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Fundamentals of Genetics Chapter 9

Fundamentals of Genetics Chapter 9. What makes you who you are, your genes or your environment????? BOTH!!!. Thalidomide (1957-1961)  -causes phocomelia (flipperlike arms/legs) Can you think of other examples?. Environmental Influences. Mendel.

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Fundamentals of Genetics Chapter 9

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  1. Fundamentals of GeneticsChapter 9 • What makes you who you are, your genes or your environment????? • BOTH!!! .

  2. Thalidomide (1957-1961)  -causes phocomelia (flipperlike arms/legs) Can you think of other examples? Environmental Influences

  3. Mendel • Gregor Mendel (Born 1822) Monk worked with pea plants

  4. Stamens:  actually anthers on the end of the stamen produces pollen which contains sperm cells inside (male structure) Stigmas:  actually ovary in pistil produces egg cells (female structure)

  5. What Mendel did with Pea Plants • Removed stamens from flowers so self-pollination could not occur. • Worked with only one visible trait at a time. • Kept detailed record of crosses and results.

  6. Terminology for Results • Parent generation P1 •  Offspring of parent generation =F1 (first filial generation) •  Offspring of offspring=F2 (second filial generation)

  7. Page 176 in book What do you notice about the observed ratio?

  8. Mendel's Experiment - P1=tall x short - F1=all tall - F2= 3/4 tall and 1/4 short -Mendel studied many different traits Mendel’s Results

  9. This led Mendel to these conclusions: • Mendel's first hypothesis:  inherited characteristics are controlled by factors (genes) which occur in pairs. ex. Tt or TT or tt

  10. 2. Mendel's second hypothesis (Principle of dominance and recessiveness):  one gene of a pair may mask (hide) the other, or prevent it from having an effect.    • Ex. Tt= TALL  

  11. Mendel's third hypothesis:  (Law of Segregation):  a pair of genes are separated during the formation of the gametes (sperm and egg). 

  12. Law of Independent Assortment:  the separation of gene pairs occurs entirely independent of the separation of all other gene pairs in an organism.

  13. Molecular Genetics Supports Mendel • Gene- segments of DNA on a chromosome *genes occur in pairs • Genes have different forms called alleles *we use letters to represent alleles ex. T or t

  14. 5 Steps to a Punnett Square

  15. Genetic Problem • In eyecolor, BROWN is dominant to blue. Pres. George Bush is heterozygous for BROWN eyes. Laura Bush has blue eyes. Complete a Punnett square showing the possible eyecolors of their twin daughters.

  16. STEP #1 Write Genotypes of Parents • Males 1st, female 2nd • If Dominant use all Capital Letters • If Recessive use lower Case 1. GT: Bb x bb

  17. STEP #2- Write Phenotypes of Parents • Write Male 1st, female second • 1.GT: Bb x bb • 2. PT: BROWN x blue

  18. STEP #3 - Punnett Square • Draw Tic Tac Toe Board • Males on vertical side • Females on horizontal • Complete Punnett Square 1. GT: Bb x bb • PT: BROWN x blue 3.

  19. Step #4- Write Genotypic Ratio or Genotypic Fraction • Compares the chances of getting different genotypes in the offspring. 1. GT: Bb x bb • PT: BROWN x blue 4. GF: 2/4 Bb, 2/4 bb

  20. STEP #5- Write Phenotypic ratio or Phenotypic Fraction • Compare the chances of different phenotypes in the offspring. • 1. GT: Bb x bb • 2. PT: BROWN x blue 3. • 4. GF: 2/4 Bb, 2/4 bb • 5. PF: 2/4 BROWN, 2/4 blue

  21. In eyecolor BROWN eyes are dominant to blue eyes. Chuck is homozygous for BROWN, his wife Lyn has blue eyes. What color eyes can their kids have? • 1. BB x bb • 2. BROWN x blue • 3. • 4. GF: 4/4 Bb • 5. PF: 4/4 BROWN

  22. Special Punnett Squares 1. Test Cross • A punnet sq. done to determine if parent is homo or heterozygous. • Involves crossing the unknown parent genotype with a homozygous recessive genotype • BB or Bb x bb • If all offspring are dominant then parent was homozygous; if some offspring are recessive then parent was heterozygous.

  23. Test Cross Question • A purple flowered pea plant is crossed with a white flowered pea plant. 5 of the 6 pea plants resulting from the cross are purple but one is white. • What is the genotype of the purple pea plant?

  24. Occurs when the heterozygous is an intermediate between the homozygous dominant and recessive. Incomplete Dominance

  25. 2. Codominance • Occurs when both alleles are fully expressed in the offspring. • Neither allele is dominant, and no blending occurs.

  26. Blood Type • Ex of codominance • Blood types M, N, MN are determined by 2 alleles LM, LN

  27. Polygenic Traits • Most human characteristics are polygenic • Polygenic traits are controlled by several genes • Ex skin color, height, hair color • AABBCCDD- dark skin • AABBccdd or AaBbCcDd or…-med skin • Aabbccdd –fair skin

  28. Dihybrid Cross

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