Mendel and the Gene Idea

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Mendel and the Gene Idea

• Mendels Law of Segregation
• Probability in Genetics

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Mendels Hypothesis

• 1. Alternative versions of genes account for
  variations in inherited characteristics.
• Most traits exist in two versions (alleles)
• 2. For each characteristic, an organism inherits
  two genes, one from each parent.
• A diploid organism has homologous pairs of
  chromosomes, one chromosome of each pair
  inherited from each parent.

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• 3. If the two alleles are different, then one, is
  fully expressed and the other will have no
  noticeable effect on the organism
• Dominant vs recessive allele
• 4. The two genes for each character segregate
  during gamete production
• The ovum and the sperm each receive only one of
  the genes that are present in two copies in the
  somatic cells of the organism. The segregation
  occurs during meiosis

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Test Cross

• If in pea plants we have a tall plant. How do we
  determine if this plant is homozygous of
  heterozygous?
• Phenotype Tall
• Genotype T_?

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• The testcross was devised by Mendel, and
  continues to be a useful tool in Biology

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Probability and Inheritance

• The rule of multiplication
• Used to obtain the probability of two events that
  are independent from each other
• In pea plants, purple flower (P) color is
  dominant over white flower (p) color. What is the
  probability that the two recessive alleles will
  join together at fertilization?

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• The rule of Addition
• The probability of an event that can occur in two
  or more different ways is the sum of separate
  probabilities
• In the cross Pp x Pp
• What is the probability that an offspring will be
  heterozygous

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