2. Genetics & The Work of Mendel

3. HOMOLOGOUS CHROMOSOME Pairs of matching chromosomes, with one being inherited from each parent.

4. ALLELES- alternative forms of the same gene. When 1 allele masks (hides) the effect of another, that allele is called DOMINANT and the hidden allele is called RECESSIVE. Dominant alleles are represented by a CAPITAL letter Recessive alleles are represented by a LOWERCASE letter A b C d e A B c d E Chromosome from MOM Chromosome from DAD ALLELES

5. What are Dominant Genes? Hereford: white face is dominant Horned is recessive to polled.

6. PHENOTYPE (what the organism LOOKS like) Examples of phenotypes: blue eyes, brown fur, striped fruit, yellow flowers GENOTYPE the genes present in the DNA of an organism 1 gene from MOM + 1 gene from DAD= 2 genes (2 letters) for offspring 3 possible GENOTYPES: "TT" – Homozygous Dominant "Tt" - Heterozygous "tt" – Homozygous Recessive

7. Genotype Symbol Genotype Vocabulary Phenotype TT homozygous DOMINANT or purebred tall tall Tt heterozygous or hybrid tall tt homozygous RECESSIVE or purebred short short

8. Gregor Mendel (1822-1884) Austrian monk Called the “Father of Genetics" for his study of the inheritance of 7 traits in pea plants.

9. Mendel collected data for 7 pea traits

10. Pollen transferred from white flower to stigma of purple flower all purple flowers result Mendel’s work ? self-pollinate Bred pea plants –cross-pollinate true breeding parents –raised seed & then observed traits –allowed offspring to self-pollinate & observed next generation

11. 2 nd generation 3:1 75% purple-flower peas 25% white-flower peas Looking closer at Mendel’s work Parents 100% 1 st generation (hybrids) 100% purple-flower peas X true-breeding purple-flower peas true-breeding white-flower peas self-pollinate

12. Making crosses Can represent alleles as letters –flower color alleles  P or p –true-breeding purple-flower peas  PP –true-breeding white-flower peas  pp PP x pp PpPp F1F1 P X purplewhite all purple

13. PP p Pp p all the F 1 (1 st filial generation) offspring are purple colored hybrids 100% purple offspring

14. Pp P p Pp x Pp Heterozygous - hybrid

15. Punnett squares Pp x Pp Pp male / sperm P p female / eggs PP 75% 25% 3:1 25% 50% 25% 1:2:1 % genotype % phenotype PPPpPp PpPppp PpPp PpPp 1 st generation (hybrids) Aaaaah, phenotype & genotype can have different ratios

16. Monohybrid Cross Example:Cross between two heterozygotes for brown eyes (Bb) BB = brown eyes Bb = brown eyes bb = blue eyes B b Bb Bb x Bb male gametes female gametes

17. Monohybrid Cross BB Bb bbB b Bb Bb x Bb 1/4 = BB - brown eyed 1/2 = Bb - brown eyed 1/4 = bb - blue eyed 1:2:1 genotype 3:1 phenotype

18. Dihybrid cross Other of Mendel’s experiments followed the inheritance of 2 different characters –seed color and seed shape –dihybrid crosses

19. Dihybrid cross true-breeding yellow, round peas true-breeding green, wrinkled peas x YYRRyyrr P 100% F 1 generation (hybrids) yellow, round peas Y = yellow R = round y = green r = wrinkled self-pollinate 9:3:3:1 9/16 yellow round peas 3/16 green round peas 3/16 yellow wrinkled peas 1/16 green wrinkled peas F 2 generation YyRr

20. Dihybrid Cross Example:cross between round and yellow heterozygous pea seeds. R= round r= wrinkled Y= yellow y= green RY Ry rY ry RY Ry rY ry RY Ry rY ry x RY Ry rY ry possible gametes produced RrYyRrYy RrYy x RrYy

21. Dihybrid cross YyRr YRYryR yr YR Yr yR yr YYRR x YYRrYyRRYyRr YYRrYYrrYyRrYyrr YyRRYyRryyRRyyRr YyRrYyrryyRryyrr 9/16 yellow round 3/16 green round 3/16 yellow wrinkled 1/16 green wrinkled YyRr YryRYR yr YyRr YRyr or

22. Incomplete Dominance Incomplete dominance is when both alleles are expressed and results in an intermediate phenotype. The hybrid is a blend of both alleles. When expressing incomplete dominant alleles, both alleles are represented by different capitalized letters.

23. Incomplete dominance Hybrids have “in-between” appearance –RR = red flowers –rr = white flowers –Rr = pink flowers make 50% less color RRRrrr  RR  WW  RW

24. Incomplete dominance true-breeding red flowers true-breeding white flowers X P 100% 100% pink flowers 1 st generation (hybrids) self-pollinate 25% white 2 nd generation 25% red 1:2:1 50% pink

25. RR W W Homozygous Incomplete Dominance P (parental) generation

26. RW R R W W Incomplete Dominance F 1 (First Filial) generation 100% pink offspring

27. RW R W Heterozygous Incomplete Dominance F 1 x F 1

28. Incomplete dominance RW male / sperm R W female / eggs RR RWWW RW 25% 1:2:1 25% 50% 25% 1:2:1 % genotype % phenotype RR RW WW 25% 50% RW x RW

29. Co-dominance Some alleles are equally strong and neither are masked by the other. Alleles which are equally expressed are said to be "co-dominant". The hybrid is a mixture of both alleles.