Patterns Of Inheritance Flashcards
Phenotype
what’s expressed
Influenced by environment (e.g. Lifestyle - diet and exercise)
Variation
Due to mutations Meiosis - crossing over - independent assortment - 2^n possibilities Humans 2^23 = 8,388,608 genetically different gametes possible
Allele
a version of a gene
Homozygous - two alleles of the gene are the same
Heterozygous - two alleles of the gene are different
Hemizygous - only one allele of a gene on the X chromosome (males only)
Genetics
Dominant - in the heterozygous state it determines phenotype
Recessive - must be in the homozygous state to be expressed
Genotype
the genetic code
Influenced by environment (e.g. damaged by radiation)
Autosomal recessive
Heterozygous is just a carrier
2 heterozygous have a 25% of having affected offspring
e.g. CF
disease can skip generations
Autosomal dominant
Affects heterozygous - 50% change of affected offspring
Disease is rarely found in homozygous state (incompatible with life)
Disease cannot skip generations
e.g. Huntington’s Disease
X-linked recessive
Hemizygous males and homozygous females affected
More common in males
Female carrier has 50% change of having affected sons
Affected males cannot give traits to sons
e.g. Haemophilia A
Co-dominance
Both alleles will contribute to the phenotype
e.g. ABO blood types
Complementation
Two genes have defects but they compliment each other - possible to have normal offspring
e.g. Albinism
Linkage
Do not show independent assortment at meiosis
Linked - on the same chromosome
Not linked - genes on different chromosomes
Recombination frequency
- dependent of the distance between the genes
- genes close together are ‘tightly linked’
- genes far apart on the same chromosome almost behave as unlinked genes
