Chapter 12: Mendelian Genetics

Gregor Mendel

Documented a mechanism of inheritance- complete dominance, with experiments using peas in 1865

Independent Assortment

Allels of unlinked genes assort independently and are randomly distributed into gametes

all’s from 1 gene do not affect which alleles from another gene a gamete will receive

produced dihybrids in F1 generation: offspring that are heterozygous for both characteristics

Law of Segregation

The two alleles for a heritable characteristic separate/segregate during gamete formation and end up in different gametes . Only 1 allele may be carried in a particular gamete or spore and subsequently in fertilization

like in meiosis 4 different gametes are produced

Peas

Normally self fertilize but Mendel manually cross pollinated plants

Character

A heritable feature like flower color

Trait

A variant of a character like purple/white flower

Locus/Loci

A specific location on a chromosome where a gene is located

Alleles

Different versions of the same gene (blue eyes vs brown eyes)

Genotype

Genetic makeup of an organism (PP or pp)

Phenotype

set of observable characteristics (purple or white)

Homozygous Dominant

AA or Purple

One allele is dominant

only one copy of the dominant allele is necessary to observe the phenotype

Homozygous Recessive

aa or white. This genotype has two copies of the recessive allele, resulting in the recessive phenotype being expressed.

Heterozygous Dominant

Aa or Purple, where one dominant allele and one recessive allele are present, resulting in the dominant phenotype.

Alleles

Alternative versions of the same gene, inherited characters that account for variation

Each phenotype has multiple alleles

Each characteristic an organisms inherits 2 alleles 1 mom 1 dad

hybridization

crossing two true breed plants

Dihybrid Cross

2 traits of interest crossed

WW-White

ww-brown

LL-Long

ll-long

The Laws of Probability

Law govern Mendelian inheritance

Probability

Expressed as a fraction or decimal equivalent over a range of 0 to 1

p=0 not happen

p=1 will happen

Rules applied to monohybrid crosses

multiplication rule, the probability that 2 or more independent events willl occur together is the product of their individual probabilities

Addition rule

rule applied to monohybrid crosses

the probability that any 1 or 2 mutually exclusive events will occur is calculated by adding their individual probabilities

Complete Dominance aka Mendelian Inheritance

When the phenotypes of the hetero Rr and dominate homo RR are identical

presence of a single dominant allele produces FULL dominant phenotype

Codominance

2 dominant allele affect the phenotype in separate and equal phenotypic traits

heterozygous individual expresses both traits

IE Human blood type

Incomplete Dominance

The phenotypes of F1 hybrids is somewhere between the phenotypes of the parental varieties

3 phenotypes usually

Blending of traits for hets

pink flower

Multiple Alleles Dominance Order

4 different alleles exist for the rabbit coat color gene

Lethal Alleles

One mutant allele can be dominant over all other phenotypes including the wild type

Pleiotropy

A gene that has multiple seeming unrelated phenotypic affects

An allele that causes multiple characteristics

Sickle Cell Anemia

The mutation of a single gene leads to this

The mutation is called beta-globing gene mutation

Polygenic

Multiple genes influence one trait, aka height

Epistatasis

A gene at 1 locus alters the phenotypic expression of a gene at another locus, gene modifiers

Quantitative Inheritance

Quantitate variation usually indicates polygenic inheritance where multiple genes influence a single trait, resulting in measurable phenotypic variations. like human height

Multifactorial Characteristics

Influenced by both genetics and environment have a huge impact on phenotype

Chromosome Theory of Inheritance

Mendelian genes have specific loci on chromosomes and chromosomes undergo segregation and independent assortment

Thomas Hunt Morgan

Provides convincing evidence that chromosomes are the location of menders heritable factors

Used fruit flies

Fruit Flies Thomas Morgan

Wild Type(wt):normal common phenotype In the fly population

Mutant Phenotype: traits alternative to the wild type

Determined: the white eye mutant allele must be located on the x chromosome

Why is Thomas Morgan Important

Solid evidence that a specific gene is associated with a specific chromosome