2. Chapter 20:2 NOTES pages 599-605 Genetics- The Study of Inheritance

3. Heredity b The way traits are passed to you from your parents b Traits are physical characteristics b Eye Color Hair Color b Height Weight b Body Structure b Facial Features b Skin Color

4. Genetics b b Genetics= the study of how traits are passed form parent to offspring b b A GENE is a section on DNA on a chromosome that has the trait information

5. Genes b Humans have thousands of different genes arranged on 23 pairs of chromosomes. Genes control all of the traits of organisms—even traits that can’t be seen, such as the size and shape of your stomach and your blood type.Genes control all of the traits of organisms—even traits that can’t be seen, such as the size and shape of your stomach and your blood type. b Genes provide all of the information needed for growth and life.

6. What determines traits? b b One pair of chromosomes can contain genes that control many different traits. b b Each gene on one chromosome of the pair has a similar gene on the other chromosome of the pair. b b Each gene of a gene pair is called an allele (uh LEEL)

7. b b The genes that make up a gene pair might or might not contain the same information about a trait. b b If a pair of chromosomes contains different alleles for a trait, that trait is called a hybrid. b b When a trait has two identical alleles, it’s called pure.

8. Dominant and Recessive b b Capital letters are called Dominant alleles. b b When these alleles are present, they take over or show. They are the “stronger” alleles b b Lower case letter are recessive alleles and are the “weaker” of the alleles.

10. Dominant Alleles b b Dominance means that one allele covers over or masks another allele of the trait. b b Purple is the dominant flower color in pea plants. b b For instance, if a pea plant has one purple-flower allele and one white-flower allele or two purple-flower alleles, its flowers will be purple. b b The dominant allele (purple) is seen when the trait is hybrid (Dr) or dominant pure (DD)

11. Recessive Alleles Recessive alleles are seen only when a trait is recessive pure (rr)Recessive alleles are seen only when a trait is recessive pure (rr)

12. Passing Traits to Offspring

13. Variation b Variation- different ways a trait appears b Several gene pairs control some traits b EX- height…..it varies in families

14. Mutations b A change in a gene b Can happen because an error during meiosis or mitosis b or because of something in the environment b Whether a mutation is beneficial, harmful, or neutral, all mutations add variation to the genes of a species.

15. Beneficial mutation example: resistance to AIDS or to heart disease Neutral mutation example: 4 leaf clover Harmful mutation example: a deformed foot Beneficial, Neutral, or Harmful

16. Selective Breeding b Sometimes, a mutation produces a different version of a trait that many people find attractive. b To continue this trait, selective breeding is practiced. b Examples: 1. Breeding fast racehorses 2. breeding cattle based on milk production

17. Homework b Page 605