Reproductive Isolating Mechanisms
Any factor that reduces gene flow between populations of
organisms.
This works to preserve the uniqueness of gene pools,
prevent hybridisation thus reinforcing separateness of
species.
Because species are finely tuned to their niche adding
genes from another species suited to another niche will
cause a reduction in fitness.
Prezygotic Mechanisms
Factors acting before a zygote forms
 Geographical (spatial) – physical barriers preventing
gene exchange. Eg different robin species in NZ can’t
breed together as they are on different islands.
 Temporal (time/season) – breeding doesn’t occur
because reproductive activities (mating, flowering)
occurs at different times, seasons, years between
species.
 Ecological (habitat) – no breeding b/c organisms
occupy different niches in same habitat. Eg ground
dwelling monkey doesn’t breed with tree dwelling
monkey.
 Gamete Mortality – Sperm and egg fail to fuse. Eg
sperm of one species may die inside female of another
species or sperm may not recognise chemical
attractant from another species’ egg.
 Behavioural (ethological) – If an organism can’t carry
out the courtship rituals of another species then mating
won’t occur (b/c male female aggression isn’t reduced,
physiological changes not synchronised (eg ovulation
at time of mating)
 Structural (morphological ) – shape of copulatory
organs (insect lock and key reproductive parts) and
mating pheromones (moths) are species specific.
Postzygotic Isolating Mechanisms
Factors acting after a zygote forms
 Hybrid sterility – offspring of two different species (eg
mule from donkey and horse) is often sterile. Usually
because offspring has an odd chromosome number
(eg 53) – pairing of chromosomes at meiosis to create
gametes can’t occur with an odd number.
 Hybrid Inviability (zygote mortality) – genetic
incompatibility means that even if a zygote forms from
two different species it won’t divide properly because
of unmatched chromosome numbers
 Hybrid breakdown – because of conflict between
genes is often infertile or inviable. Even if the first
generation is fertile (usually with reduced viability &
fertility)
Reproductive Isolating Mechanisms
Any factor that reduces g_______ flow between
p________________ of organisms.
This works to preserve the uniqueness of g______ pools,
prevent h__________n thus reinforcing separateness of
s________s.
Because species are finely tuned to their n______e adding
genes from another species suited to another niche will
cause a r________n in fitness.
Prezygotic Mechanisms
Factors acting before a z__________ forms
 Geographical (spatial) – p________ barriers
preventing gene exchange. Eg different robin species
in NZ can’t breed together as they are on different
i__________s.
 T__________l (time/season) – breeding doesn’t
occur because reproductive activities (mating,
flowering) occurs at different times, s______s, years
between species.
 Ecological (h______t) – no breeding b/c organisms
occupy different niches in same habitat. Eg ground
dwelling monkey doesn’t breed with tree dwelling
monkey.
 Gamete M______y – Sperm and egg fail to fuse. Eg
s______m of one species may die inside female of
another species or sperm may not recognise
c________l attractant from another species’ egg.
 B________l (ethological) – If an organism can’t carry
out the courtship rituals of another species then mating
won’t occur (b/c male female aggression isn’t reduced,
physiological changes not synchronised (eg ovulation
at time of mating)
 Structural (morphological ) – shape of c________y
organs (insect lock and key reproductive parts) and
mating p________s (moths) are species specific.
Postzygotic Isolating Mechanisms
Factors acting after a zygote forms
 Hybrid s________y – offspring of two different
species (eg mule from donkey and horse) is often
sterile. Usually because offspring has an odd
chromosome number (eg 53) – pairing of c________s
at meiosis to create gametes can’t occur with an odd
number.
 Hybrid I________y (zygote mortality) – genetic
incompatibility means that even if a zygote forms from
two different species it won’t divide properly because
of u________d chromosome numbers
 Hybrid breakdown – because of conflict between
genes is often i________e or inviable. Even if the first
generation is fertile (usually with reduced v________y
& f__________)
+
=
?
…not normally because of reproductive isolating mechanisms
Reproductive Isolating Mechanisms
Any factor that reduces gene flow between populations of
organisms.
This works to preserve the uniqueness of gene pools,
prevent hybridisation thus reinforcing separateness of
species.
Because species are finely tuned to their niche adding
genes from another species suited to another niche will
cause a reduction in fitness.
Reproductive Isolating Mechanisms
Any factor that reduces gene flow between populations of organisms.
This works to preserve the uniqueness of gene pools, prevent hybridisation thus reinforcing
separateness of species.
Because species are finely tuned to their niche adding genes from another species suited to
another niche will cause a reduction in fitness.
Match the terms and definitions.
1 If an organism can’t carry out the courtship
rituals of another species then mating won’t occur
(b/c male female aggression isn’t reduced,
physiological changes not synchronised (eg
ovulation at time of mating)
2 Factors acting before a zygote forms
A Gamete Mortality
B Structural (morphological )
C Geographical (spatial)
3 Shape of copulatory organs (insect lock and key
reproductive parts) and mating pheromones
(moths) are species specific.
4 Sperm and egg fail to fuse. Eg sperm of one
species may die inside female of another species
or sperm may not recognise chemical attractant
from another species’ egg.
5 No breeding b/c organisms occupy different
niches in same habitat. Eg ground dwelling
monkey doesn’t breed with tree dwelling monkey.
6 Breeding doesn’t occur because reproductive
activities (mating, flowering) occurs at different
times, seasons, years between species.
7 Physical barriers preventing gene exchange. Eg
different robin species in NZ can’t breed together
as they are on different islands.
8 Genetic incompatibility means that even if a
zygote forms from two different species it won’t
divide properly because of unmatched
chromosome numbers
9 Factors acting after a zygote forms
D Behavioural (ethological)
E Ecological (habitat)
F Prezygotic Mechanisms
G Temporal (time/season)
H Postzygotic Isolating
Mechanisms
I Hybrid breakdown
J Hybrid sterility
10 Offspring of two different species (eg mule from
donkey and horse) is often sterile. Usually
because offspring has an odd chromosome
number (eg 53) – pairing of chromosomes at
meiosis to create gametes can’t occur with an odd
number.
11 Because of conflict between genes is often
infertile or inviable. Even if the first generation is
fertile (usually with reduced viability & fertility)
K Hybrid Inviability (zygote
mortality)
A
B
C
D
E
F
G
H
I
J
K