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DNA-Testing for single gene traits: COAT COLOUR

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... (constitutive pigmentation) is perhaps best understood. The basic coat colours: ... The Beauty of Mutations Why mutations? Our environment constantly ... – PowerPoint PPT presentation

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Title: DNA-Testing for single gene traits: COAT COLOUR


1
DNA-Testing for single gene traits COAT
COLOUR
  • Dr. Munro Marx and Joubert Oosthuizen
  • Unistel Medical Laboratories (Pty) Ltd.

2
From cell to genome
  • Cells The fundamental working units of a living
    organism.
  • DNA Found in the nucleus of cells
  • All instructions to regulate the activities of
    cells are tucked up in the DNA.
  • The DNA molecule is a side by side arrangement
    of nucleotides (e.g. ATTCCGGA).
  • The Genome The organisms total DNA content is
    known as the genome
  • Genomes sizes vary in different organisms.

3
DNA, Chromosomes, Genes and Proteins
  • DNA is packaged in structures known as
    chromosomes (46 in humans, 46 in Sable antelope,
    56 in Springbok, 60 in buffalo and cattle ).
  • Several genes are located on each chromosome
  • Genes are the functional and physical units of
    inheritance. Each genome has about 25 000 genes
  • The basic structure of a gene supplies the code
    for the manufacture of Proteins.
  • Proteins provide essential functions for life
    (digestion etc.) and form and structures (cells,
    hair etc.)
  • Proteins consist of combinations of amino acids
    (20 different amino acids)
  • The sequence of amino acids, the protein form and
    structure determines function.

4
Proteins and Proteome
  • The total protein content of a cell is known as
    the proteome.
  • Proteome is a dynamic system and reacts to both
    the internal and external environment.
  • The chemistry and behaviour of a proteome is
    determined by the total gene function and
    expression in the same cell at the same time.
  • Each cell has the genetic potential to
    manufacture and express all the proteins of the
    organism.
  • Gene function and expression is selective and
    cell specific.
  • Genes activated in a specific cell provide that
    cell with its unique function and characteristic
    e.g. liver cells, coat colour.

5
Where does coat colour fit in?
  • Animals evolved different skin and coat colour
    and patterns primarily as defence against
    predators or as an aid in predation.
  • An animals phenotype (what it looks like), is a
    result of a complex interaction between its
    inherited genetic makeup (genotype) and the
    environment in which it lives.
  • Genes involved in skin and coat colour are
    amazingly similar all over the animal kingdom.

6
Colour, Melanocytes and Melanin
  • The pigment melanin is the primary determinant of
    colour and is found in cells called melanocytes .
  • Melanin is produced in melanocytes in the eye,
    skin and hair (coat).
  • Skin and coat darkness / lightness is primarily
    determined by
  • the amount of melanin in the melanocytes
  • the ratio between eumelamin (Black/Brown pigment)
    and pheomelamin (Red/Yellow).
  • Melanocytes originate in the neural crest and
    migrate during embryogenesis. This migration
    plays a role in colour patterning.

7
Genetic control of Skin and Coat Colour.
  • The skin and coat colour (pigmentation) of an
    animal is determined by GENES that code for
    different pigments.
  • Pigmentation caused by genes is constitutive
    pigmentation an intrinsic property of the
    animal.
  • Two classes of genes affecting pigmentation have
    been identified
  • Those affecting the pigment producing cells
    (melanocytes per se, especially on membrane).
  • Those affecting pigment synthesis (the inside
    workings of melanocytes).

8
Cause of colour and pattern diversity.
  • As with (virtualy) all diversity in the world of
    the living, colour and pattern diversity is
    caused by genes and their mutations.
  • The wide variety of colours and patterns observed
    is due to
  • The number of genes involved, and
  • The number of mutations per gene.
  • Advantageous mutations are evolutionary retained,
    disadvantageous ones are lost.
  • In the wild disadvantageous mutations that
    inherit recessively may be retained for
    generations. Loss of the properties assisting
    survival prevent the recessive phenotype from
    surviving, thereby keeping the mutations
    frequency low.

9
Mutations that affect melanocytes.
Melanocytes are responsible for eye, skin and
coat colour, as well as patterning. Mutations
may affect the following areas of melanocyte
function
  • Mutations affecting the melanocyte surface result
    in qualitative changes of pheomelanine or
    eumelanine .
  • These mutations influence what kind of pigment
    are produced and will influence the basic colour
    of the skin and coat.
  • Mutations affecting the inner workings of
    melanocytes.
  • These mutations result in quantitave changes in
    pigment production and may lead to changes in the
    basic colours (colour dilution).
  • Mutations affecting differentiation,
    proliferation and migration of melanocytes.
  • These mutations lead to changes in white spotting
    and MAY lead to changes in patterns

10
How do genes work to have the effect they have?
  • Genes operate in pairs, with one of each
    inherited from each parent.
  • Some genes are dominant if an animal have
    one of those genes, it will totally cancel the
    effect of the other gene.
  • Some are recessive the genes effect will
    only be noticed if both copies are recessive.
  • Some are co-dominant if two different genes
    are present, their effect will be a combination
    of the two.
  • Together with the above, a range of other
    effects may influence the inheritance and
    expression of a trait , eg
  • Incomplete penetrance
  • multigene vs single gene inheritance
  • epistase
  • epigenetic factors
  • Etc, etc.

11
Other factors affecting skin and coat colour
  • Suplementary to genes are environmental factors
    and hormones (facultative pigmentation
    inducable property). (A topic on its own, not
    for today.)

12
Colour genes illustrated the horse as
representative of the mammal (1)
  • Horse colour genetics (constitutive pigmentation)
    is perhaps best understood.
  • The basic coat colours Genes affecting the
    melanocyte surface (Extension and Agouti loci)
    determine the basic coat colours Chestnut, Bay,
    Black
  • Chestnut eumelanine (black/brown) in the skin,
    pheomelamine (red/yellow) in the hair, including
    mane and tail.
  • Black eumelanine (black). In skin and hair
    (entire body).
  • Bay pheomelanine (body) and eumelanine (mane
    and tail and lower leg) patterns.
  • So far, so good, so simple!!

13
Colour genes illustrated the horse as
representative of the mammal (2)
16 Genes influencing coat colour has so far been
found. Two are responsible for primary colour,
while the rest, some singly, some in combination,
modify the basic colour a varying degree. For
each of these genes, mutations have been
described. Mutations within these genes can
multiply the effects on colour
14
Colour and pattern genes the mouse
The mouse is the most studied mammal, also as far
as pigmentation is concerned. Some sobering data
is given in the table below. It also give us
hope that coat pattern will soon be as well
understood as colour.
302 Mouse genes and variants involved in pigmentation have been identified. The variants are mutated genes - the total number of genes is less than 302, but still many times the 16 of the horse. 302 Mouse genes and variants involved in pigmentation have been identified. The variants are mutated genes - the total number of genes is less than 302, but still many times the 16 of the horse. 302 Mouse genes and variants involved in pigmentation have been identified. The variants are mutated genes - the total number of genes is less than 302, but still many times the 16 of the horse. 302 Mouse genes and variants involved in pigmentation have been identified. The variants are mutated genes - the total number of genes is less than 302, but still many times the 16 of the horse. 302 Mouse genes and variants involved in pigmentation have been identified. The variants are mutated genes - the total number of genes is less than 302, but still many times the 16 of the horse. 302 Mouse genes and variants involved in pigmentation have been identified. The variants are mutated genes - the total number of genes is less than 302, but still many times the 16 of the horse. 302 Mouse genes and variants involved in pigmentation have been identified. The variants are mutated genes - the total number of genes is less than 302, but still many times the 16 of the horse.
Of these 171 have been cloned and studied in detail. Of these 171 have been cloned and studied in detail. Of these 171 have been cloned and studied in detail. Of these 171 have been cloned and studied in detail. Of these 171 have been cloned and studied in detail. Of these 171 have been cloned and studied in detail. Of these 171 have been cloned and studied in detail.
For each of these171 genes a human homologue has been found. There seems to be a large degree of similarity in mammalian pigmentation genetics over species. For each of these171 genes a human homologue has been found. There seems to be a large degree of similarity in mammalian pigmentation genetics over species. For each of these171 genes a human homologue has been found. There seems to be a large degree of similarity in mammalian pigmentation genetics over species. For each of these171 genes a human homologue has been found. There seems to be a large degree of similarity in mammalian pigmentation genetics over species. For each of these171 genes a human homologue has been found. There seems to be a large degree of similarity in mammalian pigmentation genetics over species. For each of these171 genes a human homologue has been found. There seems to be a large degree of similarity in mammalian pigmentation genetics over species. For each of these171 genes a human homologue has been found. There seems to be a large degree of similarity in mammalian pigmentation genetics over species.
For 149 of the 171 genes homologues have been found in the Zebra-fish. This bodes well for utilization of knowledge across species. For 149 of the 171 genes homologues have been found in the Zebra-fish. This bodes well for utilization of knowledge across species. For 149 of the 171 genes homologues have been found in the Zebra-fish. This bodes well for utilization of knowledge across species. For 149 of the 171 genes homologues have been found in the Zebra-fish. This bodes well for utilization of knowledge across species. For 149 of the 171 genes homologues have been found in the Zebra-fish. This bodes well for utilization of knowledge across species. For 149 of the 171 genes homologues have been found in the Zebra-fish. This bodes well for utilization of knowledge across species. For 149 of the 171 genes homologues have been found in the Zebra-fish. This bodes well for utilization of knowledge across species.
Coat colour - General Pattern - eg. spot, belt, stripe, toe, etc. Coat, Hair, Fur - Other effects Skin - Dark, Light, Darken, Lighten Skin - Other Effects Pigmentation - hyper, hypo, depigment. Other
22 (7 cloned) 97 (24 cloned) 52 (28 cloned) 19 (11 cloned) 7 (6 cloned) 17 (16 cloned) 88 (79 cloned)
15
What about game coat colour?
  • These same genes have been found in many mammals,
    even though they may not have exactly the same
    effect. Most will be present in most game
    species, but with slight sequence differences.
  • A starting point would be to determine the DNA
    sequences of the known primary colour genes
    (Extension and Agouti loci) of both standard and
    other phenotypes, analyse for differences and
    investigate the genetic effect, if any, of each.
  • Species for which the gene sequences are known
    that are closest to the game specie in question
    should be used as starting point.
  • A second phase would be the same procedure for
    the known genes that have a less dramatic effect
    (dilution, depigmentation, greying).
  • Literature should be carefully monitored for any
    new developments.
  • Finally breeding and breeding experiments might
    be required.

16
What about coat colour patterns?
  • Is the basis for variation in coat colour
    pattern known? Hardly !!!.
  • Mammalian coat patterns (e.g., spots, stripes)
    are hypothesized to play important roles in
    camouflage and other relevant processes, yet the
    genetic and developmental bases for these
    phenotypes are completely unknown. (Eizirik, E.
    January 2010)
  • "The question of how color patterns are
    established in vertebrates has been a black box,"
    says Marie Manceau, (Science, 2011).
  • They found that subtle changes in the Agouti
    gene's embryonic activity can also make a
    profound difference in the distribution of
    pigments across the entire body. Mary Manceau,
    Hopi E. Hoekstra et al 2011)

17
The Beauty of Mutations
  • Why mutations?
  • Our environment constantly changes, the Earth and
    its ecosystems change.
  • Populations must change to survive
  • Evolutionary change requires variation, the raw
    material on which natural selection works
  • One mechanism for variation and change is at the
    DNA level.
  • Mutations can be beneficial and enable the
    organism to adapt to a changing environment.
  • However, most mutations are deleterious, and
    cause varied genetic problems

18
BAIE DANKIE
THANK YOU BAIE
DANKIE
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