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Chromosomes and Cell Reproduction
Genetic Continuity: What does it mean?
“Reproduction of offspring with the
same features as the parent”
Every new cell needs to have an exact
copy of its parents DNA.
New exact copies are created when
cells reproduce.
The Cell Cycle
The life of a cell is composed of 2
main parts:
1) Interphase: the non-reproductive stage
where cell undergoes normal cell function.
2) Mitosis: Series of events that make up
the reproductive stage of cell life.
Cycle End
Mitosis
Interphase
Cycle Start
Interphase: non-reproductive
portion of cell cycle
-cell undergoes normal functions
-nuclear material (DNA) is
duplicated during late interphase
-cell organelles are also duplicated
WHY are the DNA and organelles
duplicated?
Interphase
Animal
Plant
Prophase: the start of mitosis
-nuclear membrane breaks down
-chromosomes coil thicker,shorter
-spindle fibers form, will anchor
chromosomes to poles of cell
Why does the nuclear membrane need to
break down?
Why does DNA have to form chromosomes
for cell division?
Prophase
Animal
Plant
Metaphase:
-chromosome pairs migrate toward
equator of cell
-centromere of each chromosome
firmly attaches to spindle fiber
What is the purpose of a centromere?
Metaphase
Animal
Plant
Anaphase:
-centromeres split
-replicated chromosomes move
apart
-cell membrane begins to pinch
inward
-in plants, new cell wall starts to
form, called the “cell plate”
Anaphase
Animal
Plant
Telophase:
-cell division is almost complete
-spindle fibers dissolve
-chromosomes uncoil, become
longer and thinner again.
-cytokinesis begins
Telophase
Animal
Plant
Cytokinesis:
-the cytoplasm of the cells is divided.
-new cell membrane is formed, and
encloses both cells.
-in plants, new cell wall is complete
-two genetically identical “daughter
cells” are formed
Chromosome Number
-Each species of organism has a
specific number of chromosomes.
Example: Humans have 46
chromosomes, Fruit flies have 8
chromosomes
Most organisms have their chromosomes arranged in pairs.
Cells with 2 of each chromosome
are called diploid.
The diploid number of chromosomes
is represented by 2n, where n is the
number of different pairs of chromosomes
Example:
Humans have 46 chromosomes,
arranged in 23 pairs.
n=23, so 2n= 46
Fruit flies have 8 chromosomes,
arranged in 4 pairs.
n= 4, so 2n=8
In diploid cells, each member of a
pair has the same basic structure.
The 2 members of a pair are called
homologs, and the pair is called a
homologous pair
Example: Each member of a homologous
pair may carry the gene for eye color:
1 member may carry the gene for blue
eyes, the other member may carry the
gene for brown eyes.
The combination of both genes will
determine the trait that is expressed.
Normal Male Human Karyotype
Meiosis:
Cell division that reduces the
chromosome number by 1/2.
The result is cells with the haploid
number of chromosomes.
The haploid number is represented
by n.
Example: In humans, the diploid
number is 2n, or 46
The haploid number is 23.
Meiosis makes it possible for sexual
reproduction, and therefore the
recombination of genes, to occur.
Sex cells are called gametes, and
are either sperm from males, or eggs
(ovum) from females.
Sperm and eggs are both haploid.