Sexual reproduction in eukaryotes, Biology

Sexual reproduction in Eukaryotes

In most eukaryotes, especially higher animals, individuals normally exhibit one or two sex phenotypes; female or male. In such species, females produce the female gametes-eggs, ovules or macrospores and males produce the male gamets -sperm, pollen or microsproes. Species with separation of sexes in different individuals are called dioecious or monosexual organisms. All higher organisms and some higher plants are dioecious. Species in which both male and female gametes are produced by each individual are called monoecious or bisexual organisms. In lower animals, the production of both eggs and sperms by the same organisms is more commonly called hermaphroditism, and individual organisms producing both the types of gametes are termed hermaphrodites.

Although the two sex phenotypes are usually quite easily distinguished in humans and fruit flies, it is not universally the case. In lower or the 'primitive' eukaryotes, the two sexes are phenotypically indistinguishable except for their reproductive organs. Indeed, in lower eukaryotes the two genetically distinct types of gametes are sometimes morphologically indistinguishable. This is called isogamy (iso meaning 'same'). Isogamy occurs in several simple eukaryotes, such as the green alga Chlamydomonas, fungi-Neurospora and protozoa-Paramecium. They may however, be identified by their sexual reproduction pattern.

1377_eukoryotes.jpg

An individual belonging to one mating type exchanges genetic material by fusing only with an individual of another mating type but never with its own mating type. Therefore, the similar looking male and female gametes, or isogametes are actually physiologically different, as is evident by their mode of reproduction. Sexual differences between indi,viduals probably originated first in their gametes. Most of the plants are hermaphrodite, producing both types of gametes, but have various adaptations to promote cross fertilisation. One such adaptation is the phenomenon of self-sterility. Its examples are cheny and tobacco plant. Due to self sterility the plants have to undergo cross fertilisation, and the [esult is the recombination of genetic material.

Posted Date: 12/11/2012 4:14:01 AM | Location : United States







Related Discussions:- Sexual reproduction in eukaryotes, Assignment Help, Ask Question on Sexual reproduction in eukaryotes, Get Answer, Expert's Help, Sexual reproduction in eukaryotes Discussions

Write discussion on Sexual reproduction in eukaryotes
Your posts are moderated
Related Questions
How many chambers do the bird heart and the mammalian heart have? Concerning temperature maintenance what is the advantage of the double and complete circulation of these animals?

Which of the following does not support evolution? biogeography the fossil record comparative anatomy radiometric dating All of these choices are evidence of/support evolution.

What is the rule for the pairing of nitrogen-containing bases in the DNA molecule? And in the RNA? The rule for the pairing of nitrogen-containing bases of the polynucleotide c

Use of Alternate Metabolic Pathways Plants surviving under water-logged conditions offer the simplest example of such a response. The submerged parts of such plants use the an

Echocardiography is one of the -most frequently used imaging modalities for diagnosing cardiovascular diseases. It i's versatile and is applicable in the entire spectrum of

Among neonates, IE typically involves the tricuspid valve of structurally normal hearts and is associated with very high mortality rates.  It is likely that many of these episodes

Q. Fibre requirement in chronic diarrhoea? Fibre: Insoluble fibre in the form of skins, seeds and structural plant materials should be strictly avoided to minimize on the irrit

GIRDLES - (i ) PECTORAL GIRDLE - 4 bones. It is located on posterolateral part of upper region of the throax. It consists of scapula & clavicle. Scapula is placed

What is the relation among fecundation and the end of the meiotic process during oogenesis? The oocyte II only completes the second meiotic division (interrupted at metaphase) i

What are the main negative ions found in living beings? The major anions found in living beings are the chlorine anion (Cl-), the phosphate anion (PO4--), the bicarbonate anion