1 Diversity, Classification And Variation Flashcards
Explain gene mutations.
- involve a change in the base sequence of chromosomes.
- substitution, one base is substitute with another.
- deletion, one base is deleted
- order of DNA bases in a gene determines order of amino acids in particular protein, so if mutation occurs in gene, sequence of amino acids it codes for could be altered.
- mutagenic agents increase rate of gene mutations
Why do not all mutations affect the order of amino acids.
- degenerate nature of genetic code means some amino acids are coded for by more than one DNA triplet, so not all substitution mutations will result in change to amino acid sequence of protein-some substitutions will code for same amino acid.
- deletion will change amino acid sequence as it changes number of bases present, which will cause a shift in all base triplets after it.
What does meiosis produce?
4 haploid cells that are genetically different from each other.
Describe chromosome mutations.
Can arise spontaneously by chromosome non-disjunction, failure of chromosomes to separate properly, during meiosis.
Describe what happens in prophase 1.
- chromosomes condense
- nuclear membrane breaks down
Describe what happens in metaphase 1.
- homologous pairs line up next to each other
- spindle forms
- attaches to centromeres
Describe what happens in anaphase 1.
- homologous pairs are separated
- pulled apart to opposite poles
Describe what happens in telophase 1.
- nuclei reform
- cell divides
Describe what happens in prophase 2.
-nuclei break down
Describe what happens in metaphase 2.
- chromosomes line up on equator
- spindle forms
- attaches to centromeres
Describe what happens in anaphase 2.
- chromatids are separated
- pulled apart to opposite poles
Describe what happens in telophase 2.
- nuclei reform
- cell divides
How does crossing over of chromatids create genetic variation.
- crossing over of chromatids occurs in meiosis 1 where a homologous pair of chromosomes pair up, the chromatids twist around each other and bits of chromatids swap over. Chromatids still contain same genes but now have different combination of alleles.
- means that each of 4 daughter cells formed contains different alleles.
How does independent segregation of chromosomes create genetic variation.
- each homologous pair in cell has 1 maternal chromosome and 1 paternal chromosome.
- when homologous pairs separated in meiosis 1, it’s random which chromosomes from each pair ends up in which daughter cell.
- so 4 daughter cells have completely different combinations of those maternal and paternal chromosomes. This leads to genetic variation.
Define genetic diversity.
The number of different alleles of genes in a population. It’s a factor enabling natural selection to occur.
Explain the principles of natural selection.
- random mutation resulting in new alleles of gene.
- many mutations harmful but, in certain environments, the new allele of gene might benefit its possessor, leading to increased reproductive success.
- advantageous allele inherited by members of next generation.
- as a result, over many generations, the new allele increases in frequency in the population.
Describe how antibiotic resistance shows directional selection.
- some individuals in population have alleles that give them resistance to an antibiotic.
- population exposed to the antibiotic, killing bacteria without resistant allele.
- resistant bacteria survive and reproduce without competition, passing on allele that gives antibiotic resistance to offspring.
- after some time, most organisms in population will carry antibiotic resistance allele.
Define directional selection.
Where individuals with alleles for characteristics of an extreme type are more likely to survive and reproduce.
Define stabilising selection.
Where individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce.
Describe how human birth weight shows stabilising selection.
- humans have range of birth weights.
- very small Babies less likely to survive.
- giving birth to large babies can be difficult, so large babies less likely to survive too.
- conditions most favourable for medium-sized babies, so weight of human babies tends to shift towards the middle of the range.
Describe 3 ways in which natural selection adapts species.
Behavioural adaptations- ways and organism acts that increase its chance of survival and reproduction.
Physiological adaptations- processes inside organisms body that increase chances of survival.
Anatomical adaptations- structural features of organism’s body that increases its chance of survival.
What is the calculation of an index of diversity?
d= N(N-1)
———
Sum of n(n-1)
N is total number of organisms of all species.
n. Is total number of organisms of each species.
What is a phylogenetic classification system?
A system that attempts to arrange species into groups based on their evolutionary origins and relationships. It uses a hierarchy in which smaller groups are placed within larger groups, with no overlap between groups. Each group called a taxon. One hierarchy comprises the taxa: domain, kingdom, phylum, class, order, family, genus and species.
Describe courtship behaviour.
- Carries out by organisms to attract a mate of the right species.
- it’s species specific, only members of same species will do and respond to that courtship behaviour. This allows members of same species to recognise each other, prevent interbreeding and make reproduction more successful.
- can be used to classify organisms.
