Ch.11-1 Mendel genetics

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

POINT > Define heredity and genetics Heredity is the transfer of characteristics from parent to offspring Genetics is the study of heredity

POINT > Define heredity and genetics Thinking into the 1800’s: Traits BLENDED between parents

Gregor Mendel (1822 – 1884) POINT > Introduce Mendel Austrian Monk High school teacher Responsible for the monastery garden Used pea plants to study heredity

POINT > Describe Mendel’s approach to his experiments Why were pea plants so useful in these expriments? 1. Easy to grow and grow quickly (reproduction ~ 90 days) 2. Lots of offspring (good for statistical analysis) 3. Easy to control plant mating (self-pollinating) 4. 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?

POINT > Describe Mendel’s approach to his experiments Pollen located in the anthers of the stamen Peas have both male (pollen) & female (ovule/egg) reproductive parts Peas often self-pollinate, which results in purebred offspring: Genetically identical to parents Ovule located in the ovary of the pistil

POINT > Describe Mendel’s approach to his experiments Mendel removed the stamen before self-pollination This allowed Mendel to control which plants crossed with each other (no self-pollination)

POINT > Describe Mendel’s approach to his experiments Mendel manually pollinated each plant So any variations were due to his experiments

POINT > Describe Mendel’s approach to his experiments Seed Shape Flower Color A trait is a specific characteristic of an individual Mendel studied seven observable traits in peas Seed Color Pod Color Plant Height

POINT > Describe Mendel’s approach to his experiments Mendel first crossed purebreds that had trait differences Green Seed Yellow Seed P (Parental) ? F1 (First Generation)

POINT > Describe Mendel’s approach to his experiments Hybrids are offspring that result from crosses between parents with different traits

POINT > Describe Mendel’s approach to his experiments Mendel first crossed purebreds that had trait differences P (Parental) All offspring were yellow F1 (First Generation) This happened with all of the traits he tested

POINT > Describe Mendel’s approach to his experiments Mendel then allowed F1 plants to self-pollinate F1 (First Generation) ? F2 (Second Generation)

POINT > Describe Mendel’s approach to his experiments Mendel then allowed F1 plants to self-pollinate F1 (First Generation) F2 (Second Generation)

POINT > Describe Mendel’s approach to his experiments Mendel then allowed F1 plants to self-pollinate 75% Yellow, 25% Green All the traits he tested had a 3:1 ratio in the F2 F2 (Second Generation)

WB CHECK: When Mendel crossed purebred plants in the P generation, what percentage of the F1 offspring had green seeds? When Mendel crossed F1 plants, what percentage of the F2 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 F1 generation self-pollinate (F1 x F1) Remember, all these plants had purple flowers

POINT > Describe Mendel’s experiments 25% of the F2 generation were white! The same was true of the other traits 75% -25%

POINT > Relate Mendel’s experiments to current knowledge Genes are factors passed from one generation to the next that determine an individual’s characteristics ex. pea color, plant height, etc

POINT > Relate Mendel’s experiments to current knowledge Alleles are different 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)

POINT > Relate Mendel’s experiments to current knowledge A dominant allele is always expressed if it is present ex. Both alleles are dominant ex. Alleles are different

POINT > Relate Mendel’s experiments to current knowledge A recessive allele is only expressed when the dominant allele is not present (ex. green seed allele)

POINT > Relate Mendel’s experiments to current knowledge Segregation is the separation of alleles during gamete formation Meiosis!! When homologous chromosomes separate, the two sets of alleles are segregated

POINT > Relate Mendel’s experiments to current knowledge 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

Next: We will apply Mendel’s principles… Read 11. 1 S. A Next: We will apply Mendel’s principles… Read 11.1 S.A. #1-2 page 312 Exam Prep