Module 6: Genes and Genetic Diseases Flashcards
Define: Gene
a sequence of DNA that encodes a protein
Define: Codon
3 nucleotides that encode one amino acid
ex. AUG- start codon
UAA, UAG, UGA = stop codons
Define: nucleotide
- molecules that contain a sugar ring (deoxyribose), an organ base (purine or pyrimidine), and a phosphate group (PO4)
- subunits of DNA, act like letters in a code
- 4 nucleotide bases in DNA:
- A-adenine
- G-guanine
- T-thymine
- C-cytosine
Define: Chromosome
- a long DNA strand with some or all of the genetic material of an organism
- Humans have 23 TYPES of chromosomes
- numbered 1-22, X and/or Y
Somatic Cells and Chromosomes
Somatic Cells: majority of cells in the body
- contain 2 copies of the DNA in the nucleus
- They are diploid:
- there are 2 of each type of chromosome
- paired chromosomes are homologous chromosomes
- encode the same genes but the information within them is slightly different depending on what is inherited
- one inherited from mother and one from father
- paired chromosomes are homologous chromosomes
- there are 2 of each type of chromosome
- Multiply via mitosis
Homologous chromosomes
- Paired chromosomes, 2 of the same type of chromosome
- encode the same genes but the information within them is slightly different depending on what is inherited
- one inherited from mother and one from father
Reproductive Cells and Chromosomes
- form gametes (oocytes in females, spermatocytes in males)
- 1 copy of DNA in each mature gamete
- haploid
- 23 x 1 = 23 chromosomes
- haploid
- multiply via meiosis I and meisosi II
Define: Locus
- Location of a gene on a chromosome
- ex. the gene for red hair is MCR1 gene and is located on chromosome 16
Define: allele
- the specific form of the gene that is present on each chromosome
- ex. MCR1 is a key gene for pigmentation, the two major pigmentations are eumelanin and pheomelanin
- R = pheomelanin (produced brown or dark hair), r = eumelanin (red or light hair)
- homozygous alleles: two copies of the same gene RR or rr
- heterozygous alleles: different variations Rr
Define: Genotype
the combination of genes carried within an individual’s chromosomes
Define: Phenotype
the traits expressed by an individual based on their genotype
Penetrance vs Age-dependent penetrance
- penetrance: % of individuals with a certain genotype that express the expected trait
- age-dependent: individuals with a certain genotype may not express the trait until later in life
Mutagens: Definition, Causes, and Inheritance
- definition: agents that increase the frequency of mutations
- causes:
- radiation: fragmentation of DNA
- mutagenic chemicals: alter DNA due to their molecular structure, by mimicking ionizing radiation, or interfere with base pairing
- Inheritance:
- mutations in somatic cells can cause disease but will not be inherited
- mutations in reproductive cells CAN be inherited
Define: Genetic Mutation
- alterations of genetic material
Whole Chromosome Non-Disjunction
- sister chromatids fail to separate during mitosis or meiosis
- monosomy
- trisomy
Partial Chromosome Breakage
- deletion
- duplication
- inversion–two breaks, reinsertion
Chromosome Translocation
- interachange genetic material between non-homologous chromosomes
Fragile Sites on Chromosomes
certain chromosomes are more prone to breakage and gaps
Point Mutations
- Alteration of a single nucleotide within DNA
- base pair substitution
- base pair deletion
- base pair addition
- redundancy of code allows for some margin of error without consequences
- HOWEVER, alterations can be profound
- missense: change of amino acid
- frameshift: change entire gene from mutation forward
- nonsense: stop gene from being produced (stop codon)
Missense Point Mutation
causes change of amino acid
Frameshift Point Mutation
change entire gene from mutation forward due to an insertion or deletion
Nonsense Point Mutation
stop gene from being produced (a stop codon)
Autosomal Dominant and Example(s)
- a pattern of inheritance in which an affected invidiaul has one copy of a mutant gene and one normal gene on a pair of autosomal chromosomes
- ex. polycystic kidney disease
- ex. Neurofibromatosis (nodules on nerve endings in skin)
Autosomal Recessive
- trait/phenotype is only expressed in homozygotes
- ex. albinism
- ex. PKU (phenylketonuria)
- ex. sickle cell anemia
X-linked Recessive
- traits whose alleles are carried only on the X chromosome and require 2 copies for expression unless they are unopposed (with a Y chromosome)
- ex. Hemophilia A
- ex. Duchenne Muscular Dystrophy
- ex. Red/Green Color blindness
Mitochondrial Inheritance
- Variable presentations:
- in individuals
- among family members
- heritability patterns
- homoplasmic/ heteroplasmic (one type of mtDNA in an individual/ more than one type)
- ex. Leber Hereditary Optic Neuropathy (LHON)–> vision loss
- ex. myoclonic epilepsy with ragged-red fiber syndrome (MERRF)
- if a mother is afflicted her children will have it; if father has it but mother does not, their children will not have it
- 95% of mtDNA comes from OVA/mom
Trinucleotide Repeat Disorder
- genetic mutations that are amplified in successive generations
- each generation has worsened phenotypes
- ex. Fragile X syndrome (mental disability)
- ex. Friedrich’s Ataxia (progressive nervous system damage and movement problems)
- Huntington’s Chorea aka huntington’s disease (breakdown of nerve cells in the brain)
Recurrence and Punnet Square
- the probability that a family member of an affected individual will have the same disease
