Biology, 11: Inheritance

• Inheritance is the transmission of characteristics from one generation to the next
• Chromosomes are long thread-like structures containing genetic material, it is located in the nucleus of a cell
• Genes are a section of DNA that codes for specific proteins that controls characteristics and functions of the cell
• DNA is a molecule containing instructions for growth and development of all organisms
• Alleles are different versions of a particular gene, it gives characteristics to different organisms.
• Body cells are diploid
• Gametes are haploid, and produced during meiosis
• Humans have diploid cells, containing 46 chromosomes
• Nucleus of haploid gamete cells contain 23 chromosomes
• Men are XY
• Women are XX
• Mitosis is the nuclear division giving rise to genetically identical cells
• When does mitosis occur?

  Produces new body cells in growth

  Repairs damaged tissues

  Replaces cells in body

  Asexual reproduction
• In mitosis, chromosomes duplicate and separate

  Each chromosome ends up in new daughter cell, therefore are identical
• Mitosis forms 2 diploid daughter cells
• Meiosis is the nuclear division giving rise to genetically different cells

  It produces gametes

  Also known as reduction division
• In meiosis, cells produced have reduced in number of chromosomes

  One chromosome for each haploid cells
• Meiosis products variation
• In meiosis, four unique daughter cells are created

  Each has half the number of chromosome of haploid parent cell
• In meiosis, two cell division occurs
• Genotype is the genetic make-up of an organism in terms of alleles present

  It can influence phenotype
• Phenotype is the observable feature of an organism
• Dominant alleles are expressed in phenotypes
• Recessive alleles are not expressed in phenotype, unless two copies are present
• Homozygous alleles are 2 copies of the same allele
• Heterozygous alleles have one dominant and one recessive cell
• When heterozygous and heterozygous alleles combine, there is:

  3:1 ratio

  75% chance of dominant gene // same phenotype
• When heterozygous and homozygous recessive alleles combine, there is:

  1:1 ratio

  50% of either

  50% same phenotype AND genotype
• When heterozygous and homozygous dominant alleles combine, there is:

  1:1 ratio of genotype

  100% of same phenotype

  50% same genotype
• In variation, phenotypic variation is caused by difference in gene
• Discontinuous variation is caused by genes

  Distinct characteristics have no intermediates, e.g. gender, blood-group, and tongue-rolling
• Continuous variation is caused by environment and genes

  Characteristics can have any value in range, e.g. body weight, height, finger length
• Mutation is a change in genetic code
• Producing a new cell can be:

  • Beneficial, gives advantage over others in same species
  • Neutral, no obvious effect and is only identifiable by looking at genetic code in detail
  • Harmful, causing early death of embryo or makes individual less likely to survive. Inherited diseases are caused by genes that produce protein in key processes.
• What is mutation produced by?

  Exposure to ionising radiation

  Chemical mutagens
• Mutations cause genetic doe to change directly, or to be miscopied frequently during cell division

  Continuing division of cells produces lump of unspecialised tissue, which is a cancer
• Individuals with the best adaptive features are most likely to survive
• What is natural selection?

  Organisms with favourable alleles and advantageous characteristics have a higher probability of surviving and reproducing in their environment.

  This is due to competition within the population for resources

  Animals with the most favourable alleles survives as they are more adapted to the environment, allowing them to reproduce offsprings with the favourable alleles.
• What is evolution?


  Population becoming more adapted to their environment over time, as a result of natural selection. Over time, negative characteristics are lost from the species as those with the characteristics are not able to live long enough to reproduce offsprings.
• Antibiotic resistance in bacteria happens as bacteria develops resistance to antibiotics due to resistance

  Strong selecting factor as most resistant bacteria will survive and the rest will die quickly