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Heredity and Genetics

Heredity and Genetics. PRINCIPLES OF GENETICS. OVERVIEW “ Like produces like, but not *exactly* like ”. REVIEW: Sexual reproduction → variation due to chromosomes. *HEREDITY: transmission of traits from parents to offspring *GENETICS: science of heredity. A History Lesson.

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Heredity and Genetics

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  1. Heredity and Genetics

  2. PRINCIPLES OF GENETICS • OVERVIEW • “Like produces like, but not *exactly* like” REVIEW: Sexual reproduction → variation due to chromosomes *HEREDITY: transmission of traits from parents to offspring *GENETICS: science of heredity

  3. A History Lesson *Gregor Mendel: 1822-1884 *monk in monastery @ Czechoslovakia *Vienna- studied science and math- became a teacher *2 yrs later- returned to monastery; plant experiments *1866- published data from 8 years of experiments *1900- finally genetics recognized as major development *Mendel’s Experiments: *Studied pea plants (b/c clearly express traits like flower color, seed shape, seed color, and plant height) *large sample sizes- help ensure actual ratios present in population

  4. *crossed “different” plants → ex. Purple flowers x white flowers *offspring of parental cross = first filial generation (F1) *offspring of 2nd cross = 2nd filial generation (F2) *Mendel produced 929 offspring– 705 were purple (3:1 ratio) *DOMINANT TRAIT: form of a trait that dominates another trait; (prevents expression of another trait) (ex. Purple flowers) *appears in F1 generation *RECESSIVE TRAIT: hidden in F1 generation

  5. *MENDEL’S HYPOTHESIS: *Mendel’s experiments saw recessive trait disappear in F1 generation but reappear in F2 generation *ASSUMPTION: for each trait, there must be a pair of factors- 1 comes from egg; 1 from sperm * “Factors” = GENES: contain information for every trait *Represented by symbols or letters *Capitals = dominant *lowercase = recessive EX. W= purple, w= white

  6. *ASSUMPTION: 2 genes segregate during gamete formation *offspring = ratio depending on genes present EX. WW x ww parents Ww Ww Ww Ww F1 Ww x Ww WW Ww Ww ww F2 RESULTS: 1WW : 2Ww: 1ww 3 purple: 1 white (similar to 705: 929)

  7. *EASIER TO SEE WITH PUNNETT SQUARES: *Chart used to determine possible combinations of genes among offspring Gametes of 1 parent Gametes of 1 parent W w EX: Ww x Ww W w

  8. *TEST OF SEGREGATION: 3:1 ratio 1st time but what if Ww x ww??? MAKE YOUR PUNNETT SQUARE: W w w Ww ww *****50% white: 50% purple!!! w Ww ww

  9. GENETICS TERMINOLOGY *ALLELE: either of 2 alternative forms of gene for particular trait ex. W or w *GENOTYPE: combo. of alleles for certain trait ex. WW, Ww, or ww *PHENOTYPE: appearance of trait ex. “purple” or “white” *HOMOZYGOUS: 2 of same alleles for given trait ex. RR, rr (deals w/ seed shape) or WW or ww *HOMOZYGOUS DOMINANT: 2 dominant alleles (WW) *HOMOZYGOUS RECESSIVE: 2 recessive alleles (ww) *HETEROZYGOUS: 2 different alleles for a trait ex. Rr or Ww

  10. Pedigree charts *are used to help determine the possible genotypes of parents and offspring

  11. karyotypes *are used to analyze the chromosomes present in a person

  12. TIME TO PRACTICE PUNNETT SQUARES!!

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