BIO 201

• Topics covered in BIO 201 (2 UNITS) COURSE OUTLINE

  • Chromosomal basis of genetics
  • Laws of genetics
  • Qualitative inheritance
  • Test of goodness of fit of explal result
  • Genotype and phenotype
  • Alteration of chromosome no
• Variant


  • Polyploidy
  • Karotype analysis
• Topics covered in GENETICS I

  • Linkage & sex linkage
  • Mutatn: Effects of radiation and chemical agents
  • Introduction to population genetics
• Reasons why Mendel used garden peas for his experiments
• Reasons why Mendel used garden peas

  • Pea plants are small and easy to cultivate
  • Pea plants have many distinctive varieties
  • They have a short generation time (span) thus results are obtained relatively quickly
  • Possess constant differentiating characteristics that are unchanging and can be completely controlled by the experiments
  • A large numbers of the breeding varieties of peas were available
  • The sexual organs are endorsed within the flower fertilization can take place automatically within an undisturbed individual- self fertilization. Or the male parts could be removed before fertilization and pollen from strain with an alternative characteristics introduced cross fertilization
  • The hybrids of the plants are capable of protecting themselves from the influence of all foreign pollen and from marked disturbances in their fertility in successive generations
  • Peas had 7 easily observed traits without intermediate forms. They were round or wrinkled, short or tall
• Chromosomes


  Rod-like or thread like gene bearing bodies. Found in the nucleus, they always appear in pairs. They are not visible except during cell division
• Genotype


  Genetic constitution (make up) of an individual. The genotype and environ will determined the phenotype
• Phenotype


  The outward appearance of an individual as a result of the genotype
• Heredity


  The passing of a trait or characteristic from one cell to the other or from one organization the other
• Genetics


  The study of heredity from one generation to the other
• ARISTOTLE proposed that the semen (motion) and menstrual fluid (matter) were purified blood and that these pools become mixed during intercourse to form the basic make-up of a new individual that will blend the parents characteristics
• Charles Darwin introduced the theory of pangenesis which states that organs produced pangene (gemmules) that were carried by blood to the reproduction cell. Each pangene was believed to have a recollection of the parts of the body from which it comes from, that would enable it to radiate that aspect of organs in the new offspring
• The theory of acquired characteristics was put forward by Lamark. This theory stated that organisms transmit to their offspring those characteristics that were developed to cope with changing environmental conditions
• Gregor Mendel was born in 1822 in Czechoslovakia near Austria. He was the only son of peasant farmers. And he was directly involved in tilling, cultivation, planting and harvesting of crops this made him developed interest in plants. The parents managed to send him to college where he studied science and philosophy later he entered the Augustinian Monestry in Brunn in 1843, where he was ordained a priest in 1847. As a monk, he was appointed to be a teacher. In 1856 while teaching Mendel began his investigations in plant breeding
• Reasons why Mendel used garden peas for his experiments

  • They are small and easy to cultivate
  • They have many easily observable characteristics
  • Have short generation span
  • Can self pollinate or can be cross pollinated
  • Do not have intermediate forms
  • Sharply contrasting and easily recognisable traits
• Mendel made hundreds of crosses by dusting the pollens of one kind of plant on the stigma of plant of another kind. For each cross Mendel obtained F, generation plant that had only one form of the crossed traits. The contrasting trait had disappeared
• Dominant traits


  The remaining or expressed traits
• Recessive traits


  The traits that were not expressed in the F, generation
• The offspring of every cross were always exactly like one of the parents. No intermediate plants were observed or any form of blending of the parents traits
• When Mendel allowed the F, plants to pollinate themselves, in the F, generation, The dominant traits appear in 75% of the offspring while the recessive traits reappeared in 25% of the offspring. No intermediates were observed i.e. the new seeds were either wrinkled or round
• Mendel observed that plants showing the recessive traits were true breeding when they were allowed to self pollinate but when plant with the dominant trait self pollinate. Mendel observed, of them were true breeding where as 2, were not
• Genotypes in the F2 generation

  • 1 true breeding dominant plants
  • 2 not true breeding dominant plants
  • 1 true breeding recessive plants
• Mendel established the basic principles of inheritance that become the foundation of modern genetics
• Mendel's principles


  • A pair of factors controls the expression of inheritable characteristics
  • Offspring inherit one member of a pair of factors from the male parent and the other member of the pair from the female parent
  • Each factor is transmitted as a discrete unit i.e. factors do not blend or become diluted in future generation
  • One member of a pair of factors may mask (dominate) or prevent the other from having any impact if so then only it will be expressed, however the recessive member will remain as a discrete unit to be expressed in future generation
  • Paired factors separate during the formation of gametes
  • Each pair of factors segregate independently of any pair of other factors
• Mendel's laws are today referred to as Mendel's principles or Mendel's laws and they form the foundation of modern genetics
• Prof Hugo De Vries hypothesized that evolution occur as a result of accumulation of slight variations (Mutation) over time
• William Bateson was responsible for the birth of genetics as a field and gave the field much of its terminology (Jargon) Genetics, Homozygous, Heterozygous, F₁, F₂ generation etc.
• Thomas Morgan bred fruit fly (Drosophila melanogaster) and found that the various Mutants of the flies were associated with four (4) pairs of chromosomes possessed by Drosophila (the fruit fly)
• Morgan's work proved that chromosomes are the elements that transmit inherited characteristics. Morgan also discovered that chromosomes are the carrier of genes which causes the expression of individual characteristics
• Chromosomes


  Filamentous rod-like or thread-like gene bearing bodies found in the nucleus during cell division. Each nucleus contains information coded in the form of DNA and organised into groups called genes. Genes are arranged on the chromosome and each gene contains enough information for the production of one protein
• Chromosomes vary widely between different organisms. The chromosome molecule may be circular or linear, typically eukaryotic cells (cells with nuclei) have large linear chromosomes and prokaryotic cells (cells without defined nuclei) have circular chromosomes
• Homologous chromosomes


  Chromosomes within a cell that occur in matched pairs, joined at the centre by a centromse. Each chromosome contains many genes, and each gene is located at a particular site on the chromosome, known as the locus
• Alleles


  Alternate forms of the same gene found on one chromosome in a pair and the other gene in the other chromosome of the pair
• In organisms that use sexual reproduction, offspring inherit one-half of their genes from each parent and then mix the two sets of genes together. This produces new combinations of genes; so that each individual is unique but still possesses the same genes as its parents
• Diploid number


  The number of chromosome pairs in an organism
• Haploid number


  The reduced number of chromosomes in the gametes (eggs and sperm)
• During fertilisation the gametes unite to form a cell known as a zygote containing the diploid number of chromosomes characteristics of the species
• Autosomes


  Complete sets of matching chromosomal pairs
• Sex chromosomes


  The pair of chromosomes that plays a dominant role in determining the sex of an organism. Females have two copies of the X chromosome while males have one Y chromosome and one X chromosome
• Diploid number


  The total number of chromosomes in the cells of an organism