4 Genetic Information: 9 Genetic Diversity Flashcards
What is a gene mutation?
A change in the base sequence of chromosomes.
When do gene mutations arise?
They arise spontaneously during DNA replication.
What are the different types of gene mutation? What happens in each?
Base deletion:
- a single base is removed
- results in a frameshift to the left in which different bases are now read as triplets
- causes severe changes to the phenotype
Base substitution:
- a single base is replaced with a different one
- could form a stop codon which results in premature termination of protein synthesis
- could form a different codon for a different amino acid which results in a different protein shape
- could form a different codon for the same amino acid which has no effect on the polypeptide (due to the degenerate nature of the genetic code)
Base insertion:
- single or more bases are added
- results in a frameshift to the right in which different bases are now read as triplets
- causes severe changes to the phenotype
- if three bases are added, there is no frameshift
What can mutagenic agents do?
Increase the rate of gene mutation.
When can chromosome mutations arise?
Spontaneously by chromosome non-disjunction during mitosis.
What does meiosis produce?
4 daughter cells that are genetically different from each other.
What is the process of meiosis?
- The DNA unravels and replicates, forming chromatids.
- The DNA condenses to form chromosomes.
- Meiosis 1 - the chromosomes arrange themselves into homologous pairs which come together and pair up
- crossing over occurs
- The homologous pairs are then separated, halving the chromosome number.
- Meiosis 2 - the centromeres in the chromosomes divide.
- Four haploid gametes that are genetically different from each other are produced.
How does meiosis create variation?
Crossing over:
- recombinant chromosomes are produced where each combines DNA inherited from each parent
1. homologous chromosomes associate and a chiasma forms
2. alleles are exchanged
3. new combinations of alleles are formed
Independent segregation of homologous chromosomes:
- in meiosis 1, it’s random which chromosome from each pair ends up in which daughter cell
- the daughter cells have completely different combinations of maternal and paternal chromosomes
Random fertilisation:
- any sperm can fertilise any egg
- produces new allele combinations
What is genetic diversity?
The number of different alleles of genes in a population.
It is a factor enabling natural selection to occur.
What are the principles of natural selection in the evolution of populations?
M - mutations result in new alleles, creating variation
A - advantageous allele
R - reproductive and survival success increases
I - inherited by offspring
A - allele frequency increases over many generations
What is directional selection?
Individuals with alleles for extreme characteristics are more likely to survive and reproduce.
Changes the characteristics of the population.
How does antibiotic resistance show directional selection?
- Some individuals in a population have the resistance allele.
- The population is exposed to the antibiotic, killing those without the resistant allele.
- The resistant bacteria survive and reproduce, passing on the resistant allele to their offspring.
- After many generations, most individuals in the population will carry the resistant allele.
What is stabilising selection?
Individuals with alleles for characteristics closest to the mean are more likely to survive and reproduce.
Preserves the characteristics of a population.
How does human birth weight show stabilising selection?
- Very small babies are less likely to survive (they find it hard to maintain their body temperature) as well as large babies (giving birth to them can be difficult).
- Conditions are most favorable for medium-sized babies so the weight of human babies tends to shift towards the mean of the range.
What does natural selection result in?
Species that are better adapted to their environment.
