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Senanu's Bio class

Human pedigree analysis (14.6)

Note that there will be an online assignment to go along with this.

OBJECTIVE: Understand how to draw a pedigree and how pedigrees can inform us about inheritance patterns

  1. Draw a pedigree of your family using the symbols in Fig 14.21. Make sure you label yourself!
  2. What is meant by the term ‘carrier’?
  3. Draw a pedigree of 2 normal parents with one normal and one affected son. Explain why this trait cannot be dominant.
  4. Draw a pedigree of an affected father and an unaffected mother, and their 2 affected and 2 unaffected children.
  5. Why may this pedigree be of a dominant condition?

  6. How may this pedigree be of a recessive condition?

    OBJECTIVE: Understand how organelle inheritance is different from autosomal or sex-linked inheritance

    NOTE: This is not covered in Chapter 14, but we’ll talk about it briefly in class.

  7. From which parent are organelle genes always inherited (several years ago, there has been a single (human) patient found where the mitochondrial genome was inherited from the other parent, but this is exceedingly rare)?
  8. Draw the following pedigree: An man affected with a mitochondrial condition marries an unaffected woman what is the probability that their child will be affected? The probability is 0 because the children inherit mitochondrial genes only from the mother.
  9. Draw the following pedigree for a mitochondrial condition: An affected woman marries an unaffected man. What is the probability that their child is affected? Probability = 1

Additional problems.

If you understand most of the material from Chapter 14, you should be able to solve these problems. We will hopefully have time in class to work on them.

  1. In sheep, white is due to a dominant gene (W), black to its recessive allele (w). A white ewe mated to a white ram produces a black lamb. List the genotypes of all the animals in this problem. If they produce another offspring could it be white? If so what are the chances? Both parents are Ww. Black lamb is ww. Other offspring could be white (p(white offspring) = 3/4)
  2. In humans, normal pigmentation is due to a dominant gene (C), albinism is due to its recessive allele (c). A normal man marries an albino woman. Their first child is an albino. What are the genotypes of these three people?
    • Normal man Cc
    • Albino woman cc
    • First child cc
  3. An albino man marries a normally pigmented woman. They have nine children all normally pigmented. What are the most probable genotypes of the parents and the children? This is like a testcross with the albino man being the tester. If the woman is a heterozygote, the probability of each child being albino is 1/2. So the probability of having 9 normal children is 1/29 (about 0.2%). If she is AA homozygote, then all children will be normally pigmented heterozygotes. This is therefore the (much) more likely genotype of the woman.
  4. In guinea pigs Black coat “B” is dominant over white coat “b”. Can two black coat parents produce white coat offspring? Can two white coat parents produce black coat offspring? Explain. White offspring are possible if both parents are heterozygotes. Two white parents cannot produce black offspring because neither of them has a ‘B’ allele.
  5. In fruit flies, straight wings is dominant over curly. Show how you would determine if a straight winged fly was heterozygous or homozygous? How would the possible outcomes inform your decision? Show the outcomes for a test cross
  6. In humans, the ability to taste phenylthiourea (PTU) is dominant. “Tasters” (TT) or (Tt) perceive an extremely bitter taste of PTU, while “non tasters” (tt) experience no sensation, or taste. What are the genotypes of Mr. and Mrs. Meadowmuffin, who can taste PTU, and who have 3 children, one of whom is a non-taster? Draw a pedigree of the Meadowmuffin family and label each person with their genotype. The fact that one child is a non-taster (tt) means that both parents must have a ‘t’ allele, but since they are both tasters, they must be heterozygotes.
  7. Yellow guinea pigs crossed with white ones always produce cream-colored offspring. Two cream guinea pigs when crossed produce offspring in a ratio of 1 yellow:2 cream:1 white. List the genotypes and phenotypic ratios produced by the following crosses:
    • yellow x cream
    • white x cream
    • What “extension” of Mendel’s hypothesis is this an example of? Incomplete dominance (like the pink snapdragons)
  8. Camellia flowers can be red or white or white and red. Draw and fill in the Punnett square and determine the expected genotypes and phenotypes from crossing homozygous red and heterozygous red and white parents. This is co-dominance. 1/2 offspring will be red (RR) and half will be red and white (RW)
  9. Can two people with type B blood have a child with type O blood? Explain. What is the probability of this happening? Yes, it’s possible. Assuming parents are both ‘Bi’, the probability of a child with type O blood is 1/4 (genotype ii)
    • What kind of child could a parent with type AB blood not have? Type O is not possible.
    • What “extension/exception(s)” of Mendel’s hypothesis is Blood Type an example of? Codominance between A and B alleles, but dominance between A and i (and also between B and i)