Notes: Overview of DNA and Genetics
A human (Eukaryotic) cell contains many organelles.
The nucleus is the control center of the cell.
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In the nucleus (of human cells) there are 23 pairs of chromosomes
(46 chromosomes total). There are 22 autosomal pairs and 1 pair of sex
chromosomes (male XY/female XX).
Chromosomes can be displayed in a karyotype
(picture showing the number and appearance
of chromosomes arranged in homologous pairs.
Mendelian Genetics
Living things inherit one copy of each gene from
each parent, which are separated when gametes
form during meiosis (Law of Segregation). Each
version of a gene is called an allele. Alleles can be
dominant or recessive. If a person has two of the
same allele, they are homozygous. If they have two
different alleles, they are heterozygous. The
segregation of alleles is random, therefore genotype
of offspring can be predicted using probability and
Punnett Squares.
DNA Replication
During S phase of Interphase (non-dividing
part of Cell Cycle) DNA is copied. The two
strands unwind and separate. New
nucleotides are added to each original
strand following the complementary base
pair rules. After DNA Replication there are
two identical strands of DNA. DNA is
replicated in preparation for Cell Division
(Mitosis or Meiosis).
Cell Division
Mitosis (in autosomal cells) creates genetically
identical diploid (2n) cells for growth and
repair.
Meiosis (in sex cells only) creates genetically
different haploid (1n) gamete cells (egg or
sperm) for reproduction.
Chromosomes are tightly
wound up strands of DNA
(Deoxyribonucleic Acid).
DNA is made up of nucleotides.
A nucleotide is made up of a
nitrogenous base (A, T, C,G), a
phosphate group and the sugar
deoxyribose, in two strands that
form a double-helix. The
complementary base pair rules
state that Adenine bonds only
with Thymine and Guanine
only with Cytosine. A segment
of DNA is a gene. The order of
nucleotides (genotype) in each
gene is a code which is read by
the cell to make proteins. The
proteins produced determine the
phenotype of the person.