Independent Assortment Mendel wanted to know: – Does the segregation of one pair of alleles affect that of another? For example: Does the allele for seed color effect the shape of the seed? 1. To find this Mendel created a two factor cross and followed two different genes as they passed from one generation to the next.
The Two Factor Cross: F1 Crossed true breeding plants for round (RR) yellow (YY)peas – 2. Genotype (RRYY) With true breeding plants for wrinkled (rr) green (yy) peas – 2. Genotype (rryy) And proceeded to observe the offspring
The Two Factor Cross: F1 ryryryryryryryry RYRYRrYy RYRY RYRY RYRY
The F1 Results: 3. This shows that the dominant alleles are present: – Phenotype: Heterozygous Round Yellow Seeds – Genotype: RrYy 4. Does this result show if genes segregate independently? – Nope
The Two Factor Cross: F2 5. Mendel took the F1 generation (heterozygous) and crossed them. He wanted to see if the two traits would separate independently of one another or if dominant would stick with dominant and recessive stay with recessive. Was very curious of the possible outcomes.
10. The Two Factor Cross: F2 RYRyrYry RY Ry rY ry
The F2 Results: 6. & 8. There was a total of 556 seeds produced: – Round Yellow: 315 – Round Green: 105 – Wrinkled Yellow: 104 – Wrinkled Green: 32 – 7. There were seeds that displayed combinations not found in the parents (RRYY and rryy) Did Independent assortment occur? – YES!
Let’s Look at the Numbers Again: 9. Count up the Phenotypes, what is the ratio? – 9:3:3:1 Round Yellow: 9 – RRYY, RrYy Round Green: 3 – RRyy, Rryy Wrinkled Yellow: 3 – rrYY, rrYy Wrinkled Green: 1 – rryy
11. Independent Assortment The alleles for a given trait segregate independently of one another and do not influence each other’s inheritance.
12. A Summary of Mendel’s Principles The inheritance of biological characteristics is determined by genes that are passed down from parents to their offspring 13. Two or more forms of a trait may exist (ex: Dominant and Recessive) The copies of genes are segregated from each other when gametes are formed The alleles for different genes usually segregate independently from one another
Beyond Dominant and Recessive 14. There are some alleles that are neither dominant or recessive, and many traits: Genetics tends to be a bit more complicated than that: – The majority of genes have more than two alleles, and important traits are controlled by many different genes.
15. Incomplete Dominance Cases in which one allele is not dominant over the other – The heterozygous phenotype is somewhere between the two homozygous phenotypes – Ex: Strawberry Blonde 4 ‘o Clock Plants
15. Codominance Both alleles contribute to the phenotype – Both alleles will be shown in the offspring Ex: – Erminette Animals Black feathers is codominant with white Offspring show both colors – Humans Proteins synthesis
15. Multipe Alleles Genes that have more than two possible alleles This does not mean that an individual can have more than two alleles for a gene – It means that there could be more than two possibilities in a population – Ex: Rabbit fur color Blood Types in humans
15. Polygenic Traits Traits that are controlled by two or more genes – Many traits are produced by the interaction of several genes – Ex: Human Skin Color 4 genes control skin color Human Eye Color
Applying Mendel’s Principles Thomas Morgan- Geneticist that worked with Fruit Flies to test Mendel’s Principles of Segregation – 16. Chose Fruit Flies because: Small in size Easy to take care of in a lab setting Capable of producing large numbers of offspring very quickly 17. The conclusion: – Mendel’s Principles apply to not just pea plants, but other organisms as well
Genetics and the Environment 18. Genes are not the only factor for determining characteristics of an organism The Environment plays a role as well – Ex: Sunflower Height is determined by the genes, but this will change depending on factors such as climate, water availability, and soil composition
Exit Slip X BbccbbCc Katy Perry Wolverine Hair Color: -B: Black -b: Blue Claws: -C: No Claws -c: Claws