X Y Chromosomes

What Are Sex Chromosomes?

Each human cell contains 23 pairs of chromosomes that carry DNA within their nucleus. The X and Y chromosomes are one such pair. They determine the biological sex, reproductive organs, and sexual characteristics that develop in a person. Female (XX) mammals inherit one X chromosome from each parent, but males (XY) receive an X from their mother and a Y sex chromosome from their father.

Diseases and conditions found only on the X chromosome are said to be sex-linked, as are rare Y-linked conditions such as male infertility. The X chromosome is larger and confers more regulatory functions throughout the brain and body. While disease such as color-blindness and hemophilia have long been understood to be X-linked, biologists and behavioral geneticists now know that important brain functions and conditions, from intelligence to autism, may be up regulated or down regulated by genes found on the X chromosome.

What Is Genomic Imprinting?

Genomic imprinting is the biological mechanism wherein genes are expressed differently depending on whether they are inherited from the mother or the father. The imprinted brain theory hypothesizes that imprinting contributes to a range of psychiatric and neurological afflictions, most commonly autism spectrum and schizophrenia spectrum disorders. There are evolutionary reasons that maternal and paternal genes might "compete" for expression. For example, fetal head-size is favorable for a mother as it ensures an easier and safer birth, and in fact head size is associated with a range of conditions that show evidence of maternal imprinting, whereas larger head circumference at birth is correlated with conditions conditions, including autism, that may reflect an over-expression of paternal genes. 


Autism, Child Development

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