Family Pedigree
FAMILY LINE PEDIGREE CHART FOR COLOUR BLINDNESS
Purpose
The purpose of the analysis is to illustrate the hereditary pattern of color blindness in a family lineage from the grandparent to the current siblings.
Phenotypic analysis
In this family, there have been a total of six color blind males; non of the grandparents had color blindness, my father and my one of my uncles are color blind, none of my aunts and stepmothers are color blind. My brother and two of my cousins are color blind; none of my sisters are color blind. This brings to a total of six color-blind individuals in the family.
Genotypic analysis
Color blindness genes are found in X chromosomes; males have only 1X chromosomes inherited from the mother. If the male X chromosome contains a pair of color blindness genes, the offspring will be color blind. If only one gene is in the X chromosome, then the child does not suffer from colour blindness but can transmit the trait to the offsprings (carrier). Suppose color gene is denoted as Xc, then it implies
Xcc – color blindness is expressed Xc – normal but is a color blindness carrier X – normal and non-carrier
Analysis
From the analysis above, the color blindness trait is only expressed in males when the X chromosome contains two pairs of the gene responsible. The color blind trait was obtained in the family through physical observation and comparing the observations and inquiry from the elder members of the family then comparing with the available inheritance rules. The inheritance of the trait followed the normal inheritance pattern; no unusual observations were noted. However, abnormality appears where both parents are carriers, but no female child inherits the trait. The only discrepancy noted was the case where normal parents were able to produce a color-blind individual. However, this was explained using the concept of dormancy and recessiveness. The color-blind gene is recessive; therefore, both parents may be normal but are gene carriers.
In general, the color blindness trait inheritance follows a distinct predictable pattern; therefore, even though I am not color blind but since my father was color-blind am expecting one of my children to acquire color blindness. This is shown in the Punnett square below.
Punnett Square
| Y | Xc | |
| Xcc | YXcc | XccX |
| Xc | YXc | XcXc |
One male color blind, one male color blind carrier, and two normal female carriers
