Flashcards in Inherited variation Deck (27):
Evolution is possible via
2 types of inherited variation?
gene variation and chromosomal variation
2 types of gene variation?
variation due to single genes and poly genes
types of inheritance for single genes?
recessive/dominant, codominant (spots), incomplete dominance (combined)
what populations can single gene variation result in?
monomorphic and polymorphic populations
define: monomorphic population
members show no variation of a particular trait (due to single gene with one allele)
define: polymorphic poluation
members show several variants of a particular trait (due to single gene with multiple alleles)
is variation for single genes discontinuous or continuous?
variation in a population forming a continuum of phenotypes. Includes heigh, eye colour.
variation in a population consisting of discrete, non-overlapping phenotypes. Include blood type, yellow/green pea seeds
is variation for polygenes continous or discontinous?
can polygene expression be affected by environment
yes but still occurs under controlled conditiosn
2 types of chromosomal variation
polyploidy and aneuploidy
when an organism has more than 2 matching sets of chromosomes
how are polyploids formed?
additional sets of chromosomes come from the same species.
additional sets of chromosomes come from another species.
many alloploids show
hybrid vigour - superior qualities to that of both parents
when the chromosome differs by a small number (usually 1-2) from the standard number of chromosomes for the species
why does aneuploidy occur?
usually due to non disjunction (also translocation...)
describe non disjunction
when a chromosome pair fails to separate during meiosis and both copies of it go to the same gamete. This results in the gametes having 2/0 copies of a particular chromosome.
Normal gamete + gamete with 0 copies of a chromosome
why is monosomy usually lethal
due to loss of key genes; though polyploids can tolerate loss of 1-2 members of a chromosome set, due to presence of other chromosomes.
example of monosomy
Turners’ syndrome 45, X0: affects females, causes sterility due to lack of uterus, abnormal breast development
Normal gamete + gamete with 2 copies of a chromosome
why is trisomy usually lethal
causing miscarriage or severe physical/mental abnormalities leading to early death. Trisomy-21 is the only exception.