Genetics

Dominant allele

Functional protein, masks other alleles

Recessive allele

Makes a malfunctioning protein

Co-dominance

2 alleles affecting the phenotype equally and separately (not blended phenotype) E.g: blood type

Incomplete Dominance

Heterozygote shows an intermediate blended phenotype. E.g: Pink flowers are the blended phenotype of red and white flowers.

Sex-Linkage

Genes on sex chromosomes as opposed to autosomal chromosomes. E.g: Hemophilia

Polygenic traits

Phenotypes determined by the additive effects of 2 or more genes on a single character. They are identifiable by the wide variation in the trait. E.g: skin colour, height, weight, intelligence, behaviours

Epistasis

One gene controls the expression of the other. It involves 2 separate genes that code for 1 trait. E.g: mouse and labrador retriever coat colour.

Mouse coat colour

* Pigment (C) or no pigment (c)
* Pigment concentration: black (B) to brown (b)
* cc = albino no matter B allele

Labrador retriever coat colour

* Pigment (E) or no pigment (e)
* Pigment concentration: black (B) to brown (b)
* eebb = yellow fur; brown nose, lips, eye rims.
* eeB_ = yellow fur; black nose, lips, eye rims.
* E_bb = chocolate lab; brown fur, nose, lips, eye rims.
* E_B_ = black lab; black fur, nose, lips, eye rims.

Pleiotropy

One gene affects more than one trait. E.g: acromegaly (gigantism), dwarfism, sickle cell anemia

Environmental effects examples

* Height and weight - nutrition, sleep, or physical exercise
* Flower colour - dependent on soil pH
* Seasonal fur colour of arctic animals - coat colour in arctic fox is influenced by heat sensitive alleles
* Melanin production - UV light

Pedigree

A flowchart that uses symbols to show the inheritance patterns of traits in a family over generations

Deletion

Loss of a chromosomal segment (error in replication)

Duplication

Repeat a segment (error in replication)

Inversion

Reverses a segment (error of crossing over)

Translocation

Moves segment from one chromosome to another (error of crossing over)

Point mutation

A genetic alteration caused by the substitution of a single nucleotide for another nucleotide

Tay-Sachs

* Non-functional enzyme fails to breakdown lipids in brain cells, fats collect in cells destroying their function.
* Has pleiotropic effects (seizures, blindness, muslce degeneration etc.)
* Autosomal recessive

Huntington’s Chorea

* Caused by single base substitutions.
* Build up of “huntingtin” protein in brain causing cell death.
* Has pleiotropic effects (memory loss, muscle tremors, jerky movements etc.)
* Autosomal dominant.

Cystic Fibrosis

* Cystic fibrosis is the deletion of phenylalanine 508.
* Normal allele codes for a membrane protein that transports Cl- across cell membrane. Defective/absent channels limit transport of Cl- and H2O across cell membrane.
* Has pleiotropic effects (mucus build-up in the pancreas, lungs, digestive tract etc.)
* Autosomal recessive.

Sickle cell anemia

* Caused by substitution of a single amino acid in hemoglobin.
* When oxygen levels are low, sickle-cell hemoglobin crystallizes into long rods.
* Has pleiotropic effects (kidney failure, pneumonia, paralysis etc.)
* Autosomal recessive

Heterozygote advantage

The case in which the heterozygous genotype has a higher evolutionary fitness than homozygotes. E.g: heterozygotes with a sickle cell anemia allele will not show symptoms of the disease nor can they get malaria.

Hemophilia