Chromosomes and Ploidy

'p' arm

p = petite Upper arm that includes the telomere

Sex chromosomes

A few of these chromosomes' genes determine the sex of the cell Represented by letters 2 types of sex chromosomes in humans -X -Y -------------- Females = XX Males = XY 'Y' chromosome is the location of the TDF (testes determining factor) gene

Karyotype

All the chromosomes in the nucleus of a cell.

Origin of the word 'Chromosome'

'Chromo' means colored and 'Soma' means body, so Chromosomes are colored bodies.

Creation of a karyotype image

1. Cells have their cell and nuclear membranes broken. 2. After cell is lysed, the chromosomes spread out (called metaphase spread) 3. Chromosomes are stained/tagged fluorescently (for identification) 4. Chromosomes are photographed 5. Each chromosome is moved/paired according to: -size -centromere location -banding pattern

How Cytogeneticists identify specific chromosomes

1. Chromosome size 2. Location of the Centromere 3. DNA Banding pattern

Location of Human Chromosomes

1. Nucleus: -Linear -Double Stranded DNA 2. Mitochondria: -Circular -Double Stranded DNA

Centromere location

Middle = metacentric Between middle and end = submetacentric Close to end = acrocentric At end = telocentric

Chromosome size

Chromosomes aren't all the same size Larger chromosomes usually contain more genes

Centromere

Densely coiled DNA (drawn as a circle on diagrams) Location varies (metacentric, submetacentric, acrocentric, telocentric) Centromeres contain the kinetochore

SKY: Spectral Karyotyping

Fluorescent dyes identify specific chromosomes, which makes chromosomal aberrations noticeably stand out.

Chromosome classification

For Mammals: -Based on sex determination ('XX' or 'XY') 2 Types -Autosomes -Sex chromosomes

Ploidy levels

Haploid (N): -1 copy of each chromosome -Gametes (Ova, Sperm, Pollen) Diploid (2N): -2 copies of each chromosome -Somatic cells in animals -Plant cells (not all) Triploid (3N): -3 copies of each chromosome -seedless plants Tetraploid (4N): -4 copies of each chromosome -domestic wheat, oversized fruit

Human karyotype & ploidy

Humans are 2N = 46 - 2N: Somatic cells have 2 copies of each chromosome - 46: There are 46 total chromosomes *Equation: ploidy level = total number of chromosomes*

Kinetochore

Located inside the centromere Where spindle fibers attach so that chromatids can be separated during nuclear / cell division

TDF

Location: -On the 'Y' chromosome, on the p arm, near the telomere The presence of the TDF gene is the distinguishing trait of a male cell.

'q' arm

Lower arm that includes telomere

Ploidy

Ploidy (N): The # of copies of each chromosome

Banding pattern

Regions where DNA is tightly coiled (these regions stain dark and create bands) Regions where DNA is loosely coiled stain light Banding pattern is chromosome specific

Chromatid

Sub-unit of a chromosome Minimun: 1 chromatid per chromosome Maximum: 2 chromatids per chromosome *Chromatid number is dependent on the stage of the cell cycle*

Telomeres

Telo = end Located at the ends of the *Linear Chromosomes* - no genes and repetitive DNA

Anatomy of a chromosome

Telomere = tips (top/bottom) Arms (upper - 'p' / lower - 'q') = anything above/below the centromere Centromere = In between the two arms; Contains the Kinetochore Kinetochore = Part of the Centromere

Chromatin

The fundamental compounds that chromosomes are built out of. Contains DNA and Protein.

Autosomes

Unrelated to the sex of the cell Numbers represent these chromosomes 22 types of autosomes in humans