Inheritance

Inheritance

1. Key words

   • Gene: A sequence of DNA that codes for a protein
   • Allele: different versions of the same gene
     • Dominant allele: when at least one allele is required for it to be expressed in the phenotype
       • Codominant allele: Where both alleles get expressed in the phenotype
         • 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
     • Recessive allele: when 2 alleles are required for the allele to be expressed
   • Genotype: The alleles on a genome
   • Phenotype: The characteristics an organism has as a result of the genotype
   • Locus: the position of a gene on a DNA Molecule
   • Homozygous: two alleles on both chromsomes
   • Heterozygous: 2 different alleles on the chromasomes

2. Monohybrid Inheritance

3. Dihybrid Inheritance

4. Linkage

   • Sex linkage
     • Sex-linked gene: When a gene is locate on the X or Y sex chromosomes
       • Males: XY
       • Females: XX
       • The Y chromosome is smaller than the X chromosome. The X Chromosome has more than 2000 genes while the Y chromosome has around 70
       • Sex linked disorders are more common in men as one faulty allele would cause a disorder, whereas in women would require two
       • Pedigree charts
         • 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?
   • Autosomal linkage
     • Autosome: All Chromosomes except for the sex chromosomes
     • Linked genes: 2 or more genes on the same chromosome
       • More linked = genes closer to each other on the chromosome
     • Linkage group: all genes on one chromosome
     • The genotypes are 'cut through the middle' to make the gametes'
       • its G + N On one chromosome, g + n on the other chromasome
       • However if crossing over occurs, the gametes would change
         • If the genes are more closely linked, Gametes are less likely to change as both genes could be swapped

5. Epistasis: When one gene masks the other

   • Example: mice
     • A= brown hair (agouti), a=black hair, B= produce melanin, b=no melanin production
       • If allele bb is present, the mouse will be white (albino), regardless of the gene A
         • 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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