Inherited variation Flashcards
Evolution is possible via
inherited variation
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?
discontinous
define: continous
variation in a population forming a continuum of phenotypes. Includes heigh, eye colour.
define: discontinous
variation in a population consisting of discrete, non-overlapping phenotypes. Include blood type, yellow/green pea seeds
is variation for polygenes continous or discontinous?
continuos
can polygene expression be affected by environment
yes but still occurs under controlled conditiosn
2 types of chromosomal variation
polyploidy and aneuploidy
define: polyploidy
when an organism has more than 2 matching sets of chromosomes
how are polyploids formed?
ASK LABROOY
define: autopolyploidy
additional sets of chromosomes come from the same species.
define: allopolyploidy
additional sets of chromosomes come from another species.
many alloploids show
hybrid vigour - superior qualities to that of both parents
define: aneuploidy
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.
define: monosomy
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
define: trisomy
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.
example of trisomy
47, XY+21 (Down’s syndrome) – characteristic facial features, mild-moderate intellectual disability.
