Saltatory speciation

Saltatory speciation - of chromosome sets in the new...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
Saltatory speciation: Richard Goldschmitt in the Material Basis of Evolution proposed the idea that Macromutations (mutations with big effects) would result in major developmental and phenotypic changes in their carriers producing the so- called hopeful monster . Ridiculed at the time; recently gained a new readership due to the molecular characterization of genes that cause major phenotypic effects (more later on evolution of development). Big problem remains: who is the hopeful monster going to mate with? Chromosomal speciation: Consider a diploid with 2N = 4 chromosomes. If two such individuals failed to undergo the reduction division of meiosis their gametes would be 2N=4. If these gametes were used in fertilization of one another, a new chromosomal number would be established: 4N = 8. If this became stabilized as a new chromosomal type (and this is common in plants), this new type can be reproductively isolated from the original 2N = 4 species. The reproductive isolation would be due to an imbalance
Background image of page 1
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: of chromosome sets in the new zygote: N = 2 gamete crossed to an N = 4 gamete results chromosomal type of 3N = 6. There can be two consequences with this imbalance: i) inviability due to failure during development or ii) instability during chromosome segregation could result in gametes with an incomplete set of chromosomes (aneuploidy). These consequences could have the effect of a reproductive barrier between the original 2N = 4 and the polyploid 4N = 8 type. Speciation can be nearly instantaneous when such chromosomal events are involved (multiples of even numbered ploidy levels: can produce gametes with some exceptions; multiples of odd numbered ploidy levels: usually cannot produce gametes due to imbalance of haploid complements) => speciation. Thus polyploid hybrids are frequency genetically isolated from their progenitors . The simple inversion model (figure 16.17, pg. 457) illustrates another way that chromosomal factors might play a role in speciation....
View Full Document

Ask a homework question - tutors are online