Genetics Flashcards
Structure of a nucleotide
Sub-unit of DNA - contains a single sugar, phosphate molecule and a nitrogenous base
Species definition
A group of individuals with shared characteristics
Alleles definition
Alternative forms of a gene; inherited from their parent and control/determine characteristics
Chromosomes
DNA tightly wrapped around histones (proteins)
Homologous pairs
A pair of genes coding for a particular trait (dominant, recessive, co-dominant)
Genotype
The inherited genetic make-up of an individual
Phenotype
The observed expression of the alleles for a characteristic - determined by genotype and the environment
Monogenic inheritance
A single pair of alleles is inherited for a particular trait; eg. blood type - these traits are discrete (either there or not) and have only two phenotypes
Polygenic Inheritance
Controlled by multiple pairs of genes, thus continuous variation in trait - Alleles have an additive effect (skin colour, weight, height)
Polygenic inheritance characteristics
Each gene has 2 forms of alleles - contributing and non-contributing
No dominance
Additive effect
Skin colour - polygenic inheritance
Continuous variation in the trait; affected by environmental factors
Effect of genotype on skin colour
Varying amounts of the enzyme tyrosinase (stimulated by UV rays to produce melanin)
Effect of environmental factors on skin colour
UV light stimulates the production of tyrosine (aa forming melanin- protein)
Dark skin
High levels of tyrosinase; increased ability to convert tyrosine to melanin
More even distribution of melanin - more tanned, less susceptible to sun burn
Light skin
Low levels of tyrosinase; decreased ability to convert tryosine to melanin
Less even distribution of melanin (freckles) - less tanned, more susceptible to sun burn
Mutagens
Agents that increase the rate at which mutations occur
Mutagen examples
UV light, X-rays, radiation, chemicals (sulphur dioxide, antibiotics)
Somatic Mutation
Occurs in a body cell - isn’t past through to next generation
Germline mutation
Occurs in the gametes - doesn’t affect individual, does affect offspring
Gene mutation
Change in a single gene - occurs in the replication of a DNA molecule before cell division
Result of a gene mutation
May code for a new amino acid thus a new protein, protein may be missing, no change
Point mutation
Change in a single base
Albinism
Point mutation in TYR gene - results in missing protein responsible for pigment
Duchenne Muscular Dystrophy
Point mutation results in missing protein dystrophin - leads to wasting of leg muscles, later other muscles; experienced at 3-5 years, resulting in death by 25 due to failure of respiratory muscles
Cystic Fibrosis
Point mutation at CFTR gene, results in different amino acids in CFTR protein; regulates development of chloride channels in cell membrane - absence means chloride ions, water can’t be transported through cells
Symptoms of Cystic Fibrosis
Salty tasting skin, persistent coughing, wheezing, digestive problems
Chromosomal mutations
Changes in whole/part of a chromosome - many genes can be affected, many symptoms; deletion, duplication, inversion
Deletion
Part of the chromosome is lost/removed - results in a shorter chromosome
Duplication
A section of a chromosome occurs twice
Chromosomal mutations
Changes in whole/part of a chromosome - many genes can be affected, many symptoms; deletion, duplication, inversion
Deletion
Part of the chromosome is lost/removed - results in a shorter chromosome - can occur as a gene or a chromosomal mutation
Translocation
Part of the chromosome breaks off and reattaches to the wrong chromosome
Gene Definition
The part of a chromosome that codes for a particular trait
Chromosome Definition
Structures carrying hereditary info found in the nucleus of a cell
Trisomy
(Non-dysjunction) - failure of one or more chromatids to separate in the second division of mitosis
down syndrome, patus syndrome, klinefelter syndrome
Non-dysjunction
Failed separation of a chromosome during meiosis - monosomy and trisomy
Down Syndrome
extra chromosome 21
Trisomy
(Non-dysjunction) Down syndrome - extra chromosome 21
Patus syndrome - extra chromosome 13; mental retardation, small head, extra finger, cleft palate, malformation of the eyes and ears
Klin
Patus syndrome
extra chromosome 13; mental retardation, small head, extra finger, cleft palate, malformation of the eyes and ears
Down Syndrome
extra chromosome 21
Klinefelter syndrome
extra x or y chromosome - nondysjunction
