Di truyền học người - Bộ gen người

Chương 2: BỘ GEN NGƯỜI
The Structure of the Human Genome
Structure of the genome
Type of DNA % of Genome Features

Single-copy (unique) ~75% Includes most genes 1

Repetitive
Interspersed ~15% Interspersed throughout genome between
and within genes; includes Alu sequences 2
and VNTRs or mini (micro) satellites

Satellite (tandem) ~10% Highly repeated, low complexity sequences
usually located in centromeres
and telomeres

2 Alu sequences are
about 300 bp in length
and are repeated about
300,000 times in the
genome. They can be
found adjacent to or
within genes in introns
or nontranslated regions.

1 Some genes are repeated a few times to thousands-fold and thus would be in
the repetitive DNA fraction
50
100
0
I I I I I I I I I
fast ~10%
intermediate
~15%
slow (single-copy)
~75%
Classes of repetitive DNA
Interspersed (dispersed) repeats (e.g., Alu sequences)
TTAGGGTTAGGGTTAGGGTTAGGG
Tandem repeats (e.g., microsatellites)
GCTGAGG
GCTGAGG
GCTGAGG
5’
3’
vùng khởi động
(promoter)

các exon (các vùng trong hộp)
các intron (giữa các exon)
vùng được phiên mã
vùng được dịch mã
mRNA trưởng thành
+1
(A) cấu trúc gene phân đoạn
(B) cấu trúc của các gene phân đoạn khác nhau
b-globin
HGPRT
(HPRT)
toàn bộ = 1.660 bp; các exon = 990 bp
histone
nhân tố VIII
toàn bộ = 400 bp; exon = 400 bp
toàn bộ = 42.830 bp; các exon = 1263 bp
toàn bộ = ~186.000 bp; các exon = ~9,000 bp
Properties of the human genome

Nuclear

the haploid human genome has ~3 X 109 bp of DNA
single-copy DNA comprises ~75% of the human genome
the human genome contains ~30,000 to 40,000 genes
most genes are single-copy in the haploid genome
genes are composed of from 1 to >75 exons
genes vary in length from <100 to>2,300,000 bp
Alu sequences are present throughout the genome

Mitochondrial

circular genome of ~17,000 bp
contains <40 genes
Exons and introns
Gene densities
Human genes vary enormously in size and exon content
Gene families
Members may exhibit high sequence homology
sometimes contain a highly conserved domain (e.g. SOX box)
sometimes contain a very short conserved “motif”
(e.g. DEAD box, asp-glu-ala-asp RNA helicases)
superfamilies (e.g. Ig superfamily)
sometimes clustered (e.g. globin genes)
Often associated with truncated and non processed pseudogenes
Tandemly repetitive DNA
Dispersed repetitive DNA
Distribution of repetitive sequences within the RB1 gene
mitochondrion
“Typical” gene
Genes within genes