chromosome, chromatid, homologues

1. Chromosomes

2. As always…
• Key concepts are underlined
• Vocabulary is in green

3. Chromosomes
• DNA gets folded into
chromosomes when cells divide
to make new cells

4. • A chromosome
is DNA that is
tightly folded into
a rod shape

5. • Made of DNA
+ proteins
called
histones

7. • One chromosome looks
like this:
1 chromosome
Draw
this

8. • After DNA is copied, the
chromosome looks like
this:
1 chromosome
Draw
this

9. • Each half is identical
• The identical halves are
called chromatids
2 chromatids
Draw
this

10. Using your paper
chromosomes:
• Line up 4 different
chromosomes
BEFORE the DNA has
been copied.

11. Using your paper
chromosomes:
• Line up different
chromosomes AFTER
the DNA has been
copied.

12. Using your paper
chromosomes:
• Now show me ONE
sister chromatid

13. Using your paper
chromosomes:
• Now show me ONE
chromosome after the
DNA has been copied

14. Using your paper
chromosomes:
• Tricky…
• Show me one
chromosome
BEFORE the DNA has
been copied

15. • The two chromatids are attached at the
centromere
Make a duplicated
chromosome (of any
color) and hold it at
the centromere

16. Chromosomes
• Normally the DNA
is more loose in
the form of
chromatin

17. Chromosomes• The number of chromosomes
varies from species to species
• Humans have 46
chromosomes
• Chimpanzees, potatoes, and
plums all have 48
chromosomes
• Dogs have 78 chromosomes
• Question: does the number of
chromosomes determine the
complexity of the organism?
Show me withShow me with
your fingers:your fingers:
How manyHow many
chromosomeschromosomes
did you makedid you make
yesterday?yesterday?

18. • 2 types of chromosomes
– Autosomes
– Sex chromosomes

19. Chromosomes
• Sex chromosomes –
determine gender
– Females - XX
– Males - XY

20. Quick Check
• Each parent gives their child 1 of
their sex chromosomes
• Females receive an X chromosome
from each parent
• Males receive an X from one parent
and a Y from the other
• Which parent, the father or theWhich parent, the father or the
mother, determines the gender ofmother, determines the gender of
the child?the child?
Write your answer in your notebookWrite your answer in your notebook

21. Chromosomes
• Humans have 44 autosomes and 2 sex
chromosomes

22. • Every cell has 2 copies of each
chromosome
• One from each parent

23. • Called homologous chromosomes
• Same genes in the same location, but
may be different versions

24. With your chromosomes
• Make a homologous pair of chromosomes
that have already been duplicated.

25. • In prokaryotes (bacteria) just one
chromosome

26. With your chromosomes
• Make chromosomes showing DNA that
has not yet been copied
• now copied
• Hold up one chromatid
• Hold up it’s sister chromatid
• Point to the centromere on a chromosome
• Hold up one of the homologous pairs