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 LanguageJanuary 12: Health/PE, Social Studies, Art,

Family Consumer ScienceJanuary 16: Health/PE, Science, MusicJanuary 17: Health/PE, Language Arts, BCIT (???)January 18: Health/PE, MathJanuary 19: Make-Up Day

Important Words for you to remember

1) Gamete2) Binary Fission3) Gene4) Chromosome5) Centromere6) Chromatid7) Homologous Chromosome8) Diploid9) Haploid10) Zygote11) Autosome12) Sex Chromosome13) Karyotype

a) Coiled up DNA & proteins.b) Two exact copies of DNA that make up

each chromosome.c) Has 2 copies of chromosomes.d) Has 1 copy of chromosomes.e) A sperm or egg cell (aka sex cell).f) The connector between chromatids.g) A fertilized egg.h) Any chromosome that is not an X or Y.i) In humans, they are the X & Y

chromosomes.j) A portion of DNA that codes for a

protein.k) A picture of chromosomes arranged by

size.l) Chromosomes similar in size, shape,

and genetic content.m) 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: 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.