1. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 2 Genetics Gregor Mendel is considered the father of genetics Published his work in 1866

2. Seven Characters Mendel Studied

3. Mendel’s Laws First Law: Segregation the two alleles of a trait separate from each other during the formation of gametes, so that half of the gametes will carry one copy and half will carry the other copy Mendel’s Second Law: Independent Assortment genes located on different chromosomes are inherited independently of one another

4. Human Genetics human somatic cell: 46 chromosomes 22 pairs same in both males/females: autosomes 1 pair different: sex chromosomes: females XX, males XY

5. Aneuploidy: errors during meiosis, leads to individuals with abnormal # chromosomes;  chromosome 21: Down syndrome  chromosome 22: individuals with delayed development and mental impairment  XXX female, taller than average  XXY Klinefelter syndrome, male, sterile, with female characteristics and diminished mental capacity  XO Turner syndrome, female, sterile with diminished stature  XYY males, fertile and normal appearance

6. human heredity: study with family trees or pedigree: sex-linked/autosomal or dominant/recessive

7. 3 Essential Terms in Genetics Genotype—the genetic makeup Phenotype—observable characteristics Diploid: Two copies of each chromosome, such as somatic cells  Homologous pair, Paternal & Maternal Haploid: Reproductive cells have only one copy of each chromosome Genetic Cross: When two individuals are mated P generation—parent generation F 1 generation—first generation F 2 generation—second generation

8. 5 Alleles : Different versions of a given gene  Human blood groups: A,B, AB, and O Three alleles of one gene:  I A : A type sugar  I B : B type sugar  i: neither A or B Homozygote—same two alleles (AA or aa) Heterozygote—two different alleles (Aa)

9. dominant traits are capitalized, lower-case letter is for recessive trait: flower color in peas  P signifies purple, p signifies white

10. Gametes: 2 from each father/mother: P or p Punnett square: shows the possible gametes and genotypes of potential offspring from a cross

11. Huntington’s disease: Huntington’s disease: progressive deterioration of brain cells, affected individuals only need 1 copy (dominant)  Expression in the 30’s

12. Sickle-cell anemia: Sickle-cell anemia: affected individuals (homozygous recessive) with defective hemoglobin that produces a sickle-shape red blood cell which cannot move through the blood vessels and tends to clot  Heterozygous individuals resistance to malaria infection

13. Hemophilia: Hemophilia: sex-linked (mostly on the X chromosome) trait, creates a difficulty of the body to stop any bleeding

14. Steps to answer properly a genetic problem: 1. Assign letters to each allele, dominant and recessive, with the corresponding phenotype 2. Determine the phenotype and genotype of the parents 3. Write down the possible gametes produced by the parents, 4. write down your cross (mating), and split the letters of the genotype for each parent and put them outside a p-square 5. Determine the genotype and phenotype of the offspring and estimate their probabilities 6. Enjoy your accomplishment

15. 21 Extensions of Mendel’s Laws Many alleles do not show complete dominance  Incomplete dominance  Codominance  Pleiotropy  Epistasis  Environmental effects  Polygenic traits

16. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 28 1. Polygenic Traits Trait is determined by two or more genes A continuous distribution – Skin color – Height

17. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 25 2. Pleiotropy A single gene influences a variety of traits: –Albinism— Absence of melanin Skin color Vision problems – characteristic of inherited disorders…..cystic fibrosis, sickle-cell anemia

18. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 26 3. Epistasis Gene interaction affects the phenotype such that one gene contributes to or masks the expression of the other gene Alleles: –BB or Bb = black –bb = brown –cc = white

19. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 27 4. Environmental Effects Internal and external conditions influence phenotype – Temperature – Chemicals – Nutrition arctic foxes: only produce fur pigment when temperatures are warm

20. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 22 5. Incomplete Dominance Heterozygote is an intermediate Horses Snapdragons

21. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e 23 6. Codominance Both alleles are expressed Seen in blood types – I A I A or I A i = type A – I B I B or I B i = type B – ii = type O – I A I B = type AB

22. –gene ABO blood type in humans: affects the membrane of red blood cells which act as recognition markers for cells in the immune system

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25. PRACTICE #1 In peas the allele for purple flower (P) is dominant to the allele for white flower (p). What gametes will be produced by a plant that has white flowers?

26. PRACTICE #2 What kinds of gametes can this genotype produce? AaBB

27. PRACTICE #3 Suppose that flower color is inherited by simple dominance and that purple flowers are dominant to white flowers. If a homozygous recessive individual is crossed with a homozygous dominant individual, what is the probability of obtaining a purple flowered offspring? Show all 5 steps for full credit.

28. PRACTICE #4 Pea plants are tall if they have the genotype TT or Tt, and the are short id they have genotype tt. A tall plant is mated with a short plant. Half the offspring are tall and half short. What do you know about the tall plant? Show all 5 steps for full credit

29. PRACTICE #5 Assume tall (T) is dominant to dwarf (t). If a homozygous dominant individual is crossed with a dwarf, What will the offspring look like? Show all 5 steps for full credit.

30. PRACTICE #6 Flower color in snapdragons is an example of incomplete dominance. If a pink-flowered plant is crossed with a pink-flowered plant, What will the progeny of plants look like? Show all 5 steps for full credit.

31. PRACTICE #7 Color in snapdragons is inherited by incomplete dominance. Suppose you cross a red (R)flowered snapdragon with a white flowered snapdragon (r). ALL of the offspring have pink flowers. What can you conclude about the genotypes of the parents and offspring? Show all 5 steps for full credit.

32. PRACTICE #8 Wanda has type A blood, and her husband has type B blood. Is it possible for this couple to have a child with type O blood? Explain your answer, and show all 5 steps for full credit.

33. PRACTICE #9 A man who has type B blood and a woman who has type A blood have a child with type O blood, How is this possible? Explain your answer, and show all 5 steps for full credit.

34. PRACTICE #10 Hemophilia is a sex linked trait. If a woman is a carrier of hemophilia and she marries a man who does not have hemophilia, what is the probability that her sons inherit the disease? Show all 5 steps for full credit.

35. Practice questions 1. Gregor Mendel studied the garden pea plants because: A) pea plants are small, easy to grow, grow quickly, and produce lots of flowers and seeds. B) he knew about studies with the garden pea that had been done for hundreds of years, and wanted to continue them, using math - counting and recording differences. C) he knew that there were many varieties available with distinctive characteristics. D) all of the above. 2. Human height shows a continuous variation from the very short to the very tall. Height is most likely controlled by: A)epistatic genes. B) environmental factors. C) sex-linked genes. D) multiple genes. 3. In the human ABO blood grouping, the four basic blood types are type A, type B, type AB, and type O. The blood proteins A and B are _________________

36. 33 4. Nondisjunction: A) occurs when homologous chromosomes or sister chromatids fail to separate during meiosis. B) may lead to Down syndrome. C) results in aneuploidy. D) All of the above. 5. A red carnation and a white carnation produce offspring that are all pink. The type of inheritance pattern occurring is: A. Complete dominance B. Incomplete dominance C. Codominance

37. 34 6. If an allele for tall plants (T) is dominant to short plants (t), what offspring would you expect from a TT x Tt cross? A. ½ tall; ½ short B. ¾ tall; ¼ short C. All tall 7. Fur color in rabbits shows incomplete dominance. F B F B individuals are brown, F B F W individuals are cream, F W F W individuals are white. What is the expected ratio of a F B F W x F W F W cross? A. 3 white : 1 brown B. 3 white : 1 cream C. 2 white : 2 cream