Genetic Variation 1/4

• Cell cycle


  Mitosis takes up 10% (division), Interphase takes up 90% (growth, DNA replication, cell functions)
• Chromosome


  • Made of proteins and DNA, DNA wrapped around proteins, 46 chromosomes in human cell, DNA condensed into chromosomes
• Centromere


  Part of chromosome where sister chromatids are held together
• Chromatids


  Strands of replicated chromosome
• Mitosis


  Division of cells, results in somatic cells, purpose is for growth and repair or to replace worn out cells
• Mitosis - Prophase


  Chromosomes condense (thickening and visible), nucleus present
• Mitosis - Metaphase


  Chromosomes in middle of cell nucleus no longer present
• Mitosis - Anaphase


  Chromosomes move away, sister chromatids separate to the poles of the cell, spindles help move chromosomes
• Mitosis - Telophase


  Chromosomes at complete opposite ends, nuclei form surrounding the chromosomes making two identical cells
• Mitosis - Cytokinesis


  Splitting of cytoplasm, final separation making two cells
• Centromere is key as we count the number of chromosomes present based off the number of centromeres
• Meiosis


  Reduction division, results in gametes (haploid cell). Meiosis develops unique and random variations of gametic cells. Females will make egg cells, males will make sperm cells.
• Haploid cell


  Half the number of chromosomes as the original cell
• Human sperm and egg cells have 23 chromosomes in each cell compared to the 46 chromosomes in a human cell. This is called a haploid cell, (haploid-half the number of chromosomes as the original cell) This is because when sperm and egg cells fuse together it will make 46 chromosomes diploid cell. This fertilized cell is also known as a zygote
• Meiosis - Division 1

  1. Prophase - Chromosomes condense becoming thicker and more visible. Homologous chromosomes line up with their homologous pairs. At this phase the homologous chromosomes match up, starting the process of 'crossing over' transferring genetic information and exchanging it between each other. This results in recombinant chromosomes

  2. Metaphase - Chromosomes move to middle in pairs

  3. Anaphase - Chromosomes pull away by spindle fibres moving to opposite sides of cell

  4. Telophase - Two new formed nuclei, nuclei surround the chromosomes
• Meiosis - Division 2

  1. Prophase - Homologous pairs, chromosomes thicken

  2. Metaphase - Chromosomes move to middle no longer in pairs

  3. Anaphase - Chromatids pulled by spindles

  4. Telophase - Cells divided meaning 4 new cells non identical, gametes
• DNA


  Deoxyribose nucleic acid, contains genetic code for making proteins
• Nucleotide


  Basic building block for nucleic acid, made of phosphate, pentose sugar, nitrogenous base
• DNA


  Deoxyribose (sugar) nucleic acid (composed of nucleotides)
• Bases


  • Adenine, Cytosine, Thymine, Guanine
• Base pairs


  AT, CG, join the two DNA strands making the double helix
• Triplet


  
  

  The base pairs that make up a gene are arranged into groups of three (triplet)

  Each triplet carries the code for a specific amino acid.
• Function of proteins

  
  

  Proteins are the building blocks of our body. Proteins play a significant structural and biochemical role in organisms. In our cells proteins in the form of enzymes do a lot of work, for example, proteins help break down food to release energy.
• Protein molecules


  Made of a long chain of amino acids
• Mutation


  Permanent change in the base sequence resulting in a new gene or allele. This can occur in either the somatic or gametic cells. results
• Mutation

  
  

  An error in DNA replication during cell division results in a permanent change in base sequences giving a new sequence of bases. As a result, there will be new triplets coding for a new protein which code for a unique and new trait (characteristic) this characteristic is called the mutation. Mutations add new traits to a gene pool
• Gene pool


  Combination of all the genes (including alleles) present in a reproducing population or species
• Mutagens

  • The rate of mutation can be influenced and increased by mutagens. Commons mutagens are chemicals in fatty foods and cigarettes, UV and radiation.
• Somatic mutation


  Mutation in a somatic cell, other cells will take over the job of the damaged cell
• Gametic mutation


  Mutation in a gametic cell, will be inherited by the offspring and all of its cells will carry this mutation
• Types of mutations


  • Neutral/silent - no observable effect on organism
  • Harmful - affects survival of an organism, e.g. cancer
  • Beneficial - gives a survival advantage over the other members of its species, enabling it to live in conditions where others die
• DNA replication


  Begins at the origin, helicase unwinds DNA, polymerase replicates DNA, primase makes RNA, ligase glues DNA fragments together
• Continuous variation


  Complete range of measurements from one extreme to another, e.g. height
• Discontinuous variation


  Characteristics that fall into a distinct number of classes or categories, e.g. eye colour
• Asexual reproduction


  Involves one parent, results in genetically identical offspring (clones). This form of reproduction is much faster and more efficient but less genetic variation occurs.
• Sexual reproduction


  Involves two parents. Results in genetic variation as offspring receive a combination of characteristics from both parents from processes such as crossing over, independent assortment and sometimes mutations.

  Offspring produced are similar but not genetically identical to parents.
• Zygote


  Fertilized ova, contains 46 chromosomes (diploid)
• Human sperm and egg cells have 23 chromosomes in each cell compared to the 46 chromosomes in a human cell. This is called a haploid cell, (haploid-half the number of chromosomes as the original cell) This is because when sperm and egg cells fuse together it will make 46 chromosomes diploid cell. This fertilized cell is also known as a zygote
• Process of mutation

  An error in DNA replication during cell division results in a permanent change in base sequences giving a new sequence of bases. As a result, there will be new triplets coding for a new protein which code for a unique and new trait (characteristic) this characteristic is called the mutation. Mutations add new traits to a gene pool
• Pros cons sexual reproduction

   

  This form of reproduction is much slower and less efficient as time and energy spent finding a mate, breeding and producing offspring. However as sexual reproduction leads to genetic variation if the species undergo a changing environment, exposure to a new disease some offspring have favourable alleles may be better suited to these changes allowing the species to survive and reach sexual maturity and be more successful overtime. Passing on the favourable alleles to their offspring.