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Transcript 
Human Chromosomes
and Genes
Sanjaya Adikari
Department of Anatomy
DNA
• DNA is the genetic material
• DNA is organized into
chromosomes
Chromosomes
DNA
histone proteins
non-histone proteins
chromatin
chromosome
Chromosomes….
chromatids
short arm (p)
cell division
centromere
long arm (q)
telomere
Autosomes and
sex chromosomes
• Total of 46 chromosomes
• 23 pairs of chromosomes
• 22 pairs of autosomes
• 1 pair of sex chromosomes, XX or XY
Karyotype
• Chromosome constitution of a cell
• Normal male
46,XY
• Normal female
46,XX
Karyotyping
Karyograph
Karyograph
Homologous pair
Haploid and diploid
1
diploid
haploid
2
3
4
5
6
in meiosis,
gametes
Somatic cell
diploid
haploid
Genes
• Gene is a sequence of DNA
coding for a polypeptide
Exon 1
Intron 1
genes
Exon 2
non coding regions
Intron 2
Exon 3
Intron 3
Exon 4
chromosome
Gene
Locus and alleles
Homologous pair
Genes residing at the same level
of the homologous pair of
chromosomes are called alleles
Alleles are in the same locus
A
A
Locus
Homozygous and
heterozygous
AA
aa
Homozygous
Aa
AB
Heterozygous
Recessive and dominant
characters
Dominant characters are expressed
in the heterozygote*
Recessive characters are expressed
#
only in the homozygote
T
t
* heterozygote=person with heterozygous genotype
#
homozygote=person with homozygous genotype
TT => tall
Tt => tall
tt => short
‘Tall’ is the dominant character
‘Short’ is the recessive character
Genetic polymorphism
Blood groups
ABO
A
A
Locus
AA
AO
BB
BO
AB
OO
group-A
group- B
group-AB
group-O
References
• Emery’s Elements of Medical genetics. Robert F. Mueller and Ian
D. Young
Medical Library Class No. 616.042
• Medical Genetics: An illustrated outline. Andrew Read
Medical Library Class No. 616.042
• Web sites
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/Chromosomes.html
http://www.csu.edu.au/faculty/health/biomed/subjects/molbol/DNAstruc.htm
http://gslc.genetics.utah.edu/units/disorders/karyotype/karyotype.cfm
http://homepages.which.net/~gk.sherman/baaaaabz.htm
http://www.eurekah.com/abstract.php?chapid=1777&bookid=118&catid=19
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