topic 3

• sexual reproduction produces genetically different cells
• sexual reproduction is where genetic information from two organisms produce offspring which are genetically different to either parent cell
• in sexual reproduction the father and mother produce gametes (reproductive cells: sperm and egg cell)
• gametes are hapliod cells that contain half the number of chromosomes of a diploid cell
• Fertilisation: a male gamete fuses with a female gamete to form a zygote (fertilised egg) with a full set of chromosomes (now diploid )
• zygote goes through mitosis to develop into an embryo that inherits characteristics from both parents and having genes from both parents
• meiosis:

  division 1:

  • cell duplicates its DNA ( chromosomes creates an X-shape)
  • the chromosomes line up in pairs at the centre of the cell
  • the pairs are pulled apart so the new cell only has one copy of each chromosome
  • each new cell has a mix of mother and father cells , creating genetic variation
• meiosis:

  division 2:

  • the second division the chromosomes line up again, chromatids are pulled apart
  • four haploid daughter cells are created all genetically different gametes
• asexual reproduction, divided my mitosis ,makes two genetically identical daughter cells
• sexual reproduction, involves meiosis, results in the production of genetically different haploid gametes which fuse to form diploid cell at fertilisation.
• asexual reproduction: advantages-

  • produce lots of offspring very quickly
  • only one parent needed, can produce whenever conditions are favourable without waiting for a mate
• asexual reproduction: disadvantage-

  • no genetic variation, cannot adapt if the environment changes
• sexual reproduction: advantage-

  • creates genetic variation within a population
  • making them able to adapt easier when environment changes
• sexual reproduction: disadvantage-

  • takes more time and energy to reproduce
  • produces fewer offspring
  • two parents are needed , be a problem if the organism is isolated
• DNA strands are polymers made up of nucleotides (repeating units), which are made up of a phosphate group, a sugar and a base
• 4 different DNA bases: (A)Adenine, (T)Thymine,(c) Cytosine,(G) Guanine
• A pairs with T with 2 weak hydrogen bonds and C pairs with G with 3 hydrogen bonds
• A DNA molecule has two strands coiled together in the shape of a double helix (double stranded spiral)
• chromosomes are long coiled up molecules of DNA found in the nucleus
• gene is a section of DNA on a chromosome that codes for a specific protein
• all of an organism's DNA makes up its genome
• extracting DNA:

  • mash strawberry
  • add to a beaker with detergent(to break down membranes)
  • add salt to make the DNA stick together
  • Filter mixture to get the big insoluble bits out
  • add ice cold alcohol to make the DNA come out of solution as it isn't soluble and a stringy white precipitate will appear(the DNA)
• DNA controls the production of proteins in a cell
• proteins are made up of a chain of amino acids with each protein having different number or order of amino acids
• amino acids fold up to give each protein a different specific and shape
• enzymes have different active sites with a specific shape so they only catalyse a specific reaction
• the order of bases in a gene decides the order of amino acids in a protein
• amino acid is coded for by a sequence of three bases in a gene (codon)
• each gene contains a different sequence of bases which is what allows it to code for a particular protein
• many regions of DNA are non-coding- they don't code for any amino acids
• all of an organism's DNA make up the organisms genome
• mutation is a rare, random change to an organism's DNA base sequence that can be inherited
• in a mutation happens in a gene it produces a allele- a different version of the gene
• the genetic variant (alleles) may code for a different sequence of amino acids which may change the shape of the final protein and so its activity for example- the activity of an enzyme might increase, decrease or stop all together
• this could end up changing the characteristics(phenotype) or an organism
• phenotype: the observable physical properties of an organism, including its appearance and behaviour, determined by its genotype
• Mutations can also happen in non-coding regions of DNA
• proteins are made in two stages: transcription and translation
• proteins are made in the cell cytoplasm by subcellular structure called ribosomes
• DNA is found in the cell nucleus