Sexual Dimorphism & Genetic Drift?

[LiL Homie]

1. What are 2 traits OTHER then size & distribution of body hair that show Sexual Dimorphism in humans?

*Would genitilia be one example? My book only gives 5 sentences on it, and it includes size & hair sistribution as the examples... and wikipedia isn't helping.

2. Why can genetic drift often lead to a reduction in genetic variation within a population?

3. Why are mutations by themself NOT considered to be a significant contributor to changing gene frequencies in a population?

*I think it's because mutation is a random process, so it doesn't occur frequent enough. I'm not sure though.
-------------------
Please Help Me, and also Let me know if I'm on the right track. I would really appreciate your help. Thank You!

[Darby]

Usually sexual dimorphism relates to things that are not involved in successful reproduction, like genitalia (primary characteristics), but rather differences between adult genders that don't directly relate (and there are several secondary sexual characteristics to choose from). In humans, some of these differences are pretty obscure, like subcutaneous fat, but several should be obvious.

[Locus]

1. What are 2 traits OTHER then size & distribution of body hair that show Sexual Dimorphism in humans?

Breasts, average high, share of hips... genitalia also - if not written that characters must be secondary.

2. Why can genetic drift often lead to a reduction in genetic variation within a population?

If within some population there is several allels of the same gene, by the result of the drift all of the allels can be lost apart from one (ultimate form of the frequensy change) - choised randomly if it is pure drift - without any selection pressure.

3. Why are mutations by themself NOT considered to be a significant contributor to changing gene frequencies in a population?

*I think it's because mutation is a random process, so it doesn't occur frequent enough. I'm not sure though.

Yes, you are right - it is reasone for this.

[AstusAleator]

#2: To clarify, genetic drift is the random deletion of segments of a population that could contain any combination of alleles, but the end result is a change in gene frequency.

#3: Mutations by themselves are not significant because without selection pressure, they have a negligible effect, like you said. The key point is that mutations are operated on by selection to cause significant changes in gene frequency.