genetics definition study of how hereditary characteristics (traits) in an individual are...
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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
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.