Download Chromosomes - TJ

Name_____________________________________________
Chromosomes
Page #______
ROLE:
How do scientists organize and analyze the DNA in a cell?
BACKGROUND: You are made of trillions of cells, each with the exact same DNA. But where did that
DNA come from? It has to do with your parents, but it’s a bit more complex than that…
FIGURE 1. Chromosomes in a Human Body Cell
DIRECTIONS: Using the figures to guide you, answer the following questions with your group. You do
NOT need to use complete sentences, unless the question asks you to.
1. Does Figure 1 show a eukaryotic or prokaryotic cell? Circle one: [ eukaryotic / prokaryotic ]
Explain how you know.
2. What organelle is magnified above?
3. What is found inside that organelle?
4. What type of DNA structure is shown in Figure 1?
Circle one: [ sister chromatids / chromosome / chromatin / double helix ]
5. How are these DNA structures organized in the magnified circle?
READ THIS BEFORE MOVING ON:
DNA is not so neatly organized as you saw in Figure 1. The chromosomes in a cell are not
naturally found lined up next to one another. Scientists take a picture of chromosomes and then
match them up by size, except the last two. The finished picture is called a karyotype, as you
see in Figure 2.
Chromosomes come in pairs for most living things, called homologous pairs. Homologous
pairs are matched by which genes are found on them. Chromosomes are found in pairs because
one chromosome comes from the mother, and the second comes from the father.
FIGURE 2. Karyotype of a Human Body Cell
6.
a.
How many chromosomes does a regular human body cell have? ______
b. How many homologous pairs of chromosomes does a regular human body cell have? ______
7. Why do chromosomes come in homologous pairs?
8.
a.
What is the name of the sex cell that contains the chromosomes from the mother?
_____________
b. What is the name of the sex cell that contains the chromosomes from the father? ______________
9. Do you think sex cells have the same amount or different amount of chromosomes as a normal body
cell? (BIG HINT: Two sex cells have to join together to make one regular cell…)
Explain your answer.
READ THIS BEFORE MOVING ON:
When a cell contains two sets of each chromosome (in other words—homologous pairs), it is
said to be diploid. When a cell contains one set of chromosomes, it is said to be haploid.
Biologists use the symbol n to represent one set of chromosomes.
FIGURE 3. Human Fertilization
10. In Figures 1 & 2, you saw pictures of a human body cell. Was this cell diploid or haploid?
11. What is the process called when a sperm and egg join together?
12. What is formed when a sperm and egg join together?
13. a. What do you think “n = 23” means?
b. What do you think “2n = 46” means?
14. a. Is the sperm diploid or haploid? ____________________
b. Is the egg diploid or haploid? ______________________
c. Is the zygote diploid or haploid? ___________________
d. Circle the cell(s) that contains homologous pairs: [ egg / sperm / zygote ]
THINKING FURTHER:
15. Explain why sex cells (sperm and egg) are haploid, and not diploid.
16. If a body cell in a dog has 78 chromosomes, how many homologous pairs does that cell have?
17. If a body cell in a dog has 78 chromosomes, how many chromosomes are found in its sperm cell?
18. Do you agree or disagree that homologous pairs of chromosomes are found in sex cells (sperm and
egg)? [ Agree / Disagree ]
Explain your answer.