Question

Your textbook authors make the claim that "sympatric species with matching chromosome numbers are rare." Why is this?

1) because allopatric speciation is far more common

2) because sympatric speciation has only been hypothesized but not documented

3) because coexisting populations need a boundary to gene flow before divergence can occur, and differences in chromosome numbers provide this

4) because macroevolution is just a theory

Answer 1

Sympatric species with matching chromosome numbers are rare because allopatric speciation is more common and sympatric speciation often involves chromosomal errors, such as polyploidy, leading to reproductive isolation.

1) because allopatric speciation is far more common

Step-by-step explanation:

The claim that "sympatric species with matching chromosome numbers are rare" primarily stems from the idea that allopatric speciation is much more common than sympatric speciation. Allopatric speciation involves geographical separation, leading to reproductive isolation and eventually genetic divergence. Sympatric speciation, however, occurs without geographic separation and can often involve chromosomal errors during cell division, such as polyploidy or aneuploidy. This mode of speciation is more frequently observed in plants and less commonly in animals. In sympatric speciation, even without physical barriers, reproductive isolation needs to be established for species divergence to occur which makes the presence of matching chromosome numbers less likely among sympatric species.