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Nonmedelian Disorders : Overview

Non-Mendelian inheritance

Non-mendelian inheritance:

1) Incomplete dominance 2) Co-dominance 3) Multiple alleles 4) Pleiotropy 5) Lethality 6) Polygenic traits 7) Environmental factors

Mendel’s laws determine the distribution of phenotypes linked to single genes on a chromosome and their expected appearance during a 
population. In some situations, the proportion of phenotypes observed doesn’t match the anticipated values. this is often called Non-mendelian inheritance and it plays a crucial role in several disease processes.

Non-mendelian inheritance can manifest as incomplete dominance, where offspring don't 
display traits of either parent but rather, a mixture of both. Two alleles produce an intermediate phenotype, instead of either one exerting a selected dominance. Incomplete dominance will provides a 1:2:1 phenotype ratio with the homozygous genotypes each showing a special feature and therefore the heterozygous showing another distinct phenotype.

An example of this is often 
the snapdragon flower, Mediterranean snapdragon , which expresses white, red and pink phenotypes. A cross between a homozygous white-flowered plant CWCW and a homozygous red-flowered plant CRCR can produce pink heterozygous CRCW flowers.

Non-Mendelian Inheritance is applicable in co-dominance where two alleles could also be 
expressed simultaneously i.e. heterozygous. there's no mixing or blending involved. The human blood group AB, where types A and B are both codominant, is an example of this. A cross between AA and BB will produce AB offspring, with both alleles being expressed equally.

Often, co-dominance is linked with a characteristic that has multiple alleles of a given gene. In many cases one among those alleles are going to be recessive and two others are going to be dominant. this provides the trait the power to follow the Mendelian Laws of heredity with simple or complete dominance or, alternatively, to possess a situation where co-dominance occurs

Non-mendelian inheritance also can 
manifest as pleiotropy, where one gene can affect multiple characteristics which may be seemingly unrelated. Pleiotropy are often observed in human genetic disorders like a hereditary disorder called Marfan Sydrome. Symptoms include thin fingers and toes, heart problems, dislocation of the lense of the attention and a strangely tall height. this is often caused by a mutation during a gene liable for the assembly of elastic fibrils that provide flexibility and support to animal tissue and function storage houses for growth hormones. the quantity of functional protein produced is reduced leading to fewer fibrils thanks to this mutation. This results in malfunctions in heart and eye development, also as an overabundance of free growth hormones within the blood stream leading to tall height.

Combinations of genes are often needed to market 
the survival of organisms. If an allele that contributes to a gene isn't expressed it can cause harmful activity. This is often referred to as lethality. A classic example of an allele that affects survival is that the lethal yellow allele, a spontaneous mutation in mice that creates their coats yellow. Mice that are homozygous die early in development. Although this particular allele is dominant, lethal alleles are often dominant or recessive, and may be expressed in homozygous or heterozygous conditions.

Some characteristics are polygenic, meaning that they’re controlled by variety 
of various genes. In polygenic inheritance, traits often form a phenotypic spectrum instead of falling into clear-cut categories, for instance complexion.

Most real-world characteristics are determined not just by genotype, but also by environmental factors that influence how genotype is translated into phenotype. for instance 
, hydrangea flowers vary in colour from blue to pink counting on the pH of soil they grow in.



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