Mendelian (“Simple”) GeneticsChapter 11

Objectives:7.0 Apply Mendel's law to determine phenotypic

and genotypic probabilities of offspring.7.1 Defining important genetic terms, including dihybrid cross, monohybrid cross, phenotype,

genotype, homozygous, heterozygous, dominant trait, recessive trait, incomplete dominance,

codominance, and allele 7.2 Interpreting inheritance patterns shown in

graphs and charts 7.3 Calculating genotypic and phenotypic

percentages and ratios using a Punnett square

Important Terms• Define and explain relationships

between terms:1. Genetics 10. Incomplete dominance 2. Trait 11. Codominance3. Allele 12. Monohybrid cross4. Dominant trait 13. Dihybrid cross5. Recessive trait6. Genotype7. Phenotype8. Heterozygous9. Homozygous

Bozeman Biology on Mendelian Genetics

• http://www.youtube.com/watch?feature=player_detailpage&v=NWqgZUnJdAY

• Video quiz

Video Quiz1. What organism did Mendel

study?2. How many different traits of the

pea plant did Mendel study?3. What is the first cross of a

genetic cross called?4. What do we call a cross of the

offspring?

5. What do we now call what Mendel called a “trait”?

6. What is shown across the top and down the side of a Punnett square?

7. What is shown in the boxes of a Punnett square?

8. What does Mendel’s law of segregation say?

9. Law of independent assortment?

Genetics:

• The study of heredity (how traits, or specific characteristics, are passed from one generation to another)

Gregor Mendel• Mendel (1822-1884) was an

Austrian monk trained in science and mathematics at the University of Vienna.

• He was a teacher, and was in charge of the monastery’s gardens.

Mendel’s Peas• He used true-breeding plants --

plants that had been allowed to self-fertilize for generations, producing offspring identical to themselves.

• The plants had the following traits with differences: height, pea (seed) color, pea shape, seed coat color, pod color, pod shape, and flower position.

• By using purebred plants, Mendel could cross-pollinate purposely and purposefully to see what would happen.

• Mendel used a paint brush to transfer pollen from one type of pea plant to another.

• Parent plants are called the P generation.

• Offspring are called the filial, or F1, generation.

• These offspring plants would be hybrids (vs. purebreds).

• What would the offspring of a cross between two F1 plants be called?

Results of Mendel’s F1 Cross-Pollinating

Experiments• Rather than the plants showing blended characteristics of the parents, the F1 plants showed characteristics of only one parent.Source:

http://scientopia.org/blogs/guestblog/2012/08/03/mud-sticks-especially-if-you-are-gregor-mendel/

• What Mendel called characteristics, or traits, scientists now call genes.

• The different forms of these traits (i.e., green peas vs. yellow peas) are called alleles.

• If an allele is dominant, an organism with that allele will always exhibit that form of the trait.

• Recessive alleles are only exhibited when dominant alleles are absent.

Results of Mendel’s F1 Crosses

• Mendel took F1 plants and allowed them to self-pollinate.

• What would you naturally expect the offspring of a self-pollinated plant to look like?

• Actual results: Traits controlled by recessive alleles reappeared in some of the F2 offspring.

Explanation of Results• Law of Segregation:

– Mendel assumed the recessive allele was masked by the dominant allele in the F1 offspring.

– At some point, the two alleles were separated. (At what point was this????)

– How would the traits exhibited by the recessive alleles show back up?