B6: Inheritance, variation and evolution flashcards (unfinished)

What is the difference between sexual (mitosis + meiosis) and asexual reproduction?

• Sexual reproduction

  • Involves the fusion of male and female gametes (sperm + egg / pollen + egg)

  • Mixing of genetic information leading to variation in the offspring

  • Meiosis produces non-identical cells; mitosis produces identical cells

• Asexual reproduction

  • Doesn’t involve gametes, just one parent

  • No mixing of genetic information so leads to clones

  • Only involves mitosis

How are gametes produced by meiosis?

• Copies of all chromosomes made in a cell

• Cell divides twice, forming four gametes (each with 23 single chromosomes - not pairs)

• All gametes genetically different from each other

• NOTE: gametes join at fertilisation to restore normal number of chromosomes. Then mitosis occurs to form an embryo.

Give advantages of sexual reproduction

• Produces variation in the offspring

• If environment changes, variation gives a survival advantage by natural selection

• Natural selection can be sped up by humans in selective breeding to increase food production

Give advantages of asexual reproduction

• Only one parent needed (so faster + more energy efficient as no need to find a mate)

• Faster than sexual reproduction

• Many identical offspring can be produced in favourable conditions (however could become an issue if conditions become unfavourable)

Give some examples of organisms that reproduce by both sexual + asexual reproduction

• Malaria parasite reproduces asexually in human host, but sexually in the mosquito

• Fungi reproduce asexually by spores but also sexually to give variation

• Many plants produce seeds sexually, but reproduce asexually by runners (e.g. strawberry plant) or bulb division (e.g. daffodils)

Define ‘gene’

A small section of DNA on a chromosome. Each gene encodes for a sequence of amino acids to make a specific protein.

What is the structure of DNA?

Two strands (made of polymers of nucleotides) which wrap around eachother to form a double helix. Nucleotides have three parts: a phosphate group, a sugar molecule, and a base (four different bases: A-T and C-G).

Define ‘genome’

The entire genetic material of an organism.

Why is it important that we have studied the entire human genome?

• Helps us search for genes that are linked to a disease (e.g. genes that increase cancer risk)

• Helps us understand + treat inherited disorders (e.g. cystic fibrosis)

• Useful to trace human migration patterns from the past

Describe the stages of protein synthesis.

The order of amino acids (3 bases —> 1 amino acid) in a protein determines its shape and function.

1. Transcription - the base sequence of the gene is copied into a complementary template molecule (mRNA).

2. Passes out of nucleus + into cytoplasm

3. Translation - mRNA molecule attaches to a ribosome. Amino acids brought to ribosome on carrier molecules (tRNA). Ribosome reads the triplets of bases on the mRNA and uses this to join together the correct amino acids in the correct order.

4. Once protein shape is complete, it folds into a unique shape which enables the protein to do its job.

What happens when a mutation happens in a base?

• Mutations happen continuously - most don’t affect protein function (because sometimes different base triplets sometimes encode for the same amino acids)

• A few mutations code for a different shaped protein, so an enzyme may no longer fit the substrate binding site or a structural protein (e.g. collagen) may lose its strength

• Parts of DNA which don’t code for protein affects how genes are expressed (turned on / off).