-Basic Structure
-chromosomes are only visible when a cell is dividing so we usually see them in their double-stranded form
-the halves of a double-stranded chromosome (chromatids) are identical to each other because the DNA (original chromosome) replicated prior to cell division
-Cells & Their Chromosomes
-every organism has a specific number of chromosomes in each of their cells
-gametes / sex cells contain the organism's haploid number
-human haploid number = 23
-somatic / body cells contain the organism's diploid number
-human diploid number = 46 (23 pairs)
-"pairs" refer to homologous chromosomes
-chromosomes that are the same size, shape, and carry
the same trait information
-"pairs" exist as a result of fertilization
click here to see an animation of fertilization
-Identification of Chromosomes
-autosomes vs. sex chromosomes
-autosomes
-same for both males & females
-chromosomes 1 - 22
-sex chromosomes
-X and Y chromosomes
-different for males vs. females
-23rd pair
-females: XX
-males: XY
In males, the 23rd pair is not homologous because the Y chromosome is not identical to the X. However, the XY pairing is appropriate because X and Y are both sex chromosomes. -chromosomes can be distinguished from one another by looking
at differences in the
-size
-banding pattern
-dark stripes are caused by the Giemsa stain
adhering to the A-T base pairs
-stripes (Giemsa bands) vary because the DNA sequence
is different on each chromosome
-centromere placement
-metacentric: centromere near the center
-submetacentric: centromere off-center
-acrocentric: centromere near one end
-Karyotyping
-Karyotype
-a photograph of an individual's chromosomes arranged in a standard format
-basic steps of karyotyping
1. cell is treated with colchicine
2. cell is lysed, stained, and fixed onto a slide
3. slide is examined for a clear chromosome spread (see below)
4. slide is photographed
5. each chromosome is cut out of the photograph and placed
in its proper location on the karyotype (see below)
[karyotype: normal human male]
-karyotypes can reveal problems with
-chromosome number
-examples:
-Down Syndrome
-Turner Syndrome
-chromosome structure
-examples:
-Cri du chat Syndrome
-CML (chronic myelogenous leukemia)
karyotypes only show chromosomal problems, gene mutations are not visible on a karyotype
to more detailed notes
