Mendelian Genetics

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Genotype & Phenotype in Flowers

Genotype of alleles: R = red flower r = yellow flower

All genes occur in pairs, so 2 alleles affect a characteristic

Possible combinations are:

Genotypes RR Rr rr

Phenotypes RED RED YELLOW

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Genotypes

Homozygous genotype - gene combination involving 2 dominant or 2 recessive genes (e.g. RR or rr); also called pure

Heterozygous genotype - gene combination of one dominant & one recessive allele (e.g. Rr); also called hybrid

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Genes and Environment Determine Characteristics

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Mendel’s Pea Plant Experiments

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Why peas, Pisum sativum?

Can be grown in a small area

Produce lots of offspring

Produce pure plants when allowed to self-pollinate several generations

Can be artificially cross-pollinated

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Reproduction in Flowering Plants

Pollen contains sperm

Produced by the stamen

Ovary contains eggs

Found inside the flower

Pollen carries sperm to the eggs for fertilization

Self-fertilization can occur in the same flower

Cross-fertilization can occur between flowers

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Mendel’s Experimental Methods

Mendel hand-pollinated flowers using a paintbrush

He could snip the stamens to prevent self-pollination

Covered each flower with a cloth bag

He traced traits through the several generations

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How Mendel Began

Mendel produced pure strains by allowing the plants to self-pollinate for several generations

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Eight Pea Plant Traits

Seed shape --- Round (R) or Wrinkled (r)

Seed Color ---- Yellow (Y) or Green (y)

Pod Shape --- Smooth (S) or wrinkled (s)

Pod Color --- Green (G) or Yellow (g)

Seed Coat Color ---Gray (G) or White (g)

Flower position---Axial (A) or Terminal (a)

Plant Height --- Tall (T) or Short (t)

Flower color --- Purple (P) or white (p)

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Mendel’s Experimental Results