Mitosis is when cells divide to produce identical daughter cells (non-sex cells).
Stages of Mitosis
Prophase
~ Chromosomes condense, become shorter and thicker
~ The centrioles move to opposite poles of the cell
~ Spindle fibers start to form
Metaphase
~ Chromosomes line up at the equatorial plate
~ Nuclear membranes completely dissolve
Anaphase
~ Spindle fibers pull each chromatid towards the poles
~ All the chromatids end up at opposite ends of cell
Telophase
~ Chromosomes lengthen again
~ Spindle fibers dissolve
~ Nuclear membrane forms
Meiosis is the production of sex cells, so no two cells are the same.
Stages of Meiosis
Prophase I
~ Homologous pairs come together (synapsis)
~ They intertwine and genetic information is exchanged (crossing over)
Metaphase I
~ Chromosomes line up in pairs along the equatorial plate
Anaphase I
~ Homologous pairs are pulled to opposite ends of the cell
~This forms two cells with 23 chromosomes each
Telophase I
~ Nuclear membrane forms again
~ The chromosomes are still composed of sister chromatids
Prophase II
~ New spindle fibers form
~ Centioles move to opposite poles
Metaphase II
~ Chromosomes line up at the equatorial plate
Anaphase II
~ Sister chromatids of each chromosome separate
~ They move to opposite poles
Telophase II
~ Chromosomes have been reduced to half
~ Cells have become gametes
~ Cytoplasm separated leaving four haploid cells
3 Reasons Cells Divide
1. Growth
2. Tissue repair and healing
3. Reproduction
Comparing Mitosis and Meiosis
~ Mitosis results only in clones of the original.
~ Both daughter cells in mitosis are genetically identical to each other and the parent cell.
~ Meiosis results in four cells that are different from each other and the parent cell.
How Meiosis Causes Variation
1. Crossing over during prophase I (exchanging genes)
2. Metaphase I, chromosomes are randomly assorted.
3. During fertilization different combinations of chromosomes and genes occur when 2 gametes unite.
Comparing Mitosis and Meiosis
~ Mitosis results only in clones of the original.
~ Both daughter cells in mitosis are genetically identical to each other and the parent cell.
~ Meiosis results in four cells that are different from each other and the parent cell.
How Meiosis Causes Variation
1. Crossing over during prophase I (exchanging genes)
2. Metaphase I, chromosomes are randomly assorted.
3. During fertilization different combinations of chromosomes and genes occur when 2 gametes unite.
Abnormal Mitosis
Abnormal mitosis in cells results in cancer.
Healthy cells divide when needed until instructed by nucleus to stop. Cancer cells divide at rates far greater then normal cells.
Abnormal Meiosis results in non-disjunction.
Non disjunction (Autosomes)
~ Trisomy 21 - Downs Syndrome
~ Trisomy 18 - Edwards Syndrome
~ Trisomy 13 - Patau Syndrome
In Sex Chromosomes
~ XXY - Klinefelter
~ XYY - Jacobs
~ XXX - Triple x
~ X - Turners
~ Trisomy 21 - Downs Syndrome
~ Trisomy 18 - Edwards Syndrome
~ Trisomy 13 - Patau Syndrome
In Sex Chromosomes
~ XXY - Klinefelter
~ XYY - Jacobs
~ XXX - Triple x
~ X - Turners
Trait Inheritance
Punnet squares are a way people can find out genotypes. The genotype can either be homozygous dominant, heterozygous dominant, or homozygous recessive.
Here is a video that shows an example of crossing eye colour.
Dominant
|
Recessive
|
Widow's peak
|
Straight hair line
|
Dimples
|
No dimples
|
Unattached earlobe
|
Attached earlobe
|
Cleft chin
|
Smooth chin
|
Straight nose
|
Turned up nose
|
Tongue roller
|
Can't tongue roll
|
Straight thumb
|
Hitchhiker's thumb
|
Freckles
|
No freckles
|
Curly hair
|
Straight hair
|
A and B blood type
|
O blood type
|
Webbed fingers
|
Separated fingers
|
Dark hair
|
Lighter hair
|
Oval shaped face
|
Square shaped face
|
Long eyelashes
|
Short eyelashes
|
Ability to move ears
|
Can't move ears
|
Dwarfism
|
Standard height
|
Crooked teeth
|
Straight teeth
|
Large nose
|
Small nose
|
Immune to poison Ivy
|
Susceptible to poison Ivy
|
Thick hair
|
Thin hair
|
There is also Dihybrid crosses, when 2 traits are crosses. Here is a video explaining that...
Now you have seen crossing, and the difference of dominance and recessive. There is also something called co-dominance, and incomplete dominance.
Co-dominance is when both alleles are expressed a the same time, but they do not blend.
Incomplete dominance is when both the alleles blend.
Besides using Punnet Squares, Pedigree charts are also used a lot in genetics.
They allow you to trace traits throught the family, and be able to see how they are passed on.
Here is an example of one.
Co-dominance is when both alleles are expressed a the same time, but they do not blend.
Incomplete dominance is when both the alleles blend.
Besides using Punnet Squares, Pedigree charts are also used a lot in genetics.
They allow you to trace traits throught the family, and be able to see how they are passed on.
Here is an example of one.
