Introduction to Genetics

1. Introduction to Genetics Life Science

2. Traits survey What causes these differences?

3. Genetics - The study of heredity (how traits are passed on) *Traits are determined by genes found on DNA or x = or

4. The study of heredity started with the work of Gregor Mendel and his pea plant garden Mendel was an Austrian Monk that lived in the mid 1800’s

5. Mendel noted that the size of pea plants varied. He cross-bred these pea plants to find some surprising results.

6. Mendel’s cross between tall pea plants yielded all tall pea plants. X =

7. His cross between small pea plants yielded all small pea plants. = X

8. Mendels’ cross between tall pea plants and small pea plants yielded all tall pea plants. x =

9. Mendel then crossed these second generation tall pea plants and ended up with 1 out 4 being small. x =

10. Mendel’s work led him to the understanding that traits such as plant height are carried in pairs of information not by single sets of information. Hereditary information (DNA) is carried in Chromosomes!

12. DNA DNA is found in all living cells • It controls all functions inside a cell • DNA stores all the genetic information for a living organism • Single cell like an amoeba • Multi cell like a human

13. Genetics Small sections of DNA are responsible for a “trait”. These small sections are called “Genes”. • Gene - A segment of DNA that codes for a specific trait • Come in different versions • Trait - A characteristic an organism can pass on to it’s offspring through DNA Gene

14. Genes Genes come in different versions: • Dominant - A gene that is ALWAYS expressed and hides others • Recessive - A gene that is only expressed when a dominant gene isn’t present (hidden)

15. Alleles- a version of a gene All organisms have two copies of each gene (one from female, one from male) Homozygous- Two copies of the same gene Heterozygous - Two different genes

16. Dominant and Recessive Genes Widows Peak • A dominant gene will hide a recessive gene! Example: • A “widows peak” is dominant, not having a widows peak is recessive. • If one parent contributes a gene for a widows peak, and the other parent doesn’t, the off- spring will have a widows peak.

17. Example: A Widows Peak, dominant trait, would be symbolized with a capital “W”, while no widows peak, recessive trait, would be symbolized with a lower case “w”. Father - No Widows Peak - w Mother - Has a Widows Peak - W

18. Example: For the widows peak: WW - has a widows peak Homozygous dominant Ww - has a widows peak Heterozygous ww - no widows peak Homozygous recessive

19. Genotype vs Phenotype • Genotype- Genes you have Ex: WW, Ww, or ww • Phenotype- physical features SHOWN Ex: WW Widows peak Ww Widows peak ww NO widows peak

20. Example: Since Herman has no widows peak, he must be ______, since Lilly has a widows peak she could be EITHER ______ or ______. ww WW or Ww

21. Punnett Square Punnett Square - A tool we use for predicting the traits of an offspring • Letters used as symbols to represent genes • Capital letters= dominant genes • Lower case letters= recessive genes • Genes always exist in pairs

22. Punnett Squares We can use a “Punnet Square” to determine what pairs of genes Lilly has • A Punnet Square begins with a box 2 x 2 • One gene is called an “allele” • One parents pair is split into alleles on top, the other along the side • Each allele is crossed with the other allele to predict the traits of the offspring Assume Lilly is heterozygous Ww Assume Herman is homozygous recessive ww W w w Ww ww w Ww ww

23. Punnett Squares Notice that when Lilly is crossed with Herman, we would predict that half the offspring would be “Ww”, the other half would be “ww” Half “Ww”, Heterozygous, and will have a widows peak Half “ww”, Homozygous, and will not have a widows peak W w w Ww ww w Ww ww

24. Try it yourself! Create a punnett square assuming Lilly is homozygous dominant (WW) W W What is the chance of the offspring having a widows peak? w w

25. Try it yourself! All of the offspring will have a widows peak! W W w Ww Ww 100% w Ww Ww

26. Genetics Recall that Herman and Lilly had another offspring, Marylin. She had NO widows peak.

27. Genetics So which is true? Is Lilly homozygous dominant (WW) or is she heterozygous (Ww)? W w W W w Ww ww w Ww Ww w Ww ww w Ww Ww

28. Genetics If Lilly were heterozygous, then 1/2 of their offspring should have a widows peak, 1/2 shouldn’t If Lilly were homozygous, all of their children will have a widows peak W w W W w Ww ww w Ww Ww w Ww ww w Ww Ww

29. Genetics So, back to the original question. What color hair will the offspring of Prince Charming and Snow White have?

30. Genetics Hair color is different from widows peak, no color is truly dominant. • Dark brown and blond are homozygous traits • Brown is dominant (BB) • Blond is recessive (bb) • Heterozygous conditions produce brown, red, etc.

31. Genetics For Snow White to have brown hair she must be homozygous dominant, “BB”, a blond Prince Charmin must be homozygous recessive, “bb”. B B b Bb Bb b Bb Bb

32. Genetics All the offspring from Prince Charming and Snow White will therefore be heterozygous, “Bb”, and since hair color is codominant….. all their children will have red hair. +

33. Cell Division (Meiosis) 1. A process of cell division where the number of chromosomes is cut in half 2. Occurs in gonads (testes, ovaries, stamens, etc) 3. Makes gametes (sperm, ova, pollen, etc)