What are the advantages of sexual reproduction?
- Produces variation in offspring as they are genetically different
- The species can adapt to different environments, survival advantage
- Prevents extinction of the species
What is the disadvantage of sexual reproduction?
Organism must find a mate which requires time and energy
What are the advantages of asexual reproduction?
- Population can increase rapidly if conditions are favourable
- Only one parent is needed
- More time and energy efficient
What is the disadvantage of asexual reproduction?
- Offspring are genetically identical so there is no variation
- If the environment changes all may die
What is sexual reproduction?
- Gamete from mother fuses with gamete from father
- Mixes genetic information from each parent
- Offspring have different combinations of genes
What does meiosis produce?
- Four daughter cells each with half the number of chromosomes
- Genetically different haploid gametes
How can you extract DNA from fruit?
- Grind kiwi up with pestle and mortar
- Mix salt (to make the DNA stick together) and washing up liquid (to break down the cell and nuclear membrane) into the kiwi
- Heat the mixture at about 60° for 5 minutes
- Filter the mixture to get the filtrate
- Cool using an ice bath and gently pour chilled ethanol (to make the DNA precipitate) on top of the filtrate
- Observe the precipitate at the top of the tube
How do genes code for proteins?
- Each triplet of bases codes for one particular amino acid
- The amino acid molecules join together in long chain to form a protein molecule (often enzymes)
- The number and sequence of amino acids determines which protein is produced
What are the stages of transcription?
- The DNA helix is unzipped by the enzyme RNA polymerase breaking the weak hydrogen bonds between base pairs
- RNA polymerase binds to a non-coding DNA just before the gene
- RNA polymerase moves along the DNA strand
- Free RNA nucleotides form hydrogen bonds with the exposed DNA strand nucleotides by complimentary base pairs forming a strand of mRNA
- T is replaced with U in RNA nucleotides
- This happens in the nucleus and when completed will travel to the ribosome
What are the stages of translation?
- The mRNA strand travels through cytoplasm and attaches to ribosome
- For every 3 mRNA bases, the ribosome lines up one complimentary molecule of tRNA (codon)
- tRNA molecules transport specific amino acids to the ribosome
- Used tRNA molecules exit and collect another specific amino acid
- The chain of amino acids in the correct order is called a polypeptide
What is a phenotype?
Visible characteristics of an organism which occur as a result of its genes
How does a genetic variant affect coding DNA?
- Will alter the sequence of bases
- Therefore will change the sequence of amino acids
- This alters the final structure of the protein produced
How does a genetic variant affect non-coding DNA?
- The enzyme RNA polymerase binds to non-coding DNA
- So a change in the order of bases can affect the amount of RNA polymerase that can bind to it
- If less RNA polymerase can bind, less mRNA can be formed and the structure of the final protein is affected
What conclusions did Gregor Mendel come to?
- Offspring inherit ‘hereditary units’ from each parent
- One unit is received from each parent
- Units can be dominant or recessive and cannot be mixed together
What is a gamete?
An organism’s reproductive cell which has half the number of chromosomes (23)
What is an allele?
The different forms of the gene
What is the difference between dominant and recessive alleles?
Dominant - only one out of the two is needed for the corresponding phenotype to be observed
Recessive – two copies are needed for the corresponding phenotype to be observed
What does homozygous mean?
Inherited alleles are the same (e.g. two dominant or two recessive alleles)
What does heterozygous mean?
When one of the inherited alleles is dominant and the other is recessive
What is a genotype?
The combination of alleles an individual has, that determine characteristics
What is a zygote?
The development stage immediately after fertilisation (a diploid cell formed from two haploid gametes)
What causes genetic variation?
Random mutation – in gametes, produces offspring with ‘brand-new’ phenotypic characteristics
Sexual reproduction – the offspring has a new combination of characteristics from its parents
What were the outcomes of the human genome project?
- Improved understanding of genes linked to different diseases
- Helped in the treatment of inherited disorders
- Helped in tracing human migration patterns from the past
