Unit 9, Part 2 Notes

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Unit 9, Part 2 Notes

• Mendel

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Gregor Mendel (1850)

• Did extensive studies on pea plant traits
• Documented traits and inheritance patterns of
  thousands of plants
• Keep in mind that DNA had not been discovered
• What he called factors we know to be genes,
  which code for particular traits

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Basic Terminology

• Genetics the study of heredity
• Heredity the passing of traits from parents to
  offspring
• Trait any characteristics that can be passed
  from parents to offspring
• examples dimples freckles
• Genes - a segment of DNA that codes for a
  specific trait

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Alleles

• Alleles are slightly different forms of a gene
• The sequence of nitrogen bases may be slightly
  different
• A person has 2 alleles for each trait
• Occur on homologous chromosomes
• Of the 2 alleles, you receive one from your
  mother and one from your father during
  fertilization

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Types of Alleles

• Dominant Allele the allele that is expressed
  the stronger allele
• Symbolized by a capital letter
• Recessive Allele the allele that is only
  expressed if two of them are present weaker
  allele
• Symbolized by a lower case letter

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Types of Alleles

• Example
• Freckles Dominant
• No Freckles Recessive
• Dominant Allele F
• Recessive Allele f
• Dimples Dominant
• No Dimples Recessive
• Dominant Allele D
• Recessive Allele d

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Genotypes Phenotypes

• Genotypes are the genetic make-up of an organism
• What do the alleles look like
• DD
• Dd
• dd
• Phenotypes are the physical appearance of a trait
• sometimes appear different due to environmental
  factors
• having dimples
• having freckles
• no dimples
• no freckles

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Genotypes Phenotypes
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Genotypes Phenotypes
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Genotypes Phenotypes
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Principles of Mendel

• Mendel develop 3 principles that hold true today
• Principle of Dominance and Recessiveness
• Principle of Segregation
• Principle of Independent Assortment

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Principles of Mendel

• Principle of Dominance and Recessiveness
• One factor in a heterozygous pair may mask the
  other factor
• The factor that is expressed is dominant, the one
  that is masked (not expressed) is recessive
• In order for a recessive trait to be expressed,
  the organism must have a homozygous recessive
  genotype

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Principles of Mendel

• Principle of Segregation
• Gametes (sperm and egg) are formed during the
  process of meiosis
• Each gamete receives only one allele for each
  trait

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Principles of Mendel

• Principle of Independent Assortment
• Alleles segregate into gametes randomly and
  independently of each other
• Therefore each egg (or sperm) cell should be
  different from the another egg (or sperm) cell
• http//www.snopes.com/photos/people/mixedtwins.asp
  

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Unit 9, Part 2 Notes

• Mendel