Heredity

• Allosteric regulation is a type of enzyme regulation where a molecule binds to a site on the enzyme that is distinct from the active site, causing a change in the enzyme's activity.
• • Reproduction is the production of offspring
  • It is a fundamental evolutionary process ensuring the continuation of life by making copies of themselves
• Fertilisation


  The union of 2 gametes - a sperm and an ovum
• Haploid


  Genetic material with only half of the normal number of chromosomes, denoted by the letter n
• Asexual reproduction requires no fertilisation
• Reproduction is a fundamental evolutionary process ensuring the continuation of life by making copies of themselves
• When fertilisation occurs

  The zygote becomes diploid (2n)
• Organisms that use external fertilisation

  • Fish, amphibians, aquatic invertebrates
• Biological reproduction


  The production of offspring
• Sexual reproduction in animals

  1. Ovulation

  2. Fertilisation
• Ways an organism can reproduce

  • Sexual
  • Asexual
• Diploid


  Having a full set of chromosomes, denoted by 2n
• Gametes

  Produced in gonads (ovaries and testes) by meiosis so they have half the normal number of chromosomes
• External fertilisation

  Females release eggs and males release sperm which swim to the egg in the environment
• Asexual reproduction

  Provides a competitive edge if an organism is well-adapted to its environment
• Asexual reproduction

  Can reproduce more quickly
• Asexual reproduction

  Can reproduce more efficiently
• Asexual reproduction

  Doesn't require finding a mate
• Asexual reproduction

  • Can reproduce more quickly and efficiently
  • Don't need to find a mate
  • Competitive edge if they live in an environment in which they are well-adapted to
• What is a mutagen ? 

  • An agent that increases the rate of genetic mutation by interfering with the function of nucleic acids 
  • Mutagen can be spontaneous  (caused by copying errors during DNA replication) or induced  by exposure to external elements Based on the type, mutagen is distinguished into chemical mutagen, physical mutagen and biological mutagen, (examples of mutagens include radioactive substances, x-rays, ultraviolet radiation and certain chemicals
• How do mutagens get into the body?

  • “All substances are poisonous; none is not a poison. The right dose differentiates a poison and a remedy”
  • inhalation: once inhaled, chemicals are either exhaled or deposited in the respiratory tract
  • Skin or eye absorption: Many chemicals can also cross the skin barrier and be absorbed into the blood system
  • Ingestion: soluble substances can be absorbed into blood 
  • Injection: Entry if skin is punctured/penetrated 
  • Once the chemical is absorbed into the body, three other processes are possible: metabolism, storage and excretion
• Criteria for distinguishing mutations: 

  1. Cause of the mutation 
  2. Amount of genetic material changed 
  3. Effect of the mutation on DNA 
  4. Effect of the mutation on phenotype
  5. Heritability of mutations 
• Changes to one base in the DNA code may involve either:

  • insertion: extra nucleotide is added
• Nonsense mutation


  • Can result in cystic fibrosis
• Deletion


  • Occur when a base is removed
• Missense mutation

  • Sickle cell anemia is a disease caused by a single base substitution mutation GAG(Glu) → GTG(Val)
• Silent mutation


  • AAA(Lys) → AAG (Lys)
• Missense mutations

  • Occur when the DNA change alters a single amino acid in the polypeptide
• Frameshift mutations

  • Occur when the addition or removal of a base alters the reading frame of the gene
• Point mutation


  A change in the DNA sequence
• Silent mutations


  Occur when the DNA change does not alter the amino acid sequence of the DNA sequence
• Chromosomal mutations 

  • Recall: chromosomes are tightly wrapped DNA 
  • Chromosomal mutations = a change in the arrangement or structure of a chromosome → instead of changing a single base are changes to large sections of DNA → large scale changes of an organism (Down syndrome) 
• Chromosomal mutations 

  • Recall: chromosomes are tightly wrapped DNA 
  • Chromosomal mutations = a change in the arrangement or structure of a chromosome → instead of changing single basethere are changes to large sections of DNA → large scale changes of an organism (Down syndrome) 
  • Chromosomal mutations occurs due to errors in cell division → more specifically, crossing over during meiosis increases the probability of error + occasionally due to mutagens 
• Process of chromosomal mutations:

  1. Deletion
  2. Inversion 
  3. Translocation 
  4. Duplication 
  5. Non-disjunctions
• Partial chromosome effects: 

  • Duplications: Part of the chromosome is copied → resulting in changes in the amount of proteins produced →  resulting in duplicate sections (potentially increases gene expression
  • Deletions: a portion of the chromosome is removed (along with any agents contained within this segment 
  • inversions: a segment of a chromosome within the chromosome in reverse order → no effect
  • Translocations: recombining gene alleles, segments of two chromosomes are exchanged (may interrupt gene sequences)
• Chromosomal mutation:  If breakage occurs in the middle of a gene, the gene will be destroyed 
• Partial chromosome effects: 

  • Duplications: Part of the chromosome is copied →  result in changes in the amount of proteins produced →  resulting in duplicate sections (potentially increases gene expression
  • Deletions: a portion of the chromosome is removed (along with any agents contained within this segment 
  • inversions: a segment of a chromosome within the chromosome in reverse order → no effect? 
  • Translocations: recombining gene alleles, segments of two chromosomes are exchanged (may interrupt gene sequences) 
• Whole chromosome being removed/added: 

  Aneuploidy: non-disjunction refers to the chromosomes resulting in gametes with an extra or one missing chromosome
• Chromosomal mutations


  Changes in the structure or number of chromosomes
• Effects of chromosomal mutations

  • Edwards Syndrome (Trisomy 18)
  • Down syndrome (Trisomy 21)
  • Turner’s syndrome/Fragile X (Monosomy X)