chromosomes, mitosis, and meiosis chapter 8 do now what is dna? where are your chromosomes located?...
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Chromosomes, Mitosis, And Meiosis
Chapter 8
Do Now
What is DNA?
Where are your chromosomes located?
How many chromosomes do humans have?
DNA
DNA – deoxyribonucleic acid
Long, thin molecule that stores genetic information
Made up of nucleotide building blocks
(Adenine, Guanine, Cytosine, Thymine)
DNA in a human cell has approximately 6 billion pairs of nucleotides
Chromosomes – rod shaped structures made of DNA and protein
Chromosomes
1. Contained in nucleus
2. When cell is not dividing, genetic info is kept in uncoiled DNA called chromatin
3. When a cell begins to divide the single DNA molecule coils around proteins called histones to form chromosomes
Chromosome Structure4. Non-histone proteins control
activity of specific DNA sequences
5. Each chromosome has two identical parts called – sister chromatids
5. The point at which they meet is called a centromere
6. Division-one chromatid from each chromosome/new cell
Info about Chromosomes
1. Entire human genome mapped – found chromosome location of approximately 23,000 genes
2. Above the centromere is the “p” region (small)
3. Below the centromere is the “q” region (large)
Chromosome Numbers
1. Every Species has a different number of chromosomes
2. Humans have 46 (23 pairs) a. 22 autosomes (do not determine the sex)b. 1 pair sex chromosomes (determine the
sex)3. Females have 2 X chromosomes, males
have an X and a Y chromosome
Haploid/Diploid
1. Homologous chromosomes (paired chromosomes) are the same size and shape and carry genes for the same traits
2. Cells with both chromosomes of a homologous pair are considered diploid (2N) – body cells - somatic cells
3. Cells with one of the two chromosomes is considered haploid (N) – sex cells
Haploid/Diploid
Karyotype
An arranged photomicrograph of chromosomes that helps determine problems in chromosome # or deletion
Karyotypes describe the number of chromosomes, and what they look like under a microscope
Attention is paid to:
chromosome length
position of the centromeres
banding pattern
differences between the sex chromosomes
Do Now
What are chromosomes made of?
What does haploid mean?
What does diploid mean?
Down’s Syndrome
Trisomy 21– 3 copies of chromosome 21 instead of 2
1 in 900 births
More common with older mothers
Some impairment of cognitive ability and physical growth
A particular set of facial characteristics
Down’s Syndrome
Turner Syndrome
Female missing one X chromosome (X0)
1 in every 2500 girls Infertile – ovaries do not develop Other female characteristics do not
develop Decreased height
Kleinfelter’s Syndrome
Male with an extra X chromosome (XXY)
Occurs in 1 out of every 1700 men Testicles do not form properly –
infertile Delayed motor function and muscle
formation Increased height, increased tiredness
Kleinfelter’s Syndrome
II. CELL DIVISION
*Virchow – all cells are derived from pre-existing cells
*Cell division - the process by which cells produce offspring cells
*It is very different for prokaryotes and eukaryotes
Cell Division in ProkaryotesBinary fission – division of a prokaryotic cell into two offspring
Single chromosome copies itself
Cell grows to 2X its size
Cell wall forms between the 2 chromosomes
Each new cell is identical
Mitosis - cell division in eukaryotes
Division of a cell’s nucleus that produces a genetically identical cell
It does not change the amount of DNA in a cell
Mitosis occurs in the reproduction of unicellular organisms and in the addition of cells to a tissue or organ of a multicellular organism
Cell Cycle
Repeating set of events that make up the life of the cell
Consists of: mitosis - cell division interphase G0 Phase – cell exits the cell cycle and
does not prepare for another division (nerve cells)
Cell Cycle
Interphase
1. Takes up 80-90% of cells lifespan2. Three distinct parts:
a. G1 (Growth Phase) – cell doubles in size, organelles double in number
b. S1 (Synthesis Phase) – chromatin replicates
c. G2 (Growth Phase) - rapid growth phase – prepare for next division
Do Now
What is cell division in prokaryotes called?
What is cell division in eukaryotes called?
What are the 4 main phases of the cell cycle?
Mitosis
1. 4 phases: Prophase, Metaphase, Anaphase, Telophase
Prophase
1. Chromatin coils and forms chromosomes, nucleolus and nuclear membrane disappear, centrosomes and spindle fibers appear
Metaphase
1. Chromosomes line up at center, or equator of cell
Anaphase
Spindle Fibers pull chromosomes towards poles of cell
Telophase
1. Centrioles and Spindle fibers disappear
2. Chromosomes unwind, and nuclear membrane and nucleolus forms in each cell
Mitosis in Plant Cells (onion)
Cytokinesis
1. Takes place after mitosis
2.Cytoplasm and organelles split and form two daughter cells
3. Each cell receives and identical
copy of the original cell’s
chromosomes and ~ half
of the cytoplasm and organelles
Do Now
What are the 4 stages of mitosis?
What are the structures that pull the chromosomes toward opposite ends of the cell?
How does cytokenesis differ in animals and plants?
Meiosis – reduction division
Process of nuclear division that reduces the # of chromosomes in each new cell to half of the original cell
This is necessary in reproductive cells called gametes so that they can fuse and form a zygote with a normal # of chromosomes
Example – human egg (haploid -1n) and sperm (haploid -1n) form an embryo (diploid -2n)
Meiosis
A. Two nuclear divisions take place
1. Meiosis I – homologous chromosomes are separated
2. Meiosis II – chromosomes are separated into chromatids for each haploid cell
3. 4 haploid cells are produced - gametes
Meiosis I – DNA copies itself just before beginning
Prophase I - similar to mitosis: DNA coils into chromosomes nuclear membrane and nucleolus disassemble spindle fibers appear
THEN Every chromosome lines up with its homologue
and forms a tetrad Synapsis – pairing of homologous
chromosomes – does not occur in mitosis
Meiosis Helps Genetic Diversity
A. During Prophase I, homologous chromosomes line up forming a tetrad
B. Chromatids can exchange pieces, called crossing – over
C. Genetic recombination results
Meiosis I
Metaphase I Tetrads line up randomly along the midline of
the cell Spindle fibers attach to centromeres and poles
of cell
Meiosis I
Anaphase I Each homologous chromosome moves to an
opposite pole of dividing cell Independent assortment – the random
separation of homologous chromosomes Genetic recombination occurs again due to
random separation of maternal (mom’s) and paternal (dad’s) chromosomes
Meiosis I
Telophase I Chromosomes reach the opposite ends of the
cell Cytokinesis begins New cells are now haploid (1n):
they contain only one homologue from each homologous pair
But they have two copies of each chromosome because the DNA copied itself right before beginning Meiosis I
Meiosis II
DNA does not copy itself before Meiosis II
Occurs in both cells formed in Meiosis I
Exactly like mitosis
Results in four new cells from each cell that began Meiosis
Each new cell (haploid – 1n) has half the number of chromosomes as the original cell (diploid – 2n)
Gamete Formation
Meiosis produces haploid reproductive cells called gametes
Meiosis only occurs in cells of the reproductive organs
Humans: Oogenesis - female ovaries produce 1 egg and 3
polar bodies (disintegrate) Spermatogenesis - male testes produce 4 sperm
Oogenesis
Spermatogenesis
Asexual Reproduction
• Production of offspring from one parent:• no union of gametes• no genetic diversity• offspring genetically identical
• Unicellular organisms -binary
fission or mitosis• Multicellular organisms - budding
Sexual Reproduction
Production of offspring through meiosis and the union of egg and sperm
Offspring are genetically different from parents
Sexual Reproduction
Except in identical twins, offspring are unique combinations of their parents’ genes
Gives an evolutionary advantage in an environment that can change – survival of the fittest
Sexual Reproduction
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