B1- You and Your Genes

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Instructions needed for organism development are found in the nucleus [the control center for every cell.]

The instructions control how the organism develops and functions.

The basic unit for instructions is called a gene [a small section of DNA in a chromosome that determines a characteristic]

The genes are found in the DNA molecules (chromosomes) [a coil of DNA made from genes found in the nucleus]

Each DNA molecule is made from 2 strands, which forms a double helix.

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There are 2 Types Of Protiens:

1. Structural- makes Collagen for the skin.

2. Functional- makes enzymes (such as amylase) that break down starch.

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There are 2 types of Variation Factors:

1. Genetic Factors- characteristics an individual inherits from mum or dad. eg. dimples, eye colour, skin colour.

2. Enviromental Factors- characteristics that change due to the surroundings. eg. scars, hair colour, weight. [weight is an environmental and genetic characteristic, it all depends on you as a person.]

Genotype: [the combination of alleles that describe the genetic makeup of an organism]

Phenotype: [the observable characteristics an organism has]

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Body Cells usually have two copies of each gene, the copies of the gene are called alleles [an alternate version of a gene].

The alleles can either be:

 Dominant: controls the development of the characteristic even if one chromosome is present.

Recessive: controls the development only when two of the same chromosome is present (and when the dominant allele is not present).

Usually the alleles of a gene is represented by letters; if the allele is dominant the letter would be capitalised. If the allele is recessive the letter would by represented by a lower case.

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Key Words:

Homozygous: when the two alleles are the same.

Heterozygous: when the two alleles are different.

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In sex cells, the eggs are produces in the ovaries [female reproductive organ] and the sperm is produced in the testes [male reproductive organ].

In sexual reproduction, each egg and sperm carry one copy of each chromosome.

All together humans have 46 chromosomes- (23 pairs) therefore the sex cells carry half the amount (23 single chromosomes).

In fertilisation [when the sperms nuclei meets the eggs nuclei] the chromosomes fuse together and create an embryo.

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As the chromosome pairing is uncontrollable, and is done at random- the offspring (the child) is going to be different to its parents. 

This leads to variation, a major advantage of sexual reproduction. 

the child would share similarites eg. nose, eye colour to its parents depending on which characteristics have come from the mum or the dad.

It would also depend on whether the allele is dominant or recessive too.

All of these points make the child different from its parents, and its siblings (brothers or sisters).

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There are 2 ways you can present or read information about genetics:

1. Familiy Trees- used to trace the inheritance of a characterisitc (helps you work out where an illness or a faulty gene was inherited from)

2. Punnett Square Diagrams- shows the possible pairings of alleles from a sperm and an egg duing fertilisation.

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One of the 23 pairs of chromosomes in a human cell is the sexchromosome.

In females the sex chromosome is the same: ** and for Males the chromosome is XY.

The Y chromosome is much shorter than the X which can be visable when looking at all the chromosomes side by side.

You can draw a punnett square to represent the posibilites on whether the offspring is going to be a girl (**) or a boy (XY).

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The gender of the embryo is determined by the the Y chromosome.

If the Y chromosome is not present, the gender of the child will remain being a girl as the ovaries will begin to grow. If the chromosome is present, then testes will begin to grow resulting in the gender of the child to be a boy.

Six weeks into fertilisation, a hormone called androgen will start to produce which stimulates the male reproductive system to start to grow.

Sometimes, the Y chromosome is present but the androgen may not be, therefore the embryo will develop into a female (having all organs except the uterus) resulting in an infertile female body.

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Most disorders are caused by a reccesive gene, but when one faulty gene (may be dominant) is present, the human/embryo will have a specific disorder.

There are 2 types of disorders:

1. Huntingtons Disease- caused by a single dominant faulty gene.

2. Cystic Fibrosis- caused by two faulty recessive alleles.

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• A Genetic disorder that affects the central nervous system.
• Caused by a faulty dominant allele on Chromosome 4
• The disease damages nerve cells in certain areas of the brain.
• Leads to physical, mental and emotional changes shown as symptoms.
• The symptoms usually develop during adulthood, meaning that the sufferes who have already had children have passed along the gene.
• Symptoms- clumsiness, memory loss, mood swings, unability of concentration.
• Everyone who inherits the Huntingtons allele will develop the disease, due to the fact that the allele is dominant. This means that only one parents needed to have the gene to pass it on to the child for them to have the disorder.

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• A Genetic disease that affects the cell membrane which produces a thick mucus substance in the lungs, gut and pancreas.
• Other symptoms of cystic fibrosis are difficulty breathing, increased number of chest infections and diffculty digesting food.
• There is no cure of this, but the scientists have begun to find ways in which they can repair and replace the faulty gene.
• Unlike Huntingtons Disease, the condition is created by two recessive genes. They can pass on the gene but unless both parents have the condition, the child is safe from the disease and they will just remain a carrier. 

They could test adults, children and embryos for faulty genes if there is a family disorder of a genetic disorder.

if the test comes out positive, the indiviual will have to now decide whether or not to have children as they will now start to pass on that specific gene for a disorder. This is called: Predictive Testing for Genetic Diseases

IVF [In Vitro Fertilisation]- Embryos can tested for embryo selection. the healthy embryos that dont have the faulty gene then gets implanted back into the mothers uterus for her to continue her pregnancy.

Pre-Implantation Genetic Diagnosis- the procedure for embryo selection. After fertilisation, the egg splits up into eight cells, they would all then get tested to see whether they carry the faulty gene or not. The result may be inaccurate and lead to the healthy embryo not being implanted, the embryo may not survive.

There are two ways to carry out a test on a developing fetus:

1. Amniocentesis Testing: carried out at 14-16weeks of pregnancy, a needle gets inserted into the uterus and a small sample of amniotic fluid gets extracted. That fluid gets tested as it carries cells from the embryo. If the embryo has the disease, it could get terminated (if decided on). The test could give the mother a higher risk of miscarraige or even an infection.

2. Chorionic Villus Testing: carried out at around 8-10weeks of pregnancy. A catheter ges inserted up into the vagina and cervix until it reacges the placenta. Chorionic Villi [finger like things] gets removed from the placenta and they are what get tested. If disorder is detected, you could also terminate the embryo (if decided to) and like the Amniocentisis Testing, the mother gains a higher risk of miscarriage.

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As no test is 100% reliable, genetic testing has 4 possible outcomes:

1. True Positive- Test result: Subject has the disorder. Reality: Subject has the disorder.

2. True Negative- Test result: Subject does not have the disorder. Reality: Subject does not have the disorder.

3. False Positive- Test Result: Subject has the disorder. Reality: Subject does not have the disorder.

4. False Positive- Test Result: Subject does not have the disorder. Reality: Subject has the disorder.

Ethical Decisions- process in which you evaluate and think about al the posible outcomes and decisions. eg. would you continue having children, should the mother terminate the embryo if still pregnant?

There is a difference between what can be done [technically possible] and what should be done [morally acceptable].

When genetic testing is done, they can be put together to create a genetic profile which contains information about their personal ethnicity to their visable characteristics.

Unfortunatly, employers could potentially refuse certain people due to their genetic information and the insurance one may have may be affected as some have a gene which could constantly make them ill. eg. a gene that would raise risk of suffering from a heart attack.

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When a cell grows and divides into two; it is a form of reproduction. As it doesnt involve se it is called ase ual reroduction.

All bacteria reproduce ase ually, same with plants and some animals. As they are formed by the 'mother' cell dividing into two 'daughter' cells the genes are exactly the same.

When an organism has the exactly same genetic information as another individual it is called a clone.

Plants such as strawberries produce shoots called Runners, they would then break off and become a new strawberry plant. Thos runners would eventually break off and then become a new strawberry plant (a clone of the original).

The following plant would then grow a bulbs which then get planteed to also grow genetically identical plants. 

Clones of animals happen nturally duing the early stages of fertilisation. teh developing embryo would get divided into two which creates identical twins.

You can now also make clones artifically by taking the nucleus from an adult body and putting it in a empty unfertillised egg cell. 

Stem Cells: cloning depending on the cells that have potential to become any cell type in a body.

Adult stem cells are unspeciallised that develop into many types of cells.

Embryonic stem cells are unspeciallised cells that can develop into ANY type of cell, includig more of the same (embryonic stem cells)

The stem cells can be used to treat some injuries and illnesses. after the zygote has divided four times to reach the 16 cell stage, the majority of the cells in an embryo become specialised.This means that the production of of protiens that are specific to the specialised cell type is encouraged. 

Specalised cells can only divide to produce the same type of specialised cell.