Biology

• Genetics


  The science that deals with the study of heredity
• Heredity


  The passing of traits from parents to offspring
• Gene


  A segment of DNA that codes of how genes are passed on from parents to offspring
• Trait


  A specific characteristic of an individual that can be determined by genes, environmental factors or a combination of both
• Character


  A broader term that encompasses a collection of traits, referring to a more general category of observable features or characteristics in an organism
• Allele


  Different forms of genes
• In the 1800's, heredity was viewed as the "blending of traits from both parents", but it doesn't explain how some traits reappear after skipping a generation

  
• Gregor Mendel


  Father of Modern Genetics, an Augustinian monk and botanist who experimented on garden peas and discovered the basic principles of inheritance, called Laws of Mendelian Inheritance, which are important because of his experimental and quantitative approach

  
• Mendel's Laws are the basic principles of inheritance
• Non-Mendelian inheritance

  Defies the simplistic ratios observed in Mendelian patterns, showcasing more complex genetic interactions
• Non-Mendelian inheritance


  • Involves traits influenced by multiple genes or factors
  • Often results in phenotypes that do not fit traditional Mendelian ratios, leading to continuous variation rather than discrete categories
  • Epigenetic factors, environmental influences, and cytoplasmic inheritance play significant roles
• Understanding non-Mendelian inheritance provides insights into the intricacies of genetic variation and inheritance, offering a broader perspective on the complexities of biological traits and their transmission across generations
• Codominance


  A type of genetic inheritance where both alleles of a gene are fully expressed in the heterozygous genotype, resulting in the simultaneous presence of both traits in the phenotype
• Codominance


  • The heterozygous individual exhibits a phenotype that expresses both alleles distinctly, without blending
  • Each allele contributes independently to the phenotype, leading to a unique combination of traits in the offspring

  
• Incomplete dominance


  A type of genetic inheritance where neither allele is completely dominant over the other, resulting in a heterozygous phenotype that is an intermediate blend of the homozygous phenotypes
• Incomplete dominance


  • The heterozygous phenotype falls between the phenotypes of the two homozygous genotypes
  • Both alleles are partially expressed, leading to an intermediate phenotype
• Lethal genes


  Genes that, when present in certain combinations or in homozygous form, result in the death of the organism before or shortly after birth
• Lethal genes


  • May exhibit various patterns depending on their mode of action (dominant lethals, recessive lethals, incomplete penetrance or expressivity)
  • Disrupt essential biological processes during development, leading to severe developmental abnormalities or functional deficiencies that are incompatible with life
• Polygenic inheritance

  The mechanism involving the additive effects of multiple genes, each contributing a small amount to the phenotype of the trait
• Polygenic inheritance


  • Environmental factors can influence the expression of polygenic traits, further contributing to the observed variation
  • The combined effects of multiple genes and environmental factors determine the final phenotype of the trait
• Sex-linked inheritance


  Refers to the inheritance pattern of genes located on the sex chromosomes (X and Y chromosomes in humans), resulting in traits that are more commonly expressed in one sex over the other
• Sex-linked inheritance


  • Recessive X-linked traits are more commonly expressed in males
  • Females are usually carriers of X-linked recessive traits and may show the trait only if they are homozygous for the recessive allele

  
• Sex-influenced inheritance


  The pattern of inheritance where the expression of a trait is influenced by the sex of the individual, but the gene responsible for the trait is located on autosomal chromosomes rather than the sex chromosomes
• Sex-influenced inheritance


  • The trait may be dominant or recessive and can be expressed differently in males and females due to hormonal or physiological differences between the sexes
• Pleiotropy


  A phenomenon in genetics where a single gene influences multiple, seemingly unrelated phenotypic traits
• Pleiotropy


  • A mutation in one gene can have multiple effects on the phenotype of an organism
  • Can result in complex inheritance patterns where seemingly disparate traits are affected by mutations in the same gene