meiosis gamete production with turning point
TRANSCRIPT
Reduction-DivisionGenetic
Recombination
1
The form of cell divisioncell division by which GAMETESGAMETES, , with HALFHALF the number of CHROMOSOMESCHROMOSOMES, , are produced.
DIPLOIDDIPLOID (2n) (2n) HAPLOIDHAPLOID (n) (n) MeiosisMeiosis is SEXUALSEXUAL
reproduction.reproduction. TWOTWO divisions divisions (MEIOSIS IMEIOSIS I and
MEIOSIS IIMEIOSIS II).2
Sex cells divide to produce GAMETESGAMETES (sperm or egg)(sperm or egg).
Gametes have HALFHALF the # of chromosomes.
Occurs only in GONADSGONADS (testes or ovaries).(testes or ovaries).
Male: Male: SPERMATOGENESISSPERMATOGENESIS
Female: Female: OOGENESISOOGENESIS
3
2n=46
humansex cell
diploid (2n)
n=23
n=23
Meiosis I
n=23
n=23
n=23
n=23
sperm
haploid (n)
Meiosis II4
2n=46
humansex cell
diploid (2n)
n=23
n=23
Meiosis I
n=23egg
Haploid (1n)
Meiosis II5
Polar Bodies (die)
Similar to mitosismitosis interphase. CHROMOSOMESCHROMOSOMES replicate in the S S
phase.phase. Each duplicated chromosomechromosome
consist of twotwo identicalidentical sistersister CHROMATIDSCHROMATIDS attached at their CENTROMERESCENTROMERES.
CENTRIOLECENTRIOLE pairs also replicate.
6
Nucleus and nucleolus visiblevisible.
nuclear membrane
nucleolus
cell membrane
chromatin
7
Cell division Cell division that reduces the chromosome number chromosome number by one-half.one-half.
Four phasesFour phases:a.a. prophase Iprophase Ib.b. metaphase Imetaphase Ic.c. anaphase Ianaphase Id.d. telophase Itelophase I
8
Prophase IProphase I
LongestLongest and and most complex most complex phase (90%).phase (90%).
ChromosomesChromosomes condense. SynapsisSynapsis occurs: homologous chromosomeshomologous chromosomes come together to form a tetradtetrad.
TetradTetrad is two chromosomes two chromosomes or four chromatids four chromatids (sister and non-sister chromatids).
9
10
Homologous chromosomes
sister chromatids sister chromatidsTetrad
11
Pair of chromosomeschromosomes (maternalmaternal and paternalpaternal) that are similar in shape similar in shape and sizeand size..
Homologous pairs ((tetradstetrads) carry ) carry genes controlling the same inherited genes controlling the same inherited traitstraits.
Each locuslocus (position of a gene) (position of a gene) is in the same position on homologues.
HumansHumans have 23 pairs 23 pairs of homologous homologous chromosomes:chromosomes:a. 22 pairs 22 pairs of autosomesautosomes
b. 1 pair of sex chromsex chromosomesosomes12
LOCLOCII
Paternal Maternal
eye color locus
eye color locus
hair color locus
hair color locus
13
Crossing over Crossing over may occur between non-sister chromatidschromatids at sites called chiasmatachiasmata.
Crossing overCrossing over: segments of nonsister chromatidschromatids break and reattach to the other chromatidchromatid.
Chiasmata (chiasma) Chiasmata (chiasma) are where chromosomes touch each other and exchange genes exchange genes (crossing overcrossing over.)
14
nonsister chromatids
chiasmata: site of crossing over
variation
Tetrad
15
16
XX chromosome - female XY chromosome - male
17
Homologs Homologs separateseparate
18
Meiosis Meiosis II
• Nucleus & Nucleolus Nucleus & Nucleolus disappear
• SpindleSpindle forms
• Chromosomes coilcoil & SynapsisSynapsis (pairing) occurs
• TetradsTetrads form & Crossing over Crossing over Occurs
centriolesspindle fiber
asterfibers
19TETRADTETRAD
Shortest phase Tetrads align on the
metaphase plate (equator).
Independent assortment occurs – chromosomes separate randomly
Formula: 2n
Example:Example: 2n = 42n = 4 then then 1n = 2 1n = 2
thusthus 222 2 = 4 = 4 combinationscombinations
20
Gametes
metaphase plate
OR
metaphase plate21
In terms of In terms of Independent Independent AssortmentAssortment -how many -how many different combinations of different combinations of sperm could a sperm could a humanhuman malemale produce? produce?
22
Formula: 2Formula: 2nn
Human chromosomes:Human chromosomes:2n = 462n = 46
n = 23n = 23 222323 = ~8 million = ~8 million combinationscombinations
23
Homologous chromosomes Homologous chromosomes separate and move towards the poles.
Sister chromatids Sister chromatids remain attached at their centromerescentromeres.
24
25
HomologsHomologs separate separate
Each pole now has haploidhaploid (1n) set of chromosomeschromosomes.
CytokinesisCytokinesis occurs and two haploid daughter cells are formed.
26
27
cytokinesis
28
Autoso
mes
Gonads
Nucle
i
Ovarie
s
17%
4%0%
78%1. Autosomes2. Gonads3. Nuclei4. Ovaries
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30 31 32 33
29
1 gamete
2 gametes
3 gametes
4 gametes
2 new cells
14%9%
14%
64%
0%
1. 1 gamete2. 2 gametes3. 3 gametes4. 4 gametes5. 2 new cells
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30 31 32 33 34
30
Mito
sis
Sperm
atoge
nesi...
Oogenesis
Binary fissi
on
0% 4%
88%
8%
1. Mitosis2. Spermatogenesi
s3. Oogenesis4. Binary fission
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30 31 32 33 34
31
10 23 46 50
0% 0%
58%
42%
1. 102. 233. 464. 50
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30 31 32 33 34
32
10 23 46 50
0% 0%0%
100%1. 102. 233. 464. 50
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30 31 32 33 34
33
Sperm
Prokaryo
tes
Chromoso
mes
Polar bodies
4%
96%
0%0%
1. Sperm2. Prokaryotes3. Chromosomes4. Polar bodies
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30 31 32 33 34
34
Chromoso
mes
Chromatids
Centromeres
Kinetoch
ores
9%5%
27%
59%
1. Chromosomes2. Chromatids3. Centromeres4. Kinetochores
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30 31 32 33 34
35
Chromoso
me num...
Chromoso
me num...
4 new cells
Prepara
tions f...
57%
17%13%13%
1. Chromosome number halved
2. Chromosome number doubled
3. 4 new cells4. Preparations for
meiosis II
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30 31 32 33 34
36
4%
83%
4%8%
1. Synapsis2. Chiasma3. Haploidism4. Crossing over
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30 31 32 33 34
37
Prophas
e I
Metaphase
I
Anaphase I
Telophase I
8%
20%
64%
8%
1. Prophase I2. Metaphase I3. Anaphase I4. Telophase I
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30 31 32 33 34
38
Prophas
e I
Metaphase
I
Anaphase I
Telophase I
76%
12%4%8%
1. Prophase I2. Metaphase I3. Anaphase I4. Telophase I
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30 31 32 33 34
39
Prophas
e I
Metaphase
I
Anaphase I
Telophase I
4%
48%
4%
43%1. Prophase I2. Metaphase I3. Anaphase I4. Telophase I
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30 31 32 33 34
40
Prophas
e I
Metaphase
I
Anaphase I
Telophase I
5%0%
27%
68%
1. Prophase I2. Metaphase I3. Anaphase I4. Telophase I
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30 31 32 33 34
Sister Sister Chromatids Chromatids SeparateSeparate
41
Meiosis IIMeiosis II
No Interphase II No Interphase II or very or very shortshort
No DNA ReplicationNo DNA Replication Remember: Meiosis II is Remember: Meiosis II is
similar to mitosissimilar to mitosis
42
Same as Same as ProphaseProphase in in mitosismitosis
43
Same as Metaphase in mitosis
metaphase platemetaphase plate44
Same as AnaphaseAnaphase in mitosismitosis
SISTER CHROMATIDS SISTER CHROMATIDS separateseparate
45
Same as Same as TelophaseTelophase in mitosis. in mitosis. Nuclei and Nucleoli Nuclei and Nucleoli reform.reform. CYTOKINESISCYTOKINESIS occurs. occurs. Remember: Remember: FOUR HAPLOID FOUR HAPLOID
DAUGHTER cells DAUGHTER cells are produced.are produced.
Called Called GAMETESGAMETES (eggs and sperm) (eggs and sperm)
46
1n Sperm cell fertilizes 1n
egg to form 2n zygote
47
2n=4
sex cell
diploid (2n)
n=2
n=2
meiosis I
n=2
n=2
n=2
n=2
sperm
haploid (n)
meiosis II48
49
Also known as Also known as GENETIC GENETIC RECOMBINATIONRECOMBINATION
Important to population as the raw Important to population as the raw material for material for NATURAL SELECTION.NATURAL SELECTION.
All organisms are All organisms are NOTNOT alike alike StrongestStrongest “ “most fit” most fit” survive to survive to
reproduce & pass on traitsreproduce & pass on traits
50
What are the What are the 33 sources of sources of genetic recombination genetic recombination or or variation? variation?
51
1.1. CROSSING OVER CROSSING OVER (prophase (prophase I)I)
2.2. INDEPENDENT ASSORTMENT INDEPENDENT ASSORTMENT (metaphase I)(metaphase I)
3.3. RANDOM FERTILIZATIONRANDOM FERTILIZATION
52
A cell containing 20 20 chromosomeschromosomes (diploid)(diploid) at the beginning of meiosis would, at its completion, produce cells containing how many chromosomeschromosomes?
53
1010 chromosomes (haploid chromosomes (haploid or 1n)or 1n)
54
AAn organized organized picture picture of the chromosomes of a human arranged in pairs arranged in pairs by size by size from largest to smallest.
PPairs 1-221-22 called AUTOSOMESAUTOSOMES
LLast pair are SEX SEX CHROMOSOMESCHROMOSOMES
55
Male - XYMale - XY
56
Female - XXFemale - XX
57
Female - XXFemale - XXDown Syndrome – Trisomy 21
The fusion of a spermsperm and eggegg to form a zygotezygote.
A zygote is a FERTILIZED EGGFERTILIZED EGG
n=23egg
sperm n=23
2n=46zygote
58
A cell containing 40 40 chromatidschromatids at the beginning of meiosis would, at its completion, produce cells containing how many chromosomeschromosomes?
59
10 chromosomes10 chromosomes
60
61
Chromoso
mes
Prophas
e
DNA Replic
atio...
Chromatids
25% 25%25%25%1. Chromosomes2. Prophase3. DNA Replication4. Chromatids
201 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30
62
Prophas
e II
Metaphase
II
Anaphase II
Telophase II
25% 25%25%25%
201 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30
1. Prophase II2. Metaphase II3. Anaphase II4. Telophase II
63
Prophas
e II
Metaphase
II
Anaphase II
Telophase II
25% 25%25%25%
201 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30
1. Prophase II2. Metaphase II3. Anaphase II4. Telophase II
64
Prophas
e II
Metaphase
II
Anaphase II
Telophase II
25% 25%25%25%
201 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30
1. Prophase II2. Metaphase II3. Anaphase II4. Telophase II
65
Prophas
e II
Metaphase
II
Anaphase II
Telophase II
25% 25%25%25%
201 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30
1. Prophase II2. Metaphase II3. Anaphase II4. Telophase II
66
Natu
ral s
elect...
Muta
tions
Homogeneous p
o...
Isolation
25% 25%25%25%1. Natural
selection2. Mutations3. Homogeneous
populations4. Isolation
201 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30
67
1 2 3 4 5
20% 20% 20%20%20%
1. 12. 23. 34. 45. 5
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30 20
68
25% 25%25%25%1. 102. 253. 504. 100
201 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30
69
Somatic c
ells
Autoso
mes
Epith
elial c
el...
Sick
le cells
25% 25%25%25%
1. Somatic cells2. Autosomes3. Epithelial cells4. Sickle cells
201 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30
70
Embryo
Zygo
te
Haploid ce
ll
Muta
tion
25% 25%25%25%1. Embryo2. Zygote3. Haploid cell4. Mutation
201 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30
71