Download Genetics Notes

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Genetics – the scientific study of heredity
Why the garden pea?
 Easy to grow
 Produce large numbers
 Mature quickly
 Reproductive organs in same flower (self fertilization
or cross fertilization)
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Step 1 – produced pure breed plants – Parental or P
generation
 Self fertilized for many generations
 Used seeds from these to produce offspring with one
form of a particular trait
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Step 2 – cross two varieties in the P generation
 F1 generation – first filial
 Crossed purple anthers and white stigmas
 Produced only purple
 Step 3 – allow F1 to self-fertilize
 F2 generation – second filial
 White reappeared (3:1 ratio – purple to white)
 Mendel developed a model to explain his results (Rules
about inheritance)
 Parents transmit information about traits to their offspring
(factors)
 Each individual has two factors from each trait (one from
each parent)
 Homozygous – same information
 Heterozygous – different information
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Step 3 continued
 Alternative forms of a factor – alleles
 The alleles an organism possesses – genotype
 Physical appearance (determined by the alleles) –
phenotype
 An individual possesses two alleles for each trait
 The presence of an allele does not mean it will be
expressed
 Dominant – allele is expressed
 Recessive – allele is NOT expressed (in heterozygous)
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Punnett square – diagram used to predict the results
of a cross
Probability – the likelihood that something will
happen
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Law of segregation – the members of each pair of
alleles separate when gametes are formed
 A gamete will receive one alleles or the other
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Law of independent assortment – two or more pairs
of alleles segregate independently of one another
during gamete formation
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Genes combine according to the rules of probability
The probability of a gamete having an allele is 50%
or one-half
Simple Punnett square is monohybrid
4 offspring
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Incomplete codominance (snapdragons)
 Homozygotes – show red or white
 Heterozygotes – show pink
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Codominance
 Both genes are fully expressed
 Roan – red and white hairs
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Traits that arise from multiple alleles
 Blood types – three alleles IA, IB, and I – four blood
groups (Table 7-2)
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Polygenic – traits controlled by many genes
 Examples – height, weight, hair and skin color
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Gene expression affected by environmental
conditions
 Arctic fox – temperature affects coat color