Reproduction Flashcards
All 30 cards in this deck
What is asexual reproduction?
Reproduction involving one parent that produces genetically identical offspring (clones).
State two advantages of asexual reproduction.
No need to find a mate, and a rapid reproductive cycle (many offspring produced quickly).
What is the main disadvantage of asexual reproduction?
There is no variation in the population, so all offspring are susceptible to the same disease or environmental change.
State one advantage and one disadvantage of sexual reproduction.
Advantage: it produces variation in the population. Disadvantage: a mate must be found.
True or false? Offspring produced by sexual reproduction are genetically identical to their parents.
False. Sexual reproduction produces genetically different offspring; asexual reproduction produces genetically identical clones.
Which type of reproduction is an advantage if the environment changes or a new disease appears, and why?
Sexual reproduction, because the variation it produces means some offspring may survive the change.
What does meiotic cell division produce?
Four genetically different haploid gametes from one parent cell.
What does 'haploid' mean?
The cell has half the number of chromosomes of a body cell (one set).
What is a gamete?
A haploid sex cell, e.g. a sperm cell or egg cell.
How do you work out the number of chromosomes in a gamete?
e.g. the diploid number of a mouse is 40
- Gametes are haploid, so they have half the diploid number.
- Divide by 2: chromosomes in a mouse sperm cell.
How do the products of meiosis differ from the products of mitosis?
Meiosis gives four genetically different haploid cells; mitosis gives two genetically identical diploid cells.
True or false? The gametes made by meiosis from one cell are all genetically identical.
False. They are genetically different from each other and from the parent cell.
Describe the structure of a DNA molecule.
A polymer of two strands of nucleotides coiled together to form a double helix.
What three parts make up a DNA nucleotide?
A sugar and a phosphate group, with one of four different bases attached to the sugar.
What type of bond joins the base pairs holding the two DNA strands together?
Weak hydrogen bonds between complementary base pairs.
Which bases pair together in DNA?
e.g. one strand reads A–C–G
A pairs with T and C pairs with G, so the complementary strand reads T–G–C.
What is the difference between a gene and a genome?
A gene is a section of a DNA molecule that codes for a specific protein; the genome is the entire DNA of an organism.
What are the steps to extract DNA from fruit?
e.g. from a strawberry
- Mash the fruit and mix with salty water and detergent – detergent breaks down cell membranes, salt makes the DNA clump.
- Filter to remove the cell debris.
- Add ice-cold ethanol – the DNA is insoluble in it and appears as white strands.
How does the order of bases in a gene decide the protein that is made?
The order of bases decides the order of amino acids, and the amino acid chain folds to give a specifically shaped protein, e.g. an enzyme.
Where does RNA polymerase bind at the start of transcription?
To non-coding DNA located in front of the gene.
What does RNA polymerase do in transcription?
It produces a complementary mRNA strand from the coding DNA of the gene.
What is a codon?
A triplet of bases in mRNA that codes for one specific amino acid.
What are the steps of translation?
e.g. an mRNA strand made from the gene for an enzyme
- The mRNA attaches to a ribosome.
- tRNA transfers amino acids to the ribosome, matching each codon of the mRNA.
- The amino acids are linked together to form a polypeptide – here, the enzyme.
How do you work out how many amino acids a length of mRNA codes for?
e.g. an mRNA strand of 12 bases
- Each amino acid is coded for by a triplet of bases (one codon).
- Divide the number of bases by 3: amino acids.
What is a genetic variant?
A different version of a gene, caused by a change in the sequence of DNA bases.
How can a genetic variant in the non-coding DNA of a gene affect phenotype?
It changes how well RNA polymerase binds, altering the quantity of protein produced.
How can a genetic variant in the coding DNA of a gene affect phenotype?
It alters the sequence of amino acids, changing the protein's shape and therefore its activity.
True or false? Genetic variants in non-coding DNA cannot affect an organism's phenotype.
False. They can alter the binding of RNA polymerase and so change the quantity of protein produced.
How can a genetic variant in the coding DNA of an enzyme's gene stop the enzyme working?
The changed amino acid sequence changes the shape of the active site, so the substrate no longer fits.
True or false? DNA is a polymer.
True. It is a long chain made of many nucleotide monomers joined together.