Genetics & Inheritance

1. Genetics & Inheritance Ch. 19

2. Goals • Know the terminology: • Gene, Chromosome, Autosome, Sex Chromosomes, Alleles, Homozygous, Heterozygous, Locus/Loci, • Understand the difference between genotype and phenotype • Can environment influence phenotype? • Understand and know how to use the Punnett square • Know the differences between dominant alleles, recessive alleles, incomplete dominance, and codominance • Know what polygenic traits depend on and the examples • Understand Linked Alleles

3. Genetics Terminology • Genes: DNA sequences that contain instructions for building proteins • Chromosomes: structures within the nucleus, composed of DNA and protein • Humans: 23 pairs of chromosomes • 22 pairs of homologous chromosomes • these are also known as autosomes • 1 pair of sex chromosomes: determine gender

4. More Terminology • Homologous chromosomes • One member of each pair is inherited from each parent • Look alike (size, shape, banding pattern) • Not identical: may have different alleles of particular genes http://cv-mrsdabbs.wikispaces.com/Homologous+Chromosomes+and+Different+Versions+of+Genes

5. More Terminology • Alleles: alternative forms of a gene • New Alleles arise from mutation • Homozygous: two identical alleles at a particular locus • Example: AA or aa • Heterozygous: two different alleles at a particular locus • Example: Aa, Bb

6. Pair of autosomes. Each automsome carries the same genes at the locus Gene locus (plural loci). The location of a specific pair of genes A pair of genes. Normally both genes have the same structure and function Alleles. Alternative versions of the same gene pair Figure 19.1

7. Genotype is the Genetic Basis of Phenotype • Genotype: an individual’s complete set of alleles • Phenotype: observable physical and functional traits • Examples • Hair color, eye color, skin color, blood type, disease susceptibility • Phenotype is determined by inherited alleles and environmental factors

8. Dominant Alleles and Recessive Alleles • Dominant allele • Masks or suppresses the expression of its complementary allele • Always expressed, even if heterozygous • Recessive allele • Will not be expressed if paired with a dominant allele (heterozygous) • Will only be expressed if individual is homozygous for the recessive allele • Dominant alleles are not always more common than recessive; sometimes they may be rare in a population

9. Dominant Recessive http://www.scienceteacherprogram.org/biology/McNeil08.html

10. Recessive Dominant http://genetics.thetech.org/ask/ask148

11. Recessive Dominant http://www.reachoutmichigan.org/funexperiments/agesubject/lessons/handouts/genetics.html

12. Dominant Recessive Recessive Dominant http://www.reachoutmichigan.org/funexperiments/agesubject/lessons/handouts/genetics.html http://mcmedgroup.com/eng/2010/08/29/lasers-for-freckle-mole-liver-spot/

13. Gregor Mendel: Basic Rules of Inheritance Pea plants in the 1850s in Austria Did multiple genetic experiments to develop basic rules of inheritance Law of segregation Gametes carry only one allele of each gene Law of independent assortment Genes are distributed to egg and sperm cells independently of each other during meiosis. Applies in most cases

14. Patterns of Genetic Inheritance Punnett square analysis Predicts patterns of inheritance Y b b Yb bb bb b Yb Y= yellow dominant b = black recessive http://fineartamerica.com/featured/young-black-labrador-lucy-swinburne.html http://www.thelabradorsite.com/?attachment_id=2943 dogs.oodle.com

15. Punnett Square • Shows the four possible combinations of alleles that could occur when gametes combine • Steps: • 1) Determine Parental Genotypes • 2) Set up Punnett Square • 3) Fill in the square • 4) Write out genotype ration • 5) Use genotypes to determine phenotypes

16. Female (diploid) Haploid sperm Haploid eggs Male (diploid) a) In a Punnett square, the possible combinations of male and female gametes are placed on two axes, and then the possible combinations of the offspring are plotted in the enclosed squares. This square shows that in a cross between two hetero- zygotes only half the offspring will be heterozygotes. Figure 19.2a

17. b) A cross between two homozygotes produces offspring that are all the same genotype as each other, but not necessarily the same genotype as their parents. Figure 19.2b

18. Y = yellow peas y = green peas Key: Yellow pea Green pea a) Mendel’s first cross between homozygous yellow-pea plants (YY) and homozygous green- pea plants (yy) yielded all yellow-pea plants. Figure 19.3a

19. Y = yellow peas y = green peas Key: b) Mendel’s second cross between two of the offspring of his first cross yielded 75% yellow-pea and 25% green- pea plants. Figure 19.3b

20. Female Key: Widow’s peak W = widow’s peak w = straight hairline Male Straight hairline Figure 19.4

21. Monohybrid Problem #1 • Two plants heterozygous for pod color (G) are crossed. What proportion of the offspring will also be heterozygous for pod color?

22. ½ of the offspring will be heterozygous

23. Monhybrid Problem #2 • In pea plants the allele for round pea shape (R) is dominant to the allele for oval pea shape (r). If a plant heterozygous for pea shape is crossed with a plant the is homozygous recessive for the trait, what percentage of the offspring will have round peas?

24. 50% of the offspring will have round peas

25. Monohybrid Problem #3 • In humans, brown eyes (B) are dominant over blue (b). A brown-eyed man marries a blue-eyed woman and they have three children, two of whom are brown-eyed and one of whom is blue-eyed. What is the man’s genotype? What are the genotypes of the children? • PS: Eye-color is not a mendilian trait in humans-This is just an example

26. Dihybrid Cross Steps • 1) Identify parental genotypes • 2) Determine possible Gametes • 3) Set up Punnett Squares using the Gametes • 4) Determine genotype ratio • 5) Use genotype ration to determine phenotype ration

27. Key: E = free earlobes e = attached earlobes W = widow’s peak w = straight hairline Female Male b) A mating between two heterozygous people with widow’s peaks and free earlobes (EeWw). Because the alleles for the two traits assort independently, some of the offspring show one dominant and one recessive trait. Figure 19.7b

28. Dihybrid Cross Problem • A female guinea pig is heterozygous for both fur color and coat texture is crossed with a male that has light fur color and is heterozygous for coat texture. • What are the possible phenotypes of the offspring can they produce? • Dark fur color is dominant (D) and light fur (d) is recessive. Rough coat texture (R) is dominant, while smooth coat (r) is recessive.

29. Step 1: Identify Genotypes • Female (heterozygous): DdRr • Male (light fur, heterozygous texture): ddRr

30. Step 2: Determine GametesHint: Think about FOIL from Math Female Gametes (DdRr) Male Gametes (ddRr) dR dr dR dr • DR • Dr • dR • dr

31. Step 3: Set Up Large Punnett Square Using Gametes dRdr dR dr DR Dr dR dr

32. Step 4: Determine Genotype Ratio dRdr dR dr DR DdRR DdRr DdRR DdRr Dr DdRr Ddrr DdRr Ddrr dR ddRR ddRr ddRR ddRr dr ddrr ddRr ddrr ddRr

33. Step 5: Use Genotypes to Figure Out Phenotypes Genotypes Pheonotypes Dark fur, Rough Coat Dark fur, Rough Coat Dark fur, Smooth coat Light fur, Rough coat Light fur, Rough coat Light fur, Smooth Coat Phenotype Ratio: 3:1:3:1 • DdRR (2) • DdRr (4) • Ddrr (2) • ddRR (2) • ddRr (4) • Ddrr (2)

34. Incomplete Dominance • NEITHER allele is dominant • Expression of BOTH alleles occurs • Result= Intermediate Phenotype • Examples • Hair • Straight hair: HH • Wavy hair: Hh • Curly hair: hh

35. hh curly hair HH straight hair Hh wavy hair Figure 19.9

36. Codominance • Codominance: products of both alleles are expressed • Example • Genes for ABO blood types • “A” gene and “B” gene are codominant • An individual heterozygous for the “A” and “B” genes will be blood type AB, expressing both “A” and “B” antigens on red blood cells

37. Type AB Type O Type A Type B Antigen A Neither A nor B antigens Antigen B Antigens A and B Red blood cells AA AO BB BO Possible genotypes AB OO Figure 19.10

38. Blood Type Problem • In a paternity suit, a women with type A blood claims a man with Type AB blood fathered her son, who has Type O blood. • Could the man be the baby’s father?

39. Codominance • Example • Sickle-cell gene • Two different alleles of hemoglobin gene • HbA: encodes normal hemoglobin • HbS encodes sickle cell hemoglobin • Sickle-cell anemia: HbSHbS(homozygous) • Sickle-cell trait: HbAHbS(heterozygous) • Affected individual makes both types of hemoglobin • BOTH alleles are EXPRESSED

40. Female Key: HbA = normal hemoglobin HbS = sickle-cell allele Sickle-cell trait Normal Male Sickle-cell anemia a) A Punnett square showing a mating between two individuals with sickle- cell trait. Figure 19.11a

41. Polygenic Inheritance • Inheritance of phenotypic traits that depend on many genes • Examples • Eye color, skin color • Height, body size and shape • Polygenic traits are usually distributed within a population as a continuous range of values

42. Parents (medium height) AaBbCc + AaBbCc AABBCC aabbcc AaBbcc AaBbCc AABbCc Median Percent of population Bell-shaped curve Taller Shorter Height Figure 19.13

43. Genotype and Environment Affect Phenotype These two mice are genetically identical and exactly the same age. Each mouse’s mother received a different, specialized diet, which switched on or off chemical clusters called methyl groups that reside near genes. Flipping these genetic switches created differences in size, fur color and health in the otherwise identical offspring. Credit: Randy Jirtle/Duke University • Phenotype isn’t determined by genotype alone • Environmental factors can profoundly influence phenotype • Example • Nutrition affects height, body size

44. Linked Alleles • Linked alleles: physically located on the same chromosome • May be inherited together • May be “shuffled” during crossing over during meiosis

45. Figure 9.19A Section of chromosome carrying linked genes g c l 17% 9% 9.5% Recombinationfrequencies

46. Sex-Linked Inheritance: X and Y Chromosomes Sex chromosomes 23rd pair of chromosomes Not homologous X and Y chromosomes carry different genes Males: have one X and one Y chromosome Females: have two X chromosomes Male 50% X-carrying gametes, 50% Y-carrying gametes Male parent determines the gender of offspring

47. Figure 19.14

48. Figure 19.15

49. Sex-Linked Inheritance Sex-linked genes are located on sex chromosomes Sex-linked or X-linked inheritance Characteristics More males than females express the disease Passed to sons by mother Father cannot pass the gene to sons Examples Red-green color blindness Hemophilia

50. http://intro.bio.umb.edu/111F98Lect/colorblind/