Patterns of Inheritance

1. Patterns of Inheritance Chapter 10

2. Gregor Mendel • Austrian monk • Father of Genetics (study of heredity) • Said parents pass on to their offspring separate and distinct genes • Studied 7 characteristics in pea plants

3. Mendel’s Peas • For a good review of Mendel’s Work, this video explains it (skip the first minute!) • http://www.youtube.com/watch?v=Wgx7SKxpdL8&NR=1&feature=endscreen

4. This is longer, but more thoroughly explained-explains all Mendel’s laws and examples: http://www.youtube.com/watch?v=5lzk-uOir_E

5. Punnett Square • Mr. Bozeman’s Tutorial • http://www.youtube.com/watch?v=Y1PCwxUDTl8

6. Reviewing Some Terms • True breeding plants • A true plant will show the same physical appearance generation after generation after self-fertilization • Cross fertilization • The sperm from the pollen of one true flower fertilizes the eggs in the flower of a different plant

7. Mendel's Experiments • Cross-fertilized 2 true-breeding plants each with contrasting traits (i.e. white and purple flowers) • What color of flowers do you think the offspring plants were?

8. Principle of Segregation • P generation • Parental plants (purebred and true breeding) • F1 generation ( F for filial “son”) • Hybrid offspring • Hybrids • The offspring of 2 different true-breeding varieties • F2 generation • When F1 self-fertilize or fertilize each other

9. Monohybrid Cross • Monohybrid cross • Cross fertilization in which only one physical characteristic is considered • In Mendel's cross, all F1 were purple but ¼ of F2 were white

10. Gene Hypotheses #1 • There are alternative forms of genes which determine physical appearances • Allele is the term • Example: Flower color can be white or purple

11. Gene Hypotheses #2 • For each characteristic, an organism has 2 alleles for genes controlling the physical appearances (one from each parent) • If 2 alleles are the same= homozygous • If 2 alleles are different =heterozygous

12. Gene Hypotheses #3 • Dominant alleles determine the physical appearance in a heterozygous individual. • Recessive allele is the other allele that does not affect the physical appearance • Capital letter represents dominant allele: P • Lower case letter represents recessive allele: p

13. Phenotype is the physical appearance • Genotype is the genetic makeup PHENOTYPE/GENOTYPE • Purple RR • Purple Rr • White rr

14. Gene Hypotheses #4 • The two alleles for a character segregate (separate) during meiosis so that each gamete carries only one allele for each character, known as principle of segregation.

15. Punnett Square • The alignment of combination of gametes to form zygotes with pairs of alleles is random • Like tossing a coin. • A Punnett Square is a diagram that shows all possible outcomes of a genetic cross. • Used to predict probabilities of outcomes if you know the genotypes of the parents

16. Punnett Squares • Show the genotype of the parents and the possible gametes they can make. • Each parent is represented on one side of the square • Each parent’s possible gamete genotype is distributed to gametes • The possible genotypes of the offspring are produced

17. Sample Crosses Tall vs short • Pure parents are crossed and all offspring are heterozygous for tall • Genotype Tt • Appear Tall (dominant trait) • If this generation are re-crossed with each other, • ¾ of offspring are tall • ¼ of offspring are short

18. Some Punnetts have Cartoons Some don’t.

19. The Testcross • Breeds an individual of unknown genotype, but dominant phenotype (purple) with a homozygous recessive individual (white) • Appearance of F1 will reveal the genotype of the mystery parent • If white flowers are produced, the unknown parent must be heterozygous (Rr) and have a recessive trait

20. Example: Test Cross • We take an unknown parent and cross with a homozygous recessive parent. • White is recessive; we know the genotype • The cross determines if the unknown parent is homo- or heterozygous • How do we know the genotype?

21. Dihybrid Cross • Two traits are observed when crossed • A parent who is Homozygous Dominant for both Round and Yellow seeds • Is crossed with a parent showing both recessive traits, wrinkled and yellow

22. If a monohybrid cross produces a possibility of 4 offspring… • How many probable offspring does a dihybrid cross need to show? • 4 X 4 = 16 if we are breeding a parent heterozygous for both traits • AaBb X AaBb • That would be, for example, RrYy X RrYy • There would be four phenotypes instead of two: • Round and yellow • Round and green • Wrinkled and yellow • Wrinkled and green

23. Section 3 • Patterns in Variation • Intermediate Dominance (chicken color, some flowers) • Multiple Alleles (blood types) • Polygenic Inheritance (many genes-skin color, height) • Environmental Influences (Siamese cats-fur color by temperature)

24. Intermediate Dominance • Heterozygotes have a phenotype intermediate between the phenotypes of the two homozygotes • This is referred to as INCOMPLETE DOMINANCE • Rules: (example: snapdragon flowers) • Capital/lower case letters not used • Instead, a C for “color” is paired with a superscript R for “red” and W for “white” • CR CRis red and CW CWis white • CR CW is pink

26. There is a breed of chicken called Andalusians, black and white parents produce F1 hybrid offspring, called "blues," with grayish-blue feathers. • Because neither the black nor white allele is dominant, capital and lowercase letters are not used to represent them.

27. Instead, a C for "color" is paired with a superscript B for "black" or W for "white" to represent the two alleles. A heterozygote chicken has one of each allele, CBCW, and is grayish-blue in color

28. . • Although the F1 phenotypes are intermediate, this inheritance pattern does not support the blending hypothesis. • This is because the parent phenotypes can reappear in the F2 generation

29. Multiple alleles • Heterozygotes express the distinct traits of both alleles • Example: Human blood system • A, B, AB, or O • The letters are antigens (proteins) found on the surface of red blood cells • Red blood cells may be coated with one protein (A), the other (B), both (AB), or neither (O) • There are six possible genotype combinations

30. ABO blood type is a genetic example of multiple alleles. There are three alleles in the gene pool for ABO blood type. IA IB i

31. IA codes for protein A IB codes for protein B i codes for neither protein A nor protein B.

32. Within this multiple allele pool the gene interactions illustrate both simple dominance as well as co-dominance. Remember each individual has only two alleles for each trait even if there are multiple alleles in the gene pool. IAIA both code for A type blood IAi

34. ABO Blood System • Antibodies (proteins) also found in the blood serum that attacks foreign antigens • Blood A has antibody Anti-B • Blood B has antibody Anti-A • Blood AB has no antibody • Blood O has Antibody Anti A and B • Blood O is the universal donor • Blood AB can receive any blood type

35. Rh Factor • Rh positive (Rh +) has protein in blood • Rh negative (Rh -) has no protein in blood • Rh+ is dominant

36. Blood Typing

38. Sex Determination in Humans • Female is XX • Male is XY • Each egg contains a single X chromosome and each sperm contains either an X or a Y • Sex of the offspring depends on whether the sperm that fertilizes the egg has an X or a Y

39. Sex-linked Genes • Any gene located on a sex chromosome (X) is called a sex-linked gene • Most are found on the X (2,000) and few on the Y (24) • One X is always inherited from the mother. • Males inherit Y from father; females inherit X from father • If the father has the trait on an X chromosome, his daughter will be a carrier (has one gene for the trait but isn’t afflicted).

40. Sex-linked traits • Written as a XRXrfor heterozygous = Carrier • Y chromosomes carry no allele; the phenotype depends on the woman’s allele • Therefore, males carry one allele for a sex-linked trait. • XRY normal; XrYafflicted (has the trait)

41. Three Alleles: Y, XR, Xr Five Genotypes • XRXr • XRXR • XrXr • XRY • XrY Five Phenotypes • Carrier female • Unafflicted female • Afflicted female • Unafflicted male • Afflicted male

42. Sex-linked disorders • Red-green blindness • Hemophilia (inability of blood to clot)

43. The end