Question 1
Autosomal Recessive Trait (6 points)
In the video linked in the introduction above, Allison and Tim have discovered that their baby is
suffering from Tay-Sachs disease. After some gene testing, they find that they are both
heterozygous for the HEXA gene that causes the disease. Both of them have inherited one
dominant allele and one recessive allele. For an autosomal recessive disease like Tay-sachs, a
heterozygous person is called a “carrier” because they carry a hidden recessive allele that can be
passed on to their children.
Question 1, Part A – Draw a simple, but accurate diagram of the chromosomes in one of Tim’s
cells in his testes at the BEGINNING stage of meiosis. LABEL the following terms and
HIGHLIGHT EACH TERM ONCE in YOUR diagram.
homologous chromosome pair #15 the two sex chromosomes
the HEXA gene locus the dominant (HEXA) alleles
the recessive (hexa) alleles sister chromatids
Answer:
Question 1, Part B – Make a similar drawing of one of Allison’s cells in her ovary at the
beginning stage of meiosis, include her #15 chromosomes and sex chromosomes. Include labels
for the terms in the TABLE above.
Question 2. (6 points)
Draw a series of three SETS of diagrams that follow the two #15 chromosomes, the HEXA and
hexa alleles, and the sex chromosomes through meiosis to produce sperm cells.
Diagram Set #1; Illustrate the chromosomes lined up in the center of the cell during the first
division of meiosis. SHOW THE TWO POSSIBLE CHROMOSOME ALIGNMENTS of the
#15 and sex chromosomes (remember independent assortment?).
Diagram Set #2; Illustrate all possible combinations of the #15 and sex chromosomes in the
cells at the end of meiosis I based on the alignment of chromosomes in your drawings in
Diagram Set #1.
Diag ram Set #3;
Illustrate all
possible
combinations of
#15 and sex
