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Introduction to Genetics

Introduction to Genetics. Chapter 9. Heredity. Transmission of characteristics from parents to offspring. Gregor Mendel. Austrian Monk Studied heredity in pea plants Studied 7 characteristics of peas. Traits. characteristic occur in two forms. 7 Characteristics of Pea Plants.

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Introduction to Genetics

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  1. Introduction to Genetics Chapter 9

  2. Heredity • Transmission of characteristics from parents to offspring

  3. Gregor Mendel • Austrian Monk • Studied heredity in pea plants • Studied 7 characteristics of peas

  4. Traits • characteristic • occur in two forms

  5. 7 Characteristics of Pea Plants • Plant height (long or short) • Flower Position along the stem (axial or terminal) • Pod Color (green or yellow) • Pod appearance (inflated or constricted)

  6. Seed texture (smooth or wrinkled) • Seed color (yellow or green) • Flower color (purple or white)

  7. 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

  8. Chromosome with genes

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

  10. Homologous Chromosomes Determines eye color Genes Determines hair color

  11. 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

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

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

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

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

  16. 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

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

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

  19. 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

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

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

  22. 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

  23. 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

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

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

  26. 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

  27. GG gg Gg gg GG Gg

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

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

  30. The Baby Elephants will be.. Aa Aa Aa Aa

  31. Monohybrid Cross a a A A

  32. How to fill in the Punnett Square

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

  34. 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

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

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

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

  38. Phenotypes? GenotypicRatio? Genotypes? Phenotypic Ratio?

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

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

  41. 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

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