inheritance - pogfish

• Gene


  Section of DNA on a chromosome that codes for a particular protein
• Allele

  Different version of a gene, coding for a different protein
• Genotype


  Describes the alleles present for a particular feature
• Phenotype


  Expression of a characteristic due to the genotype and alleles present in an individual and due to the environment
• Dominant allele


  Only one copy of this allele for the trait to be expressed and is always expressed if present
• Recessive allele


  Only expressed in the phenotype when the genotype is homozygous or no dominant allele is present
• Homozygous

  2 of the same alleles
• Heterozygous

  2 different alleles
• Monohybrid inheritance


  Inheritance of a characteristic controlled by a single gene

  
• Co-dominance


  Both alleles are expressed in the phenotype

  
• Multiple alleles

  A gene that has more than two alleles

  
• Sex-linkage


  Occurs when certain traits are determined by genes on sex chromosomes
• Pedigrees


  Family charts that help you tell how a certain trait is carried through the generations

  
• Autosomal dominance


  - Individual not expressing trait has two affected parents (heterozygous)
• Autosomal recessive


  - Individual expressing trait has two normal parents (heterozygous)

  - Two affected parents can not have an unaffected child
• Sex-linked inheritance recessive

  - No father-to-son transmission

  - Predominantly males affected

  - May skip generations

  - Affected female will need an affected father
• Sex-linked inheritance dominant


  - Present in each generation
• Epistasis


  A type of gene interaction in which one gene alters the phenotypic effects of another gene that is independently inherited

  
• Autosomal Linkage


  Inheritance of two genes at different loci on the same pair of homologous chromosomes

  
• 3:1 ratio

  Bb x Bb

  Heterozygous monohybrid cross
• 1:2:1 ratio

  AB x AB

  Heterozygous co-dominance or multiple alleles
• 9:3:3:1 ratio

  AaBb x AaBb

  Heterozygous dihybrid cross
• 1:1 ratio


  Aa x aa

  Monohybrid cross
• 1:1:1:1 ratio


  AaBb x aabb

  Dihybrid cross
• 9:3:4 ratio

  Recessive epistasis
• 12:3:1 ration

  Dominant epistasis
• How can you determine whether a ratio is demonstrating autosomal linkage?


  The ratio will be atypical due to crossing over
• Why might a ratio not be the same as expected?

  - Random fertilisation of gametes

  - Small sample size

  - Lethal genotypes

  - Genes are linked

  - Epistasis