Name____________________________ MCAS Practice: Chromosomes in cells
MCAS will try to see if you understand concepts about genetics by drawing pictures of chromosomes
and asking questions about them.
If you have one trait (height in pea plants for example):
1. Assume a pea plant is Tt. What kinds of gametes can it make? This is asking you to recognize
that a diploid organism puts one chromosome of each pair in a cell (by which process does this
happen?____________________________)
Draw 2 cells. Draw a picture of a chromosome with the appropriate letter on it.
2. Now, consider a pea plant with TWO traits. What kind of a cross do we call
this?___________________________________.Consider one whose genotype is TtBb. What
kinds of gametes will this pea plant make when it undergoes meiosis?
To answer this, draw 4 cells. How many chromatids will you draw in each?________What did
you do to find the chromosomes in each gamete?_____________________________
3. Now, draw the above pea plants cells- not the gametes, but the cells of the leaf, the cell of the
stem. Draw one cell and draw the correct # of chromatids in each.
General rules: in a gamete, there will be one chromatid of each pair. So, in humans egg or sperm, there
is one from pair one, one from pair two, one from pair three, etc. That’s why there are 23 in an egg or
sperm- one from each of the 23 pairs.
If you are looking at a body cell (give three examples of body cells
here__________________________,_____________________________________,________________),
you will see PAIRED chromatids. That is, you will see 2 of pair one, two of pair two, two of pair three.
They will be obvious as pairs because they will have the trait at the same place in each of the two.
Refer to the front side to do these problems.
4. A panda bear has the genotype G g for a trait. Draw a body cell from this animal.
5. Now, draw two sperm cells to show the possible chromosomes in its gametes.
6. Consider the same animal, but now think about two traits. Its genotype is G g F f. Draw a
body cell from it, showing the chromosomes.
7. Now, draw 4 possible sperm cells from this animal, drawing in the chromosome combinations.
(will you find pairs or singles in the sperm? ________________________Remember, a pair
means the matching ones from the mother and father that create pair one, or pair two, etc.)
How do you find the chromosomes in the gametes?__________________________
8. Draw the chromosomes that would appear in a human egg cell. The first one is done for you.
Label it 1-M or 1-F to show that it is chromosome 1 from the mother or father. REMEMBER
MEIOSIS SPLITS THE PAIRS INTO SINGLES!!!!!!!