Download Remember those chromosomes?

Remember those
chromosomes?
Well, you really need to!!
Some upcoming events
 Article Assignment due on January 12th.
 Remember midterms start on the 11th, so you may want to
turn it in early, so you have lots of time to study!
 Midterm on January 16th.
 In case you forget when your other midterms are, here you
go:
January 11: Health/PE, Technology, Foreign Language
January 12: Health/PE, Social Studies, Art,
Family Consumer Science
January 16: Health/PE, Science, Music
January 17: Health/PE, Language Arts, BCIT (???)
January 18: Health/PE, Math
January 19: Make-Up Day
Important Words for you to remember
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Gamete
Binary Fission
Gene
Chromosome
Centromere
Chromatid
Homologous Chromosome
Diploid
Haploid
Zygote
Autosome
Sex Chromosome
Karyotype
a) Coiled up DNA & proteins.
b) Two exact copies of DNA that make up
c)
d)
e)
f)
g)
h)
i)
j)
k)
l)
m)
each chromosome.
Has 2 copies of chromosomes.
Has 1 copy of chromosomes.
A sperm or egg cell (aka sex cell).
The connector between chromatids.
A fertilized egg.
Any chromosome that is not an X or Y.
In humans, they are the X & Y
chromosomes.
A portion of DNA that codes for a
protein.
A picture of chromosomes arranged by
size.
Chromosomes similar in size, shape,
and genetic content.
The method of reproduction of bacteria.
OK, so what are chromosomes again?
 DNA & proteins folded together.
 Basically, chromosomes are packaged DNA
that allows DNA to be stored in an organized
and accessible fashion.
 When do we see chromosomes?

They become visible when the cell is
preparing to divide. (Make 2 cells from 1).
Chromosomes again
 Before the cell divides, all DNA in that cell is
replicated (copied), such that each
chromosome has two copies all the DNA (and
thus two copies of each gene.)

These two copies of DNA are called the
chromatids and they are joined by the
centromere.
 Why do we need two copies of each gene
before cell division?
Chromosome #’s
 Human somatic cells (non-sex cells) have 23
pairs of chromosomes. (Total of 46)
 Each chromosome contain many different
genes that shape how our body’s develop
and function.
 Without a complete set, things go badly.

Each set is called a homologous pair of
chromosomes.


Homologous chromosomes – are similar is size,
shape, and genetic content.
One homologue comes form mama & the
other from papa.
Chromosomes # continued
 So, since all of our somatic (body) cells have
two homologous chromosomes they are said
to be DIPLOID. (23 sets/ 46 total)
 Gametes (sperm & egg) have one homologue
each, so they are HAPLOID. (23 total)
 When the sperm fertilizes the egg, it restores
the chromosome number. (23 sets/ 46 total)

A fertilized egg is called a zygote.
 Remember, the chromosome # of 46 is
specific to humans, organisms vary in their
chromosome #’s.
Sex Chromosomes
 Sex chromosomes are those that determine
what sex we will be.


XX =
XY =
 One X chromosome always comes from
momma.
 Daddy can give either the X or the Y.


So Daddy determines the sex of a child.
All those poor Queens were executed for
nothing! The King should have been blamed
for not producing a male heir. Shame on them!
Change in Chromosome #
 Alright, so I said without a complete set of
chromosomes things go badly.
 When humans have more chromosomes than they are
supposed to it is called trisomy. (Meaning three
chromosomes)

Such humans do not develop properly, only trisomy of
chromosome 21 will produce a viable offspring.
 This condition is called Down’s Syndrome.
 How does it happen?
 Nondisjunction (lack of seperation) of chromosomes
during gamete formation.
 This results in one gamete having 2 copies of the
chromosome and the other having no copies.
 This gamete joining with another gamete results in the
zygote having three copies of that chromosome.
Change in Chromosome Structure (aka
mutation)
 There are four different kinds of chromosomal
mutations:



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Deletion: piece of chromosome breaks off completely.
Results in completely missing genes, and is usually
fatal to zygote.
Duplication: chromosome fragment attaches to its
homologous chromosome – which then has 2 copies of
that gene(s).
Inversion: chromosome piece reattaches to original
chromosome, but in reverse of what it should be.
Translocation: chromosome piece reattaches to a
nonhomologous chromosome.