Seeds - Types of Seeds - Selecting Seeds Information on seeds, seed types, discussion on hybrid versus heirloom seeds. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant. The formation of the seed completes the process of reproduction in seed plants started with the development of flowers and pollinationwith the embryo developed from the zygote and the seed coat from the integuments of the ovule. Seeds have been an important development in the reproduction and spread of flowering plants, relative to more primitive plants like mosses, ferns and liverworts, which do not have seeds and use other means to propagate themselves.
A look at cichlid fish in Lake Victoria This is the first in what I hope to be a series of postings. In the series I hope to accomplish two things, establish that evolution is an active branch of mainstream science and that there is indeed an overwhelming amount of evidence in favor of the idea of evolution.
Note that no single post is meant to be a proof, just another piece of evidence that supports the theory of evolution. In the October 11th issue of Nature, Meyer et. If they all share a recent common ancestor in that lake or came from separate lineages that invaded the lake.
In their paper they sequenced a bp part of the cytochrome b gene and a bp segment of mitochondrial DNA from what is called the control region. They sequenced these genes from several species of fish in the lake and a few species from relatively nearby lakes. What they found was the sequences in the Lake Victoria species of fish were all very similar, but they were different from the sequences of fish in nearby lakes.
All the sequences are listed in the paper. They came to the conclusion that this indicated the cichlid species of Lake Victoria all derive from a recent common ancestor in the lake.
They estimate the time of divergence at aboutyears ago based on a model that assumes mutations are relatively constant over time. The lake, incidentally, had been independently dated to be-years old The News and Views section of that issue has an overview of the paper written by John Avise.
Also, the cover photo of this issue consists of a picture of several of these fish.
As I said in part one, I have two goals in for this series. One, to show that evolution is an accepted branch of mainstream science. And two, that contrary to the continual assertions of creationists, there is an overwhelming amount of data in favor of the theory of evolution. Again, note that no single post is intended as a stand alone proof.
This post is divided into two section, an introduction the part you are reading to provide a bit of background, and the actual summary of the paper discussed.
Speciation occurs when two or more possibly subsets of a formerly interbreeding population become reproductively isolated. For many years, speciation theorists thought that virtually all speciation occured when the two subsets of the population where separated by geographical boundaries.
Reproductive isolation followed physical isolation as the two, now separate lineages, diverged. This could occur for many reasons, for example mating rituals grew different or chromosome numbers changed etc. In any case the end result would be that the two lineages could no longer interbreed if they encountered each other.
Incidentally this type of speciation is called allopatric speciation. A second type of speciation, sympatric speciation, occurs when two lineages of a formerly interbreeding population diverge to the point of reproductive isolation while still residing in the same locale.
This was first demonstrated to occur by Guy Bush working on the Apple maggot fly Rhagoletis pomenella. The paper I will outline here is one found in the August 9, issue of Nature. I will continue this discussion in my next post. Isolation mediated by microorganisms In the paper outlined here Breeuwer and Werren, the authors examine two species of wasps living sympatrically in the same area.
Wasps like ants, bees and termites are haplodiploid organisms. In these organisms, females develop from fertilized eggs so there is a male and a female contribution to the genome i.
The authors of the paper experimented with two species of wasps, N.Experimental work with bacteria, eukaryotic micro-organisms and very small animals can tell us much about the occurrence and properties of mutations, including beneficial mutations.
Genetic drift (also known as allelic drift or the Sewall Wright effect) is the change in the frequency of an existing gene variant in a population due to random sampling of organisms.
The alleles in the offspring are a sample of those in the parents, and chance has a role in determining whether a given individual survives and reproduces. Genetic drift is a change in the frequency of an allele within a population over time.
This change in the frequency of the allele or gene variation must occur randomly in order for genetic drift to occur. There are no environmental influences that cause genetic drift to occur.
Examples of genetic. Genetic drift affects the genetic makeup of the population but, unlike natural selection, through an entirely random process. So although genetic drift is a mechanism of evolution, it doesn't work to produce adaptations.
There are two main mechanisms of evolution, natural selection and genetic drift. Genetic drift occurs when the frequency of an allele Allele: An alternative form of a gene; one of the different forms of a gene that can exist at a single locus.
changes over generations due to random chance. Types of Genetic Drift There are two major types of genetic drift: population bottlenecks and the founder effect. A population bottleneck is when a population's size becomes very small very quickly.