Genetics Review Lab
Answer the questions for this lab on a separate piece of paper. When you hand it in, attach your prelab table.
Part One. Dominant and Recessive Alleles.
An introduction or review of the concepts of genes, alleles, and dominance will lead into these questions. Remember, showing a dominant allele means that you are carrying one for sure, two maybe. You can only show the recessive allele if you are carrying two of them.
1. If both of 2 parents show the dominant allele for a trait we'll label "A," show: what alleles each may be carrying, and what cross combinations you can get; and what offspring combinations you could get from each parental combination. (Construct a Punnett Square)
2. Answer like #1, but for both parents showing the recessive allele for trait "A." (Construct a Punnett Square)
3. Answer like #1, but for one parent showing dominant and the other showing recessive. (Construct a Punnett Square)
4. A couple you meet both have brown eyes, but their child has blue eyes. Explain in terms of alleles. Use a Punnett Square to help explain.
Part Two. Using the Results from the Prelab Tables.
1. In light of the results from Part One, if the tables contain dominant/recessive traits, which would you expect to be in the majority, the dominant or the recessive ones?
2. The entire results from the class' tables will be tallied on the board. What sort of proportions do you find among the pairs? Do you think that you can predict which traits are dominant?
3. The actual dominant traits will be circled on the board. Which traits actually are the higher number and dominant, and which are not?
4. When surveying a population, you can actually predict numbers for dominant and recessive traits, but what important detail must you know first?
5. Looking at your pre-lab table and knowing the types of individuals you interviewed, did you find any trends? (Example: More males are left- handed.)
Part Three. Genetics of Human Blood Types.
An introduction into the biology and genetics of human blood types will lead into these questions. Remember, "A" and "B" are dominant over "o," but not over each other. Rh "+" is dominant over Rh "-" and inherited completely separately from the ABO alleles.
1. Someone with B+ blood marries someone with A- blood. Show what alleles might be present in this combination.
2. For the combination in question 1, tell whether the following blood types could show up in their children and explain! (Construct a Punnett Square to help explain – maybe a “big” Punnett square)
a) AB+?
b) A+?
c) B-?
d) O-?
3. In an old court case, a woman with O- blood has accused a man with AB+ of blood of being the father of her B- child. Could he be? Why or why not?
4. In the mother-child circumstance above, what blood type could the father not be?
5. These are the blood types of the McDarby family: dad, A+; mom, B+; son, A+. For each of the three (a 3-part answer), tell what blood type alleles, ABO and Rh, might possibly be present.
Dad -
Mom -
Son -
Part Four. Other Forms of Inheritance.
1. Using intermediate inheritance (incomplete dominance) and codominant inheritance, explain the following situation by showing the alleles involved: Breeding grey gerbils gives you offspring that are all white, all black, or all grey. Why?
2. Explain why some cows have both black and white coloring?
Part Five. Chromosomes, Linkage. Sex Linkage.
1. What purpose is served by chromosomes? What are homologous chromosomes?
2. How do chromosomes in a single organism differ, usually?
3. What is meant by Mendel’s law of segregation?
4. Explain Mendel’s law of independent assortment.
5. How is gender determined in organisms?
6. How are genes normally expressed? Why is this a problem with genes on the sex chromosomes?
7. What is a Barr body? Why do they exist?
8. In mammals, including humans, which gender is most likely to show a sex-linked trait? Why?
9. A color-blind man marries a woman with no history of color blindness in her family. What are the chances that: (Construct a Punnett Square)
a) Their sons will be color-blind?
b) Their daughters will be color-blind?
c) Their daughters will carry the color-blind allele?
10. Having extra chromosomes usually leads to major problems. (Down Syndrome is an extra 21st chromosome). However, having extra sex chromosomes (being XXX, or XYY, or XXY, or XXXX, even XXYY) is usually a minor problem only...
a) What minimizes the impact of extra X and Y chromosomes?