Lesson 4.2: Autosomal Linked Traits

• Autosomes are the first 22 homologous pairs of human chromosomes that do not influence the sex of an individual.
• Sex chromosomes are the 23rd pair of chromosomes that determine the sex of an individual.
• Autosomal

  • Assume affected outsiders are assumed to be heterozygous
  • All unaffected individuals are homozygous for the normal recessive allele. 
• Autosomal Dominant

  • If dominant allele is present on the autosome, then the individual will express the trait.

  A = dominant   a = recessive

  • Genotype of Individual w/ autosomal dominant trait: 

  AA and Aa (heterozygous are affected

  • Genotype of individual w/o autosomal dominant trait: 

  aa (homozygous recessive)
• Autosomal Recessive

  • All affected are homozygotes 
  • Unaffected outsiders are assumed to be homozygous normal 
  • Consanguineous matings are often involved
• Autosomal Recessive

  • If dominant allele is present on the autosome, then the individual will not express the trait. In order to express the trait, two recessive alleles must be present.

  A = dominant   a = recessive

  • Genotype of an individual with an autosomal recessive trait: 

  aa (homozygous recessive)

  • Genotype of an individual without the autosomal recessive trait: 

  AA or Aa
• Achondroplasia

  • Mutant allele of gene on chromosome 4 causes deficiency of receptor protein for growth factor
  • Dwarfism with short limbs; head and trunk sizes are normal
• • Mutant allele of gene on chromosome 15 causes connective tissue disorder 
  • Long limbs, sunken chest, lens dislocated, spindly fingers, weakened aorta


  Marfan syndrome
• Familial Hypercholesterolemia 

  • Mutant allele of gene on chromosome 19 encodes faulty cholesterol-binding protein
  • High cholesterol, heart disease
• Huntington disease

  Mutant allele of gene on chromosome 4 encodes protein with extra amino acids that causes it to misfold and form clumps in brain cells.

  • Progressive uncontrollable movements and personality changes, beginning in middle age
• • Mutant allele gene on chromosome 17 encodes faulty cell signaling protein
  • Brown skin marks (cafe-au-lait spots), benign tumors beneath skin


  Neurofibromatosis (type 1)
• • Multiple genes on multiple chromosomes; mechanism is unknown
  • Extra fingers or toes or both


  Polydactyly
• • Mutant allele of gene on chromosome 11 encodes faulty gene in biochemical pathway required for pigment production
  • Lack of pigment in skin, hair, and eyes


  Albinism
• • Mutant allele of gene on chromosome 7 encode faulty chloride channel protein
  • Lung infections and congestions, infertility, poor fat digestion, poor weight gain, salty sweat


  Cystic Fibrosis
• • Mutant allele of gene chromosome 12 cause enzyme deficiency in biochemical pathway that breaks down the amino acid phenylalanine
  • Buildup of phenylalanine and related compounds causes mental retardation


  Phenylketonuria (PKU)
• • Mutant allele on chromosome 15 causes deficiency of lysosome enzyme
  • Buildup of byproducts causes nervous system degeneration


  Tay-sachs disease
• Less predictable variations

  Refer to the outcomes in genetic inheritance that deviate from the expected patterns established by Mendel's principles. While Mendel showed that specific genes tend to produce consistent phenotypic traits across generations, there are instances where the observed outcomes differ from the anticipated results, even when focusing on individual genes.
• A rare, genetic abnormality that affects the shape and movement of fingers


  Camptodactyly
• • Can affect both males and females, but only passed on by females because all mitochondria of all children come from the mother; can appear in every generation


  Mitochondrial Inheritance
• Autosomal Dominant Disorders

  Achondroplasia, Familial Hypercholesterolemia , Huntington disease , Marfan syndrome, Neurofibromatosis (type 1) , Polydactyly
• Autosomal Recessive Disorders

  Albinism, Cystic Fibrosis, Phenylketonuria (PKU), Tay-sachs disease