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Senanu's Bio class

Chapter 14.1 - 14.3 – Mendelian genetics

OBJECTIVE: Be familiar with the following terms:

  • True-breeding
  • P generation, F1 generation and F2 generation
  • Allele, Dominant allele and Recessive allele
  • Homozygote and Heterozygote
  • Phenotype and Genotype
  • Monohybrid and Dihybrid
  • Law of segregation
  • Law of independent assortment

OBJECTIVE: Describe Mendel’s Experiments

  1. What question was Mendel trying to answer?
  2. What were the advantages of using peas as a model organism for his genetics experiments?
  3. Describe Mendel’s experiments with a single trait.

  4. What did Mendel conclude from his experiment? Describe the model of inheritance Mendel developed to explain the results of his monohybrid cross experiments.

    OBJECTIVE: Describe and Apply Mendel’s Law of Segregation

  5. Describe Mendel’s Law/Principle of Segregation
  6. If a plant with green peas (yy) is crossed with a true-breeding plant with yellow peas (YY):
    • What gametes does the green-pead plant produce? Only y
    • What gametes can the yellow-pead plant produce? Only Y
    • What is the genotype of the offspring (F1 generation)? all Yy
    • What is the phenotype of the offspring (F1 generation)? all Yellow
    • What gametes can the offspring (F1 generation) produce? Y and y
    • Draw a Punnett square of the offspring (F2 generation) of the F1 generation.
      Y y
    Y YY Yy
    y Yy yy

    </ans>

  7. For a gene with dominant allele (A) and recessive allele (a), what proportions of the offspring from an AA x Aa cross are expected to be:
    • homozygous dominant 1/4
    • homozygous recessive 1/4
    • heterozygous? 1/2

  8. If a cat has a long tail (the dominant phenotype), design an experiment to determine if the cat is heterozygous or homozygous. Use a test-cross by crossing this unknown with a homozygous dominant. Look at the offspring. You should be able to show both crosses and show that the offspring would be different for each.

    OBJECTIVE: Describe and Apply Mendel’s Law of Independent Assortment.

  9. Which two hypotheses did Mendel test in his experiments with two traits?
  10. Which Hypothesis was supported?
  11. Describe Mendel’s Law/Principle of Independent Assortment.
  12. Look at Figure 14.8 which is similar to Figure 13.8. Why does the presence of 4 types of gamete in equal proportion (if the parent is RrYy) demonstrate independent assortment? (hint – consider what offspring would be produced if there was just one chromosome, and the R and Y loci were on it such that the RrYy parent could produce only RY and ry gametes.)

  13. Pea Plants heterozygous for flower position (Aa) and stem length (Tt) are allowed to self-pollinate. List all the haploid gametes that could be made by an AaTt pea plant. Draw a Punnett square for this cross. How many offspring would be predicted to have terminal flowers and be dwarf? (look up which traits are dominant in table 14.2)

    OBJECTIVE: Be able to figure out what types of gametes are produced by an individual of a given genotype, and apply this to executing single and double-trait Punnett Squares.

  14. Determine the types of gametes the following individuals will produce (Note: you are being asked about gametes not offspring!)
    • aa Only a
    • Bb B and b
    • AA
    • AABB
    • CcDd
    • AABb
    • Aabb
    • CCDdee
    • AaBbcc ABc, Abc, aBc, abc

    OBJECTIVE: Understand the multiplication and addition rules and how they relate to Mendelian inheritance

  15. If you flip 2 coins:
    • what is the probability of getting 2 heads? 1/4
    • What is the probability of getting 2 tails? 1/4
    • What is the probability of getting 1 head and one tails (in any order)? 1/2
  16. If you flip 3 coins
    • what is the probability of getting 3 heads? 1/2 x 1/2 x 1/2 = 1/8
    • What is the probability of getting 3 tails? 1/2 x 1/2 x 1/2 = 1/8
    • What is the probability of getting at least one heads and at least one tails? (hint, there’s an easy and a hard way to do this, but the easy way isn’t immediately obvious. See if you can figure it out!) The only way of NOT getting at least one heads and at least one tails is to either get all heads or all tails. So this is p(all heads) = 1/8 OR p(all tails) = 1/8. So the probability is 1 - (p(all heads) OR p(all tails)) = 1 - (1/8 + 1/8) = 3/4
  17. If both parents are heterozygotes (Aa), what is the probability that a randomly chosen sperm cell carries the allele A? 50%
  18. What is the probability that a randomly chosen egg cell carries the allele ‘a’? 50%
  19. what is the probability that the offspring is AA (do this using probabilities, rather than from a Punnett square)? p(inheriting A from mother) = 0.5 * p(inheriting A from father) = 0.5 so the total probability is 0.5*0.5=0.25
  20. What is the probability the offspring is aa? 0.25
  21. What is the probability the offspring is Aa? 0.5
  22. If an individual with genotype AaBb is selfed:
    • What is the probability the offspring is AA?
    • What is the probability the offspring is BB?
    • What is the probability the offspring is AABB?
    • What is the probability the offspring is AaBb?
    • What is the probability the offspring is a homozygote at both loci?
    • CHALLENGE: What is the probability the offspring is a heterozygote for at least one locus? (hint, think how this probability relates to problem C above). This is the same as 1-p(homozygous at all loci) so 1 - [p(AABB) OR p(aabb)] = 1 - [1/16 + 1/16] = 1 - 1/8 = 7/8
  23. In a cross AaBbCc x AaBbCc (assume all genes independently assort), what is the probability of producing the genotype AABBCC? Show your work. To get AABBCC, the offspring needs to be AA AND BB AND CC. So p(AA) x p(BB) x p(CC) = 1/64
  24. For the cross in the question above, what is the probability of producing an offspring that is homozygous at each locus? Show your work. 1/8