Inheritance, variation and evolution

• DNA (deoxyriboneucleic acid)


  contain genetic material and coded information, found in chromosomes, is a polymer that's made up of two strands coiled together in the shape of a double helix
• gene - codes for a specific protein

  small section of DNA found on a chromosome, each gene codes for a particular sequence of amino acids which are put together to make a specific protein
• genome

  entire set of genetic material in an organism
• sexual reproduction

  involves the fusion of male and female gametes. Because there are two parents, the offspring contain a mixture of the parents' genes; mother and father produce gametes by meiosis
• asexual reproduction

  only one parent. There's no fusion of gametes , no mixing of chromosomes and no genetic variation between parent and offspring. Offspring are genetically identical to the parent; usually happens by mitosis
• Meiosis - produces cells with half the normal number of chromosomes


  It duplicates its genetic information which forms a copy chromosomes; after replication, the chromosomes arrange themselves into pairs; in the first division, the chromosome pairs line up in the centre of the cell; pairs are then pulled apart so each new cell only has one copy of each chromosomes; in the second division, chromosomes line up again and are pulled apart; you get 4 gametes, each are genetically different from the others
• chromosomes control whether you're female or male

  There are 23 pairs of chromosomes in every human body. the 23rd pair are labelled XY or XX; males have X and a Y chromosome; females have 2 X chromosomes
• homozygous

  two alleles for a particular gene that are the same
• heterozygous

  two alleles for a particular gene are different
• dominant or recessive

  The allele for the characteristic that is shown is called the dominant allele; the other is recessive
• genotype

  the combination of alleles
• cystic fibrosis is caused by a recessive allele


  a genetic disorder of the cell membrane which results in the body producing a lot of mucus in the air passages and pancreas; because it's recessive, people with only one copy of the allele won't have the disorder (known as carriers)
• polydactyly is caused by dominant allele

  where a baby's born with extra fingers or toes but it isn't life threatening; it is caused by a dominant allele which means that it can be inherited if only one parent carries the defective allele
• phenotype

  characteristics that an organism displays
• Theory of evolution

  All of today's species have evolved from simple life forms that first started to develop over 3 billion years ago
• speciation

  the development of new species
• extinction

  when no individuals of species remain
• selective breeding

  when humans artificially select the plants or animals that are going to breed so that the genes for particular characteristics remain in the population
• Basic process involved with selective breeding

  select ones which have the characteristics you're after; breed them with each other; select the best of the offspring and breed them together; continue this process over several generations
• problems with selective breeding

  reduces gene pool; higher chance of organism inheriting harmful genetic defects; problems if new disease appears
• genetic engineering

  to transfer a gene responsible for a desirable characteristic from one organism's genome into another organism so that it also has the desired genome
• fossils

  remains of organisms from many thousands of years ago
• bacteria can evolve and become antibiotic-resistant

  bacteria can develop mutations in their DNA; they are rapid at reproducing so they can evolve quickly
• classification- organising living organisms into groups


  In this system, living things are first divided into kingdoms. Kingdoms are subdivided into smaller groups: phylum, class, order, family, genus, species
• the process of natural selection is the survival of the fittest