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Probability and Genetics Pages 118-123

Probability and Genetics Pages 118-123. What are the chances?. Probability is the likelihood that a particular event will occur. Roll a Die. Flip A Coin!. How many sides are on a die? What is the chance that when you roll the die it will land on 4? On 2?.

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Probability and Genetics Pages 118-123

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  1. Probability and Genetics Pages 118-123

  2. What are the chances? • Probability is the likelihood that a particular event will occur.

  3. Roll a Die Flip A Coin! • How many sides are on a die? • What is the chance that when you roll the die it will land on 4? On 2? • When you flip a coin there are only two possible outcomes that could occur. • Heads • Tails Each side has an equal chance of showing up every time you flip the coin.

  4. Mendel and Probability • Mendel carefully counted the offspring of his pea plants and the traits they showed. • ¾ dominant trait • ¼ recessive trait • Mendel was the first scientist to recognize that probability can be used to predict the results of genetic crosses.

  5. Punnett Squares • A Punnett square is a chart that shows all the possible combinations of alleles that can result from a genetic cross. • Created by Reginald C. Punnett, a geneticist, who used Mendel’s experiments to show the passing of traits from one generation to the next.

  6. Punnett Squares • Each parent can pass either of their two alleles to their offspring. • The possible alleles are written across the top and left hand side of the box. • Each allele gets its own box.

  7. Punnett Squares t t • To figure out the possible allele combinations of the offspring the traits are followed from the top of the box and the side of the box. T t In a hybrid the Dominant trait goes first.

  8. What are the chances? • The allele that will be passed from parent to offspring is based on chance. Just like the flip of a coin. • There are four possible allele combinations. t t Purebred Tall - TT Hybrid Tall – Tt/tT Purebred Short - tt Tt Tt tt tt

  9. What is the probability? 2 out of 4 – tt 2 out of 4 – Tt t t Tt Tt What is the percentage that each allele combination will occur? tt tt

  10. What is the Probability? • What is the chance (in percent) of getting: • A hybrid black guinea pig? • A purebred black guinea pig? • A purebred white guinea pig? BB bb

  11. Phenotypes and Genotypes • Phenotype: an organisms’ physical appearance, or its visible traits. • Example: tall/short, purple/white, yellow/green • Genotype: an organisms’ genetic makeup, or allele combinations • Example: TT, tt, Tt

  12. Homozygous and Heterozygous • Homozygous: When an organism has two identical alleles for a trait. • Example: Purebred – TT or tt • Heterozygous: An organism that has two different alleles for a trait. • Example: Hybrid – Tt, Rr, Ll, Bb

  13. Co-dominance • In pea plants there were only two possible alleles. • Ex. Green OR Yellow • Ex. Smooth OR Pinched • Sometimes, genes have alleles that are NEITHER dominant nor recessive. • This is a co-dominant trait. In co-dominance, neither trait is masked which means that both traits are equally as dominant and the hybrid will show both. • Ex. Feather color in chickens

  14. Co-dominance • When crossing co-dominant traits we use superscripts to tell us the different allele for the trait. • Example: Feather color • purebred black = FBFB • purebred white = FWFW • mixed = FBFW • Example: Flower color • purple = CPCP • white = CWCW • striped = CPCW

  15. Example #1 • Cross a purebred black rooster with a purebred white hen. • FBFB X FWFW • Report all genotypes and phenotypes

  16. Example #2 • In petunias, petal color is a co-dominant trait. Flowers that are heterozygous and have BOTH alleles (one for purple and one for white) will phenotypically look striped. • Cross a purple petunia with a striped petunia. • Report all genotypes and phenotypes. • Is it probable to grow any white petunias from this cross?

  17. Incomplete dominance • There are times when traits show a BLEND of both the dominant and the recessive form. This is called INCOMPLETE DOMINANCE. • An organism that is a hybrid will show a phenotype that is in the “middle” of the dominant or the recessive form. • Ex. Hair texture in humans: • HH = curly, hh = straight, Hh = wavy

  18. Example #1 • In humans, lip size shows incomplete dominance. There are large lips, small lips, and hybrids, will have medium-sized lips. Cross two parents; one with small lips and one with medium-sized lips. Use the letter “L” for all alleles. Report all genotypes and phenotypes. ll X Ll

  19. Example #2 • In humans, lip size shows incomplete dominance. There are large lips, small lips, and hybrids, will have medium-sized lips. Cross two parents; one with large lips and one with medium-sized lips. Use the letter “L” for all alleles. Report all genotypes and phenotypes.

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