Ch.12 Mendels Experiments & Heredity (Bio)

Model System

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…

1. 2 alleles for every gene

2. 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