1. Chapter 11: Intro to Genetics 11-3 Other Patterns of Inheritance

2. Intro After showing that alleles segregate, Mendel also wondered if they do so independently of each other. Does the segregation of one pair of alleles affect the segregation of another pair of alleles? Ex: Does the gene for seed shape have anything to do with the gene for seed color? Does a round seed always have to be yellow? To answer this question, Mendel performed an exp (2 factor cross) and followed 2 different genes.

3. Independent Assortment What was Mendel’s experiment? The two factor cross. 1 st Mendel crossed true breeding plants that produced only round yellow peas (RRYY) with plants that produced wrinkled green peas (rryy) All offspring=round yellow peas. Yellow round were dominant over wrinkled green. Did not show if genes assort independently. Provides plants needed for next cross.

4. Independent Assortment All plants were heterozygous (RrYy) Mendel wanted to know if the 2 dominant genes would stay together or separate. He crossed RrYy with RrYy. See fig 11-10 pg 271 Results: 556 seeds produced, 315 round yellow, 32 wrinkled green, 209 had combos of phenotypes not found in either parent. This meant the allele for shape segregated independently for color—this was known as. independent assortment.

5. Independent Assortment What is the principle of independent assortment? Genes for different traits can segregate independently during the formation of gametes. Independent assortment helps account for the many genetic variations observed in plants, animals, and other organisms.

6. A Summary of Mendel’s Principles How can Mendel’s principles be summarized? Inheritance of biological characteristics is determined by genes which are passed from parents to offspring. When 2+ forms of gene for single trait exits, some alleles are dominant & some are recessive. Each adult has 2 copies of each gene—one from each parent. These genes are segregated from each other when gametes are formed. Alleles for diff genes segregate independently of each other.

7. Beyond Dominant & Recessive Do all genes show a simple pattern of dominant and recessive? NO! Genetics is more complicated in most organisms because the majority of genes have more than 2 alleles. Many important traits are controlled by more than 1 gene. Some alleles are neither dominant or recessive, and many traits are controlled by multiple genes or multiple alleles.

8. Beyond Dominant & Recessive What are the different patterns of inheritance? Incomplete Dominance Codominance Multiple Alleles Polygenic traits

9. Beyond Dominant & Recessive What is incomplete dominance? One allele is not completely dominant over another. The heterozygous phenotype is somewhere in between the 2 homozygous phenotypes. –A cross between red and white flowered plants produce pink colored flowers.

10. Beyond Dominant & Recessive What is codominance? Both alleles contribute to the phenotype of the organism. Ex: In chickens, the allele for black feathers is codominant with the allele for white feathers. Heterozygous chickens are speckled with black and white feathers.

11. Beyond Dominant & Recessive What are multiple alleles? Genes have more than 2 alleles. Does not mean that the individual has more than 2 alleles. It means that more than 2 possible alleles exist in a population. Ex: Coat color in rabbits. A rabbit’s coat color is determined by a single gene that has four different alleles. Ex: Human genes for blood type, eye color in humans

12. Beyond Dominant & Recessive What are polygenic trait? Two or more genes control a trait. Three genes are involved in making the reddish- brown pigment in the eyes of fruit flies. Polygenic traits show a wide range of phenotypes. Ex: skin color in humans—more than 4 diff genes control this trait.

13. Applying Mendel’s Principles Do Mendel’s principles only apply to plants? No! In the 1900s, Thomas Hunt Morgan, a geneticist, decided to look for a model organism to study genetics. He wanted an animal that was small, easy to keep in a lab, and able to produce large numbers of offspring in a short period of time. He chose the fruit fly (Drosophila melanogaster) Mendel’s principles also apply to humans.

14. Genetics & Environment Are the characteristics of organisms determined solely by genetics? NO! Characteristics are determined by the interaction between genes and the environment. Ex: Genes may affect the height of a plant. These characteristics are also influenced by climate, soil conditions, & availability of water. Genes provide the plan, but how the plan unfolds also depends on environment.