Topic 7 - Inheritance (part 2)

• Genome


  - entire set of genetic material of an organism

  - each gene is made of a small section of DNA that codes for particular sequences of amino acids

  - genes control our CHARACTERISTICS as they code for proteins
• Alleles


  different versions of the same gene

  - 2 alleles for each gene as we have 2 copies of each chromosome
• 2 alleles of the same type

  Homozygous

  
  

  AA

  dd
• 2 alleles of different types

  Heterozygous

  
  

  Aa

  Dd
• Female sex chromosomes


  XX (homozygous)
• Chromosomes


  threadlike structures made of DNA molecules that contain the genes

  located in nucleus of cells
• Male sex chromosomes


  XY (heterozygous)
• Gene


  short length of DNA found on chromosomes that code for particular characteristics (dictated by proteins)
• Genotype


  Combination of alleles that control each characteristic (unique sequence of DNA)
• Dominant alleles


  only needs to be inherited from ONE parent in order for characteristics to show up in phenotype

  - represented by capital letter
• Recessive alleles


  need to be inherited from BOTH parents to show up in phenotype

  - represented by small letter
• Phenotype


  The observable characteristics of an organism (eye colour) --> characteristics the alleles produce
• Pure breeding


  2 individuals who are both identically homozygous = produce SAME genotype + phenotype as parent = same characteristics

  TT

  tt
• Polygenic inheritance


  Most phenotypic features are the result of polygenic inheritance rather than single genes:

  - polygenic means characteristics that are controlled by MORE THAN ONE GENE

  - inheritance of these polygenic characteristics is called polygenic inheritance
• Monohybrid inheritance


  The inheritance of characteristics controlled by a single gene

  eg.

  Tt x Tt
• Punnett square


  genetic diagram

  - shows possible combinations of alleles that could be produced in offspring

  - can find percentage chance of specific phenotype in offspring
• Family pedigrees


  Charts of genetic relationships of individuals in families. With pedigrees they can identify inheritance patterns and track genetic abnormalities through several generations
• Mitosis


  occurs during: asexual reproduction, growth, repair, cloning, replace cells (damaged or dead - red blood cells, skin cells)

  definition: nuclear division giving rise to genetically IDENTICAL cells --> cell reproduced itself by splitting into 2 cells with identical sets of chromosomes

  
  

  1. DNA spread out in long strings

  2. before mitosis, each chromosome in nucleus copies itself EXACTLY (forming x-shaped chromosomes)

  3. chromosomes line up along centre of cell where CELL FIBRES pull them apart

  4. membranes form around each new set of chromosomes + become nuclei of the 2 new cells. cytoplasm divides

  5. cell divides into 2 (each new cell has a copy of each of the chromosomes)
• Diploid


  2 copies of each chromosomes arranged in pairs
• Meiosis


  produces 4 haploid cells whose chromosomes are NOT identical (genetically different)

  produces: gametes

  
  

  1. each chromosome makes identical copies of itself (x-shaped chromosomes formed)

  2. FIRST DIVISION: chromosomes pair up along centre of cell (one chromosome in each pair came from organism's mother, other from father) --> pulled apart by CELL FIBRES (each new cell only has one copy of each chromosome - mix of mother + father)

  3. SECOND DIVISION: chromosomes will line up along centre of cell --> CELL FIBRES pull ARMS of chromosomes apart again = 4 haploid daughter cells produced

  (each gamete only has single set of chromosomes - genetically different)

  THESE HAPLOID CELLS ARE CALLED GAMETES --> SEXUAL REPRODUCTION = GENETICALLY VARIED OFFSPRING
• reduction division


  when the chromosome number is halved from diploid to haploid in meiosis
• what pulls the chromosome pairs apart in meiosis and mitosis

  cell fibres
• haploid cell


  one complete cell of chromosomes (half no. chromosomes then diploid)

  humans - 23 chromosomes in haploid cells' nuclei

  THESE HAPLOID CELLS ARE CALLED GAMETES --> SEXUAL REPRODUCTION = GENETICALLY VARIED OFFSPRING
• Types of variation (continuous and discontinuous)


  continuous:

  - small degrees of difference for particular characteristics between individuals (eg. height, weight, finger length)

  - on graph it is smooth bell curves (bump)

  
  

  discontinuous:

  - distinct difference for characteristics (NO IN-BETWEENS)

  eg. blood type, F/M, roll tongue or not

  - on graph it is step-like shape (straight lines + fixed points)
• Mutations


  rare, random changes that occur in sequences of DNA bases in gene / chromosome

  - occur continuously

  - DNA base sequence determines order of amino acids (mutations in genes can sometimes lead to change in protein)

  - can be inherited

  - beneficial alleles are known as mutations (new adaptations to environment)
• Darwin's theory of evolution

  Life began as simple organisms from which more complex organisms evolved.

  1. each species over reproduces and offspring shows VARIATION

  2. there is a lot of COMPETITION between offspring (for food, mates, space)

  3. The ones with the best ADAPTATIONS for their environment survive and other die. This is known as THE SURVIVAL OF THE FITTEST

  4. The survivors pass their BENEFICIAL ALLELES to their OFFSPRING = become more common in the population over generations (species EVOLVE)
• Evolution definition


  change in the frequency of a phenotype in a population over many generations
• Example of evolution by natural selection


  peppered moth population:

  - variation between light + dark moths

  - population leads to dark bark on trees = environment changes. this is beneficial to dark moths as they can camouflage + hide from predators

  - dark moths more likely to survive + reproduce and pass on their beneficial alleles to offspring

  - light moths eaten by birds = less likely to reproduce

  - over time gradual increase in proportion of dark moths to light moths

  
  

  dark moths = mutated gene
• Antibiotic resistence


  Antibiotics are chemical substances made by certain fungi / bacteria that effects the working of bacterial cells (eg preventing them from reproducing, breaking down structure)

  - effective against bacteria NOT viruses

  - antibiotic overuse = antibiotic resistance has developed in many types of bacterial species (mutation)

  
  

  HOW?

  1. population of bacteria (pathogens) in gut. some have antibiotic resistance

  2. antibiotic used to kill bacteria causing illness. only some die (including healthy bacteria)

  3. with reduced competition for nutrients, the antibiotic-resistant bacteria multiple forming larger population
• Preventing resistant bacteria (antibiotics)


  - doctors avoid use of antibiotics

  - not used on non-serious infections

  - not used for viral infections (will kill good bacteria in body)

  - patients need to finish whole course (so that all bacteria killed and none are left to mutate + resist)
• Why do antibiotics not work on viruses?


  Antibiotics work by disrupting cell functions such as respiration or breaking down cell structure

  
  

  viruses do not carry out any cell functions + do not have cell walls, cell membranes