meiosis
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Meiosis. Homologous Chromosomes. In the body cells, or somatic cells , of animals and most plants, chromosomes occur in pairs. One from mom, one from dad Pairs are called homologous chromosomes - PowerPoint PPT PresentationTRANSCRIPT
Homologous Chromosomes
In the body cells, or somatic cells, of animals and most plants, chromosomes occur in pairs.One from mom, one from dadPairs are called homologous
chromosomes
Normal body cells are diploid
cells because the nave the full number of chromosomes, or 2n. In humans, 2n = 46.
Organisms that reproduce sexually need special sex cells that contain half the normal number of chromosomes. Sex cells are called gametes. These gametes are haploid cells and
have the n amount of chromosomes.In humans, n = 23.
Homologous Chromosomes
Match up the homologous chromosomes
How many autosomes are found in the human the body cell?
Meiosis
Meiosis is a two-part cell division process that produces gametes or sex cells.four daughter cells all daughter cells are haploid chromosomes are shuffled in the
process, so that each daughter cell has a unique combination of genes (crossing over)
http://www.sumanasinc.com/webcontent/anisamples/majorsbiology/meiosis.html
Crossing Over
To make things more interesting, crossing crossing overover can occur.
During prophase, the homologous chromosomes form tetrads.
Crossing Over
Crossing over takes place when two chromosomes break and then reconnect but to different end piece.
Crossing over increases the number of variations that can exist in offspring.
Fertilization
Male sex cells are called sperm.Female sex cells are called eggs.When two sex cells unite,
fertilization occurs.A fertilized egg is called a zygote.This is the first cell of the new
offspring!
NondisjunctionAlthough the events of meiosis usually
proceed accurately, sometimes an accident occurs and the chromosomes fail to separate correctly. This is known as nondisjunction.
The zygote that has been created will have an extra or missing chromosome. This would result in an inherited genetic disorder.
o In most cases, the presence of an additional chromosome or missing chromosome results in the death of the zygote.
Nondisjunction
Karyotypes
When you are born, doctors take a sample of your blood and create a karyotype. This will enable the doctor to see if you have any additional or missing chromosomes.
A karyotype is a standardized arrangement of all the chromosomes of a cell.
Karyotypes
Homologous
chromosomes are
paired up, then they are put in order from
the LARGEST chromosome pair to
the smallest.
KaryotypesEverything okay here??
What gender??
2 different sized sex chromosomes = XY = male2 different sized sex chromosomes = XY = male
Down’s syndrome
•decreased muscle tone at birth•asymmetrical or odd-shaped skull•round head with flat area at the back of the head•slanting eyes•small mouth with protruding tongue •single crease on the palm•slowed growth and development•delayed mental and social skills
Everything okay here??
Turner’s syndrome
short stature (affects almost all girls with Turner, to different degrees)
failure of ovaries to develop (90-95% of girls)
webbed neck (25%) or short neck (40%) abnormal fingernails and toenails (70%) hearing disorders (50-90%) frequent ear infections in childhood (75%)
Everything okay here??
Kleinfelter’s syndrome
No symptoms - some men are unaware they have an extra chromosome
Enlarged male breasts - only severe in about 10% of cases
Sparse facial hair Sparse body hair Inability to produce sperm Tallness - more likely to be taller than non-XXY
males. Thinness Normal intelligence Language impairment Delayed language
Patau’s Syndrome
Mental retardation, severe Seizures Small headScalp defects (absent skin) Small eyes (microphthalmia) Cleft lip and/or palate