1. Outline 11-2 Mendel’s Theory
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Outline 11-2
Mendel’s Theory
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2. I. Mendel’s Hypotheses
A. For each inherited trait, an individual has 2 copies of the gene 1. One from mother
2. One from father
B. There are alternative versions of genes
1. These are now called alleles
a. Purple vs white flowers
b. Green vs yellow seeds
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3. 1. Mendel called the expressed form dominant
C. When 2 different alleles occur together, one may be expressed, while the other has no observable effect
1. Mendel called the expressed form dominant
2. He called the trait that was not expressed recessive
3. Mendel found this to be true for all of his pea plant traits.
a. Called Law of Dominance & Recessiveness
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4. 2. Called the Law of Segregation E. Law of Independent Assortment
D. Gametes Separate
1. When gametes form, the alleles for each gene separate from one another & each gamete gets one allele for each trait
2. Called the Law of Segregation
E. Law of Independent Assortment
1. The inheritance of one trait did not have an effect on the inheritance of any other trait
2. Alleles separate independently of one another
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6. II. Modern Terminology A. Letters are used to represent alleles
1. Dominant alleles written with a capital letter
2. Recessive alleles written with the same letter, but lowercase
3. Examples:
a. P = purple p = white
b. T = tall plant t = short
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7. B. Terms for whether alleles are same or different
1. Heterozygous
a. If the 2 alleles are different
b. Example:
Tt = 1 dominant & 1 recessive
2. Homozygous
a. If the 2 alleles are the same
b. Examples:
TT = homozygous dominant
tt = homozygous recessive
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8. C. Terms for distinguishing genes from appearance
1. Genotype
a. Set of alleles an individual has
b. Example = TT, Tt , or t t
2. Phenotype
a. Physical appearance of a trait
b. Examples:
Whether a plant is tall or short
c. Phenotype is determined by the genotype
TT = tall, tt = short, Tt = tall
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