Unimonster Activity

Name: ______Date: ______Period: ______Unimonster Activity Pre-lab Discussion How are traits inherited? You can investigate this question by considering an imaginary animal called the unimonster. Suppose this animal has only one pair of chromosomes. Chromosomes carry genes, which control different genetic traits, such as hair color, height, and other physical characteristics. Different forms of a gene are called alleles. The presence of different alleles on the chromosomes of unimonsters determines whether they have one horn or two horns. During reproduction, parent unimonsters pass on alleles to their offspring.

In this investigation, you will determine the different allele combinations for the offspring of two unimonsters and ﬁgure out the number of horns the young unimonsters will have.

1. What are dominant and recessive alleles? ______

2. Deﬁne genotype and phenotype. ______

3. What does it mean to say that an organism is homozygous for a trait? Heterozygous for a trait? ______

4. How do the numbers of chromosomes in cells compare with the number of chromosomes in sex cells? During reproduction, what fraction of chromosomes does each parent contribute to its offspring? ______

Problem How can you determine the traits of a unimonster ’s offspring?

Materials (per group)

4 craft sticks (already labeled as shown in Figure 2) Procedure

1. Figure 1 shows a mother and a father unimonster, each with different genetic traits. The allele for two horns is dominant over the allele for one horn. Look at the drawing and answer question 1 in Observations.

2. The mother unimonster is heterozygous. This means that she has one allele for two horns and one allele for one horn. Each of her sex cells will have either a chromosome with the two-horn allele or a chromosome with the one-horn allele.

3. One of the mother unimonster ’s chromosomes will carry the two- horn allele. The mother unimonster ’s other chromosome will carry the one-horn allele.

4. The father unimonster is homozygous (hh).

5. During reproduction, the sex cells produced by the mother and father unimonsters combine to form a fertilized egg. The fertilized egg will grow into a young unimonster. Whether the young unimonster has one or two horns depends on the alleles on the chromosome contributed by each parent during reproduction. In Observations, use your chromosome models to answer questions 2–5. Remember that the allele for two horns is dominant. Anytime the dominant allele (H) is present, the unimonster will have two horns.

Observations 1. Which unimonster parent has the dominant allele for number of horns? How do you know? ______2. During reproduction, the sex cells containing the chromosomes M1 and F1 combine to form a fertilized egg. a. Which alleles are on each of the chromosomes? ______b. Will the young unimonster have one horn or two horns? _____ Draw the appropriate number of horns on young unimonster 1 in Figure 3.

3. During reproduction, the sex cells containing the chromosomes M1 and F2 combine to form a fertilized egg. a. Which alleles are on each of the chromosomes? ______b. Will the young unimonster have one horn or two horns? _____ Draw the appropriate number of horns on young unimonster 2 in Figure 3.

4. During reproduction, the sex cells containing the chromosomes M2 and F1 combine to form a fertilized egg. a. Which alleles are on each of the chromosomes? ______b. Will the young unimonster have one horn or two horns? _____ Draw the appropriate number of horns on young unimonster 3 in Figure 3.

5. During reproduction, the sex cells containing the chromosomes M2 and F2 combine to form a fertilized egg. a. Which alleles are on each of the chromosomes? ______b. Will the young unimonster have one horn or two horns? ____ Draw the appropriate number of horns on young unimonster 4 in Figure 3.

Analyze and Conclude 1. Which young unimonster(s) are homozygous and have one horn? ______

2. Which young unimonster(s) are heterozygous? ______

3. Are any young unimonster(s) homozygous with two horns? Explain. ______

Critical Thinking and Applications 1. If a mother unimonster is homozygous and has two horns, and a father unimonster is homozygous and has one horn, what are the phenotypes and genotypes of the possible offspring? Remember that the two-horn allele is dominant. ______

2. Predict the phenotypes and genotypes of the offspring of a mother unimonster and a father unimonster that are both heterozygous. ______

More to Explore Assume that a curly-hair allele is dominant and a straight-hair allele is recessive. The mother is homozygous and has straight hair, while the father is heterozygous. Use the Punnett Square below to find all of the possible genotypes and resulting phenotypes of the offspring.

Possible genotype(s):

Possible phenotype(s):