1. Keepers of the Genetic Code
chromosomes
Keepers of the Genetic Code

2. General Information Word CHROMOSOME means ‘color body’
Why use that word? When studying cells these structures in the nucleus darkened with stain more so than the rest of the cell’s structures. Chromosome became a descriptive term, but, did not explain how they functioned.
In prokaryotes a looped chromosome is found in
center of the cytoplasm, ringed DNA
molecules called plasmids are also found there
In eukaryotes chromosomes are found in the
nucleus, they are linear. During interphase
referred to as chromatin
Each chromosome is a single strand of coiled DNA
In most organisms, like humans, that reproduce sexually chromosomes exist in homologous pairs with one originating from female ova(maternal) and the other from the male spermatoza(paternal)

3. Chromosome numbers
Are species different because they have different numbers of chromosomes?
FALSE: The number of chromosomes can vary from species to species, however, different species can have the same number of chromosomes
Do the number of chromosomes increase as complexity increases?
FALSE: The number of chromosomes has nothing to do with the “complexity” of the organism. It’s the amount of DNA that does.
This flower, Colchicum gonarei has the
highest known number of chromosomes
at 180,000+; you have 46!

4. Identifying homologous chromosomes
BANDING PATTERNS
Homologous chromosomes contain DNA that code for the same genes, so when the chromosomes are stained the genes appear as bands which are in the same location on both.
SIZE
The amount of DNA differs from chromosome to chromosome; this results in different sized chromosomes. Homologous chromosomes are the same size
CENTROMERE
Locations of the centromeres vary. Homologues have centromeres in the same location
Genes

5. karyotypes
Once homologous pairs are identified they can be sorted and organized in a karyotype.
Remember, karyo means ‘nucleus’. So, karyotypes map the contents of the nucleus; the chromosomes
Karyotypes are developed, usually during genetic screening; in a process called amnioscentesis.
Karyotypes can show if all chromosomes are present, if some are missing or damaged. They can also determine sex of the offspring.
They cannot be used to determine if genes are defective.

6. Types of chromosomes
Chromosomes are identified based upon the kind of genetic information they contain, and in what cells they are located.
Humans have 46 chromosomes(23 homologous pairs)
First 22 pairs: AUTOSOMAL chromosomes (“self body”)
Genes on these chromosomes determine physical
structure and chemical function
Last pair: SEX chromosomes: X(large) and the Y(small)
XX= homologous pair, female
XY= non homologous pair, male
Cells of the body, or SOMATIC cells have all 46 chromosomes,
23 pairs, and are diploid or ‘2n’.
Cells produced in the testes or ovaries, the GAMETES
have only 23 chromosomes, no pairs, and are haploid or ‘n’

7. 6 XY