ORIGIN GENETIC VARIATION

• Genetics


  The study of genes and heredity--of how certain qualities or traits are passed from parents to offspring as a result of changes in DNA sequence.
• Gregor Mendel


  The first to study the science of heredity by analyzing patterns of inheritance, emphasized that genes retain permanent identities using pea plants.
• Mendel's Law of Segregation


  Pairs of alleles (a form of gene) separate during gamete formation; fertilization restores the pairs.

  
• Mendel's Law of Segregation

  If an individual’s genotype (genetic makeup) has two different alleles for a gene and only one influences the organism’s phenotype (appearance):

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  That allele is said to be DOMINANT and the other allele RECESSIVE.
• Mendel's Law of Segregation

  Alleles of a gene reside at the same locus, or position, on homologous chromosomes.

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  When the allele pair matches, the organism is homozygous, when the alleles are different, the organism is heterozygous.
• Mendel's Law of Independent Assortment

  By following the two characters at once, Mendel found that the alleles of a pair segregate independently of other allele pairs during gamete formation.

  "The inheritance of one character has no effect on the inheritance of another"
• Punnet Square


  A grid formed by 4 squares used as a way to predict a trait or genotype that comes from two different people or organisms.
• Homozygous


  Having two of the same allele (e.g. RR or rr); purebred.
• Heterozygous


  Having two different alleles for a certain trait (e.g. Rr); half-bred
• Recessive 


  Hidden or masked gene.
• Dominant 


  Expressed gene.
• Phenotype


  An organism's physical characteristics
• Genotype


  An organism's actual genetic composition.
• Determining the Unknown Genotype of a Trait

  One can cross it with homozygous recessive if the results are all dominant, half dominant, or half recessive.
• The Rules of Probability

  • The chance of inheriting a recessive allele from a heterozygous parent is 1/2.
  • The chance of inheriting it from both of two heterozygous parents is 1/4.
• Incomplete Dominance


  Refers to the phenomenon where the dominant and recessive traits seem to "blend" together in the heterozygous form.

  • Here, the phenotype is an intermediate between the dominant and recessive one

  EXAMPLE:

  red and white = pink
• ABO BLOOD GROUPS

  Example of Multiple Alleles and Codominance

  • Alleles determining blood groups are codominant; that is, both are expressed in a heterozygote.
• Difference of Codominance and Incomplete Dominance

  Co dominance - both alleles are expressed

  Incomplete dominance - both alleles are mixed together
• Pleiotropy


  One gene (such as the sickle-cell disease gene) can affect many characters (such as the multiple symptoms of the disease).
• Polygenic Inheritance

  Where multiple genes affect a single trait
• Epigenetics and the Role of Environment

  Epigenetic inheritance, the transmission of traits from one generation to the next by means of chemical modifications to DNA and proteins, may explain how environmental factors can affect genetic traits.