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Flashcards in B Test N3 S7 Deck (41):

Purpose of mitosis

Normal cell division and growth, asexual reproduction and repair (i.e. skin repair, hair, zygotes etc.) where there is an increase in the number of cells that are genetically identical to the parent cell.


Purpose of meiosis

In sexual reproduction in order to produce haploid gametes, in general, with half the chromosome number and variation.


Where does mitosis take place?

In animals: everywhere (for example the nails and hair)

In plants: in the tips of the roots and shoots (the meristems)


Where does meiosis take place?

In animals: in the ovaries and testes

In plants: in the anthers and ovaries


Result of mitosis

Two daughter cells that are genetically identical to each other and the parent cell


Result of meiosis

Four genetically different cells with half the number of chromosomes


Where does variation in meiosis occur?

Crossing over at prophase I between homologous chromosomes

Random orientation of homologous chromosomes at metaphase I.

Random orientation of homologous chromosomes containing nonsister chromatids at metaphase II.


The cell cycle


G1 phase: rapid cell growth and the synthesis of organelles

S phase: the amount of DNA in the cell doubles

G2 phase: The centrioles replicate and the microtubules begin to construct the spindle


Cytokinesis in animal cells

The centre of the cell pinches to form a division furrow due to the contraction of a ring made up of actin and myosin.


Cytokinesis in plant cells

Vesicles (containing carbohydrates: pectins and hemicelluloses) produced by the Golgi body collect on the equator and fuse to form a cell plate. This cell plate stretches across the cells to form the middle lamella and cellulose builds on either side of this to form the new cell walls.


What is cancer?

Cancer is uncontrolled mitotic division.



Nondisjunction in anaphase I or II of meiosis will lead to the abnormalities in the offspring if the resulting gamete is fertilised: Down's syndrome and Turner syndrome.


Restriction enzymes

Cut DNA into small fragments at precise sequences.


Donor DNA

A gene from one organism that can be inserted into the DNA of another.


Recombinant DNA

DNA that contains genetic material from two or more different sources


DNA ligase

Joins the backbone of the sticky ends of donor DNA and the host DNA together


Uses of restriction enzymes

Manipulation of DNA in many ways for many purposes:

Health (insulin and factor 8)
Environmental (pest resistance)
Agricultural (oil spills)
Criminology and heredity (murders and paternity testing)
Evolutionary tracing


How is an organism genetically modified

- adding a gene (human insulin used to treat diabetic patients)

- altering the gene (used in gene therapy to treat genetic disorders such as cystic fibrosis)

- deleting or turning off a gene (deactivation of the right ripening gene in tomatoes)


Gene cloning dilemmas


Safety (human health and environmental impact)
Access and intellectual property


Two methods for cloning genes

The PCR: short term such as crime scenes

Vectors: bacteria for long-term such as cystic fibrosis


Cystic fibrosis cause

Inherited recessive disease caused by a defective gene resulting from the deletion of a base triplet. An amino acid is therefore omitted from the coded protein.


Cystic fibrosis consequence

Normal gene codes for protein which transport chloride irons and therefore sodium irons and water out of the cell into mucus.

Chloride irons are not transported and the mucus is thick and sticky: air passages are blocked, the pancreatic duct can become blocked, health deterioration.


Cystic fibrosis genetic treatment

Non-defective gene is isolated and cut out by restriction enzyme and cloned with the PCR.

The genes are encapsulated in tiny spheres of lipids (liposomes).

Aerosol inhaler is used to spray the non-defective gene in the epithet cells of the lungs.

Liposomes fuse with the phospholipid bilayer of the membrane and the DNA enters the affected cells


Genetic fingerprinting process

Blood sample
DNA extracted and purified
Enzymes cut DNA into fragments
Electrophoresis separates DNA fragments
Transfer of DNA to nylon membrane
Radioactive probes bind to DNA fragments
DNA probes exposed to x-ray film
Pattern of bands appear


Genetic fingerprinting use

Used to provide forensic evidence and therefore solve crimes or match heredity.


Transgenic organisms use

AAT: cystic fibrosis

Factor 8: haemophilia


Transgenic organisms misuse

BST: infertile cows, mastitis, susceptibility to disease, effect on mothers, unnatural...


Transgenic plants

Introduction of foreign genes into plant cells


Transgenic plants use

- resistance to disease: potato leaf root virus

- nitrogen fixation: in wheat and rice

- Improved quality: tomatoes for ripening


Embryo cloning

Eggs from best cows and sperms from best bulls

Fertilisation in a Petri dish

Eggs grow into embryos

Embryo is split to produce more

Embryos transplanted into surrogate cows


Nuclear transfer

Donor cells from X and cultured to stop division

And fertilised egg removed from Y and egg removed

Dormant donor cell and recipient egg cell placed together

Electric pulse triggers cell division

Embryo implanted into Y

X is born


Gene technology method

- DNA from human cells
- restriction enzyme cuts DNA
- plasmid removed and cut
- DNA ligase attaches gene to plasmid
- recombinant plasmid taken up by treated bacterium
- bacterial cells multiply


Bacterial plasmids

Used as factors as they replicate very rapidly


Marker genes

Used to indicate that new genes have been incorporated into the host cells


Thermopile enzymes

Used as they can survive at very high temperatures and therefore withstand the PCR


Embryo stage

Used embryo cloning


Host cell



Advantages of modern gene technology as opposed to previous

- economic benefit
- Health benefit (no hepatitis or HIV)


GMO's benefits

- solving global hunger
- environmental friendly
- consumer benefits


GMO examples

- tomatoes
- GM maize (resistance to insect pest)
- GM soya (herbicide tolerant)


GMO concerns

Environmental safety
Food safety
Animal health
Changes in farming structure
Decrease in biodiversity