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Commentary on "A Role for the X Chromosome in Sex Differences in Variability in General Intelligence?" (Johnson et al., 2009)

Research output: Contribution to journalEditorial

Original languageEnglish
Pages (from-to)615 - 621
Number of pages7
JournalPerspectives On Psychological Science
Volume4
Issue number6
DOIs
Publication statusPublished - 2009

King's Authors

Abstract

Johnson et al.'s (2009) article highlights the role of X-chromosomal genes in general intelligence and draws attention to their potential role in explaining the observed greater variance for this trait in males and their excess at both extremes of the distribution. We note that this would result from a simple additive effect of X-linked intelligence genes and also discuss the potentially important contribution of recessive deleterious loci. The buffering effect of heterozygosity in females will be partly constrained by the skewing of X-inactivation patterns increasing the variance of females beyond what is expected. Furthermore, escape of some X-linked genes from inactivation may also be relevant to male-female variance comparisons. We also comment on the difficulty of establishing the extent to which the X chromosome is enriched for intelligence genes and point out that their estimates of the proportion of genes influencing general intelligence that might be located on the X chromosome rely on some doubtful premises, especially concerning the likely equivalence of X-linked gene action in males and females. Finally, we discuss the increasingly compelling evidence for the accumulation of genes on the X chromosome that have selective benefit to males, including those implicated in fertility and some manifestations of intelligence.

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