Ch 5.2 Mono and Dihybrid Crosses.notebook April 06, 2018

Transcription

1 Name 3 "Big Ideas" from our last notebook lecture: * * * 1

2 What Do You Remember?? 1. Genotype is? Phenotype is? 2. Freckles is dominant to no freckles. Does an individual with the following genotype: Ff have freckles or not? What is their genotype called? (in terms of their alleles) 3. Here is data obtained from a cross between a true breeding tall pea plant and a true breeding short pea plant, in the F 1 Generation: Trait # of Plants Tall Plants 257 Short Plants 0 a) What was the only phenotype observed in the F1 generation? b) What was the genotype of all F1 plants? Why were none of the F1 plants short? 4. The F1 Generation was then made to self fertilize (cross pollinate) and the following results showed up in the F2 Generation: Trait # of Plants Tall Plants 150 Short Plants 50 a) What is the "ratio" of tall to short plants that emerged in the F2 generation? b) This ratio is known as the ratio, after the monk who is called the "Father of Inheritance." 5. Mendel's "Law of Segregation": "Inherited traits are determined by pairs of f, (two alleles of one gene) which s during meiosis so that each of the g will have one of the a." 2

3 Learning Goal Understand and use Punnett Square method to solve basic genetics problems involving both monohybrid and dihybrid crosses 5.2 Studying Genetic Crosses 3

4 Ch 5.2 Mono and Dihybrid Crosses.notebook Think About It... Why do members of a family share similarities in appearance? Why do you inherit some characteristics and not others? 4

5 A) Using Punnett Squares in Monohybrid Crosses British geneticist, Reginald Punnett ( ) devised a visual technique to help analyze the results of crosses He used a grid system which is now called "Punnett squares" He standardized the system by always putting the male parent on the left side of the box and the female parent on top of the box (this rule is not always applied anymore) 5

6 What really happened when Mendel crossed two purebred plants from the P generation? Each parent contributed 1 allele to each offspring, one "Y" from the yellow plant, and one "y" from the green plant. The product of the cross for the F1 generation was all yellow plants with Y and y alleles. 6

7 Mendel's cross using a Punnett square: Let "Y" represent the allele for yellow plant (male parent) Let "y" represent the allele for green plant (female parent) y y Y Y Yy Yy Yy Yy All yellow plants in offspring! 7

8 Let's read together textbook pages

9 Let's try... Practice Problems 1 10 p212 9

10 If monohybrid crosses examine the inheritance of one trait at a time, then what do dihybrid crosses examine?? The inheritance of two traits at a time! :) 10

11 Mendel's Question: Does the inheritance of one trait influence the inheritance of a different trait? 11

12 Mendel tested pea plants that were true bred for two traits and each parent differed in the form of both of the traits For example: he crossed yellow & round with green & wrinkled He called this a dihybrid cross He got the same ratio results 9:3:3:1 that he had with his monohybrid cross which was 3:1 Text p214 9 dominant form of both traits 3 1 dominant and 1 recessive of each trait 3 other dominant and recessive pair of traits 1 both recessive traits 12

13 text p214 13

14 Law of Independent Assortment "During gamete formation, the two alleles for one gene segregate or assort independently of the alleles for other genes." 14

15 This means different pairs of alleles are passed on to the offspring independently of each other, so the inheritance of one trait does not influence the inheritance of another the offspring may have new combinations of alleles that are not present in either parent Example: a pea plant s ability to produce white flowers instead of purple ones does not influence its ability to produce a round pea rather than a wrinkled pea. 15

16 B) Using Punnett Squares in Dihybrid Crosses Let's read together textbook page

17 Let's try... Practice Problems p216 17

18 In 1902, Walter Sutton ( ), a graduate student at Columbia University in NewYork connects behaviour of chromosomes during Meiosis to Mendel's behaviour of factors he realized that the distribution of chromosomes into developing gametes follows the same pattern of Mendel's Law of Segregation for two alleles in a gene His work formed the basis for today's: Chromosome Theory of Inheritance "Genes are located on chromosomes, and chromosomes provide the basis for the segrgation and indpendent assortment of alleles." 18

19 Alleles (or Mendel's factors) and chromosomes both segregate during meiosis the resulting gametes are equally likely to contain each possible combination of alleles. 19

20 Review & Learning Check Read p , , & 217 Answer Q's 1,4,6,7,12 p218 20