- Huntington's disorder is an inherited disorder, it is not contagious but is passed from parents to children. The symptoms (twitching,forgetfulness) don't appear until middle age. It is fatal
- Every human body cell has 23 pairs of chromosomes, which contain pairs of genes
- Parents pass on genes through their sex cells. Men through sperm, women through eggs or ova. Sex cells contain half the parents' chromosomes. When a sperm fertilizes an egg, the fertilized ova contains a full set of chromosomes.
- Sex cells are made with copies of half of a parents chromosomes, this means that the fertilized egg has 23 pairs of chromosomes. One chromosome from each pair is from the sperm cell, the other from the egg cell
- Each chromosome contains thousands of genes. The fertilized ova has a mixture of parent genes, half from mum, half from dad
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The Human Lottery
- Most features are affected by more than gene
- Both chromosomes in a pair carry genes that control the same features, each pair of genes is in the same place on each chromosome
- Genes in a pair may not be the same, they may be slightly different versions. Alleles are different versions of the same gene
- The gene that controls dimples has 2 alleles,the D allele gives dimples, the d allele doesn't. The D allele is dominant, you only need one copy to have it's feature. The d allele is recessive, you must have two copies of the allele to have the feature
- Sex cells get one chromosome from each pair the parent has, so they have one allele from each pair. So if they have DD alleles, it is certain they will pass a D allele to their child. But if they have Dd, it is not certain
- Brothers and sisters are different because they get a different mixture of alleles from their parents. Each 1 of us has a unique set of genes, except for identical twins.
- Huntington disorder is caused by dominant allele.
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- Cystic fibrosis is a genetic disorder that causes breathing and digestion problems. Cells that make mucus don't work. The mucus is thicker and blocks the lungs. People with CF get breathless and often get chest infections.
- Most people with CF can't have children, the mucus affects their reproductive systems. So babies with CF are born to healthy parents.
- CF symptoms are caused by a faulty recessive allele. So a person who has 1 dominant allele and 1 recessive will not have CF but they will be carriers.
- The children of carriers may have CF.
- CF cannot be cured but can be treated with physiotherapy.
- CF can be prevented if during pregnancy fetal cells are collected and examined. If the fetus has the alleles for CF, parents may end the pregnancy with an abortion.
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Male or Female
- A fertilised human egg cell has 23 pairs of chromosomes. Pair 23 are sex chromosomes. Male have an X and a Y chromosome, females have 2 X's.
- When sex cells are made they get 1 chromosome from each pair. So half a mans sperm cells get an X and half get a Y. All a woman's egg cells get an X.
- When a sperm cell fertilizes an egg there is a 50% chance it will be an X or Y, a 50% chance of a boy or girl.
- A male embryo's testes develop when it is 6 weeks old. This is caused by a gene on the Y chromosome - the SRY gene.
- Testes produce the male sex hormone androgen which makes the embryo develop into a male. If there is no androgen present the embryo is a female.
- Hormones are another group of proteins. They control many processes in the cells and are made by different parts of the body.
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The Same and Different
- Children look a lot like their parents, they have inherited information from them.
- Almost all of your features are affected by inherited information but some are also affected by your environment.
- Living organisms are made up of cells, which contain nuclei, inside the nucleus of a cell are long threads called chromosomes. Each chromosomes contain 1000 of genes which control development.
- Chromosomes are made of DNA.
- A fertilized egg has the instructions for making every protein in a human, genes are instructions.
- Proteins are important, there are many different proteins in the body and each does a different job. Structural proteins build the body and enzymes speed up chemical reactions in cells.
- Genes control the proteins a cell makes, this is how they control the cell.
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Ethics- making decisions
- When a person has to make a decision about what is right or wrong, they are thinking about ethics. Some ethical questions are simple to answer, but some are more complex, like having a termination
- Genetic testing can be used to look for alleles that cause specific disorders
- Genetic tests are not completely reliable. A False Negative is when the test doesn't detect an allele when it is there. A False Positive is not as common, but may happen
- Most people only have a genetic test when they know a genetic disorder runs in the family. Testing the whole population for an allele is called genetic screening
- Genetic screening decisions are made by the government and the NHS. They have to think about the costs and the benefits
- At first glance, genetic screening may seem best for everybody, but the best decision for the majority isn't always best for everyone
- Many people think that only you and your doctor should know test results. Employers may not give a pay rise if a person has a known genetic disorder and life insurers may charge a higher premium
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Can you choose your child
- IVF ( in vitro fertilization) can be used to give people with a risk of genetic disorders children
- In this treatment, the mothers eggs are fertilized outside the body
- PGD ( pre-inplantation diagnosis), the mother takes a fertility drug so she releases ova. The fathers sperm fertilises the ova, and when the embryo's reach the 8 cell stage, one cell is removed. The cell is tested for a genetic disorder and can be implanted into teh mothers uterus
- The Human Fertilization and Embryology Authority has been set up by the government to decide when PGD can be used
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- The cell nuclei of cystic fibrosis patients contain 2 faulty, recessive alleles, one of the proteins the cells make is faulty. The faulty protein causes the symptoms of CF.
- Scientists have been trying to develop a new treatment for CF. Their plan is to remove the cystic fibrosis gene from the chromosome and to put the healthy allele into the cells of the CF patient. This treatment is Gene Therapy
- The final step ( putting copies of into thecells of CF patients) is difficult. Scientists used nose sprays to put the alleles into the lung cells. Unfortunately, the cells lining the lungs die and are replaced all the time
- But, diseases like SCID ( Severe Combined Immunodeficiency Disease) can be cured with gene therapy. The normal alleles are put into viruses, which infect bone marrow cells taken from the patients body. These modified cells are put back in the body.
- At the moment, gene therapy treatments only change the cells, not the sex cells. So even if a person is cured, they may pass the disorder to their children
- In the future, it may be possible to prevent genetic diseases. If we modify sex cells, the person and their children will have the healthy alleles
- Now, modifying sex cells is illegal, people are worried that replacing genes in sex cells is a dangerous step
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Cloning- Science fiction or science fact
- Many organisms (bacteria) only need one parent to reproduce, they reproduce asexually.
- The offspring only inherit genes from one parent, so they are genetically identical to their parent, they are clones. The only variation between them will be caused by their environment
- Larger plants and animals have different cells for different jobs. As an embryo grows, it's cells become specialized.
- Plants keep some unspecialized cells as they can become anything that the plant may need. They can also grow new plants and be used for asexual reproduction
- Larger animals do not have unspecialized cells after they have grown, so cloning is uncommon in animals
- Most animals use sexual reproduction, so the new offspring are not clones of their parents
- Clones can be produced when a fertilized egg cell splits to form to eggs. They are identical twins
- Scientists can clone animals. The nucleus can be taken from a body cell and put into an empty egg cell. When the cell grows, the animal will be a clone of the body cell donor
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- Some scientist want to clone human embryo's. Some cells (stem cells)from the cloned embryo's could be used to treat diseases
- Stem cells are unspecialized cells that can grow into any type of human cell. Stem cells can be taken from embryo's that are a few days old
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