1. Exploring Mendelian Genetics
11-3

2. Independent Assortment
Mendel wondered if the segregation of one pair of alleles affect the segregation of another pair of alleles
To find the answer, Mendel did an experiment to follow two different genes as they passed from one generation to the next

3. Two-Factor Cross
Mendel crossed true-breeding plants that produced only round yellow peas with a plant that produced wrinkled green peas
All of the F1 offspring were round and yellow
Proving round and yellow are dominant

5. To get the F2 generation, Mendel crossed two of the F1 offspring
While the cross didn’t prove if segregation happened, it provided the hybrid plants needed for the F2 generation
To get the F2 generation, Mendel crossed two of the F1 offspring
RrYy x RrYy
556 seeds were produced, with 4 different characteristics

6. 315 seeds were yellow and round 32 were green and wrinkled
Dominant traits
32 were green and wrinkled
Recessive traits
209 had a combination of traits
~1/2 were green and round
Recessive and dominant
~1/2 were yellow and wrinkled
Dominant and recessive
Phenotype ratio 9:3:3:1

8. Mendel discovered the principle of independent assortment
Genes for different traits can segregate independently during the formation of gametes
Accounts for many genetic variations among organisms

9. Summary of Mendel’s Principles
Inheritance of biological characteristics is determined by genes. Genes are passed from parents to their offspring

10. When there are 2 or more alleles, some forms are dominant and others recessive

11. In sexually reproducing organisms, each adult has 2 copies of each gene – genes are segregated when gametes form

12. Alleles for different genes usually segregate independently of one another

13. Beyond Dominant and Recessive Alleles
Despite the importance of Mendel’s work, there are exceptions
Some alleles are neither dominant or recessive
Some traits are controlled by multiple alleles or multiple genes

14. Incomplete Dominance
One allele is not completely dominant over another allele
Heterozygous individual is a blend of the two homozygous phenotypes
Ex: red (RR) x white (WW) = pink (RW)

16. Codominance
In heterozygous individuals, both traits appear at the same time
They are not blended together like in incomplete dominance
Ex: heterozygous chickens that have erminette coloration (black and white feathers)

18. Multiple Alleles
Genes that more than two alleles are said to have multiple alleles
Individuals still only have 2 copies of a gene, but there is variation in the alleles they can inherit
Ex: rabbit fur and blood types

20. Polygenic Traits Traits controlled by two or more genes
Show a wide range of phenotypes
Ex: human skin color and eye color

21. Applying Mendel’s Principles
Thomas Hunt Morgan wanted to test Mendel’s principles on organisms other than plants
He needed an animal that produced large numbers of offspring, in a short amount of time

22. Used Drosophila melanogaster – common fruit fly
Soon, other biologists tested all of Mendel’s principles on a variety of organisms and discovered that the principles applied to them as well

23. Genetics and the Environment
Characteristics of any organism are not based only on the genes they inherit
Also based on the interaction of their genes with the environment
Genes provide a plan for development, but how that plan unfolds also depends on the environment