Inheritance, Variation and Evolution.

• Meiosis is the formation of four non-identical cells from one cell.
• Mitosis is the formation of two identical cells from one cell.
• Sexual reproduction involves the joining of male and female gametes, each containing genetic information from the mother or father.
• Gametes are formed by meiosis, as they are non identical.
• A normal cell has 46 chromosomes.
• There are two sets of chromosomes (i.e 23 pairs) in each pair, one chromosome is from the father and the second set is from the mother.
• Each gamete has 23 chromosomes and they fuse in fertilisation.
• The genetic information from each parent is mixed, producing variation in the offspring.
• Asexual reproduction involves one parent with no gametes joining, it happens using the process of mitosis, where two identical cells are formed from one cell.
• There is no mixing of genetic information in asexual reproduction, it leads to clones, which are genetically identical to each other and the parent.
• Examples of organisms that reproduce this way are bacteria, some plants and some animals.
• Cells in the reproductive organs divide by meiosis to form gametes.
• Gametes only have one copy of each chromosome.
• The cell makes copies of its chromosomes, so it has double the amount of genetic information.
• The cell divides into two cells, each with half the amount of chromosomes (46).
• The cell divides again producing four cells, each with a quarter the amount of chromosomes (23).
• Factors contributing to extinction include changes in environment which the species cannot adapt fast enough to, new predators may have evolved or migrated to the area, a new disease arises and there are no resistant alleles to it, they have to compete with a species which has advantageous mutations for the same food source, and a catastrophic event can wipe out a species.
• Evolutionary trees are used to show how closely related organisms are, they are created using classification data and fossils for extinct species.
• Eukaryota are organisms who have a nucleus enclosed in membranes, including the kingdoms protists, fungi, plants and animals.
• Bacteria are labelled resistant when they are not killed by antibiotics which previously were used as cures against them.
• Bacteria are true bacteria despite having similar features to archaea.
• Fossils cannot be used to determine how life started on Earth because most early life forms are soft-bodied and decay completely, and any traces have been destroyed by geological activity.
• Resistant bacteria increase due to the creation of a new strain, exposure to antibiotics creates a selection pressure, and those with antibiotic resistance can reproduce and pass on the advantageous gene to their offspring.
• Extinction is when an entire species has died out.
• The Linnaean system divides living things into kingdoms, phylum, class, order, family, genus, species.
• The three-domain system developed by Carl Woese adds three large groups called domains above kingdoms: Archaea, Bacteria, and Eukaryota.
• The binomial system gives each organism a name which is used worldwide, the first part is their genus and the second part is their species.
• Embryonic screening allows scientists to observe whether the child will have a genetic condition or not.
• These cells are called gametes and they are all genetically different from each other because the chromosomes are shuffled during the process, resulting in random chromosomes ending up in each of the four cells.
• Family trees show the inheritance of different phenotypes over generations in the same family.
• Hormones are chemical messengers that send signals around the body.
• Dominant allele only one (out of the two alleles) is needed for it to be expressed and for the corresponding phenotype to be observed.
• Most mutations do not alter the protein or only do so slightly.
• Homozygous when both inherited alleles are the same (i.e two dominant alleles or two recessive alleles).
• A base is deleted from the code, changing the way it is read and potentially changing all the amino acids coded for after this deletion.
• A single gene cross looks at the probability of the offspring of two parents having certain genotypes and phenotypes.
• Alleles are the different forms of the gene - humans have two alleles for each gene as they inherit one from each parent.
• Inherited Disorders are caused by inheriting certain alleles, such as Polydactyly: having extra fingers or toes and Cystic fibrosis: this is a disorder of the cell membranes, resulting in thick mucus in the airways and pancreas.
• Structural protein is a strong protein used to form structures, such as collagen.
• Some mutations can have a serious effect and can change the shape of the protein.