P 1

2. P1 • Why are all first generation flowers gray? • Gray is the dominant color. • Gray is the recessive color. • Gray is the darker color. • d. It is just a coincidence. F1 F2

3. P1 • What ratio explains the gray flowers and white flower in the second generation? • 1 to 1 • 2 to 1 • 3 to 1 • d. 4 to 1 F1 F2

5. Review… • Recall that most organisms have two sets of chromosomes (each chromosome has a matching pair. Humans have 23 pairs of chromosomes, so 46 chromosomes total.) • Pairs of chromosomes have matching genes, therefore, genes also come in pairs, (2). • Not all genes in a pair are identical! • Ex.) There is one gene pair that controls flower color in pea plants, yet there are two forms of that gene- purple or white.

6. Allele One of two or more forms of a gene. One allele may be dominant over the other recessive allele. Ex.) alleles for eye color include brown and blue. Same gene, different form.

9. Phenotype • physical appearance • what the trait will look like • Determined by genotype Genotype • type(s) of genes making up a trait (alleles) • usually written as 2 letters representing a gene pair • dominant trait is capitalized • recessive trait is lower-case • example: Ee or BB

11. Heterozygous Homozygous • the alleles in a genotype are different (one is dominant and the other is recessive) • “hybrid” Ex.) Pp = Purple flowers • both alleles in a gene pair are the same (both dominant or both recessive) • “true-breeding or purebred” Ex.) PP = Purple flowers pp = white flowers

12. Why can’t heterozygous pea plants ever be white??