Genetics and inheritance
- 2. Genetics • What is genetics? study of inherited traits - “heredity” • What is heredity? passing of traits from parents to offspring (children) • What is a trait? feature an organism can pass on to offspring ex) hair color, eye color, etc
- 3. Early Ideas - Heredity • Originally believed… child’s traits were result of “blending between parent’s traits” • Gregor Mendel decided to test this idea • He knew nothing about DNA
- 4. • Genes! • Genes are… segments DNA on chromosome code for a trait by the production of a protein • There are several genes on each chromosome.
- 6. Mendel’s Pea Plants Why did Mendel use pea plants? 1) Several contrasting traits 2) Understood method reproduction
- 7. Mendel’s Experiments • The 1st thing Mendel did was cross purebred plants… • Purebred- produce young with same trait generation after generation • What will happen if cross plants with different forms of a trait? • Ex) trait – seed shape forms – round or wrinkled seed shape
- 8. Mendel’s Experiments con’t • Parental generation (P) “original group” • First filial generation (F1) offspring of the parental cross • ALL offspring resulted were ROUND
- 9. Mendel’s Conclusion • “NO blending- no ½ round ½ wrinkled seeds”
- 10. We NOW know why… • Many traits have 2 alleles • Allele- 2 contrasting forms of a trait ex) gene on chromosome for trait–seed shape 2 forms - round allele or wrinkled allele • Principle of Dominance- one allele appears and causes contrasting allele NOT to appear • dominant allele - hides the other allele; capital letter • recessive allele- form often NOT expressed,
- 11. Mendel’s 2 Experiment nd • The next question Mendel wanted to answer was: Why didn’t any of the recessive characteristics like (wrinkled) show up in the F1 generation? • To answer this question Mendel extended his experiment and allowed F1 to reproduce…
- 12. Mendel’s Results • Second filial generation (F2)- offspring of F1 • Some offspring showed recessive trait, some the dominant trait 3:1 ratio (round:wrinkled)
- 13. Mendel’s Conclusion • Why did the recessive trait disappear in the F1 and then reappear in some of the F2? • The dominant allele hides the recessive allele in the F1 • Since the recessive allele reappeared in the F2 it must have “separated” from the dominant allele • Law of Segregation- when gametes form alleles for a trait are separated (each parent gives one allele to offspring)
- 14. Mendel’s Results Summarized • Every trait is controlled by at least 2 different factors (1 gene / 2 allele) Use letters to represent contrasting forms (alleles) for a trait Example: Trait: Seed Color (letter Y) Y = yellow (dominant allele) y = green (recessive allele) • Alleles occur in pairs (1 mom/1 dad) • YY homozygous dominant – 2 same letter - capital Yy heterozygous – 2 different letters yy homozygous recessive - 2 same letter - lowercase • Phenotype - outward appearance/physical characteristic • Genotype - genetic makeup “letters”