Human Genetics

Karyotypes

  • The human genome is the full set of genetic information in DNA.

  • Chromosomes are photographed under a microscope to produce a karyotype.

  • A karyotype displays 46 chromosomes arranged in pairs of decreasing size (23 pairs) in a typical human cell.

Sex Chromosomes

  • There are 2 sex chromosomes that determine an individual's sex.

  • Females have two X chromosomes; males have one X and one Y chromosome.

  • The X chromosome has over 1400 genes, while the Y chromosome has about 158 genes.

Autosomal Chromosomes

  • The remaining 44 chromosomes are called autosomes.

Transmission of Human Traits

  • Human genes inherit in patterns similar to other organisms.

Dominant and Recessive Alleles

  • Many traits follow simple dominance patterns, like the Rhesus (Rh) blood group.

  • Rh+ (dominant) and Rh− (recessive): Rh positive blood has Rh+/Rh− genotypes, while Rh negative has Rh−/Rh− genotypes.

Codominant and Multiple Alleles

  • ABO blood group has 3 alleles: IA, IB, and i.

  • IA and IB are codominant; AB blood type has IA and IB alleles.

  • Type A (IAIA or IAi), type B (IBIB or IBi), and type O (ii).

Sex-Linkage in Human Genetics

  • Genes on sex chromosomes show a pattern of inheritance called sex-linkage.

  • Genes on the Y chromosome are male-specific; X-linked genes exist in both sexes, but males have one X chromosome.

Colorblindness and the X-Chromosome

  • Color vision genes are on the X chromosome. Colorblindness results from defective alleles; males often express this phenotype since they have only one X.

  • Recessive X-linked disorders are more common in males due to their X chromosome configuration.

X-Chromosome Inactivation

  • In females, one X chromosome is inactivated in cells, forming a Barr body, maintaining a condensed state due to special RNA.

Human Pedigrees

  • A pedigree chart displays relationships and trait presence across generations.

  • It helps infer genotypes and predict outcomes using Mendelian genetics principles.

  • Analyzing pedigrees can inform whether an allele is dominant or recessive and whether it is autosomal or sex-linked.