46 public questions tagged with this topic.
Klinefelter’s syndrome is caused by the presence of an extra X chromosome (47, XXY). This follows from NCERT principle where the relation explains the outcome clearly for students in simple steps.
Ref: NCERT Biology Textbook for Class XI and XII (Botany section), Chapter: Morphology and Anatomy of Flowering Plants, Topic: Plant structure and tissue systems.
XX male syndrome occurs frequently due to aberrant recombination during paternal meiosis where SRY-containing segment of short arm Y translocates onto distal Xp or autosome. Offspring inheriting recombined chromosome are karyotypically XX but carry functional SRY capable of initiating Sox9 activation and testis determination despite absence of other Y genes such as AZF needed for spermatogenesis. Individuals develop phenotypic males with testes, male internal ducts and external genitalia though typically azoospermic and sterile. Incidence around 1 in 20,000 males reveals sufficiency of SRY for
Ref: Gilbert, Developmental Biology, 12th ed., Chapter 6: XX males due to SRY translocation.
Visibility of individual chromosomes under light microscope depends on degree of condensation regulated by condensin complexes and histone modifications across cell cycle. Interphase chromatin exists as 10 nanometer beads-on-string fiber further folded into 30 nanometer fiber and looped domains anchored to nuclear matrix, occupying distinct chromosome territories where active transcription and replication occur, but overlapping extensively making individual chromosomes unresolvable. Entry into M phase, triggered by cyclin B-CDK1 rising activity, activates condensin I and II ATPases that extrud
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 17: Mitotic Chromosome Condensation.
Prometaphase is transitional stage converting interphase nuclear architecture to mitotic spindle structure, initiated by rising cyclin B-CDK1 activity. CDK1 phosphorylates lamins A/C and B at serine residues within tail domain, causing depolymerization of filamentous lamina and fragmentation of nuclear envelope into vesicles merging with endoplasmic reticulum. Condensed chromosomes consisting of two sister chromatids embraced by cohesin are released into cytoplasm. Concurrently, kinetochores assembled at centromeres containing CENP-A nucleosomes fully mature, forming outer plate with KMN netwo
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 17, Prometaphase Events.
Humans follow the XY system, where males are XY and females are XX.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Sex Determination Mutation and Genetic Disorders
Honeybees follow the haplodiploidy system, where females are diploid (fertilized eggs) and males are haploid (unfertilized eggs).
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Sex Determination Mutation and Genetic Disorders
Turner’s syndrome is characterized by the absence of one X chromosome, leading to a 45, XO karyotype.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Sex Determination Mutation and Genetic Disorders
Klinefelter’s syndrome is caused by the XXY karyotype, not XYY.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Sex Determination Mutation and Genetic Disorders
Turner’s syndrome is caused by monosomy of the X chromosome, leading to a 45, XO genotype.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Sex Determination Mutation and Genetic Disorders
Sutton and Boveri proposed the Chromosomal Theory of Inheritance, linking genes to chromosomes.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Chromosomal Theory Linkage Recombination Gene Mapping
The Law of Independent Assortment states that genes located on different chromosomes assort independently during gamete formation.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Chromosomal Theory Linkage Recombination Gene Mapping
Aneuploidy is caused by nondisjunction, where chromosomes fail to separate properly during meiosis.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Mendel's Laws - Dominance Segregation Independent Assortment
