The Same and Different
•Most of your biological information is inherited , but some information
is affected by your environment. This is why not all brothers and sisters,
Or twins look the same.
•Cells contain a nucleus, this nucleus contains the long threads of
chromosomes of which contain thousands of genes.
•Chromosomes are made from the chemical –DNA
•A fertilised egg cell has the instruction for making every protein , these
instructions are GENES.
•Proteins are important chemicals for cells, each protein does a different
job. Structural Proteins builds the body and enzymes speed up chemical
•Genes control the proteins that a cell makes, this is how they control
what the cell does.
•There are about 50 000 different types of proteins in the human body.
Disorders like Huntington's can’t be caught, they are inherited and passed on from parents to their children.
People in families may look similar or very different, this is because of Genes.
Parents pass on genes in sex cells, these sex cells carry half of the copied chromosomes, so when a sperm fertilises the egg, the egg now gets a full set of Chromosomes
Every human has 23 pairs of Chromosomes. Each pair are the same size and shape and carry the same genes in the same place, this means that your genes also come in pairs.
Sex cells are made with copies of half of the parents chromosomes. This makes sure that the fertilized egg has the correct number of chromosomes – 23 pairs
One chromosome from each pair comes from the egg cell and the other from the sperm cell.
Each chromosome carries thousands of genes, so the fertilized egg cell carries half of the mother’s genes and half of the father’s genes.
The Human Lottery
Human genes can be slightly different from their pair, these are called alleles.
Dominant alleles are always the capital letter, for example D allele causes dimples but the d allele doesn’t cause dimples. If you inherit both d alleles, then you won’t have dimples. However if you cause one of each (D and d) then you will have dimples as the D allele is dominant and the d allele is recessive.
You cannot work out if a child will definitely have that gene, but you can work out the possibility.
Humans have about 30 000 genes and each gene has different versions (alleles).
Sibling are different because they get a different mixture of alleles from their parents, apart from identical twins, each one of us has a unique set of genes.
Male or Female?
The 23rd pair of chromosomes are the sex cells. Males have X and Y chromosomes, where as females only have X.
Because the parents chromosomes are split, half of the male’s sperms get an X and the other half an Y, and the female’s egg cells are all X as they have two X chromosomes. When a sperm fertilises the egg cell, there is a 50% chance that it will be X or Y so there is a 50% chance it will be a boy or a girl.
Y chromosomes have a SRY gene (Sex-determining region of the Y chromosome)
Hormones are another group of proteins. They control many processes in the cells. Tiny amounts of hormones are made by different parts of the body.
Ethics - Making Decisions
Genetic testing is used to look for alleles that cause genetic disorders. They can be used to decide whether a pregnancy should be terminated or not.
The tests are not completely reliable, you can often get False Positives or False Negatives as the results are sometimes unclear.
Usually people have genetic tests as their is a known genetic disease in the family.
Testing the whole population for an allele is called genetic screening.
The decision about using genetic screening is made by the government and local NHS trusts, people in the NHS have to think about the costs, benefits and if there are better things to spend the money on.
There are many ethical questions on whether genetic screening is right such as who should know the results, what effects could the test have on people’s future decisions, is it right to interfere, should people be forced to have it?
A decision may benefit many people, but it could also cause a great amount of harm to a few people.
Can you choose your child? and Gene Therapy
IVF or In vitro fertilisation is used to fertilise a woman's egg cell outside her body.
Pre-Implantation Genetic Diagnosis (PGD) is used to chooses an embryo of a certain sex or without a certain disease.
A group called Human Fertilisation and Embryology Authority (HFEA) make the decisions or whether PGD can be used.
Gene therapy is when you put copies of the normal allele into the cells of the patient
Cloning - Science Fiction or Science Fact?
Cloning can be a natural process where some living things only need one parent to reproduce, this makes the offspring identical to their parent and to their siblings. This is called asexual reproduction and we call them genetically identical organism clones.
Asexual reproduction is common in plants but very uncommon in animals.
Most animals use sexual reproduction, the new offspring have two parents so they are not clones, but clones are sometimes produced, they are known as identical twins.
Dolly the Sheep
The nucleus was taken out of an unfertilised sheep egg cell
The nucleus was taken from a body cell from a different sheep.
This body cell nucleus was put into the empty egg cell
The cell grows to produce a new animal. Its genes will be the same as those of the animal which donated the nucleus. So it will be a clone of that animal.
The average lifespan for a sheep is 12-14 years, however Dolly died at the age of 6 of an illness.
Cloning - Science Fiction or Science Fact?
Some cells from cloned human embryos can be used to treat diseases. The useful cells are called embryos.
Stem cells are unspecialised cells. They can grow into any type of cell in the human body.
They can be taken from embryos that are only a few days old.
Cloning could be used to produce an embryo with the same genes as the patient. Stem cells from this embryo would have the same genes as the patient. So cells produced from the embryo would not be rejected by the patients body. This is called therapeutic cloning.
Inherited A feature that is passed from parents to offspring by their genes
Environment Everything that surrounds you. This is factors like the earth, the air and the water, as well as other living things
Nucleus a part of the cell containing DNA and RNA and responsible for growth and reproduction
Chromosomes Long, thin thread-like structures in the nucleus of a cell made from a molecule of DNA. Chromosomes carry the genes
Structural Proteins Proteins which are used to build cells
DNA The chemical that makes up chromosomes –Deoxyribonucleic acid. DNA carries the genetic code, which controls how an organism develops.
Protein Chemicals in living things that are polymers made by joining together amino acids
Genes A section of DNA giving the instruction for a cell about how to make one kind of protein
Enzymes A protein that catalyses (speeds up) chemical reactions in living things
Huntington’s disorder An inherited disease of the nervous system. The symptoms do not show up till middle age
Sex cells Cells produced by males and females for reproduction – egg cells and sperm cells. Sex cells carry a copy of the parent’s genetic information. They join together at fertilisation
23 pairs Human body cells have 23 pairs of chromosomes in the nucleus
Alleles Different versions of the same gene
Dominant Describes and allele that will show up in an organism even if a different allele of that gene is present. You only need to have one copy of an dominant allele to have the feature it produces
Recessive An allele which will only show up in an organism when a dominant allele of the gene is not present. You must have two copies of the recessive allele to have the feature it produces.
Cystic Fibrosis An inherited disorder. The disorder is produced by recessive alleles
Carrier Someone who has the recessive allele for a characteristic or disease but who does not have the characteristic or disease itself
Termination the removal or expulsion from the uterus of a fetus or embryo, resulting in or caused by its death
XY The pair of sex chromosomes found in a man’s body cells.
XX The pair of sex chromosomes found in a woman’s body cells.
Hormone A chemical messenger secreted by a specialised cells in animals and plants. Hormones bring about changes in cells or tissues in different parts of the animal or plant.
Ethics A set of principle which may show how to behave in a situation
False Negative A wrong test result. The test result says that a person does not have a medical condition but this is incorrect.
False Positive A wrong test result. This test result says that a person does have a medical condition but this is incorrect
Genetic Screening Testing a population for a particular allele
Pre-Implantation Genetic Diagnosis This is the technical term for embryo selection. Embryos fertilised outside the body are tester for genetic disorders. Only healthy embryos are put into the mother’s uterus
Gene Therapy Replacing fault alleles with normal alleles. The aim is to cure genetic disorders
Genetic Modification Altering the characteristics of an organism by introducing the genes of another organism into its DNA
Asexual Reproduction When a new individual is produced from just one parent.
Clones A new cell or individual made by asexual reproduction. A clone has the same genes as its parents.
Stem Cells Unspecialized animal cells that can divide and develop into specialized cells.
Therapeutic Cloning Growing new tissues and organs from cloning embryonic stem cells. The new tissues and organs are used to treat people who are ill or injured.
Most of your features are affected by your environment and your genes
Genes are found in the nuclei of cells and are instructions for making proteins.
Your chromosomes, and genes, are in pairs.
Genes have different versions called alleles
The difference between dominant and recessive alleles.
Men and women have different sex chromosomes.
How a Y chromosome causes an embryo to develop as a man.
Why you may look like your parents and siblings but not identical.
How to interpret family trees
How to complete genetic cross diagrams
The symptoms of CF and Huntington’s disorder
Why people can be carriers of Cystic Fibrosis but not Huntington’s disorder.
Doctors can test embryos, foetuses, and adults for certain alleles by genetic tests.
What happens during embryo selection (PGD)
How gene therapy could be used to treat some genetic disorders
That some organisms use asexual reproduction and have offspring that are clones
How animal clones are produced naturally and artificially
That cells in multicellular organisms become specialized very early on in the organism's development.
What stem cells are and how they could be used to treat certain diseases.