Chapter 3, section 1

1. Chapter 3, section 1 Mendel’s Work

2. The Basics • The passing of physical characteristics from parents to offspring is called heredity. • These characteristics are called traits. • The study of heredity is called genetics.

3. Gregor Mendel • Studied how traits were passed from parent to offspring in pea plants • He discovered that sometimes traits can seem to disappear in offspring and reappear in later generations • We now know this is due to some traits being dominant or recessive

4. Dominant and Recessive traits • Genes are the factors that control a trait • Example: you have a gene that controls what eye color you have • Genes exist in pairs • Humans have about 20,000 genes, located on DNA, which is organized into 23 pairs of chromosomes !

5. Alleles are the different forms of the gene • Each gene has a pair of alleles • One allele is inherited from the female parent one allele is inherited from the male parent • We represent alleles with letters (AA, Aa, aa)

6. Some alleles are dominant and others are recessive • A dominant allele is one whose trait will ALWAYS show up if the allele is present • If you inherit a dominant allele from either your mom or dad, you will have the dominant trait • We represent a dominant allele with capital letters (A)

7. A recessive allele only shows up if both alleles are recessive • You have to inherit a recessive trait from both mom AND dad to have the recessive trait • We represent recessive alleles with lower case letters (a)

8. Practice • Will these people have the dominant or recessive trait? • Tt • HH • Bb • nn • A frog inherits a dominant allele from its female parent and recessive allele from its male parent. What trait will it have? Write what its alleles would be using the letter F.

9. A purebred gene is one where both alleles are the same (AA or aa) • Also called homozygous • A hybrid gene is one where there is one dominant and one recessive allele (Aa) • Will always show the dominant trait • Also called heterozygous