1 chromosomes. 2 prokaryotic chromosome the dna of prokaryotes (bacteria) is one, circular...
TRANSCRIPT
1
Chromosomes
2
Prokaryotic Chromosome
The DNA of prokaryotes (bacteria) is one, circular chromosome attached to the inside of the cell membrane
3
Eukaryotic ChromosomesAll eukaryotic cells store
genetic information in chromosomes
Most eukaryotes have between 10 and 50 chromosomes in their body cells
Human body cells have 46 chromosomes or 23 identical pairs
4
Eukaryotic ChromosomesEach chromosome is composed
of a single, tightly coiled DNA molecule
Chromosomes can’t be seen when cells aren’t dividing and are called chromatin
5
Chromosomes in Dividing Cells
Duplicated chromosomes are called chromatids & are held together by the centromere
Called Sister Chromatids
6
KaryotypeA picture of the
chromosomes from a human cell arranged in pairs by size
First 22 pairs are called autosomes
Last pair are the sex chromosomes
XX female or XY male
7
Boy or Girl?
Y - Chromosome
X - Chromosome
The Y Chromosome Decides
8
Cell Reproduction
9
Types of Cell ReproductionAsexual reproduction involves
a single cell dividing to make 2 new, identical daughter cellsMitosis & binary fission are
examples of asexual reproductionSexual reproduction involves
two cells (egg & sperm) joining to make a new cell (zygote) that is NOT identical to the original cellsMeiosis is an example
10
MeiosisFormation of
Gametes (Eggs & Sperm)
11
Facts About Meiosis
Preceded by interphase which includes chromosome replication
Two meiotic divisions --- Meiosis I and Meiosis II
Original cell is diploid (2n)Four daughter cells produced
that are monoploid or haploid (1n)
12
Facts About MeiosisDaughter cells contain half the
number of chromosomes as the original cell
Produces gametes (eggs & sperm)
Occurs in the testes in males (Spermatogenesis)
Occurs in the ovaries in females (Oogenesis)
13
Start with 46 double stranded chromosomes (2n)
After 1 division - 23 double stranded chromosomes
After 2nd division - 23 single stranded chromosomes (n)
Occurs in our germ cells that produce gametes
More Meiosis Facts
14
Why Do we Need Meiosis?
It is the fundamental basis of sexual reproduction
Two haploid (1n) gametes are brought together through fertilization to form a diploid (2n) zygote
15
Fertilization – “Putting it all together”
1n =3
2n = 6
16
Replication of Chromosomes
Replication is the process of duplicating a chromosome
Occurs prior to division
Replicated copies are called sister chromatids
Held together at centromere
Occurs in Interphas
e
17
A Replicated Chromosome
Homologs (same genes, different alleles)
SisterChromatids(same genes,same alleles)
Gene X
Homologs separate in meiosis I and therefore different alleles separate.
18
Meiosis Forms Haploid Gametes
Meiosis must reduce the chromosome number by half
Fertilization then restores the 2n number
from mom from dad child
meiosis reducesgenetic content
toomuch!
The right number!
19
Meiosis: Two Part Cell Division
Homologsseparate
Sister chromatidsseparate
Diploid
Meiosis I
MeiosisII
Diploid
Haploid
20
Meiosis I
Nucleus Spindlefibers Nuclear
envelopeEarly
Prophase I(Chromosome number
doubled)
Late Prophas
e IMetapha
se I Anaphase I
Telophase I (diploid)
21
Prophase I
Early prophaseHomologs pair.
Crossing over occurs.
Late prophaseChromosomes condense.
Spindle forms.Nuclear envelope fragments.
22
Tetrads Form in Prophase I
Homologous chromosomes
(each with sister chromatids)
Join to form a TETRAD
Called Synapsis
23
Crossing-OverHomologous
chromosomes in a tetrad cross over each other
Pieces of chromosomes or genes are exchanged
Produces Genetic recombination in the offspring
24
Homologous Chromosomes During
Crossing-Over
25
Metaphase I
Homologous pairs of
chromosomes align along the equator of the
cell
26
Anaphase I
Homologs separate and move to opposite poles.
Sister chromatids remain attached at their centromeres.
27
Telophase I
Nuclear envelopes reassemble.
Spindle disappears.
Cytokinesis divides cell into two.
28
Meiosis II
Only one homolog of each chromosome is present in the cell.
Meiosis II produces gametes with one copy of each chromosome and thus one copy of each gene.
Sister chromatids carry identical genetic information.
Gene X
29
Meiosis II: Reducing Chromosome Number
Prophase II
Metaphase II
Anaphase II
Telophase II 4 Identical
haploid cells
30
Prophase II
Nuclear envelope fragments.
Spindle forms.
31
Metaphase II
Chromosomes align along equator of cell.
32
Anaphase II
Sister chromatids separate and move to opposite poles.
Equator
Pole
33
Telophase II
Nuclear envelope assembles.
Chromosomes decondense.
Spindle disappears.
Cytokinesis divides cell into two.
34
Results of MeiosisGametes (egg & sperm) form
Four haploid cells with one copy of each chromosome
One allele of each gene
Different combinations of alleles for different genes along the chromosome
36
Comparing Mitosis and
Meiosis
37
Mitosis Meiosis
Number of divisions
12
Number of daughter cells
2 4
Genetically identical?
Yes No
Chromosome #Same as parent
Half of parent
Where Somatic cells Germ cells
WhenThroughout
lifeAt sexual maturity
RoleGrowth and
repairSexual
reproduction
Comparison of Divisions
38
Gametogenesis
Oogenesis or
Spermatogenesis
39
SpermatogenesisOccurs in the
testesTwo divisions
produce 4 spermatids
Spermatids mature into sperm
Men produce about 250,000,000 sperm per day
40
Spermatogenesis in the Testes
Spermatid
41
Spermatogenesis
42
OogenesisOccurs in the ovariesTwo divisions produce 3 polar
bodies that die and 1 eggPolar bodies die because of
unequal division of cytoplasmImmature egg called oocyteStarting at puberty, one oocyte
matures into an ovum (egg) every 28 days
43
Oogenesis in the Ovaries
44
Oogenesis
Oogonium(diploid)
Mitosis
Primaryoocyte(diploid)
Meiosis I
Secondaryoocyte(haploid)
Meiosis II(if fertilizationoccurs)
First polar bodymay divide (haploid) Polar
bodiesdie
Ovum (egg)
Secondpolar body(haploid)
a
A
X
X
a
X
A X
a
X
a
X
Matureegg
A
X
A
X
45