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#Y chromosome

6 public questions tagged with this topic.

Sex determination-l

Absence of Y chromosome activates:

When Y chromosome absent, testis-inducing pathway cannot be triggered due to lack of Sry. Bipotential supporting precursors therefore default to ovarian trajectory driven by active Wnt4/Rspo1/β-catenin axis. In XX gonads Rspo1 sensitizes Frizzled receptors to Wnt4, inhibits β-catenin destruction complex allowing nuclear accumulation. Nuclear β-catenin activates Foxl2, Follistatin and Dax1 while repressing Sox9 and Fgf9, blocking Sertoli and Leydig differentiation. Consequently ovary forms containing granulosa cells and meiotic germ cells. Thus absence of Y chromosome indirectly activates pro-ovarian Wnt/β-catenin cascade that specifies female gonad.

Ref: NCBI Bookshelf, Developmental Biology, Wnt4/β-catenin activated in absence of Y and SRY.

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Sex determination-l

In mammals, the presence of the Y chromosome leads to the development of:

Mammalian Y chromosome harbors Sry gene considered testis-determining factor. Presence of Y means presence of Sry whose timely expression in genital ridge precursors between six to seven weeks upregulates Sox9 in pre-Sertoli cells, activating Fgf9 loop, testis cord formation, anti-Müllerian hormone secretion and testosterone synthesis from Leydig cells. Wolffian ducts thus persist while Müllerian ducts regress, generating male phenotype. Absence leaves ovarian pathway established via Wnt4/Rspo1/β-catenin directing ovary formation. Therefore presence of Y chromosome leads anatomically and molecularly to development of testes in normal mammals.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 6: Y chromosome and SRY in testis determination.

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Pedigree Analysis

Y-linked traits

Because Y chromosome exists exclusively in males under normal karyotype, Y-linked traits manifest solely in male individuals and follow strict paternal lineage inheritance without exception. Daughters do not inherit Y from father, so they never express nor transmit Y-linked trait to next generation. While pedigree might appear to skip generation if affected male has only daughters, generally trait appears in every generation via affected fathers to sons. Unlike autosomal or X-linked traits, no female carriers exist, simplifying recognition of holandric transmission.

Ref: Hartl & Ruvolo, Genetics, 6th ed., Chapter 4: Holandric Male-Limited Inheritance Patterns

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Pedigree Analysis

Y-linked traits are

Y chromosome transmission is exclusively paternal to male offspring, absent in female offspring because daughters receive paternal X. Genes located in non-recombining male-specific region of Y therefore show holandric inheritance pattern: affected father passes allele to every son, who in turn passes to all of his sons indefinitely. No females ever express trait nor transmit it. Examples include SRY sex-determining factor and some spermatogenesis genes. Such all-male paternal line pattern cannot be explained by autosomal or X-linked inheritance because daughters would be affected.

Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 4: Y-linked Inheritance Characteristics

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