could u pls present the pedigree analysis of colour blindness ?
Colour blindness is a genetic abnormality because of which a person is not able to distinguish between some of the colors, which other people can recognize easily. It is a sex linked disorder in which the genes responsible for the synthesis of photo pigments are affected , either the genes are absent or get damaged. These genes are mainly present on the X chromosome. So, colour blindness is a X-linked disorder.
Sex linked diseases are not expressed equally in males and females, unlike autosomal disorders. X-linked disorder like colour blindness can be expressed in both males and females. In case of Y-linked disease only males would suffer.
If disorder is X-linked recessive like colour blindness, then there would be smaller proportion of females suffering ( as XCXC condition is required in females to suffer, which is very rare ) while there would be higher male percentage suffering from it as they do not have corresponding X allele.
Males can never be carrier of colour blindness. Since males have only one X chromosome, the allelic counterpart is absent so the trait is always expressed in males and hence they cannot be carriers. Females can be carrier as well as colour blind (sufferer). As we know, females have XX chromosome so, if gene on one of the chromosome is affected , it will be compensated by the other and in this condition females become carrier.
Another characteristic of X-linked disease like colour blindness is that X-linked traits cannot pass from fathers to their sons. It shows crisscross inheritance because in this disorder father passes gene for disorder to carrier daughter who then transmit it son.
Here is a given a pedigree analysis for colour blindness.