregate independently during the formation of gametes. Therefore, the inheritance of one trait has no affect on the inheritance of another. • Example:Hair color and Eye color These genes segregate independently and do not influence each other’s inheritance (i.e. not all people with blonde hair will have blue eyes). “Father of Genetics”

3. Traits • Genetics – study of how traits are passed from parent to offspring

4. Traits are determined by the genes on the chromosomes. A gene is a segment of DNA that determines a trait.

5. Chromosomes come in homologous pairs, thus genes come in pairs. • Homologous pairs – matching genes – one from female parent and one from male parent • Example: Humans have 46 chromosomes or 23 pairs. • One set from dad – 23 in sperm • One set from mom – 23 in egg

6. One pair of Homologous Chromosomes: Gene for eye color(blue eyes) Homologous pair of chromosomes Gene for eye color (brown eyes) Alleles – different genes (possibilities) for the sametrait – ex: blue eyes or brown eyes

7. Gene Linkage • Genes located on same chromosome – gene linkage • Genes located on same chromosome cannot go through-- independent assortment • Chromosomes are distributed to gametes randomly or independently Package of genes inherited together

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

9. Example: Straight thumb is dominant to hitchhiker thumb T= straight thumb t = hitchhikers thumb (Always use the same letter for the same alleles— No S = straight, h = hitchhiker’s) Straight thumb = TT Straight thumb = Tt Hitchhikers thumb = tt • * Must have 2 recessive allelesfor a recessive trait to “show”

10. Both genes of a pair are the same – • homozygous or purebred • TT – homozygous dominant • tt – homozygous recessive • One dominant and one recessive gene – heterozygous or hybrid • Tt – heterozygous BB – Black Bb – Black w/ white gene bb – White

11. 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

12. Punnett Square and Probability • Used to predict the possible gene makeup of offspring – Punnett Square • Cross involving one trait -- monohybrid • Example:Black fur (B) is dominant to white fur (b) inmice • Cross a heterozygous male with a homozygous recessive female. Black fur (B) White fur (b) Heterozygous male Homozygous recessive female White fur (b) White fur (b)

13. b b B b Male = BbXFemale = bb Female gametes – N (One gene in egg) Possible offspring – 2N Male gametes - N (One gene in sperm) Write the ratios in the following orders: Genotypic ratio homozygous : heterozygous : homozygous dominant recessive Phenotypic ratio dominant : recessive Genotypic ratio =2 Bb : 2 bb 50% Bb : 50% bb Phenotypic ratio = 2 black : 2 white 50% black : 50% white

14. Cross 2 hybrid mice and give the genotypic ratio and phenotypic ratio. BbX Bb B b B b Genotypic ratio = 1 BB : 2 Bb : 1 bb 25% BB : 50% Bb : 25% bb Phenotypic ratio = 3 black : 1 white 75% black : 25% white

15. Example: A man and woman, both with brown eyes (B) marry and have a blue eyed (b) child. What arethe genotypes of the man, woman and child? What is the probability of them having a blue eyed child? • BbXBb Man = Bb Woman = Bb B b B 3 brown : 1 blue (2 carriers) ¼ or 25% blue b

16. 11/26 • Turn in Genetics Practice Problems Packet to the Alpha Sorter • Pick up Bugly Lab Answer Sheet • Pick up old graded papers!

17. 11/27 • Get out your “Genetics Problems Packet”. • Reminder: Quiz today – Monohybrid Crosses + Vocabulary

18. Crossing involving 2 traits – Dihybrid crosses • Example: In rabbits black coat (B) is dominant over brown (b) andstraight hair (H) is dominant to curly (h). Cross 2 hybridrabbits and give the phenotypic ratio for the firstgeneration of offspring. BH Bh bH bh BH Bh bH bh Possible gametes: • BbHh X BbHh BH BH BhBh bHbH bhbh Gametes Phenotypes - 9:3:3:1 9 black and straight 3 black and curly 3 brown and straight 1 brown and curly

19. BH Bh BH • Example: In rabbits black coat (B) is dominant over brown (b) and straight hair (H) is dominant to curly (h). Cross a rabbit that is homozygous dominant for both traits with a rabbit that is homozygous dominant for black coat and heterozygous for straight hair. Then give the phenotypic ratio for the first generation of offspring. BBHH X BBHh Possible gametes: BH BH Bh Gametes • Phenotypes: 100% black and straight Gametes (Hint: Only design Punnett squares to suit the number of possible gametes.)

20. Gamete Formation Practice: • Black fur (B) in guinea pigs is dominant to White Fur (b), and rough fur (R) in guinea pigs is dominant to smooth (r). Cross a heterozygous parent (BbRr) with a heterozygous parent (BbRr). • Possible Gametes: • Brown eyes (B) are dominant to blue eyes (b), and brown hair (H) is dominant to blonde hair (h). Cross a blued eyed, homozygous brown haired parent with a blue eyed, blonde haired parent. • Possible Gametes: BbRr BbRr BR Br bR br Parent 1: BR, Br, bR, br BR Br bR br Parent 2: BR, Br, bR, br bbHH bbhh Parent 1: bH bH bH bH bH bh bh bh bh Parent 2: bh

21. Sex Determination • What is the probability of a husband and wife having a boy or girl baby? Chance of having female baby? 50% male baby? 50% X X X Y Who determines the sex of the child? father