Ch.11-1 Mendel

POINT > Define heredity and genetics POINT > Introduce Mendel POINT > Describe Mendel’s approach to his experiments POINT > Relate Mendel’s experiments to current knowledge

Heredity is the transfer of characteristics from parent to offspring Genetics is the study of heredity

Thinking into the 1800’s: Traits BLENDED between parents

Austrian Monk High School Teacher Responsible for the monastery garden Used pea plants to study heredity POINT > Introduce Mendel

Why were pea plants so useful in these expriments? Easy to grow and grow quickly (reproduction ~ 90 days) Lots of offspring Easy to control plant mating (self-pollinating) Easily viewed, dichotomous traits!

WB CHECK: Which is not a reason pea plants were useful to Mendel? a) grow quickly b) self pollinate c) require very little water d) have traits that are easy to see e) easy to control mating Where did Mendel do his experiments?

Peas have both male (pollen) & female (ovule/egg) reproductive parts Often self-pollinate, which results in purebred offspring: Genetically identical to parents Pollen located in the anthers of the stamen Ovule located in the ovary of the pistil

Mendel removed the stamen before self- pollination This allowed Mendel to control which plants crossed with each other (no self-pollination)

Mendel m anually pollinated each plant So any variations were due to his experiments

A trait is a specific characteristic of an individual Mendel used SEVEN observable traits in peas Flower Color Seed Color Seed Shape Pod Color Plant Height

Mendel first crossed purebreds that had trait differences ? P (Parental) F 1 (First Generation) Green Seed Yellow Seed

Hybrids are offspring that result from crosses between parents with different traits

Mendel first crossed purebreds that had trait differences All offspring were yellow P (Parental) F 1 (First Generation) This happened with all of the traits he tested

Mendel then allowed F 1 plants to self-pollinate F 1 (First Generation) F 2 (Second Generation) ?

Mendel then allowed F 1 plants to self-pollinate F 1 (First Generation ) F 2 (Second Generation)

Mendel then allowed F 1 plants to self-pollinate F 2 (Second Generation) 75% Yellow, 25% Green All the traits he tested had a 3:1 ratio in the F 2

WB CHECK: When Mendel crossed purebred plants in the P generation, what percentage of the F 1 offspring had green seeds? When Mendel crossed F 1 plants, what percentage of the F 2 offspring had green seeds?

POINT > Describe Mendel’s experiments Another example: cross a purebred purple flower plant with a purebred white flower plant

POINT > Describe Mendel’s experiments When Mendel did this cross, purple x white, all of the offspring had purple flowers.

POINT > Describe Mendel’s experiments Mendel then let the F 1 generation self-pollinate (F 1 x F 1 ) Remember all these plants had purple flowers

POINT > Describe Mendel’s experiments 25% of the F 2 generation were white! The same was true of the other traits 75% -25%

Genes are f actors passed from one generation to the next that determine an individual’s characteristics ex. pea color, plant height, etc

Alleles are d ifferent forms of a gene that occur at the same location on a chromosome One allele is inherited from each parent (two total) Often, only one allele can be expressed (Principle of Dominance)

A dominant allele is always expressed if it is present ex. Both alleles are dominant ex. Alleles are different

A recessive allele is only expressed when the dominant allele is not present (ex. green seed allele)

Segregation is the separation of alleles during gamete formation Meiosis!! When homologous chromosomes separate, the two sets of alleles are segregated Evidenced by the reappearance of recessive alleles in the F 2 generation

Mendel deduced that factors (genes) came in pairs, which were segregated during reproduction Mendel’s work was published in 1866, but went unnoticed until many years after his death The discovery of his work led to the basic principles of genetics

We will apply Mendel’s principles… Read 11.1 S.A. #1-2 page 312