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Punnett Squares

Punnett Squares. BELL RINGER. What do these pictures show? What is unusual about this hand and foot? Look closely!!. BELL RINGER CONT. The hand and foot have six fingers and toes instead of five.

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Punnett Squares

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  1. Punnett Squares

  2. BELL RINGER What do these pictures show? What is unusual about this hand and foot? Look closely!!

  3. BELL RINGER CONT. • The hand and foot have six fingers and toes instead of five. • This is the result of a genetic disorder referred to as Polydactyly – having more than five digits.

  4. BELL RINGER CONT. What religious group do these people belong to? They are Amish - lead a simple life centered on family and religion. Large population resides in Lancaster County, PA.

  5. BELL RINGER CONT. The Amish live separately from the rest of society. They typically marry only other Amish people. What if I told you Polydactyly is more common among the Amish than in the general population. Why do you think that is true? Why might it someday be important for you to know if you are a carrier for a genetic disease?

  6. Punnett Squares : A Model used to show the possible ways genes can combine during fertilization.

  7. Punnett Squares Punnett Squares Helps you keep track of traits.

  8. . Punnett Squares Dominant and recessive alleles are represented by letters.

  9. Punnett Squares A capital letter (T) is used for dominant alleles. T

  10. Punnett Squares A lowercase letter (t) is used for recessive alleles. t

  11. Punnett Squares If you wanted to know the type of offspring a cross between two parents would produce, you can use a punnett square. Tt x Tt TT,Tt for tall Tt for short

  12. Punnett Squares The letters representing the alleles from one parent are placed along the top of the square. Tt

  13. Punnett Squares The letters representing the two alleles from the second Parent are places along the side of the square. T t

  14. Punnett Squares Tt x Tt Tt T t

  15. Punnett Squares Squares are filled by writing the letter at the top beside the letter on the side. Tt T t

  16. Punnett Squares The letters in each of the squares represents the Genotypes of the offspring that the parents could produce. TT Tt Tt t t Tt T t

  17. Punnett Squares The genotype (genetic makeup) can be used to predict the phenotype (physical appearance) of the offspring.

  18. Necessary Definitions • Homozygous: same two alleles • Heterozygous: One of each allele

  19. Punnett Sqaures Genotype Phenotype TT: Homozygous dominant tall Tt : Heterozygous tall Tt : Heterozygous tall t t : Homozygous recessive short

  20. Punnett Squares Probability: the ratio that a particular event could occur. You can give genotypic ratios and phenotypic ratios 3 would be tall 1 would be short 3:1 out of 4 offspring

  21. Give the phenotypic and genotypic ratio of this cross Punnett Squares • Look at the F1 generation and count each type • Genotypic: 1(TT): 2 (Tt): 1 (tt) • Phenotypic: 3 (Tall): 1(short) TT Tt Tt t t Tt T t

  22. Punnett Squares: • Help you keep track of traits. • Predict genotype and phenotype. • Calculate probability.

  23. WHAT IS PROBABILITY? Probability is the likelihood that a particular event will occur Example: A coin flip What are the possible outcomes when you flip a coin? Answer: There are two – it could land heads up or tails up

  24. WHAT IS PROBABILITY? CONT. Probability is the likelihood that a particular event will occur Example: A coin flip What are the chances a coin will land heads up? Answer: 50% or ½ What are the chances a coin will land tails up? Answer: 50% or ½

  25. WHAT IS PROBABILITY? CONT. If you flip a coin 3 times in a row, what is the probability it will land heads up every time? Each coin flip is an independent event – each time the coin is flipped, the probability of it landing heads up is ½ . The probability of flipping 3 heads in a row is: ½ x ½ x ½ = 1/8 Remember: Past outcomes do not effect future outcomes!

  26. HOW DOES PROBABILITY RELATE TO GENETICS? • The principles of probability can be used to predict the outcomes of genetic crosses! Coin Toss Lab • Click here to practice your probability skills

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