Download Chromosomes - Canton Local

Chromosomes
• During cell division, DNA must be neatly
packed into structures called chromosomes
– Chromosomes-rod shaped structures made of
DNA and proteins
• Contain our genes
• Chromosome
structure
– Consists of 2 identical
halves
• Each half- chromatid
• Each chromatid
represents one DNA
molecule
– Two chromatids of
chromosome are
attached at a point
called a centromere
– Chromatin- uncoiled
DNA; present in
between cell divisions
• Chromosome Numbers
–Each species has a characteristic
number of chromosomes in each cell (
ex: humans = 46; dogs = 78)
–Sex Chromosomes- chromosomes that
determine sex of organism
• Human females have two X
chromosomes
• Males have one X and one Y chromosome
–Autosomes- all other chromosomes in
an organism
• Every cell has two copies of each
autosome, one from each parent
• The 2 copies of each autosome called
homologous chromosomes
• Homologous chromosomes are same
size, shape and carry genes for same
traits
• Chromosome numbers
– Karyotype- photomicrograph of chromosomes in
a normal dividing human cell
• Chromosome numbers
– Diploid- cells having 2 sets of chromosomes
• 2 autosomes for each homologous pair
• 2 sex chromosomes
• Abbreviated 2n
• In humans, diploid or 2n number is 46- 22 pairs
of homologous autosomes and 2 sex
chromosomes
– Haploid- cells containing only one set of
chromosomes (ex. Sperm and egg)
• Only one autosome of each homologous pair
and only one sex chromosome
• Abbreviated - n
• n number = 23 in humans