- A budgie told me lovebirds said:
> From: "lovebirds" <chris@...>I spoke with a Dr. of microbiology over the weekend and she stated that yes,
> Terry, Clive, Inte, Ralph et al.
> From a purely chemical point of view, I cannot see why chiasma cannot form
> at any random point.
> (and as a long time Lovebird breeder, I don't place a lot of faith in
> D'Angieri in several areas).
> What is being discussed here is so valuable Terry, I think sometime soon we
> need to recruit a professional Microbiologist/Molecular Geneticist for us.
> Someone with no knowledge of avian genetics might in someways be more useful
> than one with preconceived ideas. Can any of our members dragoon someone to
> guide us?
chasma CAN form anywhere. She's also looking to see if she has time to
actually join the list.
(') (`} Email mailto:bandr@...
//) / ) ICQ:14256691 nick:MLO
" / / Theropod Aviary
And the budgie says:
'He is not an honest man who has burned his tongue and does not tell the
company that the soup is hot.'' - Yugoslav proverb
- From: Jaynee Salan Pieds1usa@...
Terry and All -
I would like to jump into this discussion, if you don't mind. The research
team I work with has found that Chiasmata formation can
occur anywhere along the DNA chain and can lead to crossovers at any
point. Mutations occur because of additions, deletions and/or
substitutions of base pairs. Let me explain further for the benefit of
everyone that would like to read this post.
Homologous chromosomes come together as pairs during prophase of Meiosis 1.
This pairing, or synapsis, is very precise, with homologues aligning with
each other on a gene-by-gene basis. During synapsis, genetic information is
often exchanged between the paired homologous chromosomes. A segment of a
chromatid changes places with
the equivalent segment of a homologue. Crossing over is usually a
reciprocal process in which identical lengths of chromatids are exchanged
between the two homologues. Therefore, there is no loss of
genes, but rather an exchange of genes between the two chromosomes.
Although no genes are lost, new genetic combinations nevertheless
result from the exchange of maternal and paternal chromosome segments.
Crossing over occurs with the formation of a chiasma. Let me explain
a little further. The four closely associated chromatids are called tetrads
or bivalents. Exchange of genetic material, or crossing over, occurs
between nonsister (homologous) chromatids; this event is visible in the
microscope by the appearance of X-shaped regions called chiasmata (singular,
chiasma). The long arms, we call them, of the X-shaped figure that we see
in the microscope are referred to as chromatids with the union in the middle
of the chiasma referred to as the centromere.
The recombinant frequency that you have mentioned we call Chromosome
Mapping, the ordering and spacing of genes on a chromosome on the
basis of crossover frequencies. In the construction of such maps, crossover
frequency becomes the map distance. Frequency of recombination between two
genes is a measure of how far the markers are from each other along the
chromosome. Genes located very close to each other would be less likely to
become separated by a crossover event between them than would genes that are
far apart. For example, if alleles A and B appear in the off spring in
their parental combination 85% of the time and as recombinants 15% of the
time, we would conclude that the two genes are linked (are on the same
chromosome) and are 15 map units apart.
Although this approach is widely used today to map the chromosomes of
many animal species, the information about gene loci determined from
crossover data is relative, not absolute. Recombination frequencies tell us
the sequence of linked genes and provide clues about
comparative distances between them, but this approach discloses neither the
actual locations of the genes on the chromosome nor the absolute distances
between the genes (in nanometers, for instance).
Clive - In your post on Oct. 28th you mentioned long stretches of DNA
with no apparent function. We refer to this phenomena as INTRONS and
Much of the DNA of most organisms does not code for protein. The noncoding
segments of DNA have given us one of the most surprising and
important dicoveries in recent biological research. Such unexpected
interruptions are puzzling. It is as if unintelligible sequences of letters
were randomly interspersed in an otherwise intelligibly written document.
Most of the more complex genes are interrupted by
long segments of such noncoding regions, which are called intervening
sequences or INTRONS. The coding regions, which introns interrupt, have
come to be called EXONS because they are expressed (translated).
After an RNA transcript is made, the introns are removed and the exons that
flanked them are joined to produce an mRNA molecule with a continuous coding
sequence. This process is called RNA Splicing or
RNA Processing and is also required for the production of tRNA
(transfer RNA) and rRNA (ribosomal RNA). In fact, we can tell if a
gene is active when we look at a sequence of DNA in a microscope because it
puffs itself up, due to the strong chemical bonds present. We refer to these
active genes as "puff" genes.
- Inte Wrote:
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< Can a
spangle be modified so it looks like a "normal"? Have you already heard of
the "cleartail" Budgerigar coming out of spangles? These are normal birds
with a white or yellow tail. Is it a modified spangle or what? And what
about the inconsistend results crossbreeding sex-linked clearbodies and
As I have photos of those Cleartails they look like Spangles which are
extremely heavily marked. I would like to get some of them to test pair them
myself. Being in Australia it is impossible at this time to get birds in
unless you are a zoo owner or such like.
As far as inconsistent result go with Clearbodies bred with Lacewings all I
can say is that I don't consider the results we get to be inconsistent. I
treat the Lacewing as though it were an Ino but keep in mind that a
crossover can occur and so I expect to bread a Cinnamon or Cinnamon
Clearbody now and then. This happened last year. I paired a Clearbody Dark
Green/Opaline/Lacewing/Blue cock with an Opaline Cinnamon Light Green/Blue
hen. Results were. Lacewing hens as expected in Opaline and Normal. Opaline
cocks. Clearbody Opaline hen. The only bird produced which some would say
was unexpected was a Cinnamon Cock. I just consider this a crossover event.
Down Under Budgies
- At 10:17 AM 10/30/99 +1000,"Terry Martin" <sbankvet@... wrote:
Clive, Inte, Ralph and Chris
Thanks for your replies.
I suppose what I was really getting at is can a chiasma form
>anywhere along the DNA chain, leading to crossover at any point, or doIf it is purely random at any point along the DNA chain, then the
>chiasma only form when particular base pair series occur?
>potential for crossover has significance for the blue locus where we haveI had the chance to pose this question to a geneticist this morning using
>heteroalleles. If the altered segments for two different heteroalleles are
>separated by a significant distance, then crossover has a real chance of
>happening. And if it did, then a 'new' wildtype allele would be formed on
>one chromosome and a new 'double damaged' allele on the other.
the blue locus as an example. His answer was simply: "Yes".