________________ the physical expression of a trait (tall, short) ________________ The phenotype is determined by the combination of alleles found in the genotype (TT, Tt, tt) Key Terms

________________ The dominant trait will be expressed when the dominant allele is paired with the recessive allele in a hybrid. A Tt plant will have a phenotype of tall. Capital letters represent the dominant allele. _________________ The recessive trait is the one that is not expressed when the dominant allele is present in the genotype. Lower case letters represent the recessive allele

_________________ Refers to a genotype in which the alleles are different (Tt) _________________ Describes a genotype where the alleles are the same (TT, tt) Tt x TtTt TTTTt t tt Tt x TtTt TTTTt t tt

____________________ Members of a pair of alleles for a given trait are segregated (separated) when gametes are formed. If a parent plant has the genotype Tt, then it will produce two types of gametes, T and t. Each gamete contains only one of the alleles for plant height. Tt t T Parent Gamete

___________________________________ When two or more pairs of characteristics are considered at one time, each pair shows dominance and segregation independently of the other. If a parent plant has the genotype TtRr, then it will produce four different types of gamte combinations in equal numbers, ¼ TR, ¼ Tr, ¼ tR, ¼ tr TtRr Parent TR Tr tR tr

________________________: Tt x Tt 3:1 Phenotype ratio: 3 Tall, 1 Short 1:2:1 genotype ratio: TT, Tt, Tt, tt Tt x TtTt TTTTt t tt When two heterozygous F 1 plants are crossed.

1. What are purebred pea plants? 2. How did Mendel ensure that he had a purebred pea plant? PRACTICE QUESTIONS!

3. What is a monohybrid cross? 4. What phenotypic and genotypic ratios result from such a cross? PRACTICE QUESTIONS!

5. In humans, the ability to taste phenylthiocarbamide (PTC), T, is dominant to non-tasting, t. Determine the expected genotypic and phenotypic ratios resulting from a cross between a heterozygous taster and a non-taster. PRACTICE QUESTIONS!