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Important definitions

Gene mutation - Spontaneous changes in the base sequence of DNA

Gene - Sequence of bases on a DNA molecule that codes for a polypeptide

Allele -Alternate form of a gene that exist at a single locus

Phenotype - Observable traits an individual inherits

Genotype - Genetic makeup of an individual

Homozygote - Diploid gene pair having identical alleles

Heterozygote - Diplod gene pair having different alleles

Principle of Segregation - Characters of an organism determined by a pair of alleles.

Alleles segregate from each other during formation of gamete.

Each gene carries one of the two alleles

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Change in DNA alter functions of cell

  • Change in base sequence in DNA
  • Change in base sequence in mRNA
  • Change in amino acids sequence in protein
  • Change bonding in protein
  • Change tertiary structure
  • Change protein function
  • Change in cell function
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Gene therapy

Can either be germ-line therapy/somatic-line therapy

  • Insert normal alleles of gene into DNA of target cells
  • Using vectors such as virus or liposomes
  • Normal allele transcribed and translated
  • Functioning protein produced in target cells
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Genetic screening


  • To determine if the parent is a carrier (to make decisions)
  • Determine whether or not the embryo has disease


  • False positive results/false negative result
  • Possibility of miscarriage

Ethical issues

  • Fetus is living organism -->abortion is equivalent to murder
  • Not fully understand possible risks of prenatal testing
  • Fetus has right to live
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