Meiosis

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.

Chromosome numbers

Do all organisms have the same number of chromosomes?

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.

Crossing Over

Which of the following did crossing over ONLY take place?

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.

Karyotypes

2 x chromosomes = GIRL

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??

Turner’s syndrome

Kleinfelter’s syndrome

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

Kleinfelter’s syndrome

Patau’s syndrome

Everything okay here??

Patau’s Syndrome

Mental retardation, severe Seizures Small headScalp defects (absent skin) Small eyes (microphthalmia) Cleft lip and/or palate

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