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lpetrich · 03-29-2003, 12:57 PM

This paper discusses possible reasons why sexually-reproducing organisms can have prominent haploid phases as well as prominent diploid phases.

Both haploid and diploid phases have their advantages:

Being diploid will mask bad mutations, and it offers greater genetic variety. It is good for large, long-lived organisms, those which take a long time to reproduce by cellular standards.

Being haploid is more convenient for multicellular organisms where different parts can be essentially independent, as is the case with many fungi. Bad mutations will have instand bad effects, removing them by selection. Imagine some mold growing on a loaf of bread. Mold on one end of the loaf will be independent of mold on the other end -- even if both bits of mold had grown from one spot.

Many fungi are haploid most of the time, with only a one-cell diploid phase; this is the opposite of the usual animal-kindgom situation, where it is the haploid phase that is only one cell.

But even in the animal kingdom, haploid phases sometimes reappear, as in species where the female is diploid and the male is haploid (ants, bees, wasps, etc.).

Plants have both haploid and diploid phases (gametophytes, sporophytes); the haploid phase produces gametes (sex cells) and the diploid phase spores in non-seed plants like mosses and ferns.

However, in seed plants, the haploid phase is only a few cells, and grows inside of the diploid phase (most of the plant).

lpetrich · 03-29-2003, 01:41 PM

Here are some slides for a biology class on the evolution of sexual dimorphism; they include a discussion of why there are different-sized gametes (egg and sperm cells) in multicelled organisms and shows some nice examples of different-looking sexes. Note on page 4 that the flashy-looking birds are male, while the plain-looking birds are female -- which is typical for birds.

Ted Hoffman · 03-31-2003, 04:10 AM

Thanks Lpetrich and Itzpapalotl

Itzpapalotl - couldnt you find easier links? Now I have given up on the whole damn subject. I got a glossary of genetics and got a kingsize headache.
I am trying Lpetrichs' links. DOes anyone know of a link written in English?

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03-29-2003, 12:57 PM	#11
lpetrich Contributor Join Date: Jul 2000 Location: Lebanon, OR, USA Posts: 16,829	This paper discusses possible reasons why sexually-reproducing organisms can have prominent haploid phases as well as prominent diploid phases. Both haploid and diploid phases have their advantages: Being diploid will mask bad mutations, and it offers greater genetic variety. It is good for large, long-lived organisms, those which take a long time to reproduce by cellular standards. Being haploid is more convenient for multicellular organisms where different parts can be essentially independent, as is the case with many fungi. Bad mutations will have instand bad effects, removing them by selection. Imagine some mold growing on a loaf of bread. Mold on one end of the loaf will be independent of mold on the other end -- even if both bits of mold had grown from one spot. Many fungi are haploid most of the time, with only a one-cell diploid phase; this is the opposite of the usual animal-kindgom situation, where it is the haploid phase that is only one cell. But even in the animal kingdom, haploid phases sometimes reappear, as in species where the female is diploid and the male is haploid (ants, bees, wasps, etc.). Plants have both haploid and diploid phases (gametophytes, sporophytes); the haploid phase produces gametes (sex cells) and the diploid phase spores in non-seed plants like mosses and ferns. However, in seed plants, the haploid phase is only a few cells, and grows inside of the diploid phase (most of the plant).

03-29-2003, 01:41 PM	#12
lpetrich Contributor Join Date: Jul 2000 Location: Lebanon, OR, USA Posts: 16,829	Here are some slides for a biology class on the evolution of sexual dimorphism; they include a discussion of why there are different-sized gametes (egg and sperm cells) in multicelled organisms and shows some nice examples of different-looking sexes. Note on page 4 that the flashy-looking birds are male, while the plain-looking birds are female -- which is typical for birds.

03-31-2003, 04:10 AM	#13
Ted Hoffman Veteran Member Join Date: Feb 2001 Location: "" Posts: 3,863	Thanks Lpetrich and Itzpapalotl Itzpapalotl - couldnt you find easier links? Now I have given up on the whole damn subject. I got a glossary of genetics and got a kingsize headache. I am trying Lpetrichs' links. DOes anyone know of a link written in English?

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