Study of an American Negro Family with the Rare Rh Genotype ryr (CdE/cde)
Rare Rh Genotype ryr (CdE/cde)
in Aluets or Eskimos and Incas in the Andeans have Rh Genotype ryr (CdE/cde)
The highest frequency of an extremely
rare r y (CdE) gene (=0.7%) in the Parsis is one of the most unique findings described
so far in any population of the world. In Parsis it is poplymorphic whereas it is just
sporadic in occurrence that too in a few populations only, the world over.
The very rare Rh genotype Ryr (CdE/cde) in a case of erythroblastosis foetalis.
Hemolytic disease of the newborn
Main article: Hemolytic disease of the newborn
The hemolytic condition occurs when there is an incompatibility between the blood types of the mother and the fetus. There is also potential incompatibility if the mother is Rh negative and the father is positive. When any incompatibility is detected, the mother receives an injection at 28 weeks gestation and at birth to avoid the development of antibodies toward the fetus. These terms do not indicate which specific antigen-antibody incompatibility is implicated. The disorder in the fetus due to Rh D incompatibility is known as erythroblastosis fetalis.
• Hemolytic comes from two words: "hemo" (blood) and "lysis" (destruction) or breaking down of red blood cells
• Erythroblastosis refers to the making of immature red blood cells
• Fetalis refers to the fetus.
The results at the Rh Locus in the Parsis have provided evidence for an orthodox nature
of Rh gene “r” and a variable nature of R2 gene. The highest frequency of an extremely
rare r y (CdE) gene (=0.7%) in the Parsis is one of the most unique findings described
so far in any population of the world. In Parsis it is poplymorphic whereas it is just
sporadic in occurrence that too in a few populations only, the world over. The present
analysis showed that founder’s principle i.e. genetic drift and a high degree of inbreeding
among the early small number of migrants and subsequent cloning effect in successive
generations have been responsible for such high ry gene complex among them. According
to Morgan and Spuhler (1965), “in the absence of mutation, gene flow and selection, an
idealized small population mating at random for a requisite number of generation (e.g.
excluding negative assortative mating) dependent upon the size of the population, will
reach a level of inbreeding equal to unity.” This may be true for early Parsi immigrants.
Both size could not have been more than 100 (?) people including men women and
children and close relatives during 600-700 A.D. Effective reproductive individuals will
be still smaller. Parsis brought “ry” gene with hem since not a single example of “ry”
has been reported from a vast literature available from India. “ry” gene and Heterosis:
Some form of heterosis among the possessors of the “ry” gene complex appears plausible
although difficult to prove, but the possibility cannot be excluded following Parson’s
arguments. Parson (1962) while discussing “the initial increase of a new gene under
positive assortative mating” came to the conclusion that “the condition under which new
genes will increase in frequency under mixed positive asortative mating and random
mating are discussed for populations in which two alleles are segregating at a locus.
Whereas heterozygote advantage is essential under random mating for a new gene to
become established, this is no longer a prerequisite with a proportion of assortative
mating”. So far no specific selective advantage is known for “ry”.
If any advantage is discovered them what Parsons (1963) thought of migration selection
as an evolutionary factor may be as important as drift and viability differences between
genotypes may be true for “ry” incidence among the Parsis. As a matter of fact Parsons
has been looking forward for accurate unbiased data.
“ry” gene complex appears to be of Iranian origin and it is strongly suspected that “ry” can
still be detected in population groups from central Iran. The phenotype CeDEE reported
by Sunderland and Smith (1966) could be ry R2 rather than R2 R2 as interpreted by them.
Highest frequency in the world at HLA, A,B, and DR locus antigens and also in Gm
and InV (1) loci can be explained on the basis of genetic drift in the small founder Parsi
populations as mentioned which discussing “ry” story.
Thus, the Rh system in the Parsis has provided evidences for genetic drift through “ry”
selection through R2, and high degree of genetic stability though “r”.
Erythroblastosis fetalis - Overview
• Overview
• Symptom
• Treatment
• Prevention
• All Information
Alternative Names
Hemolytic disease of the newborn
Definition of Erythroblastosis fetalis:
Erythroblastosis fetalis is a potentially life-threatening blood disorder in a fetus or newborn infant. This article provides a general overview. For more detailed information see the specific disorder:
• ABO incompatibility
• Rh incompatibility
Causes, incidence, and risk factors:
Erythroblastosis fetalis develops in an unborn infant when the mother and baby have different blood types. The mother produces substances called antibodies that attack the developing baby's red blood cells.
The most common form of erythroblastosis fetalis is ABO incompatibility, which can vary in severity.
The less common form is called Rh incompatibility, which can cause very severe anemia in the baby.
Source: http://www.umm.edu/ency/article/001298.htm#ixzz2ESaXmE8J
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