The disorder caused by an extra X chromosome in males (XXY) is:
A. Klinefelter syndrome
B. Cri du chat syndrome
C. Turner syndrome
D. Down syndrome
Answer: Option A
Solution (By JKExamLibrary)
Klinefelter syndrome (47,XXY) is a sex chromosome aneuploidy causing male hypogonadism, tall stature, gynecomastia, and infertility. Turner syndrome (45,X) affects females. Down syndrome is trisomy 21. Cri du chat is deletion in chromosome 5. Nondisjunction during meiosis leads to these aneuploidies.
Explanation:
Chiasmata become clearly visible during the diplotene stage of Prophase I. While the actual exchange of genetic material (crossing over) occurs during the pachytene stage, the homologous chromosomes begin to repel each other and move apart in diplotene, remaining connected only at the sites of crossing over, which appear as X-shaped chiasmata. Exam tip: Pachytene = crossing over; Diplotene = chiasmata visible.
Explanation:
The adult human dental formula is 2123/2123 (incisors 2, canines 1, premolars 2, molars 3) per quadrant, totaling 32 permanent teeth. Deciduous teeth formula is 2102/2102 (20 teeth). The formula represents half of the upper jaw over half of the lower jaw. Wisdom teeth (third molars) may be absent in some individuals.
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