chnages in the genetic makeup of a population Flashcards
gene pool
all the genetic information contained in a population over time
where do new alleles come from
- mutations
this is the random and unpredictable change in genetic information (base sequences)
they occur from errors in DNA replication - sexual reproduction
recombination (crossing over and independent assortment) creates new combinations of existing alleles
what are the two reasons for mutation and explain
induced: a mutation caused by the environment eg smoking / UV rays
spontaneous: a mutation due to an error in DNA replication with no known reason
germline mutations
occurs in reproductive cells
can be passed onto offspring
somatic mutation
occurs in body cells.
cannot be passes onto the offspring
polyploidy
where an individual carries three or more SETS of chromosomes (eg 3n, 4n)`
aneuploidy
individual posses an abnormal number of chromosomes (addition of one or missing one)
trisomy: extra homogulous pair
monosomy: missing one homogulous pait
what are the type of point mutations
point mutation: a change in a single base within a gene
substitution
deletion
insertion
substitution
one base is replaced by another in the sequence
can wither be missense, silent or nonsense
- missense: one amino acid alteration in polypeptide sequence. new base substitution codes for a different amino acid
- nonsense: base substitution codes for a STOP codon. has a serious effect on protein as it is shortened and may fold differently
- silent: base substitution codes for the same codon, no effect on polypeptide
deletion
one base is removed from the sequence of bases in the gene
base insertion
an extra base is added to the sequence of bases in a gene
frame shift
a change in the reading frame caused by an insertion or deletion, not a substitution
types of block mutation
block mutations are changes to sections of a chromosome inverse
translocation
duplication
block deletion
inverse
segment is removed and then replaced in reverse order
deletion
a portion of chromosome is removed
insertion
part of one chromosome is removed and then added to a different chromosome
duplication
a part of the chromosome is copied, resulting in a chromosome having two or more copies of that section
tranlocation
parts of two chromosomes are swapped
points for natural selection
- there is variation within a population
- a selection pressure means that some organisms have a better chance of reproducing than others
- the organisms that can reproduce are likely to pass favourable characteristics (alleles) to the next generation
- greater allele frequency of characteristic is present in the population
gene flow
the movement of alleles between populations by migration of the individuals carrying them.
KP: there must be sexual reproduction for new alleles to be introduced into the population
genetic drift
a chance event happening in the population that significantly changes the frequency of alleles in the population
- more prominent in small populations than in larger
- can make less suitable alleles more common in a population by chance
bottle neck
example of genetic drift
there is a random drastic reduction in the population (due to a natural disaster) which affects the gene pool
gene pool is then limited to the alleles the survivors had.
founder effect
example of genetic drift
members of a large population establish a new population in a new biologically isolated area
(for examples if beetles were blown into an island by a tornado with no other beetles they are the founder of new populations)
monomorphic populations
all members of a population shows one form of a trait
