TOPIC 6:INHERITANCE AND VARIATION (BIOLOGY)

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and parent cell Produce gametes for sexual reproduction Half (single chromosomes) Requires a mate. Slower way of producing offspring. Offspring are less likely to survive environmental changes or diseases. Cystic Fibrosis Disorder of cell membranes. Causes sticky mucus on lungs. Recessive allele CC CC or Cc Yes - genotype Cc Section 3: Genetics Key Terms 18 DNA 19 Gene 20 Chromosome 21 Genome 22 Allele 23 Dominant 24 Recessive 25 Homozygous 26 Heterozygous 27 Genotype 28 Phenotype 29 Single gene characteristics Genetic material. DNA is a polymer made up of two strands forming a double helix. The DNA makes up chromosomes. A gene is a small section of DNA on a chromosome. Each gene codes for a particular sequence of amino acids, which make a protein. A long coil of DNA. Found in the nucleus. The entire genetic material of that organism. Different versions of the same gene - dominant and recessive. A dominant allele is always expressed. Only one copy is needed. Only expressed if two copies are present. Both alleles for a gene are the same (i.e. both are dominant or both are recessive). Both alleles for a gene are different (i.e. one is dominant, the other is recessive). The alleles present for a particular gene. The physical feature expressed for a particular gene. Some characteristics are controlled by only one gene e.g. fur colour in mice, colour blindness in humans. 30 Multiple gene Most characteristics are controlled by many genes e.g. height. characteristics Section 4: Gender Inheritance 31 Human Chromosomes 32 Males 33 Females Human body cells contain 23 pairs of chromosomes. 22 pairs control characteristics only, one pair controls sex. Males have two different chromosomes - XY. Females have two chromosomes that are the same - XX. 34 Punnett square showing sex inheritance father XY XX YY sperm cells mother XX X X X XX XX X egg cells XY XY Section 5: Variation and Evolution Key Terms 35 Variation 36 Mutation 37 Evolution 38 Natural selection 39 Speciation The differences between organisms. Can be caused by genes (e.g. eye colour), the environment (e.g. scars) or both the environment and genes (e.g. weight). All variation in genes is caused by mutations. Mutations are changes in genes. Most have no effect on the phenotype. Occasionally mutations have a positive effect on phenotype and organisms with these mutations are more likely to survive. The change in the genes of a population over time. Occurs through natural selection. The process by which the individuals best adapted to the environment survive and pass on their genes. Occurs when two populations are so different that they can no longer breed to produce fertile offspring. Two new species are formed. Section 5a: Natural Selection 40 There is variation in a population's alleles caused by mutations. 42 The better adapted organisms survive, breed and pass on their alleles. 41 There is competition between individuals e.g. for food. 43 Over time the number of individuals with the better adapted alleles increases. Section 6: Selective Breeding 44 Selective Breeding (Artificial Selection) 45 Inbreeding The process by which humans breed plants and animals for particular genetic characteristics. Selective breeding can lead to 'inbreeding' where some breeds are Iparticularly prone to disease or inherited defects. 46 Process of selective breeding: 1. Choose parents with correct characteristics from the population. 2. Breed them together. 3. Choose the offspring with the desired characteristics and breed them together. 4. Continue over many generations. Section 7: Genetic Engineering 48 Genetic Engineering 49 GM Crop 50 Vector 51 Process of genetic engineering: 1. Genes are cut out by enzymes. 2. The gene is inserted into a vector (either a bacterial plasmid or virus). 3. The vector is used to insert the gene into the required cells 4. Genes are transferred to the cells of animals, plants or microorganisms at an early stage in their development so that they develop with desired characteristics. A process which involves modifying the genome of an organism by introducing a gene from another organism to give a desired characteristic. Crops that have been produced by genetic engineering. Something that can carry a gene into another organism e.g. bacterial Iplasmid or virus. DNA containing desired gene removed from cell . 47 Examples of desired characteristics: Disease resistance in food crops. Animals which produce more meat or milk. Enzymes insert gene into DNA vector . Domestic dogs with a gentle nature. Large or unusual flowers. DNA vector taken from bacterium Enzymes cut out desired gene Bacteria reproduce creating a large number of bacteria with the new characteristic O a *O *O *0 O 52 Examples of genetic engineering: Bacterial cells have human insulin gene inserted into them so that they produce insulin for diabetics. Plants that have had genes inserted that make them resistant to disease, insects or herbicides.