biology - genetics

• What are gametes?


  sex cells (sperm and egg)
• What is a zygote?


  fertilized egg
• What are the stages of mitosis?


  interphase, prophase, metaphase, anaphase, telophase, cytokinesis
• What is meiosis?


  a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes
• Describe meiosis


  - DNA duplicates

  - divides into 2 cells, each with one full set of DNA

  - crossing over occurs, mixing the DNA of the mother and father

  - the second divisions happen, leaving 4 daughter cells, each with half a set of DNA, and each with different DNA
• What are the advantages of asexual reproduction?

  Identical offspring, no special cells required, speedy process, lots of offspring, don't need a mate so can quickly take advantage of good conditions
• What are the disadvantages of asexual reproduction?

  no genetic variation - extinction is more likely if there is a change in the environment as the entire population will be affected.
• What are the advantages of sexual reproduction?

  Diverse offspring making it more likely that some of the population would survive if there were a change in the environment, adaptability, can live in different environments
• What are the disadvantages of sexual reproduction?

  - slow reproductive rate

  - smaller number of offspring

  - more energy needed
• What are the bases of DNA?

  Adenine, Thymine, Guanine, Cytosine
• What are the pairs of bases?

  A with T and G with C
• What is the structure of DNA?

  A double helix made from four bases, with a sugar phosphate backbone and weak hydrogen bonds between pairs of bases
• How can you extract DNA from fruit cells?

  1. Mash strawberries and out in beaker containing detergent and salt; mix well

  2. Detergent will break down cell membranes to release DNA; salt will make DNA clump together

  3. Filter mixture to get froth and big insoluble bits of cell out

  4. Gently add some ice-cold alcohol to filtered mixture

  5. DNA will come out of solution as it's not soluble in cold alcohol; will appear as stringy white precipitate that can be fished out with glass rod
• What is transcription?


  synthesis of an RNA molecule from a DNA template
• What is translation?


  the decoding of an mRNA message into a protein
• Describe transcription


  RNA polymerase binds to DNA, separates the strands, then uses a strand as a template to assemble mRNA as it moves along.

  Then, the mRNA will move out of the nucleus to a ribosome
• Describe translation


  The bases are read in triplets, known as codons, with each codon coding for an amino acid. The amino acids are brought by the tRNA to the mRNA, and form a chain. Then the polypeptide chain folds to form a protein. The shape it folds into (dependent on the order of amino acids), detemines the function.
• What is a mutation?


  A rare, random change in genetic material that can be inherited
• How can a mutation in the non-coding DNA affect the phenotype?

  It could affect how well the RNA polymerase can bind to it during transcription, therefore affecting how much mRNA is transcribed, and therefore the wrong amino acid may be brought.
• What are alleles?


  different versions of the same gene
• What is a genotype?


  genetic makeup of an organism
• What is a phenotype?


  physical characteristics of an organism
• What did Medel conclude?

  - characteristics are determined by "heredititary units"

  - hereditary units are passed on unchanged from both parents, one from each parent

  - hereditary units can be dominant or recessive, if an individual has both, the dominant will be shown in the phenotype
• How can genetic disorders be sex-linked?

  As the Y-chromosome is shorter, it carries fewer genes. This means that if a recessive allele for a disease is carried in the X-chromosome, there may be no allele, dominant or recessive in the Y-chromosome which could prevent the expression of this disease in the phenotype. This makes it more likely that men will get certain recessive genetic characteristics.
• What are the alleles for blood type?

  IA, IB, IO
• Which blood type alleles are codominant?

  IA IB
• What does heterozygous mean?

  two different alleles
• What does homozygous mean?

  same alleles
• What is genetic variation?

  differences that occur in individuals within a species due to having different alleles
• What is environmental variation?


  characteristics inherited from environment and lifestyle
• What is the Human Genome Project?

  Scientists in 18 different countries collaborated to decode the human genome. This is the order of bases on all the human chromosomes. The project was completed quickly because so many scientists worked on it at the same time. The work was published in 2003.
• What are the applications of the research produced by the human genome project?

  Prediction and prevention of diseases, testing and treatment for inherited disorders, as well as new and better medicines, as scientists can predict better how people will react to medicine, as well as what an appropriate dose would be.
• What are the possible drawbacks of the research produced by the human genome project?

  - increased stress if people know they have the gene for a genetic disorder

  - gene-ism: people with genetic disorders may come under pressure not to have children

  - discrimination by insurers and employers
• Explain when I advantage of using sexual reproduction to produce an offspring


  Genetic variation increase variation so more likely to survive a disease or environmental change
• explain how Mendel used homozygous tall and homozygous short plants to show that the tall allele is dominant to the short allele


  Mandel cross homozygous tall and homozygous short pe plants and produced all tall offsprings therefore all the offspring had a heterozygous genotype with one tall and one short showing that the tall was dominant
• Which term is often used to describe the expression of traits in an organism?

  Phenotype
• A child’s blood group is blood group O

  The mothers blood is in group A

  The father’s blood is in group B

  Explain how this child is blood group O

  • IO is recessive to IA and IB
  • Mothers genotype must be IAIO
  • Father’s genotype must be IBIO
  • Child must inherit two recessive IOIO alleles
  • Child’s genotype is IOIO
  • Offspring have 25% chance of being in blood group O
• Explain how two parents with a dominant phenotype can produce an offspring expressing a recessive characteristic


  Both parents must be heterozygous for the recessive allele, so the offspring must inherit the recessive allele from each parent
• Explain why sperm determine the sex of offspring at fertilisation

  • Can carry either an X or Y chromosome
  • whereas egg cells only carry X chromosomes
  • XX results in a female and XY results in a male
• Give two safety precautions needed when blood is removed from a person

  1. Gloves
  2. Clean the area of skin where blood is being removed