inheritance

• variation is the differences between individuals. it is caused by genetic and environmental factors
• interspecific - between different species
• intraspecific - within the species. eg, humans have different hair and eye colours.
• inherited phenotypes

  skin colour

  eye colour

  race

  blood type
• environmental phenotypes

  piercings

  tattoos

  hair length
• both inherited and environmental phenotypes

  hair colours

  height

  eyesight / vision

  weight
• phenotypes - a physical characterstic eg. height
• discontinuous data - definite categories and no in - between categories. eg. hair colour
• continuous - there is a complete range of phenotypes. eg. height, age, weight
• advantages of asexual reproduction


  only 1 parents is needed, pollination is not required in plants.

  reproduction is faster

  if the parents is well adapted to an area, the offspring will share an identical set of characteristics.
• disadvantages of asexual reproduction


  adverse changes to the environment mean the offspring is not adpated and will die, which could wipe out an entire species.
• advantages of sexual reproduction


  variation in offspring leads to adaptations in a species, meaning a change in the environment won't kill all of the species.
• disadvantage of sexual reproduction

  requires 2 parents and is slower
• sexual reproduction


  the sperm cells has a set of genes from the father, (23 - its a haploid). the egg cell has a set of genes from the mother (23 - haploid). the 2 gamates fuse - fertilisation. the zygote contains genes from both parnts, has 46 chromosomes - it is a diploid.
• asexual reproduction

  the parent cell copies all of its genes. a set of genes goes to the two new cells.each cell is a clone - they have the same genes
• meiosis 


  in males, meiosis occurs in the testes and produces sperm. in females, meiosis occurs in the ovaries and produces eggs. these sex cells are known as gametes. gamaetes have half of the normal number of chromosomes in comparison to body cells. this is important so that when fertilisation occurs. the zygote will have the full number of chromoses again
• stages of meiosis

  1. before the cell starts to divide. it has 2 sets of chromosomes.
  2. each chromosome makes a copy of itself - this is called replicaton.
  3. the membrane around the nucleus disappears.
  4. the pairs of chromosomes are seen to move apart. the chromosomes exchange parts.
  5. chromosomes from each pair now seperate and the cells starts to split into four.
  6. these are the gametes and there are 4 of them and they are all different.
• homozygous - the same allele combination
• heterozygous - different allele combination
• dominant - there only has to be 1 allele to take priority
• recessive - there has to be 2 alleles to the gene of the baby
• allele - a version of the gene
• males have one X and one Y chromosome, so if the father has a disease, it could be passed onto the son, paternally. these traits in the Y chromosome can only be passed paternally
• females have 2 X chromosomes because females can only produce gametes. it is the sperm that decides the gender of the baby
• gamete - a sex cells [sperm or egg]
• gene - a section of dna
• variation is caused by mutations in the dna
• mutation in the dna


  the mutation is caused by a change of bases in the dna. this can affect the amino acids that make up the protein. changing its shape, structure and function. eg. and enzyme's active site might change shape.
• what happens if there is a mutation in NON CODING dna?


  it may stop translation and alter the expression of genes
• diploid and haploid cells


  diploid is the full number of chromosomes, haploid is half. haploid cells are germ cells, diploid cells are body cells.
• 3 important findings of Gregor Mendel

  1. organisms inherit hereditary units from their parents.
  2. offspring receive units from both parents and so share traits with both parents.
  3. traits can be passed on but not visible [recessive allele]
• the discovery of the gene led to people accepting Mendel's ideas.
• what is the function of genes?


  genes determine the production of proteins and control development of different characteristics
• genotypes - all the genes and alleles an organism has
• genome - all the chromosomes and genes found in an organism
• coding DNA, non - coding DNA and proteinsynthesis can all play a role in gene expression
• haploid - has half of the normal amount of chromosomes
• gametes are haploid cells
• all cells produced in meiosis are genetically unique
• most mutations occur in non - coding DNA