Biology

• What is sexual reproduction?

  the joining and mix of male and female gametes to produce genetically different offspring by meiosis
• What are gametes?


  sex cells, haploid
• how many chromosomes does a cell have

  46
• how many chromosomes does a gamete have

  23
• What is asexual reproduction?


  The production of genetically identical haploid offspring from a single parent by mitosis.
• advantages of sexual reproduction

  genetic variation

  allows selective breeding
• disadvantages of sexual reproduction

  slower process as organism has to find a mate
• Advantages of asexual reproduction

  -Only one parent needed

  -More time and energy efficient as only need to find one mate

  -Faster than sexual reproduction

  -Many identical offspring can be produced when conditions are favourable
• Disadvantages of asexual reproduction

  no genetic variation
• What is mitosis?


  The division of one cell into two genetically identical diploid daughter cells in asexual reproduction
• What is meiosis?

  cell division that results in four genetically identical haploid daughter cells
• process of meiosis


  - The cell makes copies of its chromosomes so it has double the amount of genetic information

  - Cell divides into two cells each with half the amount of chromosomes (46)

  - The cell divides again producing four cells each with a quarter of the chromosomes (23)
• DNA STRUCTURE


  a polymer found in chromosomes in the nucleus. made up of two dna strands which are twisted together to form a double helix. made up of nucleotides with four different complementary bases
• what is a gene


  A section of DNA that codes for amino acids which are joined to make a protein
• what are nucleotides made up of

  sugar, phosphate, base, weak hydrogen bonds between bases
• four organic bases

  A,T

  C,G
• what is a genome


  The entire set of genetic material in an organism
• practical: extracting dna from fruit

  - mix cold water, salt and washing up liquid

  - pulverise the fruit to break down cell membrane

  - add the solution and filter it with a sieve

  - add ice cold ethanol so dna precipitates out
• process of transcription


  - RNA polymerase binds to non coding region in front of a gene and moves along.

  - the two strands are pulled apart and complementary bases pair together to form a strand of mRNA

  - the mRNA moves out of the nucleus through the nuclear pore and through the cytoplasm to be attached to a a ribosome
• process of translation

  - the mRNA leaves the nucleus through the nuclear pore, through the cytoplasm and binds onto a ribosome

  - tRNA carries amino acids to ribosome

  - tRNA bases match to complementary base pairs of mRNA in triplet code

  - amino acids are joined to make a polypeptide which folds to produce a protein
• what is a genotype


  genetic makeup of an organism
• What is a phenotype?

  physical characteristics of an organism
• what is a coding dna

  sequence of DNA that codes for a protein that can alter sequence of amino acids
• what is a non coding dna

  regions of DNA that do not code for proteins, control gene expression
• Who was Gregor Mendel?

  Austrian monk who worked in monastery gardens and observed the characteristics passed onto the next generation of plants by carrying out breeding experiments on peas
• mendels experiment conclusions


  offspring have some characterises that their parents have - hereditary units

  units can be dominant or recessive and cannot be mixed
• Why is Mendel's work important?

  mendel published his work in 1866 but was not recognised until after his death as genes were not yet discovered.
• what are alleles


  Different forms of a gene
• Homozygous definition


  when both alleles are the same
• Heterozygous definition

  when one of the alleles is dominant and the other recessive
• What is a zygote?


  diploid fertilized egg
• family pedigree: unaffected female

  white circle
• family pedigree: black square

  affected male
• What does the 23rd pair of chromosomes determine?


  gender
• female genotype

  XX
• male genotype


  XY
• What is codominance?


  when both alleles contribute to the phenotype: IA and IB
• A and O alleles

  IA
• Why are sex-linked disorders more common in males than in females?

  Males only have one X chromosome, so all X-linked genes are expressed in males, even if they are recessive. For females to get the gene, it would have to be linked to both X chromosomes.
• how do mutations occur

  when the sequence of bases are changed, potentially affecting the phenotype.