Complex Genetic Traits, Heritability and DNA profiling

Quantitative Genetics:

  • Deals with traits that show continuous variation (quantitative traits).
    • These traits exhibit a large range of phenotypes.
    • Examples include height, weight, and skin color.
    • Often follow a normal distribution, resembling a bell-shaped curve.
      • The graph illustrates the normal distribution of student heights, with the mean indicated.
      • Variability is shown across the height range.

Polygenic Traits:

  • Quantitative traits are polygenic.
    • They are the result of multiple genes, each with more than one allele.
    • The interaction of these multiple genes with multiple alleles leads to a wide variety of phenotypes.
    • Examples include human eye color, weight, height, and skin color.

Gene and Environment Interaction:

  • Phenotypic variation arises from both genetic and environmental differences.
    • This concept is often referred to as "nature versus nurture."

Nature vs. Nurture:

  • The example given is of identical twins, one a lifetime smoker and sun tanner, the other who never smoked and spent less time in the sun, to highlight nature versus nurture.

Human Cloning Considerations:

  • Even with human cloning, creating the exact same individual is impossible.
    • Factors such as nervous system connections, zygote formation, environmental effects, and random effects over time contribute to uniqueness.
    • Each person is a unique and irreproducible combination of genetics, environmental influences, and random occurrences.

DNA Profiling:

  • Except for identical twins, no two individuals are genetically identical.
  • Individuals have small differences in the nucleotide sequences of their DNA.
  • DNA profiling (or DNA fingerprinting) provides an unambiguous way to identify people.

Short Tandem Repeats (STRs):

  • STRs (short tandem repeats) are key to DNA profiling.
  • They consist of adjacent repeats of short DNA sequences.
  • The number of repeats varies in the human population, for example:
    • One repeat: (GATC)
    • Two repeats: (GATCGATC)
    • Three repeats: (GATCGATCGATC)
  • There are 13 core STR loci used in forensic analysis carried by all humans.

DNA Profiling Process:

Variable number tandem repeat (VNTR):

  • The diagram shows the position of forensic STR markers on human chromosomes.
  • Includes the 13 CODIS core STR loci.
  • Sex-typing is determined using AMEL (Amelogenin).

Gel Electrophoresis:

  • Process
    • Blood sample is collected
    • DNA is extracted.
    • Enzymes cut the DNA.
    • DNA fragments are separated by size using gel electrophoresis.
    • Bands are stained to make them visible, creating a 'fingerprint'.

DNA Evidence:

  • DNA profiling is used to match crime scene evidence to suspects.