Pedigree chart for colour blindness inheritance of trait ,number of normal carriers and affected progeny
The Correct Answer and Explanation is:
Correct Answer Summary:
- Color blindness is a sex-linked recessive disorder carried on the X chromosome.
- Females can be:
- Normal (XX),
- Carrier (XᴺXᶜ),
- Affected (XᶜXᶜ).
- Males are either:
- Normal (XᴺY),
- Affected (XᶜY) — because they only have one X chromosome.
📊 Pedigree Analysis Sample (Hypothetical Example)
Let’s say you are analyzing a pedigree chart where:
- I-1 (male) is normal (XᴺY)
- I-2 (female) is a carrier (XᴺXᶜ)
- They have 4 children:
- II-1 (daughter): Carrier (XᴺXᶜ)
- II-2 (son): Affected (XᶜY)
- II-3 (son): Normal (XᴺY)
- II-4 (daughter): Normal (XᴺXᴺ)
✅ Correct Tally:
- Normal Carriers: 1 (II-1)
- Affected Progeny: 1 (II-2)
- Unaffected (Normal) Progeny: 2 (II-3 and II-4)
📚 300-Word Explanation:
Color blindness is a sex-linked recessive disorder, primarily affecting males, due to their single X chromosome. The gene responsible is located on the X chromosome, and the recessive allele (Xᶜ) causes the condition.
In a pedigree chart, males are represented as squares, females as circles, shaded symbols show affected individuals, and half-shaded circles represent carrier females.
For a woman to be color blind, she must inherit two copies of the defective allele (XᶜXᶜ). This is rare. However, if she inherits only one (XᴺXᶜ), she is a carrier — unaffected herself but capable of passing it on.
Males, having one X and one Y chromosome, are more likely to be affected if their single X chromosome carries the mutation (XᶜY). Because they don’t have a second X to compensate, even one copy of the recessive gene causes the condition.
If a carrier female (XᴺXᶜ) and a normal male (XᴺY) have children:
- Each son has a 50% chance of being affected (gets Xᶜ from mom).
- Each daughter has a 50% chance of being a carrier.
Therefore, by analyzing the pedigree chart, we can determine:
- How the trait is inherited
- Which individuals are carriers
- Who is affected
This analysis is essential for genetic counseling, predicting future risk, and understanding patterns of inheritance in families.