Principle of Inheritance and VariationMediumBloom L3
Question
An abnormal human baby with 'XXX' sex chromosomes was born due to: [NEET 2015 RS]
Options
A.formation of abnormal ova in the mother
B.fusion of two ova and one sperm
C.fusion of two sperms and one ovum
D.formation of abnormal sperms in the father
Solution
Sol.(a) [Key Concept: XXX Syndrome — Maternal Non-disjunction] An XXX baby is born due to FORMATION OF ABNORMAL OVA in the MOTHER. This results from non-disjunction of the X chromosome during meiosis in the mother, producing an XX egg (instead of X). When this XX egg is fertilised by a normal X-bearing sperm (X), the resulting zygote is XXX. Non-disjunction in the mother during meiosis I (XX egg + X sperm) is the most common cause. Formula: AXX (abnormal ovum from non-disjunction) + AX (normal X-sperm) = AAXXX.
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