Inheritance

Key words
1. Gene: A sequence of DNA that codes for a protein
2. Allele: different versions of the same gene
  1. Dominant allele: when at least one allele is required for it to be expressed in the phenotype
    1. Codominant allele: Where both alleles get expressed in the phenotype
      1. Both A and B alleles are codominant, while o is recessive
        When A and B are both present in the allele, they both get expressed
  2. Recessive allele: when 2 alleles are required for the allele to be expressed
3. Genotype: The alleles on a genome
4. Phenotype: The characteristics an organism has as a result of the genotype
5. Locus: the position of a gene on a DNA Molecule
6. Homozygous: two alleles on both chromsomes
7. Heterozygous: 2 different alleles on the chromasomes
Monohybrid Inheritance
Dihybrid Inheritance
Linkage
1. Sex linkage
  1. Sex-linked gene: When a gene is locate on the X or Y sex chromosomes
    1. Males: XY
    2. Females: XX
    3. The Y chromosome is smaller than the X chromosome. The X Chromosome has more than 2000 genes while the Y chromosome has around 70
    4. Sex linked disorders are more common in men as one faulty allele would cause a disorder, whereas in women would require two
    5. Pedigree charts
      1. You may be asked:
        How is it recessive?
        If person C had offspring with a normal female, What would be the offspring phenotypes?
        How do you know that the faulty gene is on the X chromosome?
        How do ya know the faulty gene is recessive?
2. Autosomal linkage
  1. Autosome: All Chromosomes except for the sex chromosomes
  2. Linked genes: 2 or more genes on the same chromosome
    1. More linked = genes closer to each other on the chromosome
  3. Linkage group: all genes on one chromosome
  4. The genotypes are 'cut through the middle' to make the gametes'
    1. its G + N On one chromosome, g + n on the other chromasome
    2. However if crossing over occurs, the gametes would change
      1. If the genes are more closely linked, Gametes are less likely to change as both genes could be swapped
Epistasis: When one gene masks the other
1. Example: mice
  1. A= brown hair (agouti), a=black hair, B= produce melanin, b=no melanin production
    1. If allele bb is present, the mouse will be white (albino), regardless of the gene A
      1. if the mouse has allele Bb/BB, then melanin is produced and the colour of the mouse depends on gene A (Aa/AA = brown, aa=black)
        This is an example of a recessive epistatic allele, but dominant epistatic alleles exist too

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Inheritance

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