Model System
System with convenient characteristics used to study specific biological phenomenon applied to other systems
Blending Theory of Inheritance
(Proven wrong by Mendel :) )
Original parental traits are lost/absorbed by blending in the offspring
Continued Variation
Results from the action of many genes to determine a characteristic (ex. human height)
Discontinued Variation
Groups individuals into distinct categories based on a specific trait or characteristic. (ex. blood type, eye color)
True Breeding
Always produce offspring that look like the parent (parents are homozygous for the trait)
Hybridization
Mating two different “true-breeding” individuals that have different traits
Trait
A variation in the physical appearance of an inheritable characteristic
Reciprocal Cross
Paired cross where traits from the male/female in one cross become the traits of the male/female in another cross
Dominant Traits
Inherited; unchanged in hybridization
Recessive Traits
Disappear in the offspring of a hybridization
Reappear in a later offspring (“carried”)
Physical Characteristics
Expressed through genes carried on chromosomes
Alleles
Gene variants that arise by mutation & exist at the same relative locations on homologous chromosomes (determine different traits/characteristics)
Phenotype
Observable traits expressed by an organism
Genotype
Underlying genetic make-up
(physically visible & non-expressed alleles)
Homozygous
2 identical alleles
(ex. RR or rr)
Heterozygous
2 different alleles
(ex. Rr or rR)
Dominant Alleles
Expressed unit factor
Recessive Alleles
Latent unit factors
Monohybrid Cross
Fertilization that occurs between 2 “true-breeding” parents that differ in only one characteristic
Phenotypic ratio = 3:1
Punnett Square
Applied the rules of probability to predict the possible outcomes of a genetic cross & their expected frequencies
Test Cross
Dominant-expressing organism is crossed with an organism that is homozygous recessive for the same characteristic
USED ON MODEL ORGANISMS ONLY
Pedigree Analysis
Study’s the inheritance pattern of human genetic diseases
Mendels Experiments suggest…
2 alleles for every gene
Alleles maintain integrity in each generation (no blending)
3.Recessive alleles are hidden and make no contribution to the phenotype
Incomplete Dominance
Heterozygous offspring display an intermediate phenotype.
Neither allele is completely dominant/recessive
Co-dominance
Both alleles of a gene are expressed equally in the phenotype
Neither allele is completely dominant or recessive
Wild Type (+)
Standard or norm
Variants
Deviate from wild type
“Dosage” of a specific gene product
Wild type alleles supply the correct amount of gene product
Mutant alleles can not
Autosomes
Non-sex chromosomes
X-linked
Gene is present on the X chromosome but not the Y chromosome
Hemizygous
One allele for any x-linked characteristic
Recessive Lethal
Allele is only lethal in the homozygous form
Dominant Lethal
Allele is lethal in both homozygous and heterozygous form
Law of Dominance
One trait will conceal the presence of another trait for the same characteristic
Law of Segregation
Paired genes must segregate equally into gametes so that the offspring has an equal likelihood of inheriting either factor
Law of Independent Assortment
Segregation of the alleles of one gene is independent of the segregation of the alleles of another gene.
Inheritance of one trait does not affect the inheritance of another trait.
Dihybrid Cross
Cross between 2 “true-breeding” parents that express different traits for 2 characteristics
Phenotypic ratio = 9:3:3:1
Linkage
Genes that are located physically close to each other on the same chromosome are more likely to be inherited as a pair
Epistasis
One gene masks/interferes with the expression of another
Each pair of homologous chromosomes have the same…
linear order of genes