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Flashcards in Mitosis and Meiosis Deck (52):

Where are chromosomes found?

Animal and plant nuclei


What occurs just before cell division?

DNA is replicated and more histone proteins are synthesised, leading to temporarily twice the normal amount of chromatin in the cell.


What does chromatin do following replication?

Coils up even tighter, becoming shorter and fatter and forming chromosomes.


How is each chromosome shaped and why?

Roughly X shaped because it contains 2 replicated copies of the DNA. The 2 arms of the X are therefore gentically identical and are known as chromatids. They are joined at a centromere.


When are chromosomes visible?

Only when dividing so we only can see them in their replicated, double-stranded form


What are karyotypes?

The display of chromosomes stained, with fluorescent dye.


What are homologous pairs?

The pairs that chromosomes come in with same size, shape and banding pattern.


What are autosomes?

Non sex chromosomes- humans have 22 pairs


What is the different pair of chromosomes in males and females?

Sex chromosomes- homologous in females (XX)
Non-homologous in males (XY)


Why do we have 2 copies of each chromosome?

We inherit 1 from each parent, so homologous pairs consist of a maternal and paternal version of the same chromosome.


What are most cells in the body?

Somatic cells, contain homologous chromosome pairs


What are diploid cells?

Cells that contain 2 sets of chromosomes (2n)


What are haploid cells?

Cells that have only 1 chromosome set (n)


What type of cells are somatic and what do they contain in humans?

Diploid- 23 pairs


What type of cells are gametes and what do they contain in humans?

Haploid- sex cells produced in testes and ovaries, contain 23 chromosomes


What is cell division?

The process whereby a cell splits to form daughter cells.


What are the 3 main stages of the cell cycle?

•Interphase-period of synthesis and growth.
•Mitosis/meiosis- period of nuclear division.
•cell division-process of division of the cytoplasm into 2 daughter cells (known as cytokinesis).


What is the largest stage of the cell cycle and how much does it make up?

Interphase- about 90%


What are the stages of mitosis (PMAT)?

Telophase (inc. cytokinesis)


What occurs during the interphase?

•DNA replicated
-new organelles sythesised
-active process so ATP production
-protein sythesis producing more histone proteins


How does interphase appear in a diagram?

Scribbles in central nucleus. Scribbles = chromatin.


What occurs during the prophase?

-nuclear envelope + nucleolus disappears.
-duplicated chromatin condenses to form chromosomes which join at a centromeres so can now be called a pair of sister chromatids.
-in animal cells, centrioles move to opposite poles of the cell.
-spindle fibres start to form


How is the prophase shown in a diagram?

Chromosomes joined at centromere visible and scattered.
Partially formed spindle fibres visible.
Disintegrating nuclear membrane seem


What are chromosomes made of?

A single molecule of DNA tightly wrapped around proteins to form chromatin.


What happens in the metaphase?

Chromosomes randomly line up at cell's ewuator.
-they attach to the spindle fibres by their centrosomes.
*relatively short so difficult to observe on a slide section


How is metaphase shown in a diagram?

Chromatids along equator, spindle fibres run from centromeres to membrane.


What happens in the anaphase?

-centromeres divide and spindle fibres contract
-this separates the sister chromatids to the opposite poles of the cell (centromere first)
Called chromosomes once separated


How is the anaphase shown on a diagram?

Separated chromatid pairs are being pulled to opposite poles by contracted spindle fibres, centromere leading.


What occurs during the telophase?

-the chromosomes reach the poles + uncoil to form chromatin.
-the spindle fibres break down
-a nuclear envelope + nucleolus forms around each set of chromosomes.


How is telophase shown in a diagram?

Looks like two separate nuclei in a cell with breaking down spindle fibres inbetween


What happens in cytokinesis in animals?

The cell divides due to constriction of the centre of the parent cell from the outside inwards, producing a cleavage furrow.


What happens in cytokinesis in plants?

The cell divides by growth of a growth plate across the centre of the parent cell from the centre outwards.


How does cytokinesis appear in a diagram?

Looks like two cells separating.


What are the 3 significant uses of mitosis?

Repair of damaged tissues
Asexual reproduction


How is mitosis good for growth?

As multicellular organisms grow, the number of cells making up their tissues increases. New cells must be genetically identical to existing ones.


Mitosis for repair of damaged tissue with example:-

Damaged cells must be replaced by exact copies of the originals. E.g skin cells are constantly shed and must be replaced.


Mitosis for asexual reproduction 2 examples:-

Producing plants like tulips.
Bacteria, fungi and yeasts- it allows a rapid increase in numbers, advantageous when colonising new habitats.


How can cancer occur?

Cancer occurs as a result of mutations during DNA replication (interphase) can lead to the formation of groups of cells called tumours.


What are the genes involved with cancers classed as?

Proto-oncogenes or tumour supressor genes.


How do proto-oncogenes cause cancers?

Encode proteins that function to stimulate cell division, inhibit cell differentiation and halt cell death.
-Mutated version is called an oncogene- results in increased protein prod, increased cell division and inhibition of cell death.
This results in the formation of tumours.


How do tumour supressor genes work?

-can restrain inappropriate cell growth and division as well as stimulating cell death to help keep our cells in proper balance- this acts as a 'brake' to cells from becoming cancerous.
-when TS cells mutate function is lost and so leads to uncontrolled cell division.


What does meiosis do?

Occurs in diploid cells during gamete formation.
Involves 2 consecutive cell divisions and produces four haploid daughter cells from a single parent cell. Consecutive cell divisions referred to as meiosis I and meiosis II.


Where do the main differences between mitosis and meiosos occur?

Between mitosis and meiosis I as mitosis and meiosis II are almost identical


What is it important to remember about Prophase 1?

Chromatid of one chromosome crosses over with another, swapping genetic info?


What is independent assortment?

The random way chromosomes arrange themselves at the equator.


How is Prophase I different to mitosis' prophase?

Homologous chromosomes pair up to form bivalents.
Chiasmata form and crossing over may occur, giving rise to genetic variation.


How is metaphase I diff to mitosis metaphase?

Homologous chromosome pairs (bivalents) randomly line up SIDE BY SIDE at cell equator.


How is anaphase I different to mitosis' anaphase?

-centromeres don't divide
-so whole chromosomes are pulled to opposite poles of cell, not chromatids.
-chromosomes may not be genetically identical due to crossing over.


How is telophase I diff?

-half no. of chromosomes present in daughter cells
-1 pair of homologous chromosomes present in daughter cells.
-no uncoiling to form chromatin


How does interphase II work?

-in some species may be a slight delay pre meiosis II, in many is simply absent.


What uniquely occurs in prophase II?

Spindle forms at right angles to meiosis I's spindle.


What are the 4 points genetic variation can occur?

-random gamete fusion during fertilisation.
-Prophase I crossing over= homologous pair of chromosomes in a bivalent swap genes at the chiasmata
-independent assortment (metaphase I)
-natural selection (genetic variation within a population = longterm survival)