Whilst I don’t claim to be a geneticist or completely
understand all of the technical stuff involved in the genetics of finches, and
birds in general, here are some basic explanations of some of the terms you
will come across when breeding birds. If
you are aiming to understanding which pairs will produce which offspring, an
understanding of the genetics behind it all is a good idea. So here we go.
Genotype
The genotype is the genetic make up of a cell referring to a
specific characteristic. These characteristics
can be dominant (A) or recessive (a) and are the inherited instructions that a
being receives in its genetics code.
A phenotype is the observable characteristics or traits of a
being and can be anything from a physical form to a behaviour (such as building
a nest in birds). These can be a
combination of the inherited traits (genotype) and environmental factors as
well as the interaction between the two.
Chromosomes
Chromosomes are the strands that are made up of DNA. To pass genetic traits from a parent to the
offspring, the chromosomes must be copied and then divided up. For each
organism, there is a specific number of chromosomes per cell so, for example,
humans have 46 total chromosomes. These comes
in two types:
Sex chromosomes –
these determine gender so if you are female, you have two X chromosomes and if
you are male you have an X chromosomes and a Y chromosome. In birds, these are decided by the Z and W
chromosomes so males have two Z chromosomes (ZZ) and females have a W and a Z chromosomes
(WZ).
In finches, it appears that the Z chromosome is the one that
carries the information for colour while the W chromosome simply dictates that
the bird is female. This means that when
a specific colour is carried by the Z chromosome, it is said to be sex-linked.
Autosomal chromosomes
– these are all the rest, so in humans, the remaining 44 chromosomes not
involved in deciding the gender. In
birds, this number is usually different for different species but one example
is the Gouldian Finch, which has 14 chromosomes. Seven from each parent are passed to the
chick in conception.
Autosomal chromosomes
Each chromosome has an area called a locus that is specific
location of a gene or DNA sequence or even a position on the chromosome. Gene mapping is the process of determining the
locus for a particular biological trait.
Applying this to finches, if the pair of chromosomes for the
breast colour has a purple locus then this is said to be a double factor for the purple gene.
If the chromosome has a purple locus on one of the pair and a white on
the other, it is said to be a single
factor for either colour. If the
purple is on chromosome 1, the dominant one, then the breast colour will be
purple but split for white because
it still carries the white locus. If neither
of the chromosomes are dominant then a shade between purple and white (lilac?)
would be the breast colour – this is also known as codominance or as visual split in bird breeding.
Homozygous & Heterozygous
Similarly to dominant and recessive are homozygous and heterozygous. A bird that has no hidden colour traits is
called homozygous or could be terms as inheriting purely. A bird that has a hidden trait is called
heterozygous or inheriting impurely. Both
of these birds can look exactly the same but a homozygous bird’s offspring will
look just like it whereas a heterozygous bird’s offspring can be either the
same as it or the same as the hidden trait.
When describing the visual colours of a bird, this is the homozygous
while referring to its visual colour then its hidden colour is when the split
term is used. It is the visible colour split for the invisible colour.
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