Ch.9: Cell Division-Meiosis

STUDY
PLAY

Terms in this set (...)

Chromatid
A copy of a chromosome
Unreplicated vs Replicated
Unreplicated: 1 chromatid

Replicated: 2 chromatids attached to each other
Meiosis
Two rounds of cell division called Meiosis I and II
What is the purpose of Meiosis I?
Reduce the chromosome number in half (diploid to haploid)
What is the purpose of Meiosis II?
Separate replicated chromosomes
Prophase I
Crossing Over generates diversity

Each homologous pair exchanges information

Chromosomes are fully coiled and condensed

They are in replicated form

The nuclear membrane starts breaking down

Spindle fibers start to form

Four replicated chromosomes

Two homologous pairs
Metaphase I
Chromosomes align in homologous pairs down the center of the cell

Spindle fibers assist

Four replicated chromosomes

Two homologous pairs

Spindle fibers pull from each side

Four replicated chromosomes
Telophase I and Cytokinesis
Chromosomes are divided up

Nuclear membranes need to reform

Cytokinesis must occur

End result:

Two daughter cells

Two replicated chromosomes

Do not look identical to parent cell
Why is meiosis II required?
At the end of meiosis I we have two haploid cells

They both still have replicated chromosomes

The purpose of meiosis II will be to separate the chromatids so that the daughter cells have unreplicated chromosomes

This round looks like mitosis
Prophase II
Chromosomes are fully coiled and condensed

Replicated form

Nuclear membrane starts breaking down

Spindel fibers start to form

Two replicated chromosomes per cell
Metaphase II
Chromosomes align single file down the center of the cell

Spindle fibers assist

Two replicated chromosomes per cell
Anaphase II
Spindle fibers pull from each side

Sister chromatids are pulled apart

Four unreplicated chromosomes per cell
Telophase II and Cytokinesis
Chromosomes are now divided up

Nuclear membranes need to reform

Cytokinesis must occur

End result:

Four daughter cells

Two unreplicated chromosomes

They do not look like parent cell
Spermatogenesis
Creation of sperm
Oogenesis
Creation of eggs
How do you detect mistakes in meiosis?
Karyotype: provides a picture of chromosomes from a single cell for analysis

Only shows major chromosomal abnormalities

Cells can be collected via:

amniocentesis-amniotic fluid

chronic villus sampling (CVS)-tissue from placenta

blood samples-from fetal cord blood
Nondisjunction
A mistake in meiosis that leads to a gamete having the wrong number of chromosomes
-Too many or too few

Unequal distribution of chromosomes during meiosis

The resulting gametes have zero or two copies of a chromosome rather than a single copy

Not uncommon
Trisomy
A zygote/embryo with an extra chromosome
Monosomy
A zygote/emyro with a missing chromosome
Down Syndrome
Trisomy 21

Developmental and physical abnormalities
Turner Syndrome
Genotype: X

Offspring Genotype: X

Characteristics:

Short height

Web of skin between neck and shoulders

Underdeveloped ovaries; often sterile

Some learning difficulties

1 in every 2,000
Klinefelter Syndrome
Genotype: XXY

Offspring Genotype: XXY

Characteristics:

Underdeveloped testes

Lower testosterone levels; usually infertile

Development of some female features

Long limbs and slightly taller than average
"Super Males"
Genotype: XYY

Offspring Genotype: XYY

Characteristics:

Taller than average

Moderate to severe acne

Intelligence may be slightly lower than average

1/1000 live births
"Meta females"
Genotype: XXX

Offspring Genotype: XXX

Characteristics:

May be sterile

No obvious physical or mental problems

Web of skin

Constriction of aorta

Poor breast development

Under developed ovaries

Triple X Syndrome/Trisomy X

1 in 1,000 females