10.1 Flashcards
What happens in prophase of mitosis
replicated chromosome condense completely and independently and then the homologue pairs of replicated chromosome align closely before condensation is completed.
What is a synapsis
the fusion of chromosome pairs at the start of meiosis
What are sister chromatids
they have the same alleles as well as the same genes because they are identical copies of each other
What are non sister homologs chromatids
they have the same gene at the same loci but for different alleles
How does crossing over begin
Covalent bonds in the backbone of the DNA double helix at identical positions of the non-sister homologous chromatids, causing the helices to switch sides. The position of the chromatids are switched so that when the backbones are healed (ligated), a chromatid is covalently bonded to the non-sister chromatid.
What is a chiasma (chiasmata)
a point of exchange between the two non-sister chromatids that creates an X shaped connection
When do chiasmata remain
through metaphase I and they help bind the bivalent together as it is pulled to the metaphase plate
What is the result of crossing over
the exchange of alleles between non-sister chromatids
Where can crossing over occur
at almost any location along the tetrad (some have greater frequencies), leading to a nearly limitless number of possible combinations between non-sister homologous chromatids. Increasing genetic diversity present
What does a tetrad consist of?
two pairs of sister chromatids that have synapsed
What do genes found on different chromosomes show
independent assortment
what does independent assortment mean
that the allele inherited for one gene does not influence which allele is inherited for a different gene
What is geographic isolation
the separation of a population by a physical Marie that reduces or prevents the genetic flow
What is allopatric speciation
when a new species develops as a result of pat of a population becoming geographically isolated from other populations
What are types of physical barriers
things that keep populations in two separate places such as entire oceans or even a small strip of land between neighboring ponds. Sometimes after a storm, a small population may become isolated
What does geographic isolation sometimes lead to
allopatric speciation
In what conditions can populations at extreme of the geographic range no longer interbreed
when the species has a large enough Ange and slow enough gene flow
such as in salamandars
What is behavioural isolation
any behaviour that acts to reduce or eliminate gene flow between portions of a population, such as variations in courtship song o location
What is sympatric speciation
when a portion of a population develops into a new species whilst still living in the same geographic area as the ancestral population. sympatric speciation can occur due to behavioural temporal
Wan does behavioral isolation occur
when genetically influences differences in behaviour have the effect of reduction or preventing mating between different portions of the population.
What is an example of behavioral isolation
in mating song in male crickets has a preference for different variations in female tickets.
What can behavioural isolation sometimes lead to
sympatric speciation
What is temporal isolation
occurs when portions of a population are reproductively active at different times. Portions of the population may mate or flower at different times fo a day or during different seasons
Temporal isolation
any shift in the timing fo a behaviour that acts to reduce or eliminate gene flow between portions of a population
