1. Genetic Tests
1.1. Genetic testing involves analysis of a person’s DNA to see if they carry alleles that cause genetic disorders. It can be done at any stage in a person’s life.
1.1.1. Antenatal testing: This is used to analyse an individual’s DNA or chromosomes before they are born. At the moment, it cannot detect all inherited disorders
1.1.2. Prenatal testing: is offered to couples who may have an increased risk of producing a baby with an inherited disorder. It is offered to pregnant women for Down's Syndrome.
1.1.2.1. A false negative happens when a genetic test has failed to detect a certain allele or faulty chromosome. The affected individual or family would be wrongly reassured, which may lead them to decide to start a family or continue with a pregnancy that they otherwise would have avoided.
1.1.3. Neonatal Testing:This is used just after a baby has been born. Used to detect disorders such as phenylketonuria, congenital hypothyroidism and cystic fibrosis. They prickle the baby's heel.
1.1.3.1. A false positive occurs when a genetic test has wrongly detected a certain allele or faulty chromosome. The affected individual or family could believe something is wrong when it is not, which may lead them to decide against starting a family or considering an abortion in order to avoid having a baby with a genetic disorder.
1.1.4. Pre-implantation genetic diagnosis (PGD): is a procedure used on embryos before implantation. Fertility drugs are taken by the female so that several eggs are released and collected by a doctor. These eggs are then fertilised in a Petri dish by sperm, either from the father or a donor. This is known as in vitro fertilisation (IVF). Once the embryos have reached the eight-cell stage, one cell is removed from each.
2. Inheritance
2.1. female sex cells are called egg cells, or ova male sex cells are called sperm.
2.1.1. When an egg and sperm cell come together, the now fertilised egg contains 23 pairs of chromosomes. Sex chromosomes are responsible for certain genetic traits.
2.1.1.1. One chromosome in each pair comes from the mother, the other from the father.
2.1.2. Human body cells each contain 23 pairs of chromosomes. Parents pass on their genes to their offspring in their sex cells.
2.1.3. .
2.2. Alleles
2.2.1. These alleles may be the same (homozygous) on each pair of chromosomes, or different (heterozygous), for example, to give blue eyes or brown eyes.
2.2.1.1. individuals who are homozygous for a certain gene carry two copies of the same allele individuals who are heterozygous for a certain gene carry two different alleles
2.2.2. The chromosomes we get from each pair is completely random.
3. Genetic Diseases
3.1. A recessive allele only shows if the individual has two copies of it. For example, the allele for blue eyes is recessive. You need two copies of this allele to have blue eyes.
3.2. A dominant allele always shows, even if the individual only has one copy of it. For example, the allele for brown eyes is dominant. You only need one copy of it to have brown eyes. Two copies will still give you brown eyes.
3.3. When describing an organism it is important to distinguish between the genotype and phenotype. Genotype- describes the genetic make-up of an organism (the combination of alleles). Phenotype- describes the observable, physical characteristics that an organism has. This is often related to a particular gene.
3.4. Cystic Fibrosis
3.4.1. Caused by a recessive allele
3.4.1.1. You need to inherit two copies of the faulty allele to be born with CF. If you have just one copy, you are a carrier, but will not experience any symptoms. If two carriers have a child together, there is a one-in-four chance of passing on the disorder
3.4.2. People with CF produce thick and sticky mucus in their lungs and airways. As a result, they are more likely to get respiratory infections.The disease blocks tubes that take enzymes to the gut meaning food is not digested properly, leaving the person short of essential nutrients.
3.5. Huntington's Disorder
3.5.1. Huntington’s disorder is caused by a dominant allele, written as H. The symptoms usually develop in middle age, and include tremors, clumsiness, mood changes, memory loss and the inability to concentrate.
3.5.1.1. You only need one copy of the faulty allele and who will inherit the disorder, Therefore if one or both parent has one copy, the offspring can also inherit it.
4. Genes
4.1. Chromosomes
4.1.1. Found in the nucleus of most cells and they consist of lond strands of DNA
4.1.1.1. DNA (deoxyribonucleic acid)
4.1.1.2. A section of DNA that has the genetic code for making a particular protein is called a gene, The proteins can either be:
4.1.1.2.1. structural proteins such as the ones found in muscles and hair
4.1.1.2.2. enzymes, such as proteases and other digestive enzymes.
4.1.1.3. Controls the activities inside a cell, the instructions for the organism's development is found in here.
4.1.2. .
4.2. Variation
4.2.1. Individuals differ in all sorts of ways, even when they are offspring of the same parents. These differences are called variation.
4.2.1.1. Most characteristics, such as height, are determined by several genes working together. They are also influenced by environmental factors. These include:
4.2.1.1.1. climate diet physical accidents culture lifestyle
4.2.1.1.2. Twins are a good example of the interaction between inheritance and the environment. One twin does exercise and becomes a healthy person and the other doesn't. The environment changes them in many ways, eg. taste.
4.3. Genes are found in our chromosomes,which parents pass on to offspring in their sex cells in reproduction. Different versions of the same gene are called alleles, and these can determine features like eye colour, and the inheritance of disorders such as cystic fibrosis.
5. Cloning and Stem Cells
5.1. Natural cloning:Twins are genetically identical because they are formed after one egg cell is fertilised but splits to form two embryos. They have the same genes. As the genes came from both parents they are not clones of either parent, but they are natural clones of each other.
5.1.1. There are two main ways of cloning animals
5.1.1.1. Embryo Transplants-A developing embryo is removed from a pregnant animal at an early stage, before its cells have had time to become specialised. The cells are separated, grown for a while in a laboratory then transplanted into host mothers. Furthermore, the offspring wont be identical to host mother because they have genetic information from the original mother.
5.1.1.2. Fusion cell cloning: Fusion cell cloning involves replacing the nucleus of an unfertilised egg with one from a different cell. The replacement can come from an embryo. If it is from an adult cell, it is called adult cell cloning. Dolly the sheep was the first animal to cloned by adult cell cloning.
5.1.1.2.1. Dolly The Sheep's production method: 1. An egg cell was removed from the ovary of an adult female sheep, and its nucleus removed 2. The nucleus from an udder cell of a donor sheep was inserted into the empty egg cell 3. The fused cell then began to develop normally, using genetic information from the donated DNA 4. Before the dividing cells became specialised, the embryo was implanted into the uterus of a foster mother sheep. The result was Dolly, who was genetically identical to the donor sheep.
5.2. Asexual Reproduction
5.2.1. Artificial cloning It is possible to make clones artificially. The cloning of animals has many important commercial implications. It allows an individual animal that has desirable features, such as a cow that produces a lot of milk, to be duplicated several times.
5.2.2. Asexual reproduction only requires one parent, unlike sexual reproduction, which needs two. Since there is only one parent, there is no fusion of gametes, and no mixing of genetic information. As a result, the offspring are genetically identical to the parent, and to each other - so they are clones. Sea Anemones and star fishes asexually produce.
5.3. Clones are genetically identical individuals. Bacteria, plants and some animals can reproduce asexually to form clones that are genetically identical to their parent. Identical human twins are also clones: any differences between them are due to environmental factors.
5.3.1. Cloning occurs naturally in some plants and in human identical twins, and it is now possible to clone animals artificially. The subject of cloning raises a number of ethical issues that need to be considered.
5.4. Stem Cells
5.4.1. adult stem cells - these are unspecialised cells that can develop into many (but not all) types of cells embryonic stem cells - these are unspecialised cells that can develop into any type of cell.
5.4.1.1. But embryos contain a special type of cell called stem cells. These embryonic stem cells can grow into any type of cell found in the body so they are not specialised. Stem cells can be removed from human embryos that are a few days old, for example, from unused embryos left over from fertility treatment.
5.4.1.2. Here are some of the things stem cells could be used for: -making new brain cells to treat people with Parkinson’s disease -rebuilding bones and cartilage -repairing damaged immune systems -making replacement heart valves.
5.4.1.2.1. Therapeutic cloning If you were to receive medical treatment with cells grown from stem cells, your body’s immune system would recognise the cells as foreign, and they would be rejected and die. But this would not happen if you received cells with the same genes as your own.