genetics

• there are 37 genes in the mitochondria, inherited from your mother
• karyotype

  complete set of an individuals chromosomes
• aneuploidy

  abnormal chromosome number
• structural defects

  deletions, insertions, translocations, inversions
• diploid cells

  46
• haploid cells

  gamete, 23
• Human cells are diploid, thus containing two alleles of each gene
• Homozygous: alleles for a particular trait are the same
•   Heterozygous: alleles for a particular trait are different
• Genotype: describes the genetic material of an individual, and describes the alleles an individual carries for a particular gene or genetic location
• Phenotype: describes the observable characteristics of an individual, is determined by the genotype in combination of environmental factors
• mendels laws of inheritance

  segregation, independent assortment, dominance
• Law of segregation

  alleles in each pair separate when cells divide to create gametes, so that each gamete carries only 1 allele for each gene
• Law of independent assortment

  the alleles of different genes are sorted into gametes independently of one anothe
• Law of dominance

  some alleles are dominant, whilst others are recessive. An organism with at least one dominant allele will display this effect
• Autosomal dominant inheritance:

  Individuals who have one mutant allele of disease gene are affected, The presence of one normal allele cannot prevent disease. if one parent is affected: 50% risk. example: huntingtons
• autosomal recessive

  disease phenotype only when someone is homozygous for recessive disease allele, if both parents are carriers: 25% risk, eg. cystic fibrosis
• sex linked inheritance

  influenced by genes located on X or Y chromosome and exhibit unique patterns of inheritance, more common in males
• X linked recessive inheritance

  mutation on X chromosome, males more effected, no father to son transmission, eg. duchenne muscular dystrophy
• co-dominance

  Contribution of both alleles is visible in the phenotype

  E.g., ABO blood group
• Polygenic inheritance:

  determined by interactions of 2 or more genes. eg height and skin colour
• Multifactorial inheritance:

  influenced by multiple genes and environment, no specific inheritance patterns eg. diabetes
• Penetrance:

  A disease shows complete penetrance if all individuals who carry the disease gene are affected by the disease. Some traits have reduced penetrance: the phenotype does not occur as often as would be predicted by the genotype, disease may skip generations
• Expressivity

  Variable expressivity means individuals with same genotype may exhibit different degrees of the phenotype, may be caused by environmental factors
• Epigenetic inheritance:

  Disease involves changes in DNA packaging without a change to the DNA sequence e.g. DNA methylation
• Mitochondrial inheritance:

  Involve small number of genes located on mitochondrial DNA, Pattern of inheritance due to mitochondrial DNA only being inherited from mother