Section 4 : Genetic Diversity Flashcards
What is a gene mutation?
- A change in the DNA base sequence
- Can arise spontaneously during DNA replication
How does a mutation lead to a non-functional protein?
- Change in the DNA base sequence
- Changes sequence of codons on mRNA
- Changes sequence of amino acids in primary structure
- Changes position of hydrogen, ionic and disulfide bonds in the tertiary structure
- Changes tertiary structure
- Substrate can’t bind to active site and form enzyme substrate complex
What is a base deletion?
- One nucleotide/ base removed from DNA base sequence
- Frameshift
What is a base substitution?
- Nucleotide/ base in DNA replaced with another base/ nucleotide
- Can change one triplet and change amino acid
- May not (degenerative)
What is a mutagenic agent?
- Increase the rate of gene mutation
- Ultra violet light or alpha particles
What is separated in meiosis 1?
- Separates homologous chromosomes
- Chromosomes arranged in homologous pairs
What is separated in Meiosis 2?
- Sister chromatids
- Forms 4 haploid cells that are genetically different
How does meiosis create genetic variation?
-
Crossing over between homologous chromosomes
- Alleles exchanged between chromosomes. Creates new combos of mum/dad
-
Independent Segregation
- Random alignment if homologous chromosomes - random which chromosome goes into each daughter cell
- Random fertilisation when 2 games fuse
What is the importance of meiosis?
- 2 divisions create haploid gametes
- Diploid number restored at fertilisation
- Maintains chromosome number for generations
- Independent segregation and crossing over creates genetic variation
What is chromosome non-disjunction (mutation)?
- Homologous chromosomes fail to separate during meiosis 1 or sister chromatids fail to separate in meiosis 2
- One gamete has an extra copy. One has none
- Upon fertilisation zygote has 1 fewer (dies), extra (survives)
- Causes down syndrome
How do you calculate the number of possible different combinations of chromosomes in daughter cells
following meiosis?
2n where n = the number of pairs of homologous chromosomes
How do you calculate the number of different combinations of chromosomes following the random
fertilisation of two gametes
(2n)2 where n = the number of pairs of homologous chromosomes
What are the different outcomes of mitosis and meiosis?
- Mitosis produces diploid cells whereas meiosis produces haploid cells
- Daughter cells genetically identical to each other and parent cell in mitosis whereas in meiosis,
daughter cells are genetically varied - Mitosis produces 2 daughter cells whereas meiosis produces 4 daughter cells
What is genetic diversity?
- Number of different alleles of a gene in a population
What is a population?
- Population – group of interbreeding individuals of the same species living in the same area
What are the principles of natural selection?
- Variation of alleles exists in population due to random DNA mutations
- Selection pressure / change in environment
- Those with advantageous allele have increased chance of survival and reproduction
- Those surviving / reproducing pass advantageous allele to offspring
- Frequency of advantageous allele and (named) characteristic increases in the population
-
Over many generations / long period of time
(evolution: change in allele frequency over time)
What is directional selection?
- Change to the environment
- Selection pressure acts one side
of the mean - One extreme phenotype more
likely to survive and produce - Bacteria with gene for
antibiotic resistance - Mean phenotype changes
What is stabilising selection?
- Stable environment
- Selection pressure acts either side of the mean
- Both extremes of phenotype less likely to
survive and reproduce - Very small or very large babies
- Mean phenotype remains the same
What are the different types of adaptations?
- Anatomical
- Structural features of organisms body / observed structures
- E.g. whales thick layer of blubber helps keep warm in cold sea
- Physiological
- Processes inside the body - E.g. brown bears hibernate in the winter, lower metabolism to conserve energy
- Behavioural
- Ways an organism acts
- E.g. possum plays dead if they’re being threatened by a predator, to escape attack
Exam Question: There is a positive correlation between the size of snow geese and how far north they breed. A
large size results in snow geese being adapted for breeding in colder conditions. Explain how. (2
marks)
✓ Small surface area to volume ratio / more fat
✓ Lose less heat (to the environment) / for insulation
✓ When they are sitting on eggs
Exam Question: The further north, the greater the risk of snow. Use this information to explain how natural
selection might have accounted for the effect of latitude on the percentage of white snow geese. (3 marks)
✓ Snow lying longer / melts slower further north / at greater latitudes
✓ White geese better camouflaged (further north)
✓ Predation linked to survival / reproductive success
Exam Question: The scientists concluded that an increase in phosphate in the embryo was linked to growth of
the embryo. Suggest two reasons why an increase in phosphate can be linked to growth of the
embryo. (2 marks)
✓ (Phosphate required) to make RNA
✓ (Phosphate required) to make DNA
✓ (Phosphate required) to make ATP/ADP
✓ (Phosphate required) to make membranes
✓ (Phosphates required) for phosphorylation
What is a species?
- A group of similar organisms that can reproduce to produce fertile offspring
- They have the same genes but different alleles
Exam Question: How could scientists show that the two populations are the same species? (2 marks)
✓ Breed together red pandas from different areas
✓ If fertile offspring, then still same species
Why do species show courtship behaviours?
- Allows recognition of members of the same species
- Production of fertile offspring
- Indication of sexual maturity
- Recognition/attraction of opposite sex
- Stimulate release of gametes
- Establishes a pair bond to raise young
- Synchronise mating → maximum probability that sperm will fertilise ovum
What is a phylogenetic classification system?
Arranges species into groups based on their evolutionary origins (common ancestors) and
relationships
What is a hierachy?
- Smaller groups placed within larger groups
- No overlap between each group
- Each group = taxon
What are the different hierarchy groups called?
- Domain (delicious)
- Kingdom (king)
- Phylum (prawn)
- Class (curry)
- Order (or)
- Family (fat)
- Genus (greasy)
- Species (sausages)
What is the advantage of having a binomial system?
- Avoids confusion as they have the same common name
What are the ways of clarifying evolutionary relationships?
- Genome Sequencing
- Immunology
What is genome sequencing?
Compare the order of base sequence of whole genome of different species
- Higher % match = more closely related e.g. humans and chimps = 96%
What is immunology?
- DNA → mRNA → sequence of amino acids in polypeptide
- So tertiary structure of protein tells us about sequence of DNA
- If same antibody binds to a specific antigen then it is closely related
