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Genetics Unit: Punnett Squares

Genetics Unit: Punnett Squares. Genetics = the field of biology devoted to understanding how characteristics are transmitted from parents to offspring Heredity = the transmission of characteristics from parents to offspring. Mendel. “father” of modern genetics = laid the groundwork

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Genetics Unit: Punnett Squares

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  1. Genetics Unit: Punnett Squares

  2. Genetics = the field of biology devoted to understanding how characteristics are transmitted from parents to offspring Heredity = the transmission of characteristics from parents to offspring

  3. Mendel • “father” of modern genetics = laid the groundwork • experimented with garden peas - looked for traits = specific characteristics

  4. Mendel (cont) - P1 generation = parental generation - F1 generation = offspring of the parental generation - F2 generation = offspring of the F1 generation

  5. Mendel (cont) Mendel’s 1st Law = Law of Segregation • Organisms inherit two copies of each gene, one from each parent 2) Organisms donate one copy of each gene in their gametes.

  6. Mendel (cont) Mendel’s 2nd Law = Law of Independent Assortment 1) The presence of one trait does not affect the appearance of another trait

  7. Basics of Genetics - Gene = a segment of DNA on a chromosome that controls a specific trait - because chromosomes come in pairs, genes come in pairs

  8. Basics of Genetics (cont) - Allele = each of several forms of a gene - aka: letters - each allele has a specific location on a chromosome (= locus) - capital letters = dominant alleles - lowercase letters = recessive alleles

  9. Basics of Genetics (cont) - homozygous = both alleles are alike • homozygous dominant = both capital letters = BB - homozygous recessive = both lowercase letters = bb heterozygous = alleles are different = Bb

  10. Polydactyly Polydactyly is the condition of having more than the typical number of fingers or toes. The allele for polydactyly is dominant.

  11. Basics of Genetics (cont) - Genotype = genetic makeup of an organism - consists of alleles (letters) - Phenotype = the appearance of an organism as a result of its genotype - aka: what does it look like - human phenotype can be altered by behavior BB Green Eyes

  12. Monohybrid Crosses = a cross between individuals that involves one pair of traits - Example: Black hair (B) in guinea pigs is dominant to brown hair (b)

  13. Example 1:Homozygous Dominant X Homozygous Dominant B B Genotypic Ratio Phenotypic Ratio 4 BB : 0 Bb : 0 bb BB B BB BB BB B 4 Black : 0 Brown

  14. Example 2:Homozygous Recessive X Homozygous Recessive b b Genotypic Ratio Phenotypic Ratio 0 BB : 0 Bb : 4 bb bb b bb bb bb b 0 Black : 4 Brown

  15. Example 3:Homozygous Dominant X Heterozygous B B Genotypic Ratio Phenotypic Ratio 2 BB : 2 Bb : 0 bb BB B BB Bb Bb b 4 Black : 0 Brown

  16. Example 4:Homozygous Recessive X Heterozygous b b Genotypic Ratio Phenotypic Ratio 0 BB : 2 Bb : 2 bb Bb B Bb bb bb b 2 Black : 2 Brown

  17. Example 5:Heterozygous X Heterozygous B b Genotypic Ratio Phenotypic Ratio 1 BB : 2 Bb : 1 bb BB B Bb Bb bb b 3 Black : 1 Brown

  18. Testcross = an individual of unknown genotype is crossed with a homozygous recessive individual - can be used to determine the genotype of any phenotype that is dominant

  19. Example 6: Testcross b b Genotypic Ratio Phenotypic Ratio 0 BB : 2 Bb : 2 bb Bb B Bb bb bb b 2 Black : 2 Brown

  20. Example 6: Testcross b b Genotypic Ratio Phenotypic Ratio 0 BB : 4 Bb : 0 bb Bb B Bb Bb Bb B 4 Black : 0 Brown

  21. Example 6: Testcross b b Genotypic Ratio Phenotypic Ratio 0 BB : 0 Bb : 4 bb b bb bb bb bb b 0 Black : 4 Brown

  22. Dihybrid Cross = a cross between individuals that involves two pairs of traits - Example: Black hair (B) in guinea pigs is dominant to brown hair (b) and rough coat (R) is dominant to smooth coat (r)

  23. Example 1: Homozygous Dominant X Homozygous Recessive BBRR bbrr

  24. Example 1: Homozygous Dominant X Homozygous Recessive BR BR BR BR BbRr BbRr BbRr BbRr br br BbRr BbRr BbRr BbRr br BbRr BbRr BbRr BbRr BbRr BbRr BbRr BbRr br

  25. Example 2: Heterozygous X Heterozygous BbRr BbRr

  26. Example 2: Heterozygous X Heterozygous BR Br bR br BBRR BBRr BbRR BbRr BR Br BBRr BBrr BbRr Bbrr bR BbRR BbRr bbRR bbRr Bbrr bbRr bbrr BbRr br

  27. Incomplete Dominance = the F1 Generation will have a phenotype in between that of the parents - Example: Red flowers (R) and White flowers (r) can make Pink flowers (Rr)

  28. Example 7: Incomplete Dominance Pink Flower X Pink Flower R Genotypic Ratio Phenotypic Ratio r 1 RR : 2 Rr : 1 rr RR R Rr Rr rr 1 Red: 2 Pink : 1 White r

  29. Example 7: Incomplete Dominance Pink Flower X Red Flower R r Genotypic Ratio Phenotypic Ratio 2 RR : 2 Rr : 0 rr RR R Rr RR Rr R 2 Red: 2 Pink : 0 White

  30. Example 7: Incomplete Dominance White Flower X Red Flower Genotypic Ratio Phenotypic Ratio r r 0 RR : 4 Rr : 0 rr Rr R Rr Rr Rr R 0 Red: 4 Pink : 0 White

  31. Example 7: Incomplete Dominance Pink Flower X White Flower R r Genotypic Ratio Phenotypic Ratio 0 RR : 2 Rr : 2 rr Rr r rr Rr rr 0 Red: 2 Pink : 2 White r

  32. Codominance = when both alleles for a gene are expressed in a heterozygous offspring - Example: Red coat color (R) in horses is codominant with white coat color (R’) to make a horse with a mix of red and white coat color (RR’)

  33. Example 8: Codominance Red Coat X White Coat R R Genotypic Ratio Phenotypic Ratio 0 RR : 0 R'R' : 4 RR' RR' RR' R' RR' RR' R' 0 Red Coat : 0 White Coat : 4 Red/White Coat

  34. Example 8: Codominance Red/White Coat X White Coat R R' Genotypic Ratio Phenotypic Ratio 0 RR : 2 R'R' : 2 RR' RR' R'R' R' RR' R'R' R' 0 Red Coat : 2 White Coat : 2 Red/White Coat

  35. Example 8: Codominance Red/White Coat X Red Coat R R' Genotypic Ratio Phenotypic Ratio 2 RR : 0 R'R' : 2 RR' RR RR' R RR RR' R 2 Red Coat : 0 White Coat : 2 Red/White Coat

  36. 25 min. Review: https://www.khanacademy.org/science/biology/heredity-and-genetics/v/punnett-square-fun

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