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Modul no. 1: Animal Genetics Ewa Salamończyk from Siedlce University of Natural Sciences and Humanities, Faculty of Agrobioengineering and Animal Husbandry.
Genetic linkage, also known as genetic inheritance,
refers to the transmission of traits from one generation to another through genes.
almost all
genetic information
is located in
the chromosomes, located in the nucleus of the cell,
the set of all chromosomes in the somatic cells
of a given organism constitutes its karyotype.
Each plant and animal species has a fixed
and characteristic number of chromosomes.
The normal pig karyotype shown in the picture contains 38 chromosomes.
Karyotype = autosomes + sex chromosomes
Among all the chromosomes of a given species in the karyotype.
two are responsible for the sex of the animal, and we call them sex chromosomes.
The sex chromosomes in the porcine karyotype are: XX sows and
XY boars.
Genes located
on one chromosome tend to be inherited together.
We say that they are coupled and this phenomenon is called coupling
these genes
that are all
on different chromosomes,
unlinked genes
Each
chromosome contains
a large number of genes that are located some distance apart or close to each other.
Those that are some distance away can move between homologous chromosomes in the process of recombination
during meiosis.
We call such genetic
connections loose.
Those genes
that are very close to each other on the same chromosome are often inherited together.
We call such a genetic link strong
Genes can be linked in cis and trans
The genes on homologous chromosomes can be cis-linked
when dominant alleles are on one chromosome or trans
if the dominant alleles are on different chromosomes.
Thus
linked traits are traits
whose genes
have their locus on the same chromosome.
These traits are inherited together, forming a linkage.
Great.
The number of linkage groups corresponds to the number of homologous chromosome pairs in a cell.
The external manifestation of linked traits
is a reduction in the diversity of phenotypic forms because the phenomenon of linkage restricts
the number of types of gametes produced by heterozygous individuals.
Types of linked traits
There are two types of coupling,
absolute linkage and relative linkage.
Absolute linkage occurs when there is no crossing over between the genes,
relative linkage occurs when there is crossing over between genes.
Individuals with a recombined gene arrangement
are produced in relation to the parental gene arrangement.
Segregation of
linked genes
Crossing over - the phenomenon of exchange of genetic material
between non sister chromatids of homologous chromosomes.
It occurs during the prophase I of meiotic division,
hence it is also called meiotic recombination.
The resulting new forms are called recombinant.
This phenomenon, which leads to the creation of new genetic forms, is the main cause
of genetic variability in a population and the basis
for determining the linkage between any segments of DNA.
The process occurs during the pre phase of the first meiotic division or non sister chromatids
during crossing over an unstable connection called chiasma is formed
between two chromatids oriented in the same direction
as a result of completed crossing over,
there can be a permanent exchange of chromosome segments between homologous chromosomes,
either closer to the telomere or between two chiasmata.
This leads to the formation of recombinant gametes
with a different allelic arrangement than the parental gametes.
The process of crossing over is a random
event and occurs at random locations.
However, the randomness of this phenomenon at a specific chromosomal location
has a limiting effect on the occurrence of crossing over nearby interference phenomenon.
The chromatid that participated in the exchange acquires
a combination of alleles from both the paternal and maternal origins.
Unlike the situation before crossing over,
in that case the chromosome, and thus its chromatids,
had a set of alleles from only one parent, as dictated by the principle that within a pair of homologous
chromosomes, one originates from the father and the other from the mother.
Non-sister chromatids Sister chromatids Crossing over in prophase I of meiosis
Completed exchange in metaphase I of meiosis Chromosomes in gametes
Non-recombinant (parental)
chromosomes
Recombinant chromosomes
Crossing over does not occur with a constant frequency.
Crossing over is more likely to occur on long
segments of the chromosome than on short segments.
It more frequently occurs in meiosis
in females than in males.
A form of gene cooperation is the phenomenon of pleiotropy occurs
when one gene influences the development of several traits
Pleiotropy can be true an apparent
True pleiotropy occurs when a Pleiotropic Gene affects several distinct centers.
Example: the gene for platinum color in foxes.
Platinum Foxes unlike standard colored individuals, are
less lively and more excitable
individuals homozygous for this gene are not viable.
Also for SNAP was given them to go guano, sandstone and those richer.
But in the case of apparent pleiotropy,
a gene controls a specific trait that in turn influences
depending on environmental influences the variation of other traits.
For example, the gene responsible for feather curliness
in poultry also affects, among others, the metabolic rate,
heart function and digestive processes.
However, these changes are a consequence of abnormal feathering,
which does not protect the bird from excessive heat loss.
in the case of
many traits,
genes from different illegal pairs through their combined action
result in the emergence of a new form of qualitative trait.
The interaction between genes from different allele pairs
in shaping the phenotype is called allelic interaction.
Examples of Allelic interaction
Epistasis (the expression of one allele pair is dependent on the presence of another allele pair).
Additive gene action
Multiple genes from different Lockie contribute to a single trait resulting in varying degrees of expression
Thank you for your attention.