Download The DNA molecule exits for most of the cell cycle as

Why are cells small?
Surface to volume ratio
Diffusion of wastes and nutrients.
Chromosomes
The DNA molecule exists for most of the
cell cycle as chromatin, a long, uncoiled
single strand.
Chromatin will coil around proteins called
histones to form chromosomes.
Chromosomes are packages of DNA which
can be transferred to new daughter cells
when the cell reproduces through mitosis.
Chromosome Structure
Homologous chromosomes - contrasting
chromosomes of same type, one from each
parent.
Chromatid - one half of the "X"
chromosome shape. The two halves are
sister chromatids and exact copies of each
other. They will go to separate daughter
cells during meiosis.
Centromere - protein band that joins the
two sister chromatids.
Human body cells contain 46 chromosomes
23 pairs
22 pairs of autosomes
1 pair of sex chromosomes
X chromosome from mom’s egg
X or Y chromosome from dad’s
sperm
= XY, = XX
Sex-linked traits have a loci (singular locus)
on the X chromosome, so that only one
recessive allele is required for expression in
males, since males have only one X
chromosome.
Somatic (body) cells are
diploid (2n) - two sets of homologous
chromosomes, one from mom, one from
dad.
Sex cells (gametes) are
haploid (n) - one set, no homologies
Sex cells are formed through the process of
meiosis.
Multiple allele traits are those traits which
are governed by more than one single allele
(or gene)
A karyotype is a print of the chromosomes
of a cell. It is a diagnostic tool used to
evaluate the total # of chromosomes in the
cell.
Nondisjunction - the failure of two
homologies to separate during meiosis,
resulting in a condition known as trisomy
(three bodies) =
2n +1 = 47 chromosomes in humans.
Down’s syndrome (mongolism) is trisomy
21, of the 21st chromosome pair.
Aneuploidy - the condition of missing a
chromosome due to nondisjunction:
2n - 1 = 45 chromosomes.
Turner's syndrome X__