Human Chromosomes and Genes Sanjaya Adikari Department of

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/Biology. Pages/C/Chromosomes. html http: //www. csu. edu. au/faculty/health/biomed/subjects/molbol/DNAstruc. htm http: //gslc. genetics. utah. edu/units/disorders/karyotype. cfm http: //homepages. which. net/~gk. sherman/baaaaabz. htm http: //www. eurekah. com/abstract. php? chapid=1777&bookid=118&catid=19