Patho unit 2 ch.2

• Transcription: DNA to RNA
• Translation: RNA to protein

• some viruses use RNA as their genetic material 
• These carry the code for an enzyme called reverse transcriptase that converts RNA to DNA
• these viruses are called retroviruses
• DNA is then inserted into the host cell
• This is a destructive process for the host cell;damage to host cell DNA is common and results in diseases such as cancer

• DNA replication 
• All DNA must be duplicated in preparation for cell division

• DNA strands separate
• Two new DNA strands constructed using original strands as templates

• A change in the sequence of DNA which then results in a change in the sequence of mRNA
• Most of these are silent, meaning they do not change the primary protein sequence
• Some cause noticeable changes in the organism; theses are called mutations

• Any inherited alteration of genetic material
•   -any change to the nucleotide sequence of genetic material
• Chromosome changes causing congenital defects are easier to observe
•   -some mutations are very subtle and are difficult or impossible to observe
• They can be favorable or unfavorable

• do not change the reading frame 
• change only a single base (CAA CAT CAT CAT)
• Silent mutations: do not change the protein sequence
• Sometimes these do change the protein sequence
•   -missence mutations: change one amino acid to another
•   -nonsence mutations: change codon that codes for an amino acid to a stop codon, resulting in abnormally short protein

• One base pair is replaced by another,
• can result in a change in the amino acid sequence.
• *Silent substitution: amino acid change does not occur

• Insertion or deletion of one or more base pairs in the DNA moleculechange reading frame
• Deletion mutation: one base removed
• Insertion mutation: one base added

• Agents known to increase the frequency of mutations
• Ionizing radiation, chemical agents, UV radiation, viruses

• Somatic cells: almost all of the 10 trillion cells that make up our body
•   -Diploid cells (23 pairs of chromosomes 46 total)
•   -formed by mitosis 
• Gametes: Specialized sex cells
•  -spermatozoa; eggs
•   -Haploid cells (23 total chromosomes)
•   -Formed by meiosis

• An ordered display of chromosomes 
• Homologous chromosomes are paired and displayed according to their size
• Chromosome 1 is the longest, and 22 is the shortest.

enzyme carried by some viruses that converts RNA to DNA

virus that uses reverse transcriptase to convert RNA to DNA

• Nearly identical chromosomes 
• the two chromosomes that pair during meiosis
• Each member of a pair is inherited from one parent
• Crossover exchange of info occurs between homologous pairs
• chromosome XX (female)

• non-identical chromosomes
• example chromosome 9 and chromosome 22 or XY (male)

Chromosomes 1-22

• the remaining pair
• Homologous (XX)
• Non-homologous (XY)

• Amniocentesis: Sample from the amniotic fluid
• Chorionic villus sampling: Biopsy from the placenta

• multiple of 23 bigger than 2
• triploid (69 total chromosomes) 
• tetraploid (92 total chromosomes)
• fetus cannot survive with triploid or tetraploid

• a somatic cell that is not an exact multiple of 23
• trisomy (3 copies of one chromosome) fetus can survive
• monosomy (only one of any chromosome) fetus most often won't survive
• "it is better to have extra than less"

• have a multiple of the normal number/set (23) of chromosomes
• 23 x 1 and 23 x 2

• purpose is to distribute equal amounts of genetic material
• normally one copy of each gene ends up in each gamete (each normal gamete contains one allele)

failure of chromosome pairs to separate properly during meiosis 1 or 2

• nondisjunction during fertilization on chromosome 21 causing a trisomy
• closely related to maternal age
• mental retardation, low nasal bridge, epicanthal folds, protruding tongue, poor muscle tone

• (45,X)females with only one X
• absence of ovaries, short stature, webbing of neck, underdeveloped breasts, wide nipples
• single x usually inherited by mother
• high number of fetuses with single X are aborted

• (47, XXY) or (48, XXXY) or (49, XXXXY) or (50, XXXXXY)
• males with two or more X chromosomes and only one Y
• male appearance, develop female-like breasts, small testes, sparse testes, sparse body hair, long limbs
• abnormalities will increase with each extra X

(47, XXX)-phenotypically female, sterility, menstrual irregularity and/or mental retardation, symptoms worsen with each additional X

• agents of chromosome breakage
• ionizing radiation, chemicals, certain viruses

breakage followed by a reversal of the fragment during re-insertionABCDEFGH may become ABEDCFGH

• Cry of the cat
• Deletion of the short arm of chromosome 5
• Low birth weight, mental retardation, microencephaly

Different form or copy of a particular gene

When two alleles of a particular gene on a pair of homologous chromosomes are identical

When two alleles of a particular gene on a pair of homologous cheomosomes are not identical

The genetic makeup of an organismWhat they have

What they demonstrate

Abnormal allele is dominant normal allele is recessive, and allele exist on autosomes

• Abnormal allele is recessive and a person must be homozygous for the abnormal allele to express the disease
• Affects both genders equally

The proportion of individuals of a particular genotype that express its phenotypic effect in a given environment.

• result when a mutation causes the protein product of a single gene to be altered or missing
• examples include: galactosemia, cystic fibrosis, alpha-1 antitrypsin deficiency, Adenosine deaminase (ADA) deficiency,  Huntington's Disease,maple syrup urine disease,  neurofibromatosis type 1, phenylketonuria (PKU, Severe Combined Immunodeficiency (SCID, sickle cell disease,Smith-Lemli-Opitz syndrome,  PACHYONYCHIA CONGENITA

• entire chromosomes or large segments of them, are missing, duplicated, or otherwise altered
• Examples include: Cri-du-Chat syndrome, Down syndrome, Klinefelter syndrome, Turner syndrome, Williams syndrome,

• result from mutations in multiple genes, often coupled with environmental factors
• Examples include: hypothyroidism, colon cancer, breast/ovarian cancer, Alzheimer's disease