Mutations and development of species

The building plan of a species (DNA) is copied with every reproduction of cells. This is a very precise developing process. This is the reason that every new generation of Bourke's looks like all the other wild-type Bourke's. But there is always some variation in format, in vitality, in colour and other qualities.

Development of species

The influence of the natural environment.

Darwin landed in 1854 with his ship, the Beagle at the Galapagos isles. He found animals who don’t live anywhere else. He saw finches, who were different from the finches in the South Americas continent. He developed this journey his idea about the development of species under influence of environmental factors. The development is guided by climate, availability of food, natural enemies, and so on. One finch was specialised to crack big, hard seeds. He had developed a strong broad beak. Another finch developed a fine delicate beak for tiny seeds.
He was not the only one who had this idea of evolution. Independent of Darwin, Wallace was studying the animals and birds in the Indian Archipelago and described the development and distribution of species in their mutual cohesion.
The evolution theory became known and accepted world wide. Now we call it a micro-evolution theory. This theory is about precise adaptation to the natural environment of the species.
Adaptation and change are playing an important role. An accidental transforming of genes, what is beneficial for the adaptation is preserved. The packet of genes of a species becomes more optimal after countless mutations. Evolution is going on for millions of years. The Bourke, who is living in an arid landscape, is perfect adapted to the dry natural conditions. For instance: The use of drink water is minimal because he utilizes all the moist from the seeds. Seldom he is bathing. But he he is reacting very exited to every rain shower. The colours and the colour structure are balanced and adapted to the natural environment also. This is changed by the time the Bourke came in the avian culture. Breeders fixed the mutations and developed whole new colour varieties.

Influence of man

Man became an important factor in the development of bird species. One of these activities is the preservation of mutations when they happen. By altering of the genes new colourvarieties came out. The mutation breeders can work on it when they know what the effect is on the plumage and what kind of inheritance the mutation factors have.

A new rung in the DNA ladder

(Mutation)

A mutation changes a gene, one of the rungs of the DNA ladder. This is happening during the copying of the DNA. This can be a simple substitution of one of the characters of a gene. This is named a point-mutation. If this is happening and at what moment is just unpredictable as a type fault of the secretary or a problem with the copy apparatus in the office. Such a fault can have big consequences.

When one character in a pair is substituted, the other character of the same pair is changed too. The composition of the gene is changed, because of one of the letter pairs has been changed. Letters always appear in fixed combinations. A gene is composed by three pairs. When one pair is changed the whole gene is changed.
Such an changed pair we call an allel or mutation factor. The altered gene is laying at the same place on the chromosome but has a changed function. A mutated gene has other attributes then the original gene.

Because of the change of the gene the activity of the protein will be changed. A change of the function is the consequence. Some examples are: less oxidation of the eumelanin grains, brown in stead of black, decrease of the melanin production, total drop out of the melanin, etc. Because we know that a gene includes three pairs of letters, we know that the total change of a gene can be concerning three pairs.

Most times the fault in the gene is noticed and repaired because of the control during the reproduction. But sometimes a fault is not noticed and an altered gene is the result. When an organism is older more reproduction faults can happen. The lutino was born out of an old couple Bourke.

Such a changed gene we call a mutation factor (allel). This new gene is found at the same place on the chromosome as the original (locus). A change of a letter pair is called allel. Sometimes more than one letter pair is changed. We call this a multiple allel.

There are other kind of mutations also. It is possible that a character drops out. The consequence is that a code pair drops out. This gives a chain reaction in the DNA. One of the three code pairs is falling out. Then the whole division of code pairs is shifting. This means chaos.
It is possible too that by mutation a character is added. Also this addition gives an radical change. Only a point-mutation can result in a change that make sense. The other kinds of mutation do not.

Summary: A point-mutation is the cause of an alteration of a genetic attribute, a change of the gene. For every change is responsible a mutated gene, named allel or mutation factor.
Because there are three pairs of letters in a gene, it is possible that there appear more than one point-mutations in the same gene. A letter pair that is changed we call allel. When there are more changed letter pairs in the same gene, we call this a multiple allel.


Doubling of the DNA

Cell division and growth of the organism

(Mitose)

A complex organism consists of innumerable cells. All these cells come from cell division of the first cell, the zygote, who came into being through fertilisation. When the organism is growing the cells are dividing. In every division both DNA chains are duplicated, because every cell contains two whole DNA chains. Mitose is the reproduction of the DNA.

This process goes as follows: The twisted DNA ladder is partly straightened. Then this part is fission longitudinal in two parts, left part and right part. Compare this with a zip fastener, what is opened.
Because of this action the pairs of letters are disconnected. Then the letters of the left halve of the ladder are completed. The right halve is completed too. Because there are only fixed letter combinations, the supplement of the letters is predictable. In this way two new pairs of letters come into being. The two new rows of letter pairs are identical to the original. The DNA is copied. This is the first phase, the process of reproduction of the two DNA chains in the cell.

Clarification: To present the process only two chromosomes are reproduced. One is laying at one DNA ladder, the other is laying at the other DNA ladder. The red and black dot represent a gene at the chromosome, both genes are found at another location.

1. Zygote, 2. doubling the chromosome, 3. division of the cell, 4 doubling and division.

Doubling and division: In the first phase of the reproduction process (1-2) doubling is taken place. T the second phase of the reproduction process takes place. The cell division. The cell is divided (2-3). This process of reproduction of the DNA and the division of cells continues. (3-4). There come out two, four, eight cells etc. Every new cell contains two complete DNA ladders.
The process is carefully controlled by a special protein, the DNA polymerize. When something is going wrong this can have a bad influence in the whole organism. This defect gene has to be destroyed and replaced by a normal one immediately. This makes that the process of reproduction an cell dividing is very accurate process.


A new unique DNA ladder

Fertilization of the egg cell and reproduction

(Meiose)

Fertilisation means the transfer of the genetic material from hen and cock to the offspring. Every cell of the bird has two DNA chains, one from the hen, one from the cock. But the germ cell of the cock and the egg cell of the hen have only one DNA chain. By the combination of the chromosomes of the parents a new, unique pair of chromosomes arises.

How does it goes? By reproduction and dividing four gametes proceed from a double pair of chromosomes. Every gamete has only one copy of one of the chromosomes. In the seedling this is happening before the fertilisation. Only one of the seedlings with one gamete can penetrate into the ripe egg cell.
In the egg cell this reproduction of the DNA and the division of cells is happening during the fertilisation. The kernel of the the egg cell is moving away from the centre towards the other side. Through combination of a gamete of the cock and one gamete of the hen a new unique organism starts. After fertilisation the process of reproduction and dividing of cells starts immediately.

meiose drawing

Clarification: To simplify the picture only one pair of chromosomes is represented. 1. The germ cell of the cock, 2. Doubling of the chromosomes, 3. Dividing into four gametes, 4. The kernel of the egg cell is moving away from the germ cell that intrudes, in the meanwhile doubling and deviding in four gametes, 5. The germ cell, the tail needed to the movement of the germ is destroyed.

The gamete of the cock combined with the gamete of the hen forms a new pair of chromosomes. The first cell of a new organism, the zygote comes into being. One chromosome comes from the hen, one from the cock. After fertilisation the normal process of doubling and division takes place. The organism growth. Cells are specialising. Skin and organs are developing. The complete information packet is the building plan of the new organism.

When a fault happens during copying it is possible that one of the gametes get this changed piece of DNA. If this gamete is united with one of the gametes of the hen the changed DNA is transferred. The DNA of the new organism has two complete DNA chains. The gene of the hen can compensate the altered gene of the cock. For instance the gene that is due to the pastel colour variety. Only as both chains contains this faulty piece of DNA the change is visible in the plumage. We call this a recessive inheriting mutation factor. An other possibility is that the changed DNA dominates over the original DNA of the wildtype. The influence is direct visible in the plumage. We call this inheritance dominant over the wildtype.


A rupture in the DNA chain

(Crossing over)

A special accident can happen during the meiosis. When the pair of chromosomes of the cock is copied, it can happen that a rupture find place. One part of the chromosome of the one chromosome is attached to a part of the chromosome of the other chromosome and the other way around. A number of genes is moving from one chromosome to the other. The breakage is stacked together in a wrong way. A new mix of qualities is the result. Because this is happening in the fertilisation phase, this can influence the offspring in a direct way. We call this crossing over.

Nobody can predict at what point a rupture will happen. Crossing over is happening spontaneous, just like point-mutations. The result of a crossing over can give a tremendous contribution to the development of species. This crossing over can only happen in the DNA of the male.

Suppose there is a mutation factor at a X-chromosome of the male. For instance an opaline factor. Suppose there is another mutation factor laying on the other X- chromosome. For instance an ino factor. The cock is as we say double split. This factors do not come to expression in the plumage. Both mutated genes are compensated by the normal gene at the other chromosome. We represent this by: wild-type/i/o.

drawing crossing over

Explanation: 1. Reproduction cell of the male, 2. Doubling of the chromosomes. 3. Revision in four gametes, 4. Fertilisation, in this moment the chromosomes in the egg cell are doubling and deviding, 5. The breakage is represented by a black line. A crossing over is happening during the phase of copying the chromosomes. A part of the chromosome is crossing from one chromosome to the other. When in this part accidentally a mutation factor lays, the result is that the two mutation factors come at the same chromosome. We represent this by: wildtype /io.

Remarks: The both mutation factor (red dot and blue dot) are laying far from each other. It is easy to understand that crossing over of two mutation factors is most easy when this mutation factors are laying far from each other. When mutation factors are laying close to each other it is not likely that the rupture is laying just in between. The percentages of crossing over of mutation factors are varying from about 7% to about 42%. When there was a full analysis of the DNA of birds we did know much more about the inheritance of qualities then today. Today we do not know always on which chromosome the genes are located. What we know is derived from praxis.

Sometimes a colour characteristic is bound together with another physical characteristic, because they are laying near to each other at a chromosome. When one is changing the other is changing too. This is not crossing over. This is named “linking”. The genes are laying so close on the chromosome that the are inheriting together. Linked genes are like neighbours, located next to each other. Crossed over genes are like people who exchanged there homes.

Conclusion: The breeder has an important role. Point mutations and crossing over are unpredictable. By systematic mating the colour varieties are preserved. Variability of the species is stimulated strongly by men.

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Copyright 2004 by Bob Fregeres

E-mail: fregeres@bourkes-parakeet.nl

1/19/04