________________ • 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 Tt T t

T TT Tt

t Tt tt

Tt x Tt T t

T TT Tt

t Tt 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

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 Tt T t

T TT Tt

t Tt tt

When two heterozygous F1 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!