The alternation of generations in gametophytes

Plants[ change change source ] In ferns, the gametophyte is smaller than the sporophyte.

The alternation of generations in gametophytes

By Editors Gametophyte Definition Gametophytes are the stage which produces sex cells in plants and algae that undergo alternation of generations.

Unlike animals and other organisms that use sexual reproductiongametophytes do not produce their sex cells through meiosis. Instead, all cells within a gametophyte organism are haploid — that is, possessing only one copy of each chromosome — and these haploid organisms produce gametes through mitosis.

The alternation of generations in gametophytes

This is in contrast to animals and other organisms who are diploid — having two copies of each chromosome — and who must cut their number of chromosomes in half before they can create sex cells that have the right number of chromosomes to produce healthy diploid offspring.

But in a surprising twist, the diploid offspring of gametophytes are called sporophytes. Instead of using meiosis to produce sex cells, they use meiosis to produce spores — which then undergo mitosis to grow into whole new haploid organisms, a. This alternation of generations is a survival strategy in which a plant or algae alternates between different reproductive techniques.

The gametophyte — usually considered to be the first stage of the cycle — reproduces sexually, combining reproductive cells from two different organisms to produce genetically diverse offspring. This allows the plant population to mix and match traits during gametophyte reproduction, which makes the populations more immune to disease and more adaptable to changing environmental conditions.

The sporophyte offspring of gametophytes, on the other hand, can spread rapidly and do not need partners to reproduce. This allows a single sporophyte to found a whole new population, which can then mix genes with neighboring populations in the gametophyte generation.

Spores can also survive for many years in hostile conditions, while sperm and egg cells cannot.

Alternation of generations is a type of life cycle found in terrestrial plants and some algae in which subsequent generations of individuals alternate between haploid and diploid organisms. This can be contrasted to sexual reproduction in animals, in which both . Gametophytes are the stage which produces sex cells in plants and algae that undergo alternation of generations. Among land plants, these sex cells may be referred to as “sperm” and “eggs,” with “male” and “female” sex cells combining to produce offspring. Alternation of generations (also known as metagenesis) is the type of life cycle that occurs in those plants and algae in the Archaeplastida and the Heterokontophyta that have distinct sexual haploid and asexual diploid stages. In these groups, a multicellular gametophyte, which is haploid with n chromosomes, alternates with a multicellular .

This alternation of generations allows the parent plant to take advantage of both the benefits of sexual reproduction — such as genetic recombination which promotes genetic diversity — and the benefits of asexual reproductionsuch as speed and rapid growth.

Common plants which use alternation of generations include mosses, ferns, and pine trees. In a strange evolutionary reversal, seed plants which use alternation of generations, such as conifers and other pine trees, develop their whole gametophyte life cycle stage inside of an enclosed cone.

By contrast, in some other species, the alternation of generations is quite visible. Among ferns, for example, the sporophyte is the familiar large, leafed plant often seen on forest floors. The gametophyte, on the other hand, is a tiny heart-shaped plant that may be easily mistaken for a totally different species from the sporophyte generation.

There are many known benefits to sexual reproduction, as the ability to combine genetic traits from two individuals results in a variety of different combinations of traits within the population. This diversity is extremely beneficial for disease resistance and the ability to respond to environmental change.

For a practical example of the benefits of sexual reproduction, look no further than the Irish Potato Famine. In Ireland at the time of the famine, potato crops which reproduced asexually had been grown for many years and had spread across the islands.

That meant that the crops feeding the Irish people were all genetically identical to each other, having been asexually produced from a tiny parent population.

The alternation of generations in gametophytes

The result was one of the worst humanitarian disasters in history, because all of the potato crops people were relying on for food died off. As a result, millions of Irish people were forced to leave Ireland in search of better lives — and millions more died.

A die-off of ferns would not be disastrous for the human population, but it would be disastrous for the fern population — so ferns and other plants that practice alternation of generations use gametophytes to perform sexual reproduction, and keep their populations genetically diverse.

Examples of Gametophytes Ferns The fern you imagine when you think of Jurassic Park or a forest floor is a gametophyte. The graceful, fringed leaves are haploid — meaning they have only one set of chromosomes and produce sex cells through mitosis, like all gametophyte plants.

If you ever see a fern with what appear to be brown dots covering its leaves, look closer. Those dots are actually separate plants: The tiny sporophyte plants are diploid — meaning that they have two pairs of chromosomes, and will undergo meiosis in order to produce spores.

These spores can be seen as a fine powder coming off of the brown dots on the fern leaves when the time comes. A single fern spore can be carried by the wind, land in a new place, and grow into a gametophyte plant.

That single gametophyte plant can then self-fertilize and produce a generation of new sporophytes! Mosses The moss you think of when you imagine a carpet of rough, green plant material is a gametophyte.

The gametophyte stage of the moss is more long-lived, while sporophytes appear more briefly as long stalks that rise up to release spores into the wind. Moss sporophytes may easily be mistaken for part of the moss gametophyte plant, because they often grow up right from the gametophyte carpet.

Characteristics of Gametophytes

However, the sporophyte stalks are actually independent organisms with different genes from the moss carpet below them.

The sporophytes are created by the merging of gametophyte sex cells. As a result, they have twice the number of chromosomes compared to the gametophyte generation, and contain a unique mixture of genetic traits as a result.

Hornwort Though not as glamorous in name as ferns or mosses, hornworts are in fact a pretty woodland plant whose gametophyte stage consists of small, emerald green leaves that grow in moist soils.In terms of alternation of generations, the internal parts of the pollen grains of seed-producing plants are most similar to a a) fern sporophyte.

b) moss sporophyte. The 'alternation of generations' in the life cycle is thus between a diploid (2n) generation of sporophytes and a haploid (n) generation of gametophytes. Gametophyte of the fern Onoclea sensibilis (the flat thallus at the bottom of the picture) with a descendant sporophyte beginning to grow from it (the small frond at the top of the picture).

the land surface. There is a rich fossil record showing that pteridophytes have ancestors dating back nearly four hundred million years. Jan 10,  · The alternation of Generations is a phrase that describes the life cycle of a plant. The life cycle of a plant is divided into two phases: a sexual phase and a growth phase.

Alternation of Generations Life Cycle

Alternation of Generations A life cycle which there is both a multicellular diploid form, the sporophyte, and a multicellular haploid form, the gametophyte; characteristic of plants and some algae *Distinguished by haploid and diploid stages that are both multicellular.

Characteristics of Bryophytes There are several characteristic features of bryophytes. First, the green tissue that makes up most of the plant body is not vascularized; it does not have xylem and phloem cells.

This absence of specialized tissues for transporting water and dissolved food throughout the organism limits terrestrial forms to being very short .

SparkNotes: The Life Cycle of Plants: Alternation of Generations