Genetics

1. Genetics

2. A. Heredity is the passing on of characteristics from parents to offspring. *Genetics- science of heredity I. Introduction to Genetics

3. B. Gregor Mendel- father of genetics 1. Studied pea plants Why? Grow easily, produce large #s of offspring, pollen can be transferred to different plants.

4. 2. Predicted how traits are transferred from one generation to the next.

5. 3. Concluded that each organism inherits a gene for a particular trait from each parent. Genes have different forms called alleles. Ex. Height is the gene. The alleles are tall and short.

6. C. Mendel’s Laws or Findings Law of Unit Factors- an organism inherits 2 alleles for each trait.

7. 2. Law of Dominance- one allele may mask or cover the other. Ex. The tall allele is dominant over the short.

8. 3. Law of Segregation- During meiosis, homologous chromosomes separate from each other and an offspring inherits one allele for a trait from each parent.

9. 4. Law of Independent Assortment- genes for different traits are inherited independently from each other. Ex. Round yellow seeds, green wrinkled seeds, wrinkled yellow seeds, round green seeds. -colors & texture come from different alleles

10. II. Punnett Square A. Dominant alleles are represented by a capital letter. (Tall allele= T) Recessive alleles by a lowercase letter (short= t)

11. B. An organism is homozygous for a trait if its two alleles for a trait are the same. • TT is homozygous dominant (tall) • tt is homozygous recessive (short)

12. C. An organism is heterozygous for a trait if its 2 alleles for a trait are different. Ex. Tt

13. D. Two organisms can look alike but have different gene combinations. TT vs. Tt The way an organism looks is called its phenotype. The gene combination an organism contains is called its genotype.

14. Phenotype & Genotype Example- Eye color: • brown eyes are dominant to other colors so… Phenotype: brown Genotype: BB or Bb

15. E. A Punnett Square is a way of finding the possible genotypes in the offspring of a cross.

16. 1. The basic p-square looks like a window pane. 2. Review- In a type of bird a red throat is the dominant trait and white throat is recessive.

18. 3. Basic steps to a making a Punnett square. a. Determine the genotypes of the parents. b. Write down the cross. (genotype) c. Draw a p-square.

19. d. Split the letters of the genotype for each parent and put them outside the square. e. Determine the possible genotypes of the offspring by filling in the p-square. f. Summarize results (phenotypes and genotypes of the offspring)

20. F. Examples of monohybrid crosses (when only 1 trait is studied) 1. Example: You cross a white-throated bird with a homozygous (hom) dominant red-throated bird. What are the possible offspring?

21. a. White is rr and hom dominant is RR. b. rr x RR c. r r R R

22. d. The offspring will all be red-throated and heterozygous. -100% red-throated; 100% Rr

23. 2. Example: In pea plants, the allele for tallness is represented by the letter T. The allele for shortness is t. A short plant is crossed with a heterozygous (het) Tall plant. What are the offspring produced?

24. a. short plant: tt; het plant Tt b. tt x Tt • t t T t

25. d. Phenotype: ½ plants tall, ½ plants short OR 1 tall: 1 short - Genotype: ½ plants Tt and ½ plants tt OR 1 Tt: 1 tt

26. 3. Example: In guinea pigs, black hair color is dominant and brown is recessive. Cross a brown individual with a hom dominant individual.

27. III. Complex Patterns of Inheritance A. Incomplete dominance- neither allele is dominant and an intermediate trait is formed.

28. Ex. Hom. Red Snapdragon x Hom. White Snapdragon= Heterozygous Pink Snapdragon

29. B. Codominance- when 1 allele is not dominant over another and both are expressed equally Ex. Black Feathered Chicken x White Chicken = Black and White Chicken

30. +

31. C. Multiple Alleles- when more than 2 alleles control a trait. Ex. Human blood types

32. 1. There are three different alleles for human blood type:

33. 2. However, combinations of these alleles will give someone their blood type.

34. D. Sex- linked Inheritance • 1. Traits that are controlled by genes located on sex chromosomes are known as sex-linked traits. X or Y

35. 2. In humans, the diploid # is 46 (23 pairs) • a. 22 pairs of chromosomes are known as autosomes

36. b. 1 pair is known a sex chromosomes- these determine sex XX XY

37. 3. Males have a greater chance of inheriting a sex-linked trait.

38. 4. Ex. Red-green colorblindness, Hemophilia

44. E. Polygenic Inheritance- continuous range of phenotypes controlled by 2 or more genes. Ex. Skin color, Eye color, Height

45. IV. TESTCROSSES & PEDIGREES • Testcrosses 1.Cross of individual of unknown genotype with an individual of known genotype in order to determine the unknown genotype

46. 2. Usually the known test organism is homozygous recessive for the trait 3. Example a. In guinea pigs, black coat color is dominant (B) and a brown coat is recessive (b).

47. What are the possible genotypes of a black guinea pig? • b. What is the genotype of the brown guinea pig? • c. If a black guinea pig is mated with a brown guinea pig and all the offspring are black, what is the genotype of the black guinea pig parent? Show a punnett to proveyour answer. • d. What must be the genotype of an unknown guinea pig if offspring of that pig and a brown pig are all brown?

48. B. Pedigrees 1. Graphic representation of an individual’s family tree

49. 2. Uses a. Predict the chances of offspring receiving a trait b. Determine the inheritance pattern of a particular trait

50. c. Know if an individual possesses a given allele C. Pedigree Chart: shows relationships within a family & if individual has gene Key: male female carrier affected Male Female