Genetic Recombination 1 Meiosis Mitosis asexual reproduction Meiosis sexual reproduction Mitosis 2 identical cells Meiosis 4 unique sex cells spermeggs 2 Meiosis The form of ID: 691715
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MEIOSIS
Reduction-DivisionGenetic Recombination
1Slide2
MeiosisMitosis – asexual reproduction
Meiosis – sexual reproductionMitosis – 2 identical cellsMeiosis – 4 unique sex cells (sperm/eggs)
2Slide3
Meiosis
The form of
cell division by which GAMETES
,
with
HALF
the number of
CHROMOSOMES
, are produced.DIPLOID (2n) HAPLOID (n)
3Slide4
Meiosis
Haploid – (n) one copy of every chromosomeSperm and eggs have 23 chromosomes eachDiploid – (2n) two copies of every chromosomeThe rest of your body has 2 copies of each chromosome in every cell, 46 chromosomes totalFlipping between haploid and diploid in order to produce new organisms is
called alternation of generations
4Slide5
5
Haploid
DiploidSlide6
Stages of Meiosis
TWO divisions (MEIOSIS I
and MEIOSIS II)
I-PMAT-PMAT
6Slide7
Interphase I
Similar to mitosis
interphase.
CHROMOSOMES
(DNA)
replicate in the S phase Each duplicated
chromosome consist of two identical SISTER CHROMATIDS
attached
at their
CENTROMERES
.
CENTRIOLE
pairs also replicate
.
7Slide8
Meiosis I (four phases)
Cell division that reduces
the chromosome number by
one-half.
Four phases
:
a. Prophase I
b. Metaphase I c. Anaphase I
d. Telophase I
8
Prophase ISlide9
Prophase I
Longest
and most complex phase (90% of meiosis).
Chromosomes
condense
, nucleus/nucleolus disappear.
Synapsis
occurs - Homologous chromosomes come togetherto form a
tetrad.
Tetrad
is
two
chromosomes
or
four chromatids
(sister and non-sister chromatids).
9Slide10
Non-Sister Chromatids-HOMOLOGS
10
Homologs contain DNA that codes for the same genes
,
but different versions of those genes
Genes
occur
at
the same loci (location)Slide11
Prophase I - Synapsis
Homologous chromosomes
sister chromatids
sister chromatids
Tetrad
11Slide12
Homologous Chromosomes
Pair of chromosomes
(maternal and
paternal
) that are
similar in shape and size
.
Homologous pairs
(tetrads) carry GENES controlling the
SAME inherited traits.Each
locus
(position of a gene)
is
in
the
same position
on homologues.
Humans
have
23 pairs
of
homologous chromosomes:
a.
First
22
pairs
of
autosomes
b.
Last pair
of
sex chrom
osomes
12
LOCISlide13
Homologous Chromosomes
Paternal
Maternal
eye color
locus
eye color
locus
hair color
locus
hair color
locus
13Slide14
Metaphase I
Shortest phaseTetrads
align on the equator.
Independent assortment
occurs –
chromosomes separate randomly
causing GENETIC RECOMBINATION
14Slide15
Metaphase I
Homologs line up at equator or metaphase plate
OR
15Slide16
# of combos: 2n
Example: 2n = 4 then 1n = 2
thus 22
= 4
combinations
16Slide17
Question:
In terms of
Independent Assortment -how many different combinations of sperm could a human
male
produce?
17Slide18
Answer
Formula: 2n
Human chromosomes: 2n = 46
n = 23
2
23
= ~8 million combinations
18Slide19
Anaphase I
Homologous chromosomes separate
and move towards the poles.
Sister chromatids
remain attached
at their
centromeres
.
19Slide20
Anaphase I
20
Homologs separateSlide21
Telophase I
Each pole now has haploid
(1n) set of duplicated chromosomes
.
Cytokinesis
occurs and two haploid daughter cells are formed.
21Slide22
Telophase I
22
cytokinesisSlide23
MEIOSIS II
Sister Chromatids Separate
23
Meiosis IISlide24
Meiosis II
No Interphase II or it’s very short
No DNA Replication
Remember: Meiosis II is similar to mitosis
24Slide25
Prophase II
Same as Prophase in mitosis
Nucleus & nucleolus disappear
Chromosomes condense
Spindle forms
25Slide26
Metaphase II
Same as Metaphase in mitosis
Chromosomes (not homologs) line up at equator
26Slide27
Anaphase II
Same as Anaphase in
mitosis
SISTER CHROMATIDS separate
27Slide28
Telophase II
Same as Telophase in mitosis.
Nuclei and Nucleoli
reform
, spindle disappears
CYTOKINESIS
occurs
.
Remember:
FOUR HAPLOID DAUGHTER cells are produced.
Called
GAMETES
(eggs and sperm)
28
1n Sperm cell fertilizes 1n egg to form 2n zygoteSlide29
Telophase II
29Slide30
Question:
A cell containing 20 chromosomes
(diploid)
at the beginning of meiosis would, at its completion, produce cells containing how many
chromosomes
?
30Slide31
Answer:
10
chromosomes (haploid or 1n)
31Slide32
Karyotype
An
organized picture of the chromosomes of a human
arranged in pairs by size
from largest to smallest.
P
airs
1-22
called AUTOSOMESLast pair are
SEX CHROMOSOMES
32
Male - XYSlide33
Karyotype
33
Female - XXSlide34
Karyotype
34
Female - XX
Down Syndrome – Trisomy 21Slide35
Crossing Over
Crossing over: segments of nonsister
chromatids break and reattach to the other chromatid.
Chiasmata (chiasma)
are where chromosomes touch each other and
exchange genes
(
crossing over
.)Causes Genetic Recombination
35Slide36
Genetic Recombination
nonsister chromatids
chiasmata: site of crossing over
variation
Tetrad
36Slide37
37Slide38
Sex Chromosomes
XX chromosome - female
XY chromosome - male
38Slide39
Variation
Also known as
GENETIC RECOMBINATIONImportant to population as the raw material for
NATURAL SELECTION
.
All organisms are
NOT
alike
Strongest “most fit”
survive to reproduce & pass on traits
39Slide40
Question:
What are the
3 sources of
genetic recombination
or variation?
40Slide41
Answer:
CROSSING OVER
(prophase I)
INDEPENDENT ASSORTMENT
(metaphase I)
RANDOM FERTILIZATION
41