Topic 3 - Reproductive isolation

Different criteria are used to define a species depending on the mode of reproduction. A species that reproduces sexually can be defined by the ability of its members to actually or potentially interbreed to produce fertile offspring. Other criteria used to define a species include: – morphological similarity – biochemical similarity – sharing a common gene pool. Reproductive isolating mechanisms act to maintain distinct species. ● Describe pre-zygotic mechanisms (prevention of zygote formation) including: – temporal isolation – behavioural isolation – mechanical isolation – gamete isolation. ● Describe post-zygotic mechanisms (prevention of fertile hybrids) including: Hybrid inviability Hybrid sterility

what is reproductive isolation

if speciation is to occur and maintned there needs to be some form of reproductive isolation or barrier

what are the 2 types of reproductive isolation

• prezygotic mechanisms

• postzygotic isolation

what is prezygotic mechanisms

prevents fertilisation and zygote formation

what are the types of prezyhotic mechanisms

• mechanial - incompatibility between the sexual organs of different species

• temporal - different breeding seasons due to the time of year

• behavioural - highly specific calls or rituals to member of a population

• geographical - physical distance between species

• gamete - fusion cannot occur and no zygote will be formed

what are the some reasons why fusion will not occur between gametes

• male gamete is not attracted to the egg

• male gamete cannot penetrate the egg cell

• penetrates egg but fusion cannot occur

what is post-zygotic isolation

prevetns fertile offspringe between different species

what are the types of post-zygotic isolation

Hybrid inviability - due to things such as birth defects or other issues the offspring is unlikely to reach reproductive age

hybrid sterility - hybrid is sterile and as a consequence reproductive isolation is mainted