1. Flip your two coins to figure out which chromosomes are contained in the egg. This indicates which alleles are passed on to the baby dragon. Put a I in the appropriate box in the chart below to record the genotype of the resulting baby dragon. Mother ( WwHh ) wh wH Wh WH Father ( wwhh ) wh Genotype of baby = wwhh Number of babies with this genotype =____ Genotype of baby = wwHh Number of babies with this genotype =____ Genotype of baby = Wwhh Number of babies with this genotype =____ Genotype of baby = WwHh Number of babies with this genotype =____ 2. Repeat step 1 three times to make and record three more baby dragons. 4
3. To illustrate how the Law of Independent Assortment applies to humans , consider the inheritance of the recessive allele for sickle cell anemia ( s , located on chromosome 11) and the SRY gene. The SRY gene is located on the Y chromosome and the SRY gene results in male development. This explains why a person who has both an X chromosome and a Y chromosome in each cell is a male, and a person who has two X chromosomes and no Y chromosome is a female. Suppose that a father and mother are both heterozygous for the allele for sickle cell anemia ( Ss ). The following Punnett square shows the inheritance of the sickle cell and SRY genes, with X representing the X chromosome with no SRY gene and Y representing the Y chromosome which does have an SRY gene. Complete the Punnett square. Mother (SsXX) SX sX SX sX Father (SsXY) SX sX SY sY Based on this Punnett square, what fraction of the sons will have sickle cell anemia? What fraction of the daughters will have sickle cell anemia? Is there any sex difference in the risk of inheriting sickle cell anemia? The Law of Independent Assortment applies to genes which are located on different chromosomes, but it does not apply to genes which are located near each other on the same chromosome, as you will see in the next activity. Genetic Linkage -- Inheritance of Genes which are Close Together on the Same Chromosome Obviously, real chromosomes have more than one gene each. In this activity, you will analyze the inheritance of multiple genes which are close together on the same chromosome. We will consider three genes on Chromosome 1 and one gene on Chromosome 2, as indicated in the following table. Dominant Alleles Recessive Alleles Chromosome 1 W = has wings w = no wings F = fire- breathing f = no fire- breathing N = long fangs n = short fangs Chromosome 2 H = big horns h = small horns 5
For this activity, the father is heterozygous for each of these genes ( WwFfNnHh ), and the mother is homozygous for the recessive alleles ( wwffnnhh ). For the three genes on chromosome 1 for the father, the dominant alleles are all located on one chromosome and the recessive alleles are all located on the other homologous chromosome.
You've reached the end of your free preview.
Want to read all 8 pages?