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Probability and Heredity EQ: How does probability affect the way traits are inherited? Previously, in life science… • You learned that alleles for traits are inherited according to definite patterns. Now, you will discover the mathematical foundation for these patterns. 1. What is Probability? • The likelihood that a particular event will occur. • Coin Toss (20X) H T prediction actual • Probability predicts what is LIKELY TO OCCUR…Not necessarily what will occur • Each event occurs INDEPENDENTLY What is probability? A number that describes how likely it is that a certain event will occur 2. What are Punnett Squares? • Chart used to show possible allele combination What is a Punnett square? A chart that shows all the possible combinations of alleles that can result from a genetic cross. 3. How do you use Punnett squares? Show possible combination 1. Draw a square. Divide it into 4 sections. 2. One parent’s alleles on the top 3. One parent’s alleles on the side 4. Cross alleles (like multiplication!) What is the probability that an offspring will have white fur? 0% ! What is the probability that an offspring will have black fur? 100% ! 4. What is phenotype? • An organism’s appearance, or visible traits. • Example: Purple or white flowers 5. What is genotype? • An organism’s genetic makeup, or allele combinations. • Example: PP or Pp or pp 6. What is homozygous? • having 2 identical alleles example: PP or pp 7. What is heterozygous? • having 2 different alleles example: Pp 8. Make a chart showing the genotypes and phenotypes B = Brown; b = blue genotype phenotype Homozygous or Heterozygous? 8. Make a chart showing the genotypes and phenotypes B = Brown; b = blue genotype BB B___ b ___ phenotype Homozygous or Heterozygous? How many genotypes are there for the smooth-pod phenotype? Two! 9. Cross homozygous brown (BB) with a homozygous blue (bb) 9. Example #1 Cross homozygous brown (BB) with a homozygous blue (bb) B B b b Genotype: BB = Bb = bb = Phenotype: Brown eyes = Blue eyes = 9. Example #1 Cross homozygous brown (BB) with a homozygous blue (bb) B B Bb Bb Bb Bb b b Genotype: BB = 0/4 or 0% Bb = 4/4 or 100% bb = 0/4 or 0% Phenotype: Brown eyes = 4/4 or 100% Blue eyes = 0/4 or 0% 10. Cross heterozygous brown (Bb) with a heterozygous brown (Bb) Example #2 Cross heterozygous brown (Bb) with a heterozygous brown (Bb) B b BB Bb Bb B Bb Bb bb b Genotypes: BB = 1/4 or 25% Bb = 2/4 or 50% Bb = 1/4 or 25% Phenotypes: Brown = ¾ or 75% Blue = ¼ or 25% 11. How is probability related to genetics? • Mendel discovered that probability can be used to predict the results of genetic crosses! • Probability is used to PREDICT the RESULTS of a genetic cross 12. What is codominance? • Neither allele is dominant or recessive, both alleles are expressed in the offspring. Will the offspring be heterozygous or homozygous? heterozygous! They have alleles for white and black feathers. DISCLAIMER: ROOSTER NEED TO MATE WITH A CHICKEN NOT ANOTHER ROOSTER!