Types of Mutations
Chromosomal Numerical Abnormalities Chromosomal numerical abnormalities occur when there is a gain or loss of an entire chromosome. Monosomy is a loss of 1 chromosome (pair becomes 1 chromosome): Trisomy is a gain of 1 chromosome (pair becomes 3 chromosomes): Point Mutations General A point mutation is a mutation that affects only 1 nucleotide in […]
Mendel’s Laws of Genetics
Mendel’s Experiments and Punnett Squares Mendel’s experiments Mendel chose pea plants as the experimental model. Mendel reasoned pea plants were a good model of inheritance because of the following properties: Mendel cross-fertilized plants truebred (purebred) for certain traits. Mendel selected 7 true-breeding traits: True-breeding traits are referred to as homozygous alleles (genes). Example of determining […]
Autosomal Recessive and Autosomal Dominant Inheritance
Definitions Overview Autosomal recessive inheritance Recessive alleles are only manifested when they are homozygous, which means that the individual inherited a recessive allele from each parent. Autosomal dominant inheritance Dominance is a key concept in Mendelian inheritance and classical genetics. Often, the dominant allele codes for a functional protein, whereas the recessive allele does not. […]
Sex Determination
Overview Definitions The following definitions are relevant to the understanding of normal sex development: Overview of typical sex development Overview of genital structures Secondary sexual characteristics Secondary sexual characteristics develop based on the hormonal milieu at puberty. The Sex Chromosomes There are 2 sex chromosomes in humans: X and Y. Y chromosome X chromosome The […]
Mitochondrial Inheritance
Mitochondrial DNA and Inheritance Pattern Mitochondrial DNA (mtDNA) Inheritance pattern Mitochondrial Disorders Mitochondrial disorders are extremely variable and may range from mild to severe clinical presentation within the same family owing to heteroplasmy. References
Sex-Linked Inheritance
Definition Sex-linked inheritance occurs when genetic traits are inherited on either the X or the Y chromosome. There are 2 major sex-linked modes of inheritance: X-linked recessive and X-linked dominant. X-linked recessive inheritance: X-linked dominant inheritance: X-Linked Recessive Inheritance and Diseases X-linked recessive inheritance Children of an unaffected father and a heterozygous (carrier) mother have […]
Population Genetics
Hardy-Weinberg Equilibrium Introduction Population genetics studies genetic variation within a group. A given population possesses a common gene pool. Gene flow is created when individuals migrate into or away from the population. Definition The Hardy-Weinberg equilibrium says that within a given population, both allele and genotype frequencies remain constant, without evolutionary influences. Assumptions of the […]
Basic Terms of Genetics
Terms Starting with A–D Terms Starting with E–L Terms Starting with M–Q Terms Starting with R–Z References
Congenital Disorders of Sexual Development
Overview of Sex Development Definition Disorders of sexual development are a group of conditions characterized by atypical sexual development in an individual, involving abnormalities in the structure and/or function of both the internal reproductive organs and/or external genitalia. Overview of typical sex development Sex organs and characteristics Typical male development Male development begins due to […]
Patau Syndrome (Trisomy 13)
Overview Definition Trisomy 13 or Patau syndrome is defined by the presence of 3 copies of chromosome 13. Epidemiology Etiology Mnemonic “At 13 you enter Puberty”: P as in Patau syndrome or 13 for Trisomy 13 Pathophysiology Genetics Nondisjunction Robertsonian translocation Mosaicism Clinical Presentation Diagnosis Maternal screening Table: Maternal screening during 1st and 2nd trimesters […]