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Genetic Central Dogma
- Transcription: DNA to RNA
- Translation: RNA to protein
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Exceptions to the Central Dogma
- 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
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S phase
- DNA replication
- All DNA must be duplicated in preparation for cell division
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DNA Replication
- DNA strands separate
- Two new DNA strands constructed using original strands as templates
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Gene polymorphism Mutation
- 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
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Mutation
- 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
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Point mutations
- 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
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Types of Mutations:
Base-pair substitution
- 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
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Types of Mutations:
Frameshift mutation
- 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
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Mutagens
- Agents known to increase the frequency of mutations
- Ionizing radiation, chemical agents, UV radiation, viruses
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What are the two basic types of human cells?
- 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
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Karyotype
- 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.
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reverse transcriptase
enzyme carried by some viruses that converts RNA to DNA
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retrovirus
virus that uses reverse transcriptase to convert RNA to DNA
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Homologous chromosomes
- 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)
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Non-homologous chromosomes
- non-identical chromosomes
- example chromosome 9 and chromosome 22 or XY (male)
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Autosomes
Chromosomes 1-22
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Sex chromosomes
- the remaining pair
- Homologous (XX)
- Non-homologous (XY)
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how can we detect chromosome abnormalities?
- Amniocentesis: Sample from the amniotic fluid
- Chorionic villus sampling: Biopsy from the placenta
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polyploidy
- multiple of 23 bigger than 2
- triploid (69 total chromosomes)
- tetraploid (92 total chromosomes)
- fetus cannot survive with triploid or tetraploid
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aneuploid
- 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"
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euploid
- have a multiple of the normal number/set (23) of chromosomes
- 23 x 1 and 23 x 2
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disjunction
- 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)
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nondisjunction
failure of chromosome pairs to separate properly during meiosis 1 or 2
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down syndrome
- 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
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turner syndrome
- (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
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klinefelter syndrome
- (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
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Triplo-X
(47, XXX)-phenotypically female, sterility, menstrual irregularity and/or mental retardation, symptoms worsen with each additional X
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clastogens
- agents of chromosome breakage
- ionizing radiation, chemicals, certain viruses
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inversions
breakage followed by a reversal of the fragment during re-insertionABCDEFGH may become ABEDCFGH
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Cri du chat syndrome
- Cry of the cat
- Deletion of the short arm of chromosome 5
- Low birth weight, mental retardation, microencephaly
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Allele
Different form or copy of a particular gene
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Homozygous
When two alleles of a particular gene on a pair of homologous chromosomes are identical
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Heterozygous
When two alleles of a particular gene on a pair of homologous cheomosomes are not identical
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Geneotype
The genetic makeup of an organismWhat they have
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Phenotype
What they demonstrate
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Autosomal dominant disease
Abnormal allele is dominant normal allele is recessive, and allele exist on autosomes
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Autosomal recessive disease
- Abnormal allele is recessive and a person must be homozygous for the abnormal allele to express the disease
- Affects both genders equally
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Penetrance
The proportion of individuals of a particular genotype that express its phenotypic effect in a given environment.
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single gene disorders
- 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
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Level 2 genetic disorders:
Chromosome abnormalities
- 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,
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Level 3 genetic disorders:
Multifactorial disorders
- result from mutations in multiple genes, often coupled with environmental factors
- Examples include: hypothyroidism, colon cancer, breast/ovarian cancer, Alzheimer's disease
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