Biology help?

Question

1. Which of the following can occur to two segments of a population if they are geographically isolated?
A. They can only share some types of genes.
B. Eventually, they become separate species.
C. They find a way to come back together.
D. Both groups most likely become extinct.


2. Which of the following best explains why organisms of the same species that become isolated eventually become different from each other over time?

A. They do not have any of the same genes.
B. They are exposed to different environments.
C. Their DNA mutates.
D. They both find ways to survive

Answer 1

The answers your teacher wants:
1B
2B

The correct answers:
1D Most species have become extinct. Extinction is the eventual scenario for almost all species.
2C The way that new alleles arise is through mutation. Without new alleles, the two populations would remain the same species.

Answer 2

Wow, those are some seriously poorly worded questions.

1 depends on how long they are geographically isolated.

A - Can't be true, since if they are isolated, they can't share any genes any more, however they would still have very similar genes having started out as members of the same population.

B - This is possible, but not necessarily going to happen. It would depend on how long they were isolated, if there were any differences in allele frequencies amongst the two separate populations, and the selective pressures on each population.

C - This is also possible. If the two populations are only isolated for a few generations, they can probably reintegrate with no problems. If they have been separated for hundreds or millions of generations, then genetic drift among each population may well make interbreeding no longer viable.

D - This is also quite possible. A lot of species go extinct. Most of the ones that have ever existed have gone extinct. Eventually, it's quite likely that the species that make up each population will indeed go extinct.

The 'best' answer is probably B, but 'best' isn't saying much. Very poor question construction.

2 - Almost as bad.

A - Not true, since they started out as the same species, the two populations will have very similar genetic make-ups, initially. Many of their genes will be the same, at least to start with.

B - This is true, but it is the selective pressures of those different environments that drives the selection of different alleles, not the environmental exposure itself.

C - This is also true, however without the selective pressure of the environment, the mutations in the DNA within each population will not be selected. C doesn't matter except when combined with B. Also, even if there were no mutations, selective pressures from the different environments each population finds itself in could select existing variation in the genetics of each population, creating a species shift even if there are no new mutations present.

D - Also true. It is the selection of those individuals in the population that are able to survive and reproduce in the conditions presented by the new environment, combined with the potential variability inherited from the genetic make-up of the population at the time of isolation, as well as any new mutations that might arise in the population that drive the evolutionary process. So it is inextricably linked between B, C and D.

I'd have to say the 'best' answer for 2 is D, since if the populations don't survive, any other changes (selective pressure from the environment, or new mutations in the population) are pretty much a moot point.

Overall, an appalingly constructed question, and your teacher should be ashamed of having it displayed in public.

Answer 3

When a population is split into two geographically isolated populations, the cannot share genes, and if they're isolated they can't "find" a way to come back together. I don't like D either, because that would be pointless. So, you're left with B (This answer is also implied by the next question).

For this one, C is the best answer, but not a complete answer. Their DNA's both mutate, but because they are exposed to different environments, natural selection will affect the two populations differently, so they will naturally diverge over time, eventually giving 2 distinct species.

Answer 4

1b (but phrased "can occur" they could come back together in some circumstances)

2. b c and d are possible
2 is a stupid question they MIGHT be exposed to diff environronments but not necissarilly, they MIGHT undergo mutations that differ from other population but maybe not, and they MIGHT find different ways to survive.
They share all the same genes but possibly different allele frequencies due to founder effect or something. But my pont is they might not change at all or signifigantly and b c and d could all contribute to changes between the populations but not necicarily.... tell your teacher to go back and take high school biology again

Answer 5

1 B
2 C

Answer 6

1-B
2-B the genetic factor is stable the variable is environment