Download What are chromosomes?

What are chromosomes?
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of a cell that
chromosome [KROH-muh-sohml: threadlike structures in the nucleus
control heredity
gamete: sex cell
gene: part of a chromosome that controls inherited traits
genetics Iiuh-NET-iksl: study of heredity
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I
F
(
AZ’
H
” How
“Mary has her mother’s eyes.” “Torn is built just like his father.
often have you heard remarks like these?
traits.
All people resemble their parents in some ways. They have similar
And it is no accident. Many traits are passed on from parents to
The anoffspring. We say they are inherited. How are they inherited?
swer is found in the cell nucleus.
The nucleus has tiny bodies called chromosomes [KROH-muh-sohmsj.
pairs.
Most are rod-shaped. In body cells, chromosomes are found in
Body cells are all the cells except sperm and egg cells.
Each kind of organism has a specific number of chromosomes. For
a
example, every body cell of a fruit fly has S chromosomes (4 pairs);
human has 46 (23 pairs); a garden pea has 14 (7 pairs).
is a
Along each chromosome there are many dark bands. Each band
genes,
many
are
many,
small part of a chromosome called a gene. There
of an
at least one million in every nucleus. Genes determine the traits
organism.
the
There are genes for height, genes for nose size and shape, genes for
any
color of hair, skin, and eyes. In fact, there are genes for most traits
individual has. Some genes even affect traits like voice, intelligence and
behavior. Genes also control the life processes of your cells.
F
H
[1
genes) are
In both asexual and sexual reproduction, chromosomes (and
each
passed from parents to offspring. During asexual reproduction,
The
cell.
parent
single
a
daughter cell receives chromosomes from
the
and
sms
organi
daughter cell is an exact copy of the parent. Some
body cells of ll organisms reproduce asexually.
LI
During sexual reproduction, an offspring receives chromosomes from
cells, are jgj
each parent cell. The chromosomes in gametes, or sex
osomes
paired. A sperm or an egg cell has only half the number of chrom
cell and the egg
as a body cell. When fertilization takes place, the sperm
full number of
the
to
up
add
cell unite. Together, their chromosomes
or zygote, has
egg,
ed
chromosomes found in body cells. The fertiliz
both par
from
chromosomes from both of its parents. It also has traits
ents.
S
U
CHROMOSOMES AND GENES
Every cell has a nucleus.
C
1. Figure A shows an animal cell.
a) Draw a line to the nucleus.
b) Label it “nucleus.”
Figure A
2. A nucleus contains tiny rod-shaped
bodies. What are they called?
nucleus
3. A chromosome is made up of even
smaller bodies. What are they called?
Figure B
4. Figure C shows a pair of chromo
somes and their genes.
a) The chromosomes are labeled
1S1
1*)
ii
SI
eL_a
Il
b) Two genes are labeled
5. Why are genes important?
*1
I1
i•I It!
Figure C
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Figure D shows what actual human chro
mosomes look like.
S
p
‘
1%
V
ai
•
Every body cell of a particular organ
ism has the same chromosomes.
•
No two indjviduals that reproduce
sexually have the same chromosomes.
You have trillions of body cells. Each cell
has the same chromosomes. No one else
in the world has the same chromosomes.
There is no “duplicate” of you—anywhere!
‘C
Figure D
Human chromosomes
The study of traits and how they are passed
on is called genetics [juh-NET-iks}.
•
All living things have traits.
•
All living things have genes.
•
Only living things have genes.
Genes contain the “plans” for the traits an
organism has.
What are genes made of? Scientists have
discovered that genes are made of a com
plicated compound called DNA. DNA
stands for deoxyribonucleic fdee-oks-ee
ry-boh-noo-KLEE-ik] acid. Try to pro
nounce it.
Figure E
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_
____
_____
__________
FILL IN THE BLANK
C
Write your answers in the
Complete each statement using a term or terms from the list below.
spaces provided. Some words may be used more than once.
genes
pairs
inherited
specific
23
chromosomes
46
genetics
traits
1. The characteristics an individual has are called
way of saying this is
2. Traits are passed down from parents to offspring. Another
“traits
are
3. The study of heredity is called
4. The nucleus has tiny rod-shaped bodies called
5. A chromosome is made up of a chain of
6. Genes determine the
of an individual.
number of chromosomes.
7. Every organism has a
8. In body cells, chromosomes are found in
9. Each of your body cells has
This is a total of
10. A human sperm or egg has
pairs of chromosomes.
single chromosomes.
single chromosomes.
MATCHING
the correct letter in the
Match each term in Column A with its description in Column B. Write
space provided.
Column A
Column B
1. genes
a) compound that makes up genes
2. chrowosomes
b) made up of many genes
3. DNA
c) have unpaired chromosomes
4. body cells
d) pass on traits
5. gametes
e) have paired chromosomes
II
____
____
____
____
-
r
WHAT DO THE PICTURES SHOW?
from parent to offspring during asexual and
The pictures below show how chromosomes are passed
er the questions.
sexual reproduction. Study Figures F and C. Then answ
n
Chromosomes
Figure F
Asexual reproduction
cell in Figure F have?
1. How many chromosomes does the parent
hter cell have?
2. How many chromosomes does each daug
mosomes compare to the daughter cell’s
3. In Figure F, how do the parent cell’s chro
chromosomes?
duce?
4. Which Figure shows how body cells repro
s does each sperm cell contain?
5. a. In Figure C, how many chromosome
cell contain?
b. How many chromosomes does each egg
6. Gametes have
the
half, twice
chromosomes
number of chromosomes as body cells.
body cells
7. Fertilization produces a single cell. What is it
d?
calle
8. How many chromosomes does the zygote in
?
have
re
Figu
C
9. How many chromosomes will each body cell
of the organism have?
10. The offspring will have traits of both the
mother and father. Why?
Figure C
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Sexual reproduction
________
NUMBER, F:
(
Fill in the missing number of chromosomes.
Chromosomes In
each body cell
Organism
Chromosomes in each
sperm or egg
1.
Human
46
2.
Horse
60
3.
Housefly
4.
Dog
5.
Grasshopper
7
6.
Mosquito
3
7.
Chicken
8.
Apple
9.
Spinach
10.
6
78
18
17
12
12
Lily
the number of chromosomes that a body cell has.
11. A gamete has
half, twice
following?
12. How many pairs of chromosomes are there in each body cell of the
a) horse
d) lily
b) mosquito
e) human
c) spinach
1) housefly
ktnj
—
words and write
Below are several scrambled words you have used in this Lesson. Unscramble the
your answers in the spaces provided.
I. NEEC
4
2. HERINIT
3. NEGITECS
4. ETEMAG
5. CHOMEOSORM
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__________
__________
_________
________
_________
TRUE OR FALSE
in the space provided, write “true” if the sentence is true. Write “false” if the sentence is false.
1. Traits are the characteristics of living things.
2. Only animals have traits.
3. Traits are passed on from offspring to parents.
4. Traits are passed on by genes.
5. A cell has only a few genes.
6. Only animals have genes.
7. Different genes control different traits.
8. Genes form chromosomes.
9. Every organism has the same number of chromosomes.
10. Body cells have paired chromosomes.
11. Gametes have paired chromosomes.
12. A body cell and a sex cell have the same number of chromosomes.
13. Gametes have half the number of chromosomes of body cells.
14. A human body cell has a total of 23 chromosomes.
15. A human gamete has 23 single chromosomes.
REACI-{LNC OUT
Which organism would more closely resemble its parent, one produced by asexual
reproduction, or one produced by sexual reproduction? Why?
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