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  Section: Genetics » Sex Linked, Sex Influenced and Sex Limited Traits
 
 
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Sex Limited Traits (cock feathering in poultry and baldness in man)

 
     
 
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Sex Linked, Sex Influenced and Sex Limited Traits
Sex linked traits 
Sex linkage in Drosophila
Sex linked lethals in Drosophila
Sex linkage in human beings
Sex linkage in poultry
Non-disjunction of sex chromosomes in Drosophila
Sex Influenced Traits (horned character in sheep)
Sex Limited Traits (cock feathering in poultry and baldness in man).

In above cases of sex influenced traits, same allele had different expressions in male and female individuals, but both alternative forms of trait are known in each sex. For instance, both horned and hornless sheep are known as ♀and ♂. In still other cases, we find, that a particular trait may not express at all in one of the two sexes. In poultry, for example, plumage is one such character, where cock feathering is never seen in female, although hen feathering is common among males. In most breeds of domestic poultry, male is cock feathered and female is hen feathered, so that plumage of two sexes is strikingly different. However, in some cases (e.g. some Sebright bantams), both sexes are hen feathered while in still other cases (e.g. Hamburgh breed), males may be either hen feathered or cock feathered. It has been shown through appropriate crosses, that hen feathering (h+)is a dominant character, so that both male as well as female with genotypes h+h+ or h+h will be hen feathered. However, homozygous recessive (hh)is cock feathered in male, but hen feathered in female, suggesting that in the presence of female hormone, hh can not express its cock feathering character (Table 16.2). This was confirmed through experiments of gonadectomies (removal of gonad). When ovary of hh female was removed, it resulted into cock feathering. Similarly in castrated males (festes removed), expression of h+ is inhibited.

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In man also, some traits have been considered to be sex limited, e.g. premature baldness (baldness in twenties or early thirties). On the basis of statistical analysis, it was suggested that premature baldness is controlled by a dominant gene, which expresses only in the presence of a certain level of male (androgenic) hormone, which is never reached in females, but always reached in normal male. This premature baldness is, however, very different than other cases of baldness which are explained by abnormalities in thyroid metabolism and infectious diseases.

Milk production in cattle is also sex limited, since genes for milk production are carried both by males and females, but they express only in females.








 
     
 
 
     




     
 
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