He thus managed to establish the fact that genes come by pairs, which separate when reproductive cells are formed (gamete) and that the gametes are paired at random during fecundation! (Fig. 1)
The factor of chance, nowadays called probability, which can be calculated mathematically through statistics, is an important part of genetic!
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 Fig 1 |
He defined terms such as F1 and F2, the first and second generation of descent. The genotype with its character: the phenotype, the hereditary determining gene of a defined characteristic or the alleles, the different form of the gene itself like R for the smooth or r for wrinkled. C for curly and R for straight, heterozygote and homozygote, dominant or recessive are terms that were only defined after his work was discovered. |
The factor of chance, nowadays called probability, which can be calculated mathematically through statistics, is an important part of genetic!
Men, as horses, inherit of half of their mother’s genetic material and of half of their father’s. Each parent transmits what is now known as chromosomes, which after pairing reconstruct the genetic inheritance, present in each cell! (fig.2) |
 Fig 2 (ex du petit pois) |
Chromosomes are made of DNA, deoxyribonucleic acid. Found in the cell, it was discovered in 1953 by Watson and Crick. The DNA segments that carry the genetic information are called genes. DNA structure, as seen on fig. 3, is made of two strands which run in opposite directions to each other, making a double helix. Each strand is composed of nucleotides which each contains one of the 4 chemical constituents called bases. A, Adenine, T, Thymine, G, Guanine and C, Cytosine. The bases are paired, A always facing T and C always facing G (base pairing). Incredible but true, each gene is a “simple” sequence of some thousands of those bases (one molecule of DNA made of 65 millions of nucleotides measures when unwind 22 mm). Each gene commands the fabrication of a specific protein or enzyme, and will determine the color of the eyes, of the skin, of the hair and the way it will curl. |
 Fig 3 |
Le dédoublement du double brin qui donne naissance à deux molécules identiques est appelé réplication, au niveau de la cellule visible au microscope on l’appelle la mitose : le matériel génétique est copié et peut être transmis à l’identique. La formation des gamètes en passant par l’haploide au niveau de la cellule s’appelle la meiose!
On doit donc bien comprendre que chaque gamète est génétiquement différent ! Elle ne comporte la réplique de que d’un brin de l’hélice, sa rencontre pendant la fécondation avec un gamète de l’autre sexe dépend complètement du hasard, si le père a des yeux bleus, sa fille peut très bien avoir des yeux marron!
C’est bien ça la reproduction ! Et le plus incroyable est peut être que cela fonctionne de la même façon pour un petit pois que pour l’homme ou le cheval , seul le nombre de chromosomes et leur taille diffèrent, sans aucun rapport au degré de développement ! voir fig 2 et 3
(Le cheval possède 32 paires de chromosomes, l'homme 23 !)
Voilà pour l’initiation à la génétique , on comprend peut être mieux que chaque individu, à sa conception, reçoit deux gènes pour chaque fonction ou caractère vital ou distinctif, le résultat final, ce qu’on verra à la naissance, s’appelle le phénotype, ce qui dépend donc de la composition des deux allèles du gène qui détermine le caractère qui nous intéresse, et pour nous, c’est surtout le gène Curly!!
The splitting of the two strands of the double helix which create 2 identical molecules is called replication. On the cell level, visible through a microscope it is called mitosis; the genetic material is copied and an identical copy is transmitted. The formation of gametes through the haploid on the cell level is called the meiosis! Each gamete is genetically different, and only carries the replica of one strand of the helix. The result of the pairing of two gametes during fecundation will lead to the creation of certain characteristic. A blue eyed father can have a brown eyed daughter; it is a sort of a lottery.
It’s what reproduction is about. The principle is the same for peas and for human beings or for horse. The number and the sizes of the chromosomes are different for each species regardless of their degree of development, fig. 2 and 3. Horses have got 32 pairs of chromosomes, men only 23!)
Each person receives 2 genes for each function or vital or distinctive character. At birth, the final result, the phenotype is seen. In our case the curly gene, composed of the two alleles of the gene and which determines a character, is what we are interested in.
If the 2 alleles of the gene given by the parents are identical, for example curly, the foal will be Homozygote and will therefore be curly. If the 2 allele are different, one curly and straight, the foal will be heterozygote, and the texture of the hair will be determined by the dominant allele.
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On its site, ICHO proposes a hypothesis for a genetic formula to define horse hair:
| C = dominant curly gene. |
| c = recessive straight allele on the same locus, indissociable, called linked alleles of the curly gene. |
| R = straight dominant gene, found on another locus than the straight recessive gene on the C locus |
| r = recessive curly allele linked to the dominant straight gene, on the same locus |
All this is far from simple. lets have a look to what it may lead to
| Ccrr : has curly hair, but will only transmit the gene 1 out of 2 times, possesses 2 curly recessive gene, can also produce straight when coupled to heterozygote curly or with straight |
| CCRR : homozygote and curly dominant, has curly hair and will always have curly offspring, the straight gene is present, but apparently on a recessive locus |
| CcRR : heterozygote but has curly hair, only 50 % of the offspring will be curly |
| CCRr : has curly hair, but only transmit the curly gene to 50 % of its offspring, even though we cannot notice it for the C dominant is always present |
| CcRr : has curly hair, can produce 50 % of curly dominant, and also transmit 50 % of recessive gene |
| CCrr : has curly hair and will always give birth to curly that will always bare a recessive gene |
| ccRR : straight, cannot have curly offspring, is not hypoallergenic |
| ccRr : straight, when coupled with an homozygote C, 50 % chance to produce a curly. |
| ccrr : can be curly, can be straight, no dominant gene, curly offspring if the other parent bring in the C dominant |
If you understood everything: well done!!! Now one must know that genetic regarding coats is probably more complex.
Do not hesitate to send your question and remarks, regarding allergy and genetic, to : @Jeroen |
