Chapter 9 - Introduction to Genetics

1. Chapter 9 - Introduction to Genetics Genetics – the branch of Biology that studies heredity – how traits are passed on.

3. Chromosomes • Humans have 46 chromosomes arranged in 23 pairs (44 autosomes and 2 sex chromosomes) • Chromosomes are made up of DNA and Proteins • Chromosomes and therefore the DNA can be divided into genes • Genes are short segments of DNA

4. Chromosome with genes

7. Allele – alternate form of a gene • Example: Brown/blue, tall/short • can be represented by a letter Example: Brown – B Blue - b

8. Homologous Chromosomes Determines eye color Genes Determines hair color

9. Brown Allele Blue Alleles Blue Allele b b b B One pair of your chromosomes for eye color One pair of your chromosomes for eye color

10. Brown Allele Blue alleles Blue Allele b b b B Homozygous – alleles are the same Heterozygous – alleles are different

11. Homozygous (pure) • The two alleles are the same • The two letters are the same • BB or bb • Homozygous Dominant – BB • Homozygous Recessive - bb

12. Heterozygous (hybrid) • The two alleles are different • The two letters are different • Bb

13. Dominant Gene • A gene that will be expressed if it is present • Examples – brown, tall, green, purple • Written as a capital letter

14. Recessive Gene • A gene that will only be expressed if there are two alleles present • Recessive genes are not expressed if there is a dominant gene present • Short, blue, yellow, white • Written as a lower case letter

15. Genotype • The two alleles an organism has • What the genes “say” • Ex. BB, Bb, bb

16. Phenotype • Physical appearance of an organism • The result of the expression of the genes • Example: tall, short, brown, blue

17. The Goal • The goal of genetics is to determine the possible offspring that can be produced from two parents • The likelihood of an outcome is determined through the laws of probability

18. Probability • The likelihood that a specific event will occur • Can be expressed as a decimal, percent or a fraction

19. Equation for Probability Number of times an event is expected to happen Probability = The number of opportunities for an event to happen

20. Probability Example • You flip a coin once • The probability of getting tails is ½ • You flip a coin twice • The probability of getting tails twice is 1/4 1 1 1 = X 4 2 2

21. T H or First Flip Second Flip If I got Tails on the first flip I can either get heads or tails On the second flip H T

22. Second Probability of getting: First H 1/4 H T 1/4 H 1/4 T T 1/4

23. Gametes • Egg or sperm • Haploid • Contains half the number of chromosomes • One gene from each homologous pair

25. Early Ideas on Heredity • Until the 19th century it was thought that the reason people look like their parents is because they were a blend of both parents. • The work of Gregor Mendel changed the views of how characteristics are passed on from 1 generation to the next.

26. Gregor Mendel • Born in 1822 in Austria • Studied at the University of Vienna • Became a priest and lived in a monastery • He was in charge of the garden and he studied pea plants

27. Gregor Mendel • Pea flowers have both male and female parts • They normally produce seeds through self-pollination • The pollen from the male flower part fertilizes the egg from the female flower part of the same flower • These seeds would inherit all their characteristics from the single plant that bore them

28. Gregor Mendel • Mendel figured out that self-pollination could be prevented • He cut the male parts off of 1 plant and the female parts off another plant • Then he pollinated the 2 plants by dusting the pollen from one onto the flower of the other • This is known as cross-pollination • Produces seeds with the characteristics of both plants

29. Gregor Mendel • Mendel had a stock of peas that were purebred • They would only produce offspring that were identical to them • He decided to cross plants with different characteristics to produce hybrids • He studied a few isolated characteristics to simplify his experiments

30. Gregor Mendel • Pea Traits Studied

31. Genetic Crosses • When doing genetic crosses it is important to keep tract of the generations • P1 – parents • F1 – children of the parents (P1) • F2 – Children of the F1’s

32. GG gg Gg gg GG Gg

33. A Genetic Cross Punnett Square – used to predict the possible outcomes of a cross

34. AA aa aa Male produces one type of sperm with the gene A Female produces one type of egg with the gene a

35. The Baby Elephants will be.. Aa Aa Aa Aa

36. Monohybrid Cross a a A A

37. How to fill in the Punnett Square

38. Monohybrid Cross • Cross where one trait is looked at • Dark elephant vs. light elephant

39. Aa Aa Male produces two types of sperm with the gene A or a Female produces two type of eggs with the gene A or a

40. The Baby Elephants will be.. Aa AA aa Aa

42. Genotypic Ratio • Ratio of the offspring's genotypes Genotypic Ratio: 1:2:1 EE – 1 Ee – 2 ee – 1

43. Phenotypic Ratio • Ratio of the offspring's phenotypes Phenotypic ratio: 3:1 3 – smooth 1- wrinkled

44. Phenotypes? GenotypicRatio? Genotypes? Phenotypic Ratio?

45. Law of Segregation • A pair of genes is segregated or separated during the formation of gametes

46. Law of Independent Assortment • Genes for different characteristics are not connected • They are inherited independently

47. Dihybrid Cross • A cross between individuals that involves two pairs of contrasting traits • Look at hair color and eye color at the same time • Look at height and color at the same time

48. Dihybrid Cross Punnett Square

49. AABB aabb AB ab ab AB AB AB ab ab

50. Sperm Egg AB ab Fertilization AB ab AaBb Genes in the fertilized egg