Inherited Traits

1. Inherited Traits The Law of Dominance

2. Questions to Ponder… • Why do some people look like their parents or grandparents? • How is it possible for a blond-haired child to have two brown-haired parents? • Why do brothers in one family resemble each other and in one family have no resemblance?

3. Gregor Mendel –1860s • Grew up on a farm in Austria and became a monk • Observed pea plants and wondered why generations passed on traits he observed • Experimented with pea plants and learned many things related to heredity • Father of Modern Genetics

4. Dominant and Recessive Traits Handout

5. Dominant & Recessive Traits • Dominant traits are “stronger” and more likely to be visible • Recessive traits are “weaker” and less likely to be visible • Law of Dominance: dominant traits “trump” recessive traits

6. Dominant & Recessive Traits • Genes occur in pairs (alleles) • The combination of gene pairs determines the offspring’s phenotype (physical trait) • One gene comes from the mother and the other comes from the father

7. Dominant & Recessive Traits • Offspring receives… • dominant trait from mother • dominant trait from father • Offspring phenotype is… • dominant trait • Curly hair is dominant & straight hair is recessive • A boy inherits the gene for curly hair from both his mother and father, and he has curly hair

8. Dominant & Recessive Traits • Offspring receives… • dominant trait from mother • recessivetrait from father • Offspring phenotype is… • dominant trait • Curly hair is dominant & straight hair is recessive • A girl inherits curly hair from her mother but straight hair from her father, and she has curly hair

9. Dominant & Recessive Traits • Offspring receives… • recessivetrait from mother • recessivetrait from father • Offspring phenotype is… • recessive trait • Curly hair is dominant & straight hair is recessive • A boy inherits straight hair from both his mother and father, and he has straight hair

10. Dominant & Recessive Traits • dominant + dominant = dominant • homozygous: gene pairs (alleles) are the same • dominant + recessive = dominant • heterozygous: gene pairs (alleles) are different • recessive + recessive = recessive • homozygous

11. Dominant & Recessive Traits • Genes occur in pairs, alleles • The combination of gene pairs (genotype) determines the offspring’s phenotype • One gene comes from the mother and the other comes from the father

12. Dominant & Recessive Traits • dominant + dominant = dominant • homozygous: gene pairs (alleles) are the same • Height in Pea Plants: TT genotype • dominant + recessive = dominant • heterozygous: gene pairs (alleles) are different • Height in Pea Plants: Tt genotype • recessive + recessive = recessive • homozygous • Height in Pea Plants: tt genotype

13. Application • Charlie cannot roll his tongue. His mother cannot roll her tongue. • Can you determine his father’s phenotype? • Can you determine any of their genotypes?

14. Application • Maria has unattached ear lobes. Her father has attached ear lobes. • Can you determine any of their phenotypes? • Can you determine any of their genotypes? • Can you determine if Maria could have a child with attached ear lobes?

15. Application • Mr. Henderson has a bent little finger, and so does his wife, Mrs. Henderson. • Can you determine any of their phenotypes? • Is it possible for their son and daughter to have different phenotypes? • Can you determine any of their genotypes?