genetic crosses and probability

1. Genetic Crosses and Probability Chapter 9 Sec. 9.2

3. Genetics Vocabulary continued… Homozygous- when both alleles of a pair are the same for a gene Homozygouse Dominant- PP Homozygous Recessive- pp Heterozygous- when the 2 alleles in the pair are different for a gene Heterozygous for flower color: Pp

4. What is Probability? Probability is the likelihood that a particular event will occur. It does not ALWAYS happen (think Deal or No Deal) Can be written as a decimal, percentage, ratio, or fraction How do we use the principles of probability in our daily lives? Ex. Horse racing NCAA March Madness Superbowl Coin Toss Atlantic City $$$$$

5. Determining probability Number of times the event is expected Number of times it could have happened What is the probability that you picked an odd number when picking from 1-10? There are five odd numbers between 1 and 10. The probability is 5:5. Or you can express it as a fraction: 5/10. Since it's a fraction, why not reduce it? The probability that you will pick an odd number is 1/2. Probability can also be expressed as a percent...1/2=50% Or as a decimal...1/2=50%=.5

6. The Principles of Probability The Principles of probability can be used to predict the outcomes of genetic crosses Alleles segregate by complete randomness Similar to a coin flip!

7. What is a Punnett Square? A punnett square is a diagram showing the gene combinations that might result from a genetic cross The letters in punnett squares represent alleles. A capital letter is used to show the dominant alleles. A lower case letter is used to show the recessive alleles. Monohybrid cross- a cross between individuals that involve one pair of traits

8. How do you fill in a Punnett Square?

9. How do you fill in a Punnett Square?

10. How do you fill in a Punnett Square?

11. How do you fill in a Punnett Square?

12. What do the alleles mean? Homozygous Dominant Homozygous recessive Heterozygous Dominant ? GG ? gg ? Gg

13. To find the ratio of offspring in a punnett square… Count the number of different offspring For a genotypic ratio count the different genotypes For a phenotypic ratio count the different phenotypes

14. Genotypic ratio 1 GG 2 Gg 1 gg So the genotypic ratio is 1:2: 1

15. Phenotypic ratio 3 green plants 1 yellow plant So the ratio is 3:1

16. Ex 1: Homozygous x HomozygousLet’s cross a pure bred purple colored flower and a white flower. Purple is a dominant color and white is a recessive color. Cross: PP x pp P P (purple x white) p p

17. Ex 2: Homozygous x HeterozygousA guinea pig who is homozygous dominant for black fur crosses with a guinea pig who is heterozygous for this trait (black fur) Cross: BB x Bb B B B b

18. Ex 3: Heterozygous x HeterozygousIn rabbits, the allele for black coat color is dominant (B) over the allele for brown coat color (b). Cross 2 rabbits that are heterozygous for coat color B b Cross: Bb x Bb B b

19. Design your own peas….

20. Independent Assortment Does the segregation of one pair of alleles affect the segregation of another pair of alleles? Does the gene that determines round or wrinkled peas have anything to do with pea seed color? NO! Genes for different traits can separate independently during the formation of gametes So one pair of alleles do not influence each other’s inheritance.

21. Complete Dominance In Mendelian traits if you are homozygous dominant OR heterozygous you will show the dominant trait This is called having complete dominance Example, Rolling your tongue: RR and Rr can roll their tongue rr cannot roll their tongue

22. Exceptions to the dominance rules Incomplete dominance Codominance

23. Incomplete Dominance- The phenotypes MIX when the genotype is heterozygous. Two or more alleles contribute to phenotype, resulting in a phenotype in the middle between the dominant and recessive trait. Neither allele is completely dominant over the. Ex. Four o’clock flowers RR=RED (when all red flowers cross?RED) rr= WHITE (when all white flowers cross ?WHITE) or rr Rr= PINK (when a red crosses with a white we get ? PINK) Incomplete dominance is like mixing paint, you get a blend of the 2 colors

25. Codominance- when both phenotypes/alleles for a gene are shown in heterozygous offspring Both alleles of the gene contribute to the phenotype of the organism. Neither allele is dominant or recessive Codominance is like mixing glitter together, you can still see the individual glitter colors Example: Horses The genes for white and red coat color is called ROAN Homozygous Dominant RR=red coat Homozygous Recessive R’R’=white coat Heterozygous RR’= roan (both red and white hairs can be seen)

26. Dihybrid Crosses These are done when we want to determine the inheritance of 2 traits at the same time. For example, pea color and pea texture… If the parents genotypes are heterozygous for both traits… (use Y for color and R for texture) Parents genotype is: YyRr Note: Remember to use 1 letter for EACH trait

27. The heterozygous parents will give off gametes YyRr parents will give off 4 different gametes because of independent assortment and segregation YR Yr yR yr

28. Dihybrid Crosses Cross: RrYy X RrYy Dihybrid Cross – a cross involving 2 different traits Pea Shape: Round (R) Dominant Wrinkled (r) recessive Pea Color: Yellow (Y) Dominant Green (y) Recessive

29. So when we cross 2 heterozygous parents…