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1

genetics

study of..

how traits are inhereted from one generation to the next

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basic unit of heredity

gene

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genes composed of

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genes are located on the

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alleles

genes existing in more than one form

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genotype

genetic makeup of an individual

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phenotype

physical manifestation of genotype

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phenotypes can correspond to a single or several of these

genotypes

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Gregor Mendel

1860s

basic principles of genetics

garden pea experiments

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garden pea experiment

inheritance of individual pea traits by performing genetic crosses

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genetic crosses

mendel's pea experiments

true-breeding individuals with different traits

mated them

statistically analyzed inheretance of traits in progeny

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mendel's first law

law of segregation

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mendel's four postulates of inheritance

(law of segregation)

1. genes exist in alternative forms (alleles)

2. organism has two alleles for each inherited trait, one from each parent

3. two alleles segregate during meiosis ---> gametes carry one allele for any given trait

4. two alleles in individual are different - only one expressed, other is silent

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dominant allele

allele which is expressed

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recessive allele

allele which is silent in presence of dominant allele

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homozygous

organisms that contain two copies of same allele

homozygous for that trait

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heterozygous

organisms that carry two different alleles

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Mendel's law of dominance

dominant allele appears in phenotype

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monohybrid cross

(mendel's first law - law of segregation)

only one trait studied in particular mating 

(i.e. color)

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Parental or P Generation

(mendelian genetics)

individuals being crossed

 

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filial / F generation

progeny generations

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Punnett Square Diagram

(Mendel's First Law - Law of Segregation)

used to predict genotypes expected from a cross

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Testcross

Reasoning

(Mendel's First Law - Law of Segregation)

genotype can only be predicted from recessive phenotype

dominant phenotype - homozygous or heterozygous

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testcross

used to

 determine unknown genotype of org with dominant phenotype

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test cross

(aka back cross)

definition

organism with dominant phenotype of unknown genotype (Ax) crossed with phenotypically recessive organism (genotype aa)

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results of test cross

P: AA x aa 

F1: 100% Aa; 100% dominant phenotype

P: Aa x aa

F1: 50% Aa; 50% dominant phenotype

50% aa; 50% recessive phenotype

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Mendel's Second Law

Law of independent assortment

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law of independent assortment

(principle)

law of segregation applies as long as genes are on separate chromosomes and assort independently

genes on same chromosomes stay together unless crossing over occurs

 

 

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law of independent assortment

dihybrid cross

P generation:

purple flower tall pea plant (TTPP)

x

white flowered dwarf pea plant (ttpp)

F1 progeny - TtPp genotype

dominant phenotype

 

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crossing over

(application to law of independent assortment)

crossing over may break linkage of certain pattern

i.e. redheads + freckles; sometimes blondes have freckles