Prokaryotes
Binary fission. Fig
9.1
Eukaryotes
Somatic, or body cells undergo
mitosis, while germ
cells
in reproductive organs undergo meiosis. The life cycle of a cell is called
the cell cycle. Fig
9.2 Movie
Chromosome
structure - DNA, which is negatively charged, is wrapped around postively
charged proteins called histones, then coiled tightly. Fig
9.5
Chromosome
Number
Eukaryotic somatic cells have
two copies
(diploid or
2n) of each
chromosome, known as homologous chromosomes (homologues).
Gametes (sex cells or sperm and egg) are haploid
(1n) because they have
half the normal chromosome number
Humans have 46, or 23 pairs, of chromosomes. Fig.
9.4
Before cell division, each homologue
replicates into two identical copies called sister chromatids.
Fig.
9.3
Stages
of the cell cycle in mitosis Fig 9.6a
and Fig
9.6b
Interphase:
Mitosis.
Cytokinesis (Fig
9.7) Movie
1. cleavage furrow
2. cell plate. Image
Cell
Death
(Fig
9.8)
Meiosis - A
reduction division
required to reduce the number of chromosomes to half so sexual reproduction can
occur. (Fig
10.1)
The Sexual Life Cycle In animals (Fig
10.4)
Germ-Line Tissues
The
Stages of Meiosis Movie
Prior to meiosis I, during interphase, the
DNA replicates, forming 2 sister chromatids for each chromosome.
Meiosis
I - divides
the two homologous chromosomes. Fig.
10.8a
Crossing over may occur when
pieces of homologuous chromosomes (fig.
10.5) (nonsister chromatids) line up with each other
(synapsis) and exchange pieces to promote new genetic combinations
in the offspring. Because of crossing over, no two haploid cells are
the same.
Independent assortment - the alignment
of homologous pairs along the center of the cell is random, with different
combinations of parental chromosomes possible for each daughter cell. Fig.
10.6 Movie
Meiosis
II - separates
the two replicas of each chromosome. The result is the separation of the sister
chromatids to form four haploid daughter cells or gametes, each with a
different genetic make-up. Fig
10.8b
Stages
of meiosis
A comparison of mitosis and meiosis. Fig 10.10
Movie
The
Evolutionary Consequences of Sex Movie
Sexual reproduction. Fig
10.4
Independent Assortment. Fig.
10.11
Synapsis and crossing over. fig.
10.9
Random Fertilization
Asexual reproduction animal plants
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