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You and Your Genes

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by

Holly Brady

on 13 May 2013

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Transcript of You and Your Genes

You and Your Genes B1 Bacteria and other single cell organisms can reproduce by dividing to form two 'new' individuals, or clones. This is called asexual reproduction. Variation in organisms that reproduce asexually is usually caused by environmental factors. Animal clones can occur naturally, through the cells of an embryo separating, and developing into twins. sex chromosomes: Genetic Testing and Embryo Selection It is possible to test someone for a faulty allele END OF TOPIC QUIZ 1) Why are genetic tests carried out on foetuses?
2) What does IVF stand for?
3) How do sperm decide the sex of the baby?
4) What is the name of the hormone which testes start to produce 6 weeks after fertilisation?
5) What does it mean to be homozygous?
6) Which system does HD affect?
7) How many faulty alleles do you need to be a carrier of CF?
8) What does a false negative mean?
9) What is pre selection?
10) Name the two types of stem cells. Genes are sections of DNA. They
control the development of different
characteristics by issuing
instructions to the cell. The cell
carries out these instructions by
producing Huntington's Disease Huntington's is caused by a single allele
It is a genetic disorder affecting the central nervous system, caused by a faulty gene on the fourth pair of chromosomes.
It damages the brain's nerve cells
It causes gradual changes, which develop into symptoms including involuntary movement, clumsiness, memory loss, mood changes and inability to concentrate.
It is incurable and leads to premature death.
Symptoms develop in adulthood, so you may never know you have the disease until your mid 30s, and sufferers may have already passed on the gene.
HD is dominant. Cystic Fybrosis This is a recessive disease, which affects cell membranes.
It causes a thick, sticky mucus, especially in the lungs, gut and pancreas.
Symptoms can include weight loss, difficulty in breathing, chest infections and difficulty in digesting food.
There is no cure, but scientists have identified the allele that causes it.
Because it is a recessive disease, if a person possesses one allele for it, theu will have no symptoms at all, but will be a carrier.
This means they carry the allele and could pass it onto their children. The basics Asexual reproduction Into further detail... Notes Variation and Genetics key words so far... variation: differences between individuals of the same species
chromosome: long molecule found in the nucleus of all cells containing DNA
DNA: molecules that code genetic information and make up chromosomes
gene: small section of DNA of a chromosome that determines a particular characteristic
nucleus: the control centre of a cell
protein: large organic compounds made of animo acids Variation is the differences between
individuals of the same species. This
may be due to environmental factors
(scars, height etc) or genetic factors
(eye colour, hair colour etc) inside a cell nucleus... ...there are long threads of genetic information, which contain thousands of genes and are made up of DNA these are called chromosomes inside the chromosome... ...there are sections of DNA. They control how you develop and give instructions on how to make a kind of protein, these are called genes About chromosomes... They normally come in pairs both chromosomes in a pair have the same genes in the same place
human cells contain 23 pairs of chromosomes (46 in total) sex cells contain single
chromosomes sperm + egg = fertilised egg cell 23
chromosomes + 23
chromosomes = 46
chromosomes inside the gene... there are molecules which form a complete set of instructions for how each organism should be constructed and how each cell should function.

these are called DNA proteins Different types of proteins... The proteins formed inside a cell can be... structural proteins: for cell growth and repair (e.g. collagen) functional proteins: to speed up chemical reactions (e.g. enzymes such as amylase) alleles... A gene can have different versions, called alleles. For each gene, you inherit one allele from your father and one from your mother you can inherit two alleles that are the same this is called homozygous or you can inherit two alleles that are different this is called heterozygous brothers and sisters randomly inherit different combinations of alleles, which is why they can be different allelles can be dominant or recessive (the dominant allele controls the development of a characteristic, even if it's present in only one chromosome in a pair. the recessive allele controls the development of a characteristic only if a dominant allele isn't present, i.e. if the recessive allele is present on both chromosomes in a pair) the combination of alleles you have is called your genotype and the actual characteristic you show is called your phenotype. genetic diagrams These are used to show all the possible combinations of alleles and outcomes for a particular gene. They consist of a capital letters (to show dominant alleles) and lower case letters (to show recessive alleles). Also called Punnett squares or family trees). Quick Test! 1) What does heterozygous mean?

2) what type of allele needs to be present on only one chromosone to control a characteristic?

3) How many pairs of chromosomes do we have? one of the 23 pairs of chromosomes in a human body cell is the sex chromosomes. In females, the sex chromosomes are identical; both X

In males, there is an X and a Y chromsome. The Y is much shorter than the X. Half the sperm carry X chromosomes and half carry Y chromosomes. All the eggs carry X chromosomes If an X sperm fertilises the egg a girl is produced If a Y sperm fertilises the egg a boy is produced Sex-determining region Y The sex of an individual is determined by a gene on the Y chromosome called the SRY gene.

If the gene isn't present and so there are two X chromosomes present, the embryo will develop into a girl.

If it is present and so there is an X and a Y chromosome, testes begin to develop. Six weeks after fertilisation, the testes start producing a hormone called androgen. Specialised receptors in the embryo detect the androgen and male reproductive organs begin to grow. Sometimes the Y chromsome is present but androgen isn't detected. When this happens, the embryo develops female sex organs apart from the uterus and the baby has a femal body but is not fertile Diseases Quick Test!!! 1) What does it mean to be a carrier of a disease>

2) Name 3 symptoms of Huntington's Disease.

3) Which of the two diseases is recessive?

4) Which of the two diseases damages the brain's nerve cells? When adults are tested, if a positive result is obtained, they may decide on not having any children or perhaps adopting instead. They may however, decide on still having a child but just taking the risk of passing the disorder on. Children are tested to see if they have any disease causing genes, so that possible preventable measures can be taken. These tests can also carried out before the prescription of certain drugs that could have a negative efect on the individual due to their genetic make up. In this way, more effective treatment can be undertaken. The fluid surrounding the foetus or placenta can be tested for faulty alleles. This carries a small risk of miscarriage. If a faulty allele is detected, the parents have to consider whther or not to continue on with the pregnancy and whether other family members who may also carry the allele should be told. There are many ethical issues with this situation (possible effects this may have on an individual or their relationships / whether the pregnancy should be terminated) No test is 100% reliable, and so genetic testing on a foetus can have a number of outcomes (true positive, true negative, false positive and false negative). There are many issues here, for example, the test shows that the foetus has the disorder, the pregnancy is terminated, and it was healthy the whole time. The fluid surrounding the foetus or placenta can be tested for faulty alleles. This carries a small risk of miscarriage. If a faulty allele is detected, the parents have to consider whther or not to continue on with the pregnancy and whether other family members who may also carry the allele should be told. There are many ethical issues with this situation (possible effects this may have on an individual or their relationships / whether the pregnancy should be terminated) Embryo selection is another way of preventing babies from having genetic disorders. Embryos can be produced by in vitro fertilisation (IVF). This is a controversial topic as some people believe it is unnatural and there are concerns that people could select certain characteristics in advance (pre selection). This could reduce variation (e.g. if most people selected blue eyes for their baby, the brown eye allele could disappear in time). Stem cells Stem cells are unspecialised cells that can develop into different cell types.

early human embryos contain stem cells
embryonic stem cells are most useful because they can develop into any cell type found in the body embryonic stem cells adult stem cells unspecialised more flexible less likely to have mutations change into any cell type 'destroying' a life easier for scientists to control bigger number of them unspecialised less flexible likely to have mutations change into only one cell type won't be rejected by body harder for scientists to control lower numbers
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