bio complex inheritance

• plieotropy


  a single gene affects multiple phenotypic traits

  -ex. sickle-cell disease, albinism
• traits determined by more than one gene

  • epistasis
  • polygenic
  • environmental impact
• Quantitative characters vary along continuum of numeric values rather than discrete categories
• Quantitative traits are usually polygenic: multiple genes contribute to a single phenotype (additive effect)

  -ex. skin color and height in humans
• epistasis


  one gene alters phenotypic expression of another gene
• Sometimes phenotype depends on environment as well as genotype
• trait's norm of reaction


  range of phenotypes produced by given genotype under different environmental conditions

  ex. same hydrangea phenotypes produce different colored flowers depending on soil acidity
• some alleles are heat-sensitive
• linked genes


  Genes located on same chromosome tend to be inherited together
• sex-linked gene


  gene located on either sex chromosome
• Sex chromosomes contain genes for characters unrelated to sex
• Males are hemizygous: have only one copy of X chromosome instead of two
• In female mammals, one X chromosome in each somatic cell is randomly inactivated during embryonic development

  -making same amount of proteins in females as in males
• Inactive X condenses ->Barr body (methyl groups attach to histones (proteins) that are bound to DNA -> de-activate it; reversed in sex cells (before meiosis)
• What is the interaction between the genes controlling hair color in mice an example of?

  Epistasis
• What is gene interaction?


  • The way different genes work together to produce a single phenotype
  • One gene's expression can be influenced or masked by another gene
  • Different from simple Mendelian inheritance
• What is the definition of epistasis?


  A specific type of gene interaction where one gene masks or modifies another gene's expression
• What are the key points of epistasis?


  • Involves at least two genes affecting a single trait
  • The epistatic gene can suppress or alter the effect of the hypostatic gene
  • Results in phenotypic ratios that deviate from Mendelian inheritance
• What is the difference between epistasis and pleiotropy?


  Epistasis involves multiple genes affecting a single trait, while pleiotropy involves one gene affecting multiple traits
• What determines coat color in cats?

  Genes on the X chromosome
• Why can male cats not be tortoiseshell?


  They only have one X chromosome, so they can only express one coat color allele
• What is X-chromosome inactivation?


  A process where one of the two X chromosomes in female mammals is randomly inactivated
• What happens to the inactivated X chromosome during X-chromosome inactivation?


  It becomes a Barr body
• How does X-chromosome inactivation affect tortoiseshell cats' coat pattern?


  It leads to a mosaic expression of X-linked genes, resulting in patches of orange and black fur