GENETICSDefinition

Study of how hereditary characteristics (traits) in an individual are transmitted from one generation to the next.

MilestonesMendel

“Genes and the Rules of Inheritance”Watson & Crick

“The Structure of DNA”Human Genome Project

“Sequencing DNA & Cataloging Genes”

Levels of Genetic Analysis

ClassicalStructure and Behavior of ChromosomesNature of Genetic Material

MolecularDefining DNA SequencesRecombinationGene Manipulation

PopulationVariation of Genetic MakeupsInheritance of Traits

Mendelian GeneticsGregor Mendel

ContributionsLaw of SegregationDominant and Recessive Traits

Fig. 23.1

Mendel's Studies of InheritanceHypothesis

Pea plants inherit two “units of information” (genes) for a trait, one from each parent

Monohybrid ExperimentParental Monohybrid Cross Design

True breeding strains of purple (P) flowered peas were crossed with true strains of white(p) flowered peas. * True breeding = homozygous

PP X pp

http://skepticwiki.org/index.php/Image:Pisum_sativum.jpg

PP

x

PP

pp

FORMATION OF GAMETES

PP x pp

P P pp

F1 Generation Punnett Square

AnalysisPP X pp

P P

p

p

F1 Generation Punnett Square

AnalysisPP X pp

P P

p

p

Pp Pp

Pp Pp

F1 Generation Punnett Square

AnalysisGenotype: Pp Phenotype: Purple

F2 Generation Punnett Square Analysis

F1 Generation Monohybrid Cross

Design Crossing of two F1 generation plants

Pp PpX

PP

x

PP

pp

F2 Generation Punnett Square Analysis

P p

P

p

PP Pp

Pp pp

F2 Generation Punnett Square Analysis

Genotypes: PP, Pp, pp

Phenotypes:PurpleWhite

Genotypic Ratio1 (25%): Homozygous Dominant2 (50%): Heterozygous1 (25%): homozygous recessivePhenotypic Ratio3 (75%): Purple1 (25%): White

MENDELIAN GENETICS

Conclusions1) Each trait (gene) has two forms (alleles)

which segregate at the formation of gametes

2) One allele which is dominant masks the appearance of the other allele which is recessive.

Dihybrid Experiment

Parental Dihybrid CrossDesign

True breeding strains of peas that were homozygous for red (R) flower color

and green (G) seed pod color were crossed with true breeding strains that were

homozygous for white (r) flower color and yellow (g) seed pod color.

RR

GG

rr

g

x

RR

GG

rr

g

R R R

INDEPENDENT ASSORTMENT RRxRR GGxGG

RRxRR GGxGG

RGRG

RRGG RRGG

RG RG

INDEPENDENT ASSORTMENT rrxrr ggxgg

rrxrr ggxgg

rg rg

rrgg rrgg

rg rg

F1 Generation Punnett Square Analysis

RRGG X rrgg rg rg rg rg RG

RG RG

RG

RrGg RrGg RrGg

F2 Generation Punnett Square Analysis

F1 Generation Dihybrid Cross

DesignCrossing two F1 generation plants

RrGg X RrGgPossible Gametes

RG, Rg, rG, rg

GG

rr

g

x

RR rr

g

rr

g

RR

GG

GG g

orRR rrrr

g

RR

GG

INDEPENDENT ASSORTMENT

INDEPENDENT ASSORTMENT RRxrr GGxgg

RRxrr GGxgg

RGrg

RRGG rrgg

RG rg

INDEPENDENT ASSORTMENT RRxrr GGxgg

RRxrr ggxGG

RgrG

RRgg rrGG

Rg rG

RRGG

RRGg

RrGG RrGg

RRGg

RRgg RrGg Rrgg

RrGG RrGg rrGG rrGg

RrGg Rrgg rrGg rrgg

RG Rg rG rg RG

Rg

rG

rg

F2 Generation Punnett Square Analysis

GenotypesRRGG RRGgRrGg RrGGRrgg RRggrrGG rrgg

PhenotypesRed Flowers, Green PodsRed Flowers, yellow podswhite Flowers, Green podswhite flowers, yellow pods

Genotypic Ratios1: RRGG 2: RRGg4: RrGg 2: RrGG2: Rrgg 1: RRgg1: rrGG 1: rrgg2: rrGg

Phenotypic Ratios9: Red, Green3: Red, yellow3: white, Green1: white, yellow

DYHIBRID CROSSConclusion

Independent Assortment

1)As meiosis ends, genes on pairs of homologous chromosomes have been sorted out for distribution into one gamete or another, independently of gene pairs on other chromosomes.

2) Independent Assortment leads to genetic diversity in populations.