heredity and mendel n.
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Heredity and Mendel

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  1. Heredity and Mendel

  2. Heredity • The passing of parents characteristics onto the offspring • Genetics is the branch of biology that studies heredity

  3. Gregor Mendel • Considered the father of genetics • Was an Austrian monk that used pea plants to study heredity • Pea plants self pollinate usually self pollinate so their genetic information can be controlled • By carefully recording his data he made some great findings

  4. Mendel Crossed Plants with different variations • Mendel crossed a tall pea plant with a short pea plant to see what would happen • x • The result was that the offspring (first generation) were all tall • However when crossed the second generation, ¼ were short

  5. Mendel repeated these crosses for all the different variations • He discovered that in the 2nd generation (F2)that the trait that had disappeared in the first generation (F1) reappeared again, always. • Genetic generation abbreviations • P1= parent generation • F1= first generation • F2=second generation

  6. Mendel's findings • 1. Mendel concluded that each organism has 2 factors called genes that control each trait • Alleles are different gene forms that determine the different form of the trait • For example the gene for height has an allele for tall and another for small • Typically we use upper and lower case letters to identify these T=tall allele and t=short allele • Genes can either be homozygous or heterozygous • Homozygous has the same 2 alleles ie TT or tt • Heterozygous has different alleles ieTt

  7. Mendel'sfindings • 2. Principle of Dominance = some alleles are dominant and will mask a recessive allele • So TT or Tt will both be tall, whereas tt will be short • Dominant genes are represented by upper case letters and recessive (non-dominant) by lower case • TT= Tt= tt=

  8. Mendel's findings • Noticed that alleles segregate when forming gametes • Also noticed alleles segregate independently of each other – called Independent Assortment

  9. Monohybrid crosses illustrate Mendel's findings • A monohybrid cross is one that looks at only one specific trait and how it segregates • Easy to do this using the punnett square method

  10. Determining Genotype and Phenotype • Genotype refers to the allele makeup of a gene • For example the genotype of the punnett square is ¼ TT, ½ Tt, and ¼ tt • This gives a genotypic ratio of 1:2:1 • Phenotype refers to the trait the is expressed by the organism or what it looks like • Since both TT and Tt are tall, the phenotype of the punnett square is ¾ tall and ¼ short • The phenotypic ratio is 3:1

  11. Dihybrid crosses • Dihybrid crosses look at 2 different traits passed on from parents • Ex: In peas, seed shape & seed color • R = roundY = yellow • r = wrinkledy = green

  12. Dihybrid Crosses • One Parent is RRYY (homozygous dominant) • The other is rryy (homozygous recessive) • So RRYY X rryy • Step 1: find all possible gamete combinations by using FOIL (First Outer Inner Last) • There will always be 4 different combinations in dihybrid Crosses • Possible gametes: RY RYRYRY x ryryry

  13. Dihybrid crosses • Step 2: Set up 4x4 punnett square and put possible gametes from parents on top and side, then fill in squares for possible offspring • All offspring are heterozygous for both seed shape and seed color - RrYy, what is their phenotype and genotype?

  14. Dihybrid crosses • Now cross two F1 plants. • RrYy x RrYy • Possible gametes: RY RyrYry x RY RyrYry

  15. Phenotypic Ratio for a Dihybrid Cross: • For this cross, find the number of each - round yellow : round green : wrinkled yellow : wrinkled green • 9/16 round yellow (R_Y_) • 3/16 round green (R_yy) • 3/16 wrinkled yellow (rrY_) • 1/16 wrinkled green (rryy) • Phenotypic Ratio = 9 : 3 : 3 : 1