Chromosomes

Chromosomes

• Each organism has a set # of chromosomes

• Individuals of the same species have the same # of chromosomes

• Humans– 46

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Karyotype

• Display of chromosomes

• All the chromosomes in a cell

• Arranged by homologous chromosomes

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Homologous Chromosomes

• One from each parent• There are 23 pairs of

homologous chromosomes in each body cell

• Have the same sequence of genes on DNA

• Control the same traits

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

More Karyotypes

• Normal Male– 22 pairs of body

chromosomes

– 1 pair of sex chromosomes• 1 X Chromosome

• 1Y Chromosome

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

• Normal Female– 22 pairs of body

chromosomes

– 1 pair of sex chromosomes

• 2 X chromosomes

Diploid

• Contain 2 of ever chromosome

• 46 is the diploid # in humans

• 2n• Body Cells

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Haploid

• Contain 1 of each chromosome

• 23 is the haploid # in humans

• n• Sex Cells

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

What does this have to do with anything?

SEX!

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Fertilization

• The fusion between the sperm and the egg

• Creates a Zygote– The first cell of a

human

• 23 chromosomes from the male and 23 chromosomes from the female (46 total)

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

How do we make sex cells?

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Meiosis (sex cell division)

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Let’s Remember…

• In Mitosis– Each of the 46 chromosomes double in

interphase…92 total chromosomes at the start of prophase

– The doubled chromosome

look like this…QuickTime™ and a

TIFF (Uncompressed) decompressorare needed to see this picture.

Interphase I:

• Each chromosome has been replicated, exactly as in mitosis.

• The cell grows in size.

Lily Anther Cell: Meiosis I (Male)

Prophase I:

• The chromosomes shorten and thicken.

• The nuclear membrane disappears.

• Homologous chromosomes stick to each other and form a Tetrad.

• Crossing Over occurs

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

Metaphase I:

• The spindle fibers form.

• The centromeres (middle of the tetrad) become attached to the spindle fibers.

• The chromosomes line up in the middle of the cell.

Anaphase I:

• Double-stranded homologous chromosomes move apart.

• The homologous chromosomes that separated are different.

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

Telophase I:

• The chromosomes are at opposite poles.

• Cytokinesis separates the two new nuclei into two haploid sister cells.

Prophase II:

• The chromatids of each chromosome are not wound tightly around each other.

• Spindle fibers form again.

Lily Anther Cell: Meiosis II

Metaphase II:

• The chromosomes line up in the middle.

• Note that both sister cells are undergoing the process at the same time.

Anaphase II:

• The sister centromeres and the sister chromatids separate.

Telophase II:

• The chromatids are at opposite poles.

• Cytokinesis splits the cells

• The result is four separate haploid cells.

Mitosis makes Body Cells

• 1 cell division• Produces 2 cells• The same number of chromosomes as the parent

cell• 46 Chromosomes in humans• Creates body cells (somatic)

– Blood, bone, muscle, nerve, skin…

• Takes place all over your body except in your testes or ovaries.

Meiosis makes sex cells

• 2 cell divisions• Produces four cells• 1/2 the number of chromosomes as the parent• 23 chromosomes in humans• Creates sex cells (gametes)

– Sperm

– Egg

• Takes place in the testes and ovaries

Errors in Meiosis (Nondisjunction)

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Ex. Down Syndrome

Errors in Meiosis(Translocation)

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Ex. •Leukemia•Carcinomas

Errors in Meiosis(Deletion)

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Ex. •Muscular Dystrophy•Cri-Du-Chat Syndrome