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Understanding Genetics: Heredity & Genetic Crosses

Explore the transmission of traits from parents to offspring through genetics. Dive into Gregor Mendel's study on pea plants to understand alleles, chromosomes, genotypes, phenotypes, and genetic crosses. Learn how genes determine physical characteristics and discover the laws of probability in genetics. From monohybrid crosses to dihybrid crosses, unravel the complexities of inheritance and genetic diversity.

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Understanding Genetics: Heredity & Genetic Crosses

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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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