Topic 3 - Genetics Flashcards
Describe the stages of
Protein Synthesis, including transcription & translation
TRANSCRIPTION
1) RNA polymerase binds to non-coding DNA located in front of a gene
2) Two DNA strands unzip and the RNA polymerase moves along the DNA strand.
3) RNA polymerase produces a complementary mRNA strand from the coding DNA of the gene .
4) Once made, the mRNA molecule leaves the nucleus through a nuclear pore & enters the cytoplasm
TRANSLATION
1) In the cytoplasm, the mRNA strand attaches itself to the ribosome.
2) tRNA molecules bind with their specific amino acid
3) The anticodon on each tRNA molecule pairs with a complimentary triplet (codon) on mRNA molecule.
4) The amino acids are joined together by the ribosome & this forms a polypeptide chain (proteins)
Advantages & Disadvantages of asexual reproduction
ADVANTAGES
• produces lots of offspring very quickly because the reproductive cycle is so fast
• e.g. bacteria (E. coli) divides every half an hour —> this allows organisms to colonise a new area very rapidly
• one parent is needed so they don’t need to find a mate
DISADVANTAGES
• no genetic variation between offspring in population
—> this may affect the whole population if the environment changes and conditions become unfavourable.
• e.g. Black Sigatoka is a disease that affects banana plants & this can affect all banana plants as there’s none resistant to it.
Advantages & Disadvantages of sexual reproduction
ADVANTAGES
• creates genetic variation within population —> this means they have different characteristics.
• if environmental conditions change, some individuals will survive —> this can lead to natural selection and evolution as species become better adapted to their new environment .
DISADVANTAGES
• produces fewer offspring as it takes more time & energy
• as there is a requirement to find a mate
—> e.g. male bowerbirds build structures out of twigs and dance to impress females.
• two parents are needed
—> e.g. polar bears live alone, so males have to walk 100 miles to find a mate.
Describe the work of Mendel in discovering the basis of genetics and recognise the difficulties of understanding inheritance before the mechanism was discovered
THE WORK OF MENDEL
• Mendel crossed 2 pea plants of different heights
• offspring produced were all tall pea plants
• then, he bred 2 tall offsprings
—> he discovered that 3 tall offsprings were produced for every one dwarf offspring
• 3:1 ratio of tall : dwarf plants
DIFFICULTIES OF UNDERSTANDING INHERITANCE BEFORE THE MECHANISM WAS DISCOVERED
• Scientists didn’t have background knowledge to properly understand Mendel’s discoveries because they didn’t know about genes, DNA and chromosomes
The Work of Mendel
MENDEL’S CONCLUSIONS ABOUT HEREDITY IN PLANTS:
• characteristics in plants are determined by “hereditary units”
• Hereditary units are passed on to offspring unchanged from both parents, one unit from each parent
• Hereditary units can be dominant / recessive .
—> dominant characteristic will be expressed if an individual has both dominant and recessive unit for a characteristic
