Bio

• Sex-linked traits


  Inheritance of genes located on the sex chromosomes, typically the X chromosome in humans
• Sex chromosomes in humans

  • Females have two X chromosomes (XX)
  • Males have one X and one Y chromosome (XY)
• Other sex-related traits

  • Sex-influenced traits
  • Sex-limited traits
• Sex-influenced traits


  Traits found in both sexes but expressed more in one sex than the other
• Sex-limited traits


  Traits with genes found in both sexes but only one sex expresses the phenotype
• In X-linked inheritance, the heterozygous genotype in females results in a carrier female, unlike Mendelian inheritance where the heterozygous genotype expresses the dominant trait
• Sex-influenced traits


  Controlled by autosomal genes, found in both sexes but one expresses it more than the other
• Sex-influenced trait


  • Human pattern baldness
• Sex-limited traits


  Controlled by autosomal genes, found in both sexes but only one sex expresses the phenotype
• Sex-limited trait

  • Lactation (female-limited)
• Recombination


  Mechanism where homologous pairs of chromosomes exchange genes
• Sex linkage


  Phenotypic manifestation and inheritance patterns vary between males and females, genes go along with either sex chromosome
• Pedigree


  A pictorial representation of how a trait is transmitted among the members of a family
• Pedigree analysis


  • Identification of the mode of inheritance of an unknown genetic trait
  • Determination of the genotype of an individual with respect to a trait
  • Determination of the risk of recurrence of a genetic condition in a family
• A major challenge in pedigree analysis is being able to collect substantial and accurate information regarding the history of a family with regard to a genetic condition
• In problems involving pedigree analysis, it is rare that the specific trait or characteristic is provided in the problem. This will somehow defeat the purpose of the analysis
• The "half-shaded" symbol is not used to denote the carrier status of an individual. It is the purpose of the analysis to determine whether an individual is a carrier or not
• Autosomal traits

  Traits with genes located on autosomes, which are the 44 chromosomes (22 pairs) common for both males and females
• Autosomal dominant inheritance


  • Affected individuals manifest the corresponding trait
  • Affected individuals should have at least one affected parent
  • Autosomal dominant traits have the tendency to not skip generations
  • Genotypes can be assigned to all of the individuals with respect to the identified inheritance pattern
• Autosomal dominant conditions

  • Achondroplasia
  • Marfan syndrome
• Autosomal recessive inheritance


  • Individuals may have the allele but do not express them (i.e., carriers)
  • Affected individuals may have both unaffected parents
  • Autosomal recessive traits have the tendency to skip generations
  • Genotypes can be assigned to all of the individuals with respect to the identified inheritance pattern
• Autosomal recessive conditions

  • Cystic fibrosis
  • Sickle cell anemia
• Controlled matings are not possible in humans
• Generation time is longer in humans than in peas
• Pedigree analysis can help assess the risk of recurrence of a genetic disorder
• The analysis of the inheritance of traits in humans is a far more complicated task compared with that of peas and fruit flies
• Challenges of analyzing human inheritance


  • Longer generation time
  • Limited sample size for analysis
  • Impossibility of performing matings in controlled environments
• Pedigree analysis


  A method to observe and analyze how a trait runs in families, using a pictorial representation of the transmission of a characteristic in at least two generations of families
• Uses of pedigrees

  • Basic research
  • Genetic counseling
• Individuals with an autosomal dominant trait usually have at least one affected parent
• Individuals with an autosomal recessive trait usually have no affected parents, although there are cases when one parent is also affected by the recessive condition
• Genes are segments of DNA that code for specific traits or characteristics.
• Alleles are different forms of genes that can be inherited from either parent.