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Genetics 11.1 & 11.2

Genetics 11.1 & 11.2. The scientific study of heredity. What is Heredity ?. The passing of traits from parents to their offspring. 1860s: Gregor Mendel. “Father of Genetics” @Mendel figured out how traits are passed on@ before we knew about DNA, or chromosomes or meiosis.

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Genetics 11.1 & 11.2

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  1. Genetics11.1 & 11.2 The scientific study of heredity.

  2. What is Heredity ? • The passing of traits from parents to their offspring

  3. 1860s: Gregor Mendel • “Father of Genetics” • @Mendel figured out how traits are passed on@ • before we knew about DNA, or chromosomes or meiosis

  4. Mendelstudied heredity with pea plants • Why pea plants? (was it luck?) • 1. Small • 2. Easy to grow • 3. Produces large numbers of offspring • 4. Matures quickly • 5. Plants can self or cross fertilize • 6. Many varieties • 7. Each trait has two forms • Tall/short purple/white flowers • green/yellow seeds colored/white seed coat • green/yellow seed pods inflated/narrowed seed pod • wrinkled/smooth seed

  5. The Role of Fertilization Mendel knew that the male part of each flower makes pollen, which contains sperm—the plant’s male reproductive cells. Similarly, Mendel knew that the female portion of each flower produces reproductive cells called eggs.

  6. To begin, Mendel self fertilized to create pure breeding plants all pure purple • Purple white all pure white

  7. First Cross: pure purple with pure white • Cross fertilized P (Parental) generation • Pure purple with pure white • P Generation F1 Generation purple white X All purple

  8. Second Cross:Cross 2 F1 plants • Cross fertilized two of the offspring of the F1 generation purple purple purple purple X purple white These were the F2 This was always 3:1 ratio or out of 929, 705 : 224

  9. Genes and Alleles For each trait studied in Mendel’s experiments, all the offspring had the characteristics of only one of their parents, as shown in the table. @An individual’s characteristics are determined by factors (genes) that are passed from parent to offspring@

  10. Mendel’s Experiments led him to 3 Laws of Inheritance • The Law of Dominance • The Law of Segregation • The Law of Independent Assortment

  11. The Law of Dominance: • Each individual has TWO factors for each trait known as alleles • @Some alleles dominate over others – the dominant allele is expressed in the offspring@ • Homologous chromosomes-same traits -different forms These are alleles Freckles No Freckles Dimples No dimples Tongue roller Non-roller From Dad From Mom

  12. Alleles are: • Represented by a letter of the alphabet Capital = dominant allele A lowercase = recessive allele a • Each allele corresponds to a gene on a chromosome - the alleles represent different forms of the gene

  13. Law of Segregation • The two alleles for each trait separate and move into different gametes – meiosis • Since only one egg or one sperm will contribute to the new offspring, only one allele for a trait is passed on • @The chance that any allele will be passed on is 50%@

  14. Law of Independent Assortment • the inheritance of alleles for one trait doesn’t affect the inheritance of alleles for another trait - occurs in meiosis during metaphase 1

  15. Genotype: • Genotype is the combination of alleles for a particular expressed with letters • Homozygous dominant: • TT - two capital letters • Heterozygous • Tt - one of each letter (big and small) • Homozygous recessive • tt - two lower case letters

  16. Phenotype: • Phenotype is physical expression of the genotype Genotype Phenotype TT tall plant Tt tall plant (dominant allele always is expressed over the recessive allele) tt short plant (recessive trait is expressed only if there is no dominant gene)

  17. If R = red, and r = white • What is the genotype of homozygous dominant? • RR • What is the heterozygous genotype? • Rr • What is the homozygous recessive genotype? • rr

  18. If R=red and r =white • What is the phenotype of of RR? • Red • What is the phenotype of Rr? • Red • What is the phenotype of rr? • White

  19. If two parents are crossed (TT X tt), what are the resulting offspring? You can determine phenotypes using a Punnet square. T T parent Tt Tt t Genotypes: 4 Tt Tt Tt Phenotypes: 4 Tall t This is the first or parent generation parent

  20. Now try on your paper a cross of two of the offspring from the parent generation. This is called the first generation or the F1. T t T Tt TT Tt tt t Genotypes: 1TT: 2Tt : 1tt Phenotypes: 3 Tall: 1 Short.

  21. The Two-Factor Cross: F2 @Mendel’s experimental results were very close to the 9:3:3:1 ratio@ Mendel had discovered the principle of independent assortment. The principle of independent assortment states that genes for different traits can segregate independently during gamete formation.

  22. http://www.youtube.com/watch?v=CBezq1fFUEA

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