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…. 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 male46,XY Normal female46,XX

Karyotyping Karyograph

Homologous pair Karyograph

Haploid and diploid haploid diploid

Somatic cell haploid gametes in 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 AA aa Homozygous Aa AB Heterozygous

Recessive and dominant characters Tt 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 Locus A A Blood groups ABO 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 Medical Genetics: An illustrated outline. Andrew Read Medical Library Class No Web sites