CONNECTIONS BETWEEN CELL DIVISION AND REPRODUCTION Mitosis – division of a cell to produce two...
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Transcript of CONNECTIONS BETWEEN CELL DIVISION AND REPRODUCTION Mitosis – division of a cell to produce two...
CONNECTIONS BETWEEN CELL DIVISION AND REPRODUCTION
• Mitosis – division of a cell to produce two identical cells; used mainly for growth and cell replacement
• Meiosis – division of cells to produce 4 daughter cells (gametes) with a single set of chromosomes
Copyright © 2009 Pearson Education, Inc.
8.1 Like begets like, more or less
– Living organisms reproduce by two methods– Asexual reproduction
– Offspring are identical to the original cell or organism– Involves inheritance of all genes from one parent
– Sexual reproduction– Offspring are similar to parents, but show variations in traits– Involves inheritance of unique sets of genes from two parents
Copyright © 2009 Pearson Education, Inc.
Sexual reproduction produces offspring with unique combinations of genes
– Cell division perpetuates life– Cell division is the reproduction of cells
Growth and reproduction of organisms are made possible through cell division
Copyright © 2009 Pearson Education, Inc.
Cell division results in genetically identical daughter cells
• Most cell division results in daughter cells with identical genetic information, DNA
• A special type of division produces nonidentical daughter cells (gametes, or sperm and egg cells)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Terms
• All the DNA in a cell constitutes the cell’s genome
• DNA molecules in a cell are packaged into chromosomes
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Terms
• Every eukaryotic species has a characteristic number of chromosomes in each cell nucleus
• Somatic cells (nonreproductive cells) have two sets of chromosomes. Most all cells in body
– They are diploid. (2n)
• Gametes (reproductive cells: sperm and eggs) have half as many chromosomes as somatic cells
– They are haploid. (1n)Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Terms
• Eukaryotic chromosomes consist of chromatin, a complex of DNA and protein that condenses during cell division
• In preparation for cell division, DNA is replicated (duplicated) and the chromatin condenses so you can see the chromosomes
• Each duplicated chromosome has two sister chromatids, which separate during cell division
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Mitosis – division of a cell to produce two identical cells; used mainly for growth and cell replacement
Copyright © 2009 Pearson Education, Inc.
The cell cycle is an ordered sequence of events for cell division
It consists of two stages– Interphase: duplication of cell contents
including DNA– G1—growth, increase in cytoplasm
– S—duplication of chromosomes
– G2—growth, preparation for division
– Mitotic phase: division
– Mitosis—division of the nucleus
– Cytokinesis—division of cytoplasm
8.5 The cell cycle multiplies cells
Copyright © 2009 Pearson Education, Inc.
S
(DNA synthesis)G1
G2
Cytokinesis
Mito
sis
INTERPHASE
MITOTICPHASE (M)
Cell cycle
Centrosomes(with centriole pairs)
Early mitoticspindle
Chromatin
INTERPHASE PROPHASE
Centrosome
Plasmamembrane
Chromosome, consistingof two sister chromatids
Nuclearenvelope
Nucleolus
Centromere
Interphase
– In the cytoplasm
– Cytoplasmic contents double
– In the nucleus
– Chromosomes duplicate during the S phase
8.6 Cell division is a continuum of dynamic changes
Copyright © 2009 Pearson Education, Inc.
Chromatid
One duplicatedchromosome
Centromere
One unduplicatedchromosome
– Chromosome Monitor:Human cells have 46 chromosomes. By the end of interphase
– How many chromosomes are present in one cell?
– How many chromatids are present in one cell?
8.6 Cell division is a continuum of dynamic changes
Copyright © 2009 Pearson Education, Inc.
Prophase
– In the nucleus
– Chromosomes coil and become compact
8.6 Cell division is a continuum of dynamic changes
Copyright © 2009 Pearson Education, Inc.
Metaphaseplate
Nucleolusforming
METAPHASE TELOPHASE AND CYTOKINESISANAPHASE
Cleavagefurrow
Daughterchromosomes
NuclearenvelopeformingSpindle
Metaphase
– Chromosomes align at the cell equator
– Chromosome Monitor:By the end of metaphase
– How many chromosomes are present in one human cell?
– How many chromatids are present in one human cell?
8.6 Cell division is a continuum of dynamic changes
Copyright © 2009 Pearson Education, Inc.
Anaphase – Sister chromatids separate at the centromeres– Daughter chromosomes are moved to opposite
poles of the cell– Chromosome Monitor:
By the end of anaphase – How many chromosomes are present in one
human cell?– How many chromatids are present in one human
cell?
8.6 Cell division is a continuum of dynamic changes
Copyright © 2009 Pearson Education, Inc.
Telophase– The cell continues to elongate– The nuclear envelope forms around
chromosomes at each pole, establishing daughter nuclei
– Chromatin uncoils – Chromosome Monitor:
By the end of telophase – How many chromosomes are present in one
nucleus within the human cell?– Are the nuclei identical or different?
8.6 Cell division is a continuum of dynamic changes
Copyright © 2009 Pearson Education, Inc.
Cytokinesis
– Cytoplasm is divided into separate cells
– The cell begins to look like a figure 8 because cytokinesis is occuring
8.6 Cell division is a continuum of dynamic changes
Copyright © 2009 Pearson Education, Inc.
Cleavagefurrow
Contracting ring ofmicrofilaments
Daughter cells
Cleavage furrow
Mitosis
Correctly label phases of mitosis in this onion root tip specimen.
– Mitosis produces genetically identical cells for – Growth– Replacement– Asexual reproduction
8.11 Review: Mitosis provides for growth, cell replacement, and asexual reproduction
Copyright © 2009 Pearson Education, Inc.
MEIOSIS AND CROSSING OVER
Copyright © 2009 Pearson Education, Inc.
Somatic cells have pairs of homologous chromosomes, receiving one member of each pair from each parent
Homologous chromosomes are matched in
– Length
– Centromere position
– Gene locations
– A locus (plural, loci) is the position of a gene
– Different versions of a gene may be found at the same locus on maternal and paternal chromosomes
8.12 Chromosomes are matched in homologous pairs
Copyright © 2009 Pearson Education, Inc.
Sister chromatids One duplicatedchromosome
Centromere
Homologous pair ofchromosomes
Identify homologous pairs of chromosomesOne from mother; one from father
Identify duplicatedchromosomesIdentify sister chromatids
8.17 Homologous chromosomes can carry different versions of genes
Separation of homologous chromosomes during meiosis can lead to genetic differences between gametes
– Homologous chromosomes may have different versions of a gene at the same locus
– One version was inherited from the maternal parent, and the other came from the paternal parent
– Homologues do not end up in the same cell at the end of meiosis so, gametes will receive either the maternal or paternal version of the gene
Copyright © 2009 Pearson Education, Inc.
The human sex chromosomes X and Y differ in size and genetic composition
Pairs of autosomes have the same size and genetic composition
Chromosome Monitor:
– Humans have 46 chromosomes; how many homologous pairs does that represent?
– If there is one pair of sex chromosomes, how many pairs of autosomes are found in humans?
8.12 Chromosomes are matched in homologous pairs
Copyright © 2009 Pearson Education, Inc.
Meiosis is a process that converts diploid nuclei to haploid nuclei
– Diploid cells have two homologous sets of chromosomes
– Haploid cells have one set of chromosomes
– Meiosis occurs in the sex organs, producing gametes—sperm and eggs
Fertilization is the union of sperm and egg
– The zygote has a diploid chromosome number, one set from each parent
8.13 Gametes have a single set of chromosomes
Copyright © 2009 Pearson Education, Inc.
Haploid gametes (n = 23)
nEgg cell
Sperm cellFertilizationMeiosis
Multicellulardiploid adults
(2n = 46)
Mitosis anddevelopment
n
2n
Diploidzygote
(2n = 46)
The human life cycle
Like mitosis, meiosis is preceded by interphase
– Chromosomes duplicate during the S phase
Unlike mitosis, meiosis has two divisions
– During meiosis I, homologous chromosomes separate
– The chromosome number is reduced by half
– During meiosis II, sister chromatids separate
– The chromosome number remains the same
8.14 Meiosis reduces the chromosome number from diploid to haploid
Copyright © 2009 Pearson Education, Inc.
Events in the nucleus during meiosis I
– Prophase I
– Chromosomes coil and become compact
– Homologous chromosomes come together as pairs by synapsis
– Each pair, with four chromatids, is called a tetrad
– Nonsister chromatids exchange genetic material by crossing over
8.14 Meiosis reduces the chromosome number from diploid to haploid
Copyright © 2009 Pearson Education, Inc.
Genetic recombination is the production of new combinations of genes due to crossing over
Crossing over involves exchange of genetic material between homologous chromosomes
– Nonsister chromatids join at a chiasma (plural, chiasmata), the site of attachment and crossing over
– Corresponding amounts of genetic material are exchanged between maternal and paternal (nonsister) chromatids
8.18 Crossing over further increases genetic variability
Copyright © 2009 Pearson Education, Inc.
Animation: Crossing Over
Centromere
Chiasma
Tetrad
– Chromosome Monitor:Human cells have 46 chromosomes. At the end of prophase I
– How many chromosomes are present in one cell?
– How many chromatids are present in one cell?
8.14 Meiosis reduces the chromosome number from diploid to haploid
Copyright © 2009 Pearson Education, Inc.
Events in the nucleus during meiosis I
– Metaphase I– Tetrads align at the cell equator
– Anaphase I– Homologous pairs separate and move toward
opposite poles of the cell
8.14 Meiosis reduces the chromosome number from diploid to haploid
Copyright © 2009 Pearson Education, Inc.
Centrosomes(with centriolepairs)
PROPHASE I
Microtubulesattached tokinetochore
INTERPHASE
Sites of crossing over Metaphaseplate
Spindle
MEIOSIS I: Homologous chromosomes separate
METAPHASE I
Sister chromatidsremain attached
ANAPHASE I
Nuclearenvelope
Sisterchromatids
Centromere(with kinetochore)
Homologouschromosomes separateChromatin
Tetrad
Events in the nucleus during meiosis I – Telophase I
– Duplicated chromosomes have reached the poles
– A nuclear envelope forms around chromosomes in some species
– Each nucleus has the haploid number of chromosomes
– Chromosome Monitor:After telophase I and cytokinesis
– How many chromosomes are present in one human cell?
– How many chromatids are present in one human cell?
8.14 Meiosis reduces the chromosome number from diploid to haploid
Copyright © 2009 Pearson Education, Inc.
Meiosis II follows meiosis I without chromosome duplication
Each of the two haploid products enters meiosis II
Events in the nucleus during meiosis II
– Prophase II
– Chromosomes coil and become compact
8.14 Meiosis reduces the chromosome number from diploid to haploid
Copyright © 2009 Pearson Education, Inc.
Events in the nucleus during meiosis II
– Metaphase II
– Duplicated chromosomes align at the cell equator
– Anaphase II
– Sister chromatids separate and chromosomes move toward opposite poles
8.14 Meiosis reduces the chromosome number from diploid to haploid
Copyright © 2009 Pearson Education, Inc.
Events in the nucleus during meiosis II
– Telophase II
– Chromosomes have reached the poles of the cell
– A nuclear envelope forms around each set of chromosomes
– With cytokinesis, four haploid cells are produced
– Chromosome Monitor:After telophase II and cytokinesis
– How many chromosomes are present in one human cell?
– How many chromatids are present in one human cell?
8.14 Meiosis reduces the chromosome number from diploid to haploid
Copyright © 2009 Pearson Education, Inc.
PROPHASE I
MEIOSIS II: Sister chromatids separate
METAPHASE II ANAPHASE II
Cleavagefurrow
TELOPHASE IIAND CYTOKINESIS
Sister chromatidsseparate
Haploid daughtercells forming
TELOPHASE IIAND CYTOKINESIS
Comparing Mitosis and Meiosis
Mitosis
Meiosis
Which characteristics are similar for mitosis and meiosis?
– One duplication of chromosomes
Which characteristics are unique to meiosis?
– Two divisions of cells: meiosis I and meiosis II to create 4 cells instead of 2
– Occurs to create haploid gametes
– Pairing of homologous chromosomes for crossing over and across the metaphase plate in metaphase I
– Exchange of genetic material by crossing over
8.15 Mitosis and meiosis have important similarities and differences
Copyright © 2009 Pearson Education, Inc.
What is the outcome of each process?– Mitosis: two genetically identical cells, with the
same chromosome number as the original cell
– Meiosis: four genetically different cells, with half the chromosome number of the original cell
8.15 Mitosis and meiosis have important similarities and differences
Copyright © 2009 Pearson Education, Inc.
Mitosis:
Loss of Regulation/Cancer
Copyright © 2009 Pearson Education, Inc.
Cells anchor todish surfaceand divide.
When cells haveformed a completesingle layer, theystop dividing (density-dependent inhibition).
If some cells arescraped away, theremaining cells divideto fill the dish with asingle layer and thenstop (density-dependent inhibition).
G1 checkpoint
Controlsystem
M
S
G2
G1
M checkpoint
G2 checkpoint
G0
Cancer cells have genetic mutations that allow them to override these checkpoints and multiply indeterminately
Cancer cells escape controls on the cell cycle
– Cancer cells divide rapidly, often in the absence of growth factors
– They spread to other tissues through the circulatory system
– Growth is not inhibited by other cells, and tumors form
– Malignant tumors spread to other locations by metastasis
– Benign tumors remain at the original site
Growing out of control, cancer cells produce malignant tumors
Copyright © 2009 Pearson Education, Inc.
Cells anchor todish surfaceand divide.
When cells haveformed a completesingle layer, theystop dividing (density-dependent inhibition).
If some cells arescraped away, theremaining cells divideto fill the dish with asingle layer and thenstop (density-dependent inhibition).
Cancer -cells will not stop
dividing
It is estimated that 1,437,180 people will be diagnosed with and 565,650 men and women will die of cancer in 2008 in the US
No cure for cancer because of the high variability of the disease between type and individuals
Growing out of control, cancer cells produce malignant tumors
Copyright © 2009 Pearson Education, Inc.SEER Cancer Statistics
Tumors
Benign tumor is a contained mass of gradually multiplying cells resembling its tissue of origin and is seldom fatal
Can grow to be so large because they don’t metastasize
Ex. (Neither ex is always benign)
Teratoma – can grow teeth and hair
Lipoma – tumor of the adipose tissue
Man with Thigh TumorThe Gordon Museum
ALTERATIONS OF CHROMOSOME NUMBER AND
STRUCTURE
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Nondisjunction is the failure of chromosomes or chromatids to separate during meiosis
– During Meiosis I
– Both members of a homologous pair go to one pole
– During Meiosis II
– Both sister chromatids go to one pole
Fertilization after nondisjunction yields zygotes with altered numbers of chromosomes
8.21 Accidents during meiosis can alter chromosome number
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Nondisjunctionin meiosis II
Normalmeiosis I
Gametes
Number of chromosomes
n + 1 n – 1 n n
Abnormal chromosome number: aneuploidy
Trisomy 21 involves the inheritance of three copies of chromosome 21
– Trisomy 21 is the most common human chromosome abnormality
– Chromosome 21 is one of the smallest human chromosomes (containing a relatively small number of genes). This provides an explanation as to why this condition is not fatal, while a trisomy involving another, larger autosome that controls many more genes would most likely be fatal.
An extra copy of chromosome 21 causes Down syndrome
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Down syndrome An imbalance in chromosome number
causes Down syndrome, which is characterized by Characteristic facial features Susceptibility to disease Shortened life span Mental retardation Variation in characteristics
The probability of conceiving a baby with trisomy 21 increases with age of mother At maternal age 20 to 24, the probability is 1/1562
35 - 39 the probability is 1/214
>45 the probability is 1/19
Average lifespan of about 45-50 years
Most begin to suffer from dementia if they live into their 40’s or 50’s
Christopher Joseph Burke (Life Goes on and Touched by an Angel)(age 43)
Infa
nts
wit
h D
ow
n s
yn
dro
me
(per
1,0
00 b
irth
s)
Age of mother
90
70
60
50
40
30
20
10
0
80
20 40353025 5045
First described in 1942
Klinefelter's syndrome is the most common sex chromosome disorder
The principal effects are development of small testicles and reduced fertility
A variety of other physical and behavioral differences and problems are common, though severity varies and many boys and men with the condition have few detectable symptoms
The condition exists in roughly 1 out of every 500 males
Cannot fix chromosmal abnormality, but testosterone treatment is an option for some individuals who desire a more masculine appearance and identity
Klinefelter’s syndrome (XXY)
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17 year old twins with Klinefelter’s- exhibit gynecomastia and present with high pitched voices.
More aneuploidy
Male
Taller than fathers and brothers
Some studies claim are more aggressiveand likely to be in prison (debatable)
Commonly go through life without diagnosis
XXX
Female
taller than average
Commonly go through life without diagnosis
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XYY
Only syndrome in humans where having 45 chromosomes is not fatal
Usually have the genotype X0
First described in 1938
Occurring in 1 out of every 2500 girls
There are characteristic physical abnormalities, such as short stature, lymphoedema, broad chest, low hairline, low-set ears, and webbed neck
Exhibit gonadal dysfunction with amenorrhea and infertility
Approximately 98% of all fetuses with Turner syndrome result in miscarriage
Turner syndrome (XO)
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