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Revised End Start B1: You and Your Genes (Higher) Variation is the differences in characteristics between individuals. Characteristics may be affected by genes, the environment or both together. Most characteristics are affected by several genes working together e.g. height. Some characteristics e.g. tongue-rolling and disorders e.g. cystic fibrosis, are controlled by a single gene. Genes are instructions for making proteins, found on chromosomes in the nuclei of cells. Chromosomes (and genes) come in pairs. One chromosome is inherited from the mother and the other from the father. Sex cells (egg and sperm) carry one chromosome from each pair. Sex chromosomes of a woman are XX. Sex chromosomes of a man are XY. A gene on the Y chromosome tells the embryo to develop into a male. Each chromosome in a pair carries the same genes in the same place. Alleles are different versions of a gene and may be dominant or recessive. Children look like their parents because they inherit half their genes from each parent. Brothers and sisters look similar, but are not identical, because they inherit a different combination of genes from their parents. Interpret the inheritance of characteristics controlled by a single gene, using family trees and genetic cross diagrams. Carriers have one copy of a recessive allele and can pass it on to their children. Symptoms and inheritance of cystic fibrosis, a genetic disorder caused by a single, recessive allele. Symptoms and inheritance of Huntington’s disorder, a genetic disorder caused by a single, dominant allele. Adults, foetuses and embryos can be tested for the presence of certain alleles. Implications of genetic testing for individuals. Implications of the use of genetic information by other organisations e.g. genetic screening programmes, employers and insurers. Stages in embryo selection (pre-implantation genetic diagnosis or PGD). Gene therapy can be used to treat some genetic disorders by inserting a normal allele into cells of the patient. Clones are genetically identical organisms. Differences between clones are due to the environment. Some organisms use asexual reproduction to produce offspring that are clones of the parent. Animal clones can be produced naturally, when cells of an embryo separate (identical twins), or artificially. Artificial animal cloning involves the transfer of a nucleus from an adult body cell into an unfertilised egg cell, which has had its own nucleus removed. Stem cells are unspecialised cells that can develop into different cell types. In the future, stem cells may be used to treat certain degenerative diseases. Therapeutic cloning involves treating a patient with stem cells taken from an embryo clone of the patient. Cells in a multi-cellular organism become specialised early in development. Revised End Start B1: You and Your Genes (Foundation) Variation is the differences in characteristics between individuals. Characteristics may be affected by genes, the environment or both together. Most characteristics are affected by several genes working together e.g. height. Some characteristics e.g. tongue-rolling and disorders e.g. cystic fibrosis, are controlled by a single gene. Genes are instructions for making proteins, found on chromosomes in the nuclei of cells. Chromosomes (and genes) come in pairs. One chromosome is inherited from the mother and the other from the father. Sex cells (egg and sperm) carry one chromosome from each pair. Sex chromosomes of a woman are XX. Sex chromosomes of a man are XY. Each chromosome in a pair carries the same genes in the same place. Alleles are different versions of a gene and may be dominant or recessive. Children look like their parents because they inherit half their genes from each parent. Brothers and sisters look similar, but are not identical, because they inherit a different combination of genes from their parents. Interpret the inheritance of characteristics controlled by a single gene, using family trees and genetic cross diagrams. Revised End Start Carriers have one copy of a recessive allele and can pass it on to their children. Symptoms and inheritance of cystic fibrosis, a genetic disorder caused by a single, recessive allele. Symptoms and inheritance of Huntington’s disorder, a genetic disorder caused by a single, dominant allele. Adults, foetuses and embryos can be tested for the presence of certain alleles. Implications of genetic testing for individuals. Stages in embryo selection. Gene therapy can be used to treat some genetic disorders by inserting a normal allele into cells of the patient. Clones are genetically identical organisms. Differences between clones are due to the environment. Some organisms use asexual reproduction to produce offspring that are clones of the parent. Animal clones can be produced naturally, when cells of an embryo separate (identical twins), or artificially. Stem cells are unspecialised cells that can develop into different cell types. In the future, stem cells may be used to treat certain degenerative diseases. Therapeutic cloning involves treating a patient with stem cells taken from an embryo clone of the patient. Cells in a multi-cellular organism become specialised early in development. I must revise the following: