Human Chromosomes and

Genes

Sanjaya Adikari

Department of Anatomy

DNA

• DNA is the genetic

material

• DNA is organized into

chromosomes

Chromosomes

DNAhistone proteinsnon-histone proteins

chromatin

chromosome

Chromosomes….

cell division

chromatids

short arm (p)

long arm (q)

centromere

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

Homologous pairKaryograph

Haploid and diploid

haploid

diploid

1 2 3 4 5 6

diploid

Somatic cell

haploid

gametesin meiosis,

Genes

• Gene is a sequence of DNA coding for a polypeptide

Exon 1

Intron 1

Exon 2

Intron 2

Intron 3

Exon 3

Exon 4

Gene

genes

non coding regions

chromosome

Locus and alleles

A A

Genes residing at the same level of the homologous pair of chromosomes are called alleles

Homologous pair

Locus

Alleles are in the same locus

Homozygous and heterozygous

AAaa

Homozygous

AaAB

Heterozygous

Recessive and dominant characters

T t

Dominant characters are expressed in the heterozygote*

Recessive characters are expressed only in the homozygote#

* 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

LocusA A

Blood groups

ABO

AAAOBBBOABOO

group-A

group- B

group-ABgroup-O

References• Emery’s Elements of Medical genetics. Robert F. Mueller

and Ian D. YoungMedical Library Class No. 616.042

• Medical Genetics: An illustrated outline. Andrew Read Medical Library Class No. 616.042

• Web siteshttp://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