Unit 1

• cross/hybridization - when two distinct individuals w/ different characteristics are bred to each other
• hybrids - offspring of cross/hybridization
• trait - observable or measurable feature/characteristics, ex green or yellow
• characters - a quality and traits that describe it
• gene - section of coding DNA for a character
• allele - version of a gene that codes for a trait
• genotype - alleles present, genetic makeup
• phenotype - observable qualities pertaining to a genotype
• monohybrid - only looking at one trait, ex Tt
• dihybrid - looking at two traits, ex TtXx
• Law of Segregation - two copies of a gene segregate from each other during the process that creates gametes
• Law of Independent Assortment - two different genes will randomly assort their alleles during the process that gives rise to gametes, rather phenotypes don't travel together
• simple mendelian inheritance - all individuals w/ dominant alleles have the dominant phenotype, and two recessive alleles are required to show the recessive phenotype
• incomplete penetrance - some individuals express the trait their genotype codes for while others do not, despite the fact that both have the allele necessary for the trait (not necessarily dominant or recessive)
• incomplete dominance - two different alleles but neither end up dominant, instead the phenotype presents as a mixing of both traits
• overdominance - the heterozygous phenotype has significant advantages over both of the homozygous phenotypes, ex sickle cell disease
• codominance - both traits are expressed, but in distinct patches rather than mixing
• x-linked - gene is physically on the X chromosome
• sons always get their X from their mothers and their Y from their fathers
• daughters get an X from both parents
• sex-influenced - not on X or Y, but the trait is still influenced by the sex of the individual, ex allele is dominant in one sex but recessive in the other
• sex-limited - not on X or Y, despite this the trait is only expressed in one sex
• lethal alleles - allele/genotype's presence is fatal to an individual. onset can occur at any time
• semilethal alleles - allele is only lethal in some cases, despite many individuals having the genotype
• conditional lethal allele - a genotype is only lethal if certain external conditions are met
• epistasis - expression of one gene is modified by the expression of other genes
• complementation - type of gene interaction, both alleles are needed to create the desired phenotype
• nonessential genes - genes that are not required for survival but likely to be beneficial to the organism
• possible explanations for overdominance benefits:

  • infectious organisms may recognize only a specific functional protein
  • proteins produced by alleles have a broader range of environmental tolerance
  • heterozygous individuals can produce more varieties of homodimer proteins
  • alleles produce two different proteins with slightly different functions
• a paralog can explain the lack of phenotype for a gene knockout
• pleiotropy - a single gene has multiple effects on an organism's phenotype
• gene redundancy - the loss of function for one gene has no phenotypic effect, but the loss of function in two genes does
• paralogs - duplicate genes that are not identical due to accumulation of changes (from mutations)
• wild type - most prevalent allele in a population, usually encodes a protein that is made in the proper amount and functions normally
• gene interaction - two or more genes are required to produce a specific trait
• in sex influenced traits, both sexes can express the trait depending on their genotype, but in sex limited inheritance, a particular sex can only have one phenotype for the trait in question
• the principle of linkage:

  • two or more genes that are physically connected on a chromosome
  • genes that are transmitted to the next generation as a group
• genetic linkage maps only estimate the distance between two genes
• crossing over is more likely to occur between genes that are far apart on a chromosome
• testcrosses are always performed between heterozygous and homozygous recessive individuals