Genetics HL Flashcards
What is S phase of Interphase
DNA replication that will result in two chromosomes that contain two identical DNA strands
What is S phase of Interphase
DNA replication that will result in two chromosomes that contain two identical DNA strands called sister chromatids. Held together by a centromere
What happens to sister chromatids in meiosis II
Become independent chromosomes each made of a single DNA strand
Meiosis Phases
Two divisions following the same pattern
Prophase, Metaphase, Anaphase, Telophase
Meiosis I
reduction division (diploid → haploid) where chromosomes are separated
P-1: Chromosomes condense and the nuclear membrane breaks down. Homologous chromosomes form bivalent where they cross over
Prophase I
Chromosomes condense and the nuclear membrane breaks down. Homologous chromosomes form bivalent where they cross over
Metaphase I
Spindle fibres from opposing centrosomes connect to bivalent at the centromeres and align them along the middle of the cell
Anaphase I
Spindle fibres contract and split at the bivalent and the homologous chromosomes move to opposite ends of cell
Telophase I
Chromosomes condense and the nuclear membrane reforms. cell divides (cytokinesis) to form two haploid daughter cells
Meiosis II
Separated the sister chromatids and are not identical during crossing over in prophase I
Prophase II
Chromosomes condense and the nuclear membrane breaks down. Centrosomes move to opposite poles (perpendicular to before)
Metaphase II
Spindle fibres from opposing centrosomes attach to chromosomes and align along equator
Anaphase II
spindle contract and separate the sister chromatids. Now chromatids called chromosomes move to opposite poles
Telophase II
Chromosomes decondense, nuclear membrane reforms, cells divide (cytokinesis) to form four haploid daughter cells
What is the final product of meiosis
four genetically destinct haploid daughter cells
independent assortment
how pairs of alleles separate independently from one another during gamete formation
the inheritance of one trait is dependent to the inheritance of any other trait. True or false
False
it is independent
How does Independent assortment come about
Random orientation of pairs of homologous chromosomes in meiosis I
When will independent assortment not occur
if two genes are located on the same chromosome
Synapsis
How homologous chromosomes become connected in prophase I. Connected by a protein-RNA
bivalent
bi = two chromosomes
autosomes always undergo synapsis during meiosis, sex chromosomes often remain unpaired. True or False
true
Chiasmata
hold the homologous chromosomes together as a bivalent until anaphase I
How do chiasmata form
- non-sister chromatids break and recombine with their homologous partner (crossing over)
- non-sister chromatids remain physically connected at these points of exchange
Chiasmata formation between non-sister chromatids can result in the exchange of alleles (recombination)
Crossing over cannot increase genetic diversity. True or false
False
It can
what does a large gene pool suggest
High amounts of genetic diversity increase the chances of biological fitness
5 Mechanisms of Change
- Mutation
- Gene Flow
- Sexual reproduction
- Genetic Drift
- Natural Selection
Population Bottlenecks
When a population side reduces by more than 50%. The surviving population has less genetic variability than before and will be subject to a higher level of genetic drift. As the newly developing gene pool will be divergent to the original
Founder Effect
when a small group breaks away from a larger population to colonise a new territory. It does not have the same level of diversity and can result in more genetic drift. And as they increase in size the gene pool will not represent the original gene pool
What are the three types of selection
Stabilising Selection
Directional Selection
Disruptive Selection
Stabilising Selection
intermediate phenotype is favoured at the expense of both phenotypic extremes
- Remove extreme phenotypes and happens when environmental conditions are stable and competition is low
Directional Selection
phenotypic extreme is selected at the cost of the other phenotypic extreme
- Clear shift in one direction the beneficial extreme
- Happens in response to gradual changes in environmental condition
Disruptive Selection
both phenotypic extremes are favoured at the expense of the intermediate phenotypic ranges
- phenotypic distribution to deviate from the centre and results in a bimodal spread
- occurs when fluctuating environmental conditions
- Continued separation of phenotypic variants may eventually split the population into two distinct sub-populations
Types of reproductive isolation
- Prezygotic isolation – occurs before fertilisation can occur (no offspring are produced)
- Postzygotic isolation – occurs after fertilisation (offspring are either not viable or infertile)
Temporal Isolation
two populations differ in their periods of activity or reproductive cycles
Behavioural Isolation
two populations exhibit different specific courtship patterns
Geographic Isolation
two populations occupy different habitats
Speciation
the evolutionary process that results in the formation of a new species from a pre-existing species. And occur when isolating mechanisms prevent two breeding organisms from producing fertile, viable offspring
Two mechanisms can occur during speciation
- Allopatric speciation (geographical isolation)
- Sympatric speciation (reproductive isolation)
Allopatric Speciation
when a geographical barrier physically isolates populations of an ancestral species
- two populations begin to evolve separately as a result of cumulative mutation, genetic drift and natural selection
Sympatric Speciation
divergence of species within the same geographical location (no physical barrier)
- Results of reproductive isolation of two populations as a result of genetic abnormalities
Polyploidy Offspring
viable and fertile but cannot interbreed with the original parent population
what do fertile polyploid offspring require
two polyploid parents as reproduction with the original parent results I’m offspring with uneven amount of chromosome sets
Phyletic Gradualism
continuous change
Punctuated Equilibrium
Rapid change then stable
