Chromosomes (Eukaryotic DNA Structure)

When the cell is not dividing, DNA is long and stringy and called chromatin.

When the cell is dividing, DNA is tightly coiled around proteins and is called chromosomes.

Chromosome Numbers Each species has a specific number of chromosomes in the nucleus in its cells. For example, humans have 46 chromosomes in each body cell, dogs have 78 in each body cell.

Chromosome Numbers There is a tongue fern that has 1262 in each body cell! The number of chromosomes that an organism has is NOT related to the complexity of the organism!

Chromosome Pairs In body cells (any cell that is not a gamete), chromosomes come in pairs. Chromosomes come in pairs because you inherited one copy of the chromosome from your mother and on copy of the chromosome from your father. The two chromosomes in each pair are called homologous chromosomes because they have the same size and shape and carry the same genes.

Diploid vs. Haploid Cells that have pairs of chromosomes (body cells) are diploid (2n), which means they have 2 sets of chromosomes (one from each parent). The diploid number represents how many chromosomes are in these cells.

Diploid vs. Haploid Sex cells (a.k.a. gametes, a.k.a. sperm and egg) have only one of each chromosome. They are called haploid (n), which means they only have 1 set of chromosomes. The haploid number will always be half the diploid number.

Organism# of chromosomes in body cells (diploid number) # of chromosomes in sex cells (haploid number) Human46 Fruit fly4 Dog78 Sand dollar26 Cat16 Carrot18 horse

Types of Chromosomes Sex chromosomes are the pair of chromosomes that determine the sex of the organism. In humans, the sex chromosomes are X and Y. Normal females have 2 X chromosomes, and normal males have 1 X and 1 Y.

Types of Chromosomes All of the other chromosomes are called autosomes. So, in humans: –22 pairs or 44 chromosomes are autosomes –1 pair or 2 chromosomes are sex chromosomes There are certain disorders associated with having too little or too many chromosomes.

Chromosome Abnormalities 1.Down syndrome – 3 copies of chromosome #21 (trisomy 21)

Chromosomes Abnormalities 2.Turner syndrome – female with only 1X chromosome (XO) (monosomy X)

Chromosome Abnormalities 3.Klinefelter syndrome – male with XXY

XYY Syndrome 4. XYY Syndrome – a male with an extra Y chromosome

Chromosome Abnormalities 5.Patau syndrome – 3 copies of # 13

Doctors can detect these conditions before birth: –Amniocentesis – removes amniotic fluid from around baby … –Chromosomes are photographed and organized onto a chart called a karyotype.