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2/20/2018
1
- Double-stranded molecule made of
nucleotides that stores genetic information
(double helix)
How does it store it?
- as a long, continuous thread that consists
of many genes
Chromatin: loosely compacted single strand
Chromatid: tightly compacted, one of a pair
Chromosome: two tightly compacted sister
chromatids joined at the centromere
Humans have 23 pairs of chromosomes:
Autosomes
- chromosome pairs 1 through 22
- contain genes not directly related to the sex
of an organism
Ex. Eye and hair color
Sex Chromosome
- the 23rd pair of chromosomes
- control development of sex characteristics
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Gametes: sex cells
- female (egg)
- male (sperm)
*** DNA in gametes is
passed on to
offspring
Somatic Cells: body
cells
- make up tissue
and organs
*** DNA is NOT
passed on to
offspring through cell
division
Why do cells need to divide?
1- growth
2- reproduction3- repair
1. Interphase
- where DNA duplicate and form
chromosomes
2. Mitosis
- where the chromosomes divide and
separate from each other
3. Cytokinesis
- Cytoplasm divides into two daughter cells
90% of the cell cycle is spent in interphase
Chromosomes appear as loose coils called
chromatin
Three phases:
Gap 1, Synthesis and Gap 2
The cell grows and checks DNA to make
sure code is undamaged then it duplicates
the DNA and checks it again for any
damaged code
Occurs in 4 phases:
PMAT
First stage of Mitosis
- DNA long strands condense into short coils
- Nuclear envelope breaks down
- Centrioles begin to move to opposite poles
- Spindle fibers form
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Chromosomes line up in the center of the cell
Spindle fibers attach to the centromere of each chromosome
Spindle fibers shorten and pull sister
chromatids apart, towards opposite poles
2 nuclear membranes begin to form around
chromosomes (one for each new cell)
Chromosomes begin to uncoil
Spindle fibers fall apart
Divides cytoplasm into two cells and
completes a full stage of the cell cycle
Begins during Telophase
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Meiosis consists of two cell divisions without
Interphase in the middle
Occurs in gametes (sex cells) only
Mitosis is in my toes; Meiosis is in the ovaries
OR
Meiosis is what makes me unique (genetically
unique as opposed to a genetic duplicate)
When your skin cells replicate, you want them
to create an exact copy (mitosis)
When creating a new organism
(reproduction), genetic variation increases
survival of the species (meiosis).
Egg and sperm each have 1 set of DNA
- Sex cells are called haploid cells
(n = 23 chromosomes)
When the sperm fertilizes the egg, the
resulting zygote now has 2 sets of DNA
- Somatic cells are called diploid cells
(2n = 46 chromosomes)
Fertilization:
- egg and sperm come together and the cell
now has a complete set of DNA (23 pairs, one
from each parent)
Cell makes a copy of DNA from Mom and from Dad.
23 from egg duplicates to 46
23 from sperm duplicates to 46
Total chromosomes is 92
- Copies of each chromatid are made; they join at the
centromere (cell must reduce chromosome number)
- Homologous chromosomes pair up: one from each
parent
- Crossing over may occur
Nuclear membrane disappears
Centrioles move to poles
Spindle fibers form
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Chromosome pairs line up at equator of cell
Spindle fibers attach to one of each
chromosome pair
Chromosomes line up
randomly on either side of
the equator
Paired chromosomes are pulled apart by
spindle fibers
Each side will have some from Mom and
some from Dad
Nuclear membranes form around two sets of
DNA; spindle fibers detach
Cytokinesis forms two unique cells, each with
23 pairs of chromosomes
Second cell division
Prophase II
Metaphase II
Anaphase II
Telophase II
Cytokinesis that
results in 4 genetically
unique daughter cells
egg + sperm = zygote
haploid + haploid = diploid
n + n = 2n
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Mitosis MeiosisDiploid or Haploid daughter cells
# of Divisions
Cell Type
Number of daughter cells
Daughter cells are:
Diploid (2n=46) Haploid (n=23)
1 2
2 4
Somatic cells(body cells)
Sex Cells(gametes)
Genetically identical Genetically unique
Interphase Gap 1 (G1)
Synthesis (S)
Gap 2 (G2)
Mitosis Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
INTERPHASE HAS THREE PHASES
Interphase Gap 1 (G1)
Synthesis (S)
Gap 2 (G2)
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Interphase Gap 1 (G1)
During G1 the cell grows, caries out normal functions, and replicates its organelles. There is also a CRTICAL CHECKPOINT. The cell checks to see if it has enough nutrition, has adequate size, and that DNA is undamaged.
Interphase Gap 1 (G1)
Synthesis (S)
During Synthesis (S phase) DNA is synthesized (made) that is: copied, replicated, duplicated.
Interphase Gap 1 (G1)
Synthesis (S)
Gap 2 (G2)
During G2 the cell undergoes additional growth. There is also a CRITICAL CHECKPOINT.
The cell checks to see if it has enough nutrition, has adequate size, and that DNA is undamaged.
Interphase
Mitosis Prophase
Metaphase
Anaphase
Telophase
CytokinesisCytoplasm divides,
the cell divides.