Transcript Chapter 6 “Chromosomes & Cell Reproduction”

Chapter 10
“Chromosomes & Cell
Reproduction”
• Gene- DNA that is
organized into units and
codes for a protein. Genes
play an important role in
determining how a
person’s body develops
and functions.
• Chromosome
(colored body)coiled up
structure of
DNA. Before a
eukaryotic cell
divides, the
DNA & proteins
coil up into a
chromosome.
• Chromatid-Two
exact copies of
DNA that make
up each
chromosome.
Often called
“sister
chromatids”.
• CentromereThe place at
which the 2
chromatids are
attached and
held together.
Chromosome Number
• Human Somatic
(“soma” means
body) Cell- 46 total
chromosomes or 23
pairs. The pairs
differ in shape, size
and set of genes
contained within the
chromosomes.
• Human Gamete (sex cell)- female- egg;
male- sperm. Each have only 23
chromosomes.
• Homologous
chromosomessimilar in size,
shape & genetic
content. Each
homologue within
the pair comes
from one of the two
parents.
• Diploid- Somatic
(body) cells
contain 2 sets of
chromosomes
(one set is from
mom, other set is
from dad).
• Haploid- Gametes (sex cells) contain 1
set of chromosomes. The fusion of 2
haploid gametes (fertilization) forms a
diploid zygote.
• Zygote- fertilized egg cell. It is the first cell
of a new organism.
• The number of chromosomes in cells is
the same within a species. Although most
species have different numbers of
chromosomes, some species by chance
have the same number.
Sex Determination
• Autosomes- 22 pairs
of the 23 total pairs of
chromosomes in
human somatic cells.
They are not directly
involved in
determining the sex
(gender).
• Sex
chromosomesonly one of the
23 pairs of
c’somes in
humans that
contain genes
that determine
the sex of an
individual.
• XX- female
• XY- male
• Because a female can only donate an “x”
to her offspring, the sex of the offspring is
determined by the male.
Change in chromosome number
• Trisomy (three
bodies)- humans with
more than 2 copies of
a chromosome.
Examples include
Trisomy 13 & 21.
Improper
development is a
result.
• Karyotype- a
photo of the
chromosomes in
a dividing cell
that shows the
chromosomes
arranged by size.
Change in Chromosome
Structure
• Deletion- a
piece of a
chromosome
breaks off
completely.
Usually proves to
be fatal for the
developing
zygote.
• Duplication- a
chromosome
fragment attaches
to its homologous
chromosome,
which will then
carry 2 copies of a
certain set of
genes.
• Inversion- a
chromosome piece
reattaches to the
original
chromosome but
backwards.
• Translocationwhen a piece
reattaches to a
non-homologous
chromosome.
Cell Cycle & Mitosis and
Cytokinesis
Cell Cycle
• Repeated sequence of
cellular growth and
division. Composed of 5
total stages (IPMAT).
• How do cells “know”
when to divide? Cells
have a “red-light/greenlight” mechanism that is
controlled by feedback
from the cell.
Interphase
• Cells spend 90% of
its time in the 3
stages of
Interphase.
• It’s the longest and
busiest stage.
• Chromosomes are
copied before the
cell divides and
new organelles are
being made.
• Mitosis aka
“Cell Reproduction” produces
new cells
that are
identical to
the original
cell.
Composed
of 4 stages
(PMAT).
1. ProphaseLongest stage in
mitosischromosomes
coil up and
become visible,
nuclear envelope
dissolves and
spindle forms.
2. MetaphaseChromosomes move
to the middle. Spindle
fibers link the
chromatids of each
chromosome to
opposite poles.
AnaphaseCentromeres divide
and the spindle fibers
pull half of the
chromosome to each
end.
Telophasechromosomes
uncoil, spindle
dissolves and
CYTOKINESIS
(cell pinching)
begins.
Cytokinesis