inheritance, variation & evolution

• there are 2 types of cell division: mitosis and meiosis
• mitosis results in the formation of 2 genetically identical daughter cells, and is used in asexual reproduction
• meiosis results in the formation of 4 genetically non-identical daughter cells, and is used in sexual reproduction
• sexual reproduction is the fusion of male and female gametes
• cells in reproductive organs divide by meiosis to create gametes, which contain half the number of chromosomes found in all body cells
• in mitosis, the cell begins to divide. the dna replicates to form 2 copies of each chromosome. the nuclear membrane breaks down and the chromosomes line up across the centre of the cell. 1 set of chromosomes is pulled to each end of the cell and the nucleus divides. the cytoplasm and cell membranes divide to form 2 identical cells
• in meiosis, in a parent cell chromosomes make identical copies of themselves. similar chromosomes pair up. sections of dna get swapped. first cell division - chromosome pairs separate. second cell division - separate again
• the process of reproduction where the nuclei of 2 gametes fuse to form a zygote, known as fertilisation, producing offspring that are genetically different to one another
• one key feature of sexual reproduction is that male and female gametes fuse
• one key feature of sexual reproduction is that there are 2 parents
• one key feature of sexual reproduction is that the offspring produced are non-identical
• one key feature of sexual reproduction is that the cells divide by meiosis
• asexual reproduction is the process of reproduction that forms genetically identical offspring from only 1 parent
• asexual reproduction is common in single-celled organisms and some plants
• one key feature of asexual reproduction is that there is no gamete fusion
• one key feature of asexual reproduction is that there is only 1 parent
• one key feature of asexual reproduction is that cells divide by mitosis
• one key feature of asexual reproduction is that the offspring produced are clones
• the genome is the entire genetic material of an organism, and within a genome, there are lots of levels of organisation
• dna is a double helix polymer, which means it is a polymer made up of 2 strands forming a twisted ladder shape
• a gene is a small section of dna which codes for s sequence of amino acids, which combine to give a specific protein
• long strands of dna are coiled up to from chromosomes which contain many genes, with human body cells containing 23 pairs of chromosomes, one of each pair coming from each parent
• in 2003, the human genome project was completed, where researchers had successfully studied the entire human genome
• since the human genome project, extensive research has been caried out on it, resulting in a vast increase in our understanding
• since the human genome project, identifying genes linked to different disorders has been made possible, allowing those at risk to make informed lifestyle decisions based on the known risk factors
• since the human genome project, our understanding of the causes of inherited disorders and how we should be treating them has improved
• since the human genome project, it has been made possible to investigate human evolutionary history, including how humans migrated in the past
• a mutation is a permanent change in the nucleotide sequence of dna
• mutations happen continuously and normally only slightly affect proteins or don't affect them at all
• occasionally, a mutation may change the structure or shape of a protein
• the outcome of a mutation is almost always detrimental to protein function, for example in enzymes, the substrate may no longer be able to bind to the active site, and in structural proteins, their strength may be reduced
• more rarely, a mutation may give a survival advantage, such as resistance to an antibiotic in bacteria, which can be beneficial and represent the foundation of evolution by natural selection
• alleles are different forms of the same gene
• humans have pairs of every gene and in one gene, each half of the pair may have different alleles
• people's characteristics are determined by the alleles that they have, and the alleles can either be dominant or recessive
• a dominant allele is always expressed, regardless of the identity of the other allele
• a dominant allele only needs one copy present to be expressed, and is represented by a capital letter
• a recessive allele is only expressed if the other allele is also recessive
• a recessive allele is represented by a lowercase letter
• when talking about the inheritance of characteristics, we use the words genotype and phenotype