Genetics , variation and independence

• What is a genetic mutation

  Change in sequence of base pairs in DNA molecule resulting in altered polypeptide chain that genes code for

  most mutations do not alter polypeptide chain or only alter slightly so that its structure or function is not changed as genetic code degenerate
• what is a insertion mutation

  when a nucleotide is inserted and causes a frame shift in sequence causing change to triplet codes and amino acids coded for has a knock on affect
• what is a deletion mutation 


  when a nucleotide is deleted from sequence. can have a nock on effect by changing groups of three bases further on in DNA sequence as it causes a frame shift . can change polypeptide coded for and function
• what is a substitution mutation 


  base in DNA randomly swapped for different base . will only change amino acid replaced and does not cause a frame shift . might not have a drastic affect due to degenerate code

  can be a problem as it can produce a early stop codon therefore affecting final protein structure (Nonsense mutations)

  missense mutations is when mutation only alters a single amino acid
• what are mutagenic agents and examples

  environmental factors that increase risk of mutation in cells

  e.g Uv light

  ionising radiation like X rays

  toxic chemical such as peroxides
• what is a non disjunction mutation 


  occurs when a chromosome fails to separate during meiosis . gametes with one extra copy of chromosome or non at all

  if abnormal gametes take part in fertilisation chromosome mutation occurs as diploid cell will have incorrect number of chromosomes.
• what is a chromosome mutation

  involves a change in number of chromosomes e.g down sy drone has total of 47 chromosomes in genome
• stages of meiosis 


  interphase 1x

  prophase 2x

  metaphase 2x

  anaphase 2x

  telophase 2x
• process of meiosis 1

  interphase : DNA replicates and chromatids produced

  prophase : chromatids condense and arrange in homologous pairs , crossing over occurs and nuclear envelope breaks down and spindle fibres form

  metaphase: chromatids line u[ on equator and spindle fibres attach

  anaphase : spindle fibres contract and separate chromosomes

  telophase: chromosomes on opposite poles and nuclear envelope reforms . cytokinesis occurs and form two daughter cells
• process of meiosis 2

  prophase 2: chromosomes condense and nuclear envelope disintegrates and spindle fibres are formed

  metaphase 2: chromosomes attach to spindle fibre by centromeres

  anaphase 2: spindle fibres contract and serrate chromatids

  telophase 2: chromatids reach opposite poles of cell

  nuclear envelopes forms and cytokinesis occurs .

  Four genetically unique daughter cells produced
• uses of meiosis 


  form of nuclear division and produces haploid cells to form diploid cells

  produces gametes in plants and animals that are used in sexual reproduction
• what is a haploid cell

  cell or nucleus containing a single unpaired chromosome
• what us a gamete cell

  reproductive sex cell that fuses with another gamete cell during fertilisation . contains half of genetic info
• cytokinesis in animal cells

  cell surface membrane pinches inwards creating cleavage furrow in middle that contracts and divides cytoplasm in half
• cytokinesis in plant cell

  vesicles from Golgi body gather along equator of spindle . vesicles merge to form new cell surface membrane and secretes calcium pectate which becomes middle lamella , layers of cellulose are laid upon lamella to form primary and secondary walls of cells
• benefits of meiosis and and sexual reproduction

  produces genetically different offspring and cells and can be advantageous in natural selection .
• how does miosis produce genetic variation

  During , crossing over , independent segregation and random fertilisation
• process of crossing over 


  During meiosis 1 , homologous chromosomes pair up and are close .

  non sister chromatids cross over and become entangled . happens of chiasmata

  entanglement places stress on DNA molecule and sections of chromatids from one chromosome may break and re-join with chromatid from other chromosome

  creates new combination of alleles on two chromosome
• process of independent segregation

  when homologous pairs line up on equator order is completely random and when separated apart on poles gives rise to different chromosomes in each daughter cell
• what is a zygote 


  the diploid cell from which an organism develops it forms from the fusion of gametes
• formula to calculate number of combinations of chromosomes after random fertilisation of two gametes

  (2^n)^2

  n is haploid number and ^2 is number of gametes
• differences between mitosis and meiosis

  mitosis contributes to cell growth and repair and asexula re productions .produces 2 genetically identical daugthter cells

  meiosis , used for asexual reproduction ,produces 4 genetically different daughter cells