CHROMOSOME
The entire human genome consists of 23 pairs of chromosomes – long, coiled
strands of DNA. Each chromosome may contain thousands of genes – sections
of DNA that encode the information needed to create the proteins that are
essential for all biological functions.
NUCLEOSOME
1 Researchers combined the genetic
information of thousands of
healthy individuals with a database
that reveals which genetic
elements are active during
prenatal brain development.
They used this to identify a set of
exons that are highly expressed in
the brain but rarely vary from
person to person.
MUTATION RATE
HIGH
HISTONE
They then excluded from that set
all exons that are thought to play an
important role elsewhere in the body.
This left a set of exons that may play
a unique role in brain development.
Many of those exons turned out to
be in genes that had previously been
linked to autism and other complex
brain disorders – suggesting that
the distinguishing characteristics of
human cognition may have first
arisen in these genes.
LOW
DNA
HIGH
RATE OF EXPRESSION
LOW
2
HIGH
HIGH
EXON
EXON
INTRON
EXON
INTRON
GENE
TONIA COWAN/THE GLOBE AND MAIL 66
TEXT: IVAN SEMENIUK/THE GLOBE AND
MAIL 66 SOURCE: THE HOSPITAL FOR
SICK CHILDREN AND NATURE GENETICS
An individual gene is made up of exons, which contain the encoded
information, and introns, which do not. When a gene is “read” prior to
creating a protein, the information from the exons is spliced together.
Different exons have different rates of variation among individuals.