7.2.d Students know plant and animal cells contain many thousands of different genes and typically have two copies of every gene. The two copies (or alleles) of the gene may or may not be identical, and one may be dominant in determining the phenotype while the other is recessive.

Mendel Gregory Mendel was a priest in Europe who did

an experiment with pea plants Heredity- passing of traits from parent to

offspring Trait- form of a characteristic like height or seed

color Genetics- the study of heredity

Mendel’s Experiments Fertilization-

when the male and female sex cells join

Pollination- when pollen reaches the pistil

Purebred- same 2 alleles for a trait

P generation- Parental generation

• Pea plants are self-pollinating

• Self-pollinating- pollen lands on pistil of same flower

Crossing Pea PlantsGregor Mendel crossed pea plants that had

different traits. The illustrations show how he did this.

Mendel crossed 2 plants by taking pollen from one flower and brushing it onto a flower of another plant

F1 generation- Offspring from the P generation

F2 generation- Offspring from the F1 generation

Mendel crossed one short with one tall pea plant

All of F1 were tall and ¾ of the F2 were tall

Mendel’s Experiments

Experiments With Other Traits

Key concept: “In all of Mendel’s crosses, only one form of the trait appeared in the F1 generation. However, in the F2 generation, the “lost” form of the trait always reappeared in about one fourth of the plants.”

Dominant and Recessive AllelesMendel demonstrated that factors

control inheritance of traitsThose factors come in pairs: one

from the female (mom) and one from the male (dad)

Gene- factors that control a traitAlleles- different forms of the

geneKey concept: “An organism’s

traits are determined by the alleles it inherits from its parents. Some alleles are dominant, while other alleles are recessive.”

Dominated allele- trait that always shows up in an organism when it is present (Tt, TT)

Recessive allele- trait that is hidden whenever the dominant allele is there (tt)

Dominant and Recessive Alleles

Hybrid- has 2 different alleles for a traitBefore Mendel people thought that

traits were blended when there were 2 different traits which was incorrect

Traits are determined by individual alleles inherited from each parent

Capital letter represents dominate traitLowercase letter represents recessive

traitBecause of Mendel’s work with genetics

he has been called the Father of Genetics

Dominant and Recessive Alleles

What were the results of Mendel’s experiments, or crosses?

What controls the inheritance of traits in organisms?