every human cell (except 1 type) has 46 chromosomes = diploid (2n) number.review since we don’t...
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• Every human cell (except 1 type) has 46 chromosomes = Diploid (2n) number.
ReviewReview
Since we don’t want more then 46 chromosomes in our cells, then the gametes must have HALF the normal # of chromosomes= HAPLOID (n)
•The form of cell division by which gametes, with half the number of chromosomes are produced. •Diploid (2n) haploid (n)
MEIOSIS
• Meiosis is sexual reproduction
• TWO divisions (meiosis I and meiosis II
•Sex cells divide to produce gametes (sperm or egg)
•The new cells are called Haploid, they have half the number of chromosomes
• Meiosis is similar to mitosis with some chromosomal differences
Meiosis needs two divisions!
Main difference between mitosis and meiosis:Meiosis produces 4 new gametes! We need 4 gametes every division for
GENETIC VARIATION!
1. Crossing Over Occurs during Prophase I
2. Independent Assortment Occurs during Metaphase I
3. Random Fertilization Sperm joins with the egg cell
Crossing over can occur between “nonsister” chromatids
Segments of the chromatidsbreak and reattach to the otherchromatid
describes how different genes independently separate from one another when reproductive cells develop. the combinations of traits in the offspring do not always match the
combinations of traits in the parent
Assort randomly at the middle of the cell
Non disjunction is the failure of chromosome pairs to separate properly during meiosis stage 1 or stage 2
This could arise from a failure of homologous chromosomes to separate in meiosis I, or the failure of sister chromatids to separate during meiosis II or mitosis. The result of this error is a cell with an imbalance of chromosomes.
• chromatin becomes chromosomes
PROPHASE 1PROPHASE 1
• the nuclear membrane disintegrates
• homologous chromosomes pair up- crossing over may occur
the chromosomes condense
centrioles move to opposite poles of cell & begin making the spindle.
the nuclear membrane breaks down
PROPHASE 1PROPHASE 1
Each pair is assortedindependently
So this pair could have assorted like this
METAPHASE 1METAPHASE 1
So this pair could have assorted like this
•new nuclear membrane forms around each group of chromosomes forming haploid nuclei.
TELOPHASE 1TELOPHASE 1
•Now, BOTH haploid cells will begin Meiosis II
CYTOKINESIS 1CYTOKINESIS 1
•in this division, sister chromatids will separate
• the nuclear membrane breaks down
PROPHASE 2PROPHASE 2
• centrioles move to opposite poles of the parent cell
•new nuclear membrane forms around each group of chromosomes
•cytokinesis occurs
TELOPHASE 2TELOPHASE 2
Trisomy: having an extra or 3rd chromosome Many down syndrome cases can be identified
by having an extra chromosome
Women and girls with turner’s, have only one X chromosome
This is an example of monosomy
Symptoms include lack of ovarian development, short stature, webbed neck, arms that turn slightly at the elbow
Men and boys with Klinefelter have a Y chromosome and 2 X chromosomes.
This is an example of trisomy Men and boys are usually
tall, and lack secondary sex characteristics such as underarm and facial hair
Diploid – number of chromosomes in a somatic cell- 46
Haploid/ monoploid- number of chromosomes in a gamete- 23
Homologous chromosome- same size and shape
Gametes- reproductive cells- sex cells Zygote- the first cells as a result of
fertilization of the egg and sperm cell- has a diploid number of chromosomes
Gonads- the organs that make gametes
GeneSegment of DNA that controls the production of proteins
Enzymetype of protein in all living things that
changes the rate of reactions Production of enzymes is directed by genes
Cyclin protein that controls the cell cycle and is
activates the enzymes
How?
Failure to produce enzymes Overproduction of enzymes Production of the wrong enzyme
-What can happen?- Cancer: a malignant growth resulting from
uncontrolled cell division.
Results from changes in genes that control the cell cycle
Malignant TumorMass of cancerous cells, can deprive normal
cells of nutrients
Metastasis Cancer cells spread through bloodstream to
other organs of the body
Causes GeneticsEnvironmental factors ( where you live,
cigarette smoke, UV radiation, viral infections)
PreventionHealthy lifestyleDiet, avoiding alcohol, drugs, smokingProtecting from the sunCancer screening (pap smear, colonoscopy,
mammogram)
Embryonic stem cells: unspecialized cells that have the potential to become a wide variety of specialized cells.Produce every tissue in the bodyFound in embryos
Adult Stem Cells-found in the umbilical cord and bone marrow.- can produce some different types of cells but
not all Example: bone marrow stem cells can only
produce different types of blood cells.