Week 8 Genetics Plfsom Jr

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genetic diversity among individuals in a population is generated as a result of:

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mutations (mitosis and meiosis), and recombination and random assortment of homologs (meiosis)

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genes

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individual hereditary units

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locus

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the location of a gene on a chromosome

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telomere

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the repetitive DNA sequence at the ends of chromosomes

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centromere

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the constricted region in a human chromosome

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human genome

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consists of 23 pairs of chromosomes

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how many homologous chromosomes?

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22 pairs

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How many sex chromosomes?

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1 pair

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diploid

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containing 2 sets of chromosomes (2n)

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2n=

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46

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haploid

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containing a single copy or set of chromosomes (n)

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n=23=

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haploid number in humans

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alleles

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alternative forms of a gene. Each diploid individual has two alleles, one on each homologous chromosome

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mitotic cycle

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process by which somatic cells undergo cell dividiosn and produce two diploid daughter cells identical to the original cell

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Meiotic cycle

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process by which germline cells divide and form haploid gamees containing only half the DNA of the parent diploid germline cell

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Interphase

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DNA replication, Centrosome duplication

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Prophase

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chromosomes condense, centrosomes separate

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prometaphase

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nuclear membrane break down, spindle forms (microtubules), chromosomes attach to spindle (via kineticore)

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metaphase

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chromosomes align on spindle equator (metaphase plate)

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anaphase

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sister chromatids separate and move to opposite pole (A), poles separate (B), cleavage furrow starts to form

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telophase

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sister chromatids reach the poles, cleavage furrow constricts (Actin), nuclear envelope reassembles arround the chromosomes (2N DNA content inside the two new nuclei)

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cytokinesis

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chromosomes decondense, daughter cells separate, interphase microtubules network reforms

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Average of how many crossover events that occur per chromosome pair?

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one to three

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Copy DNA once, divide once

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Mitosis

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Copy once, divide twice

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Meiosis

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polymorphism

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a mutation that has a population frequency of at least 1%

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allelic heterogenity

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different mutations within the same gene

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Tautomerisation

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A change in location of an hydrogen atom on a base. Amino group (NH2) can tautomerize in imino (=NH) group or likewise a keto group (C=O) in an enol group =C-OH). These transient tautomers can form nonstandart base pairing thet fit double helix. Imino tautomer of adenine can pair with cytosine and allow C to be incorporated during replication

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Depurination

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removes the base (A or G) in the nucleotide leaving the sugar behind

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Base analogs

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like 5 bromo uracil (analog of thymine) pair with adenine but its enol tautomer can pair with Guanine instead.

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Base modifiers

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such as Nitrous acid (HNO2) can deaminate adenine into hypoxanthine, cytosine into uracil ang guanine to xanthanine. This change base pairing where hypoxanthine pairs with cytosine rather than thymine

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Intercalating agent

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such as acridine, destabilize the helix and lead to insertion or deletion of nucleotides

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UV induce

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covalent link between adjacent pyrimidines. The dimers disturb helix structure and block replication and transcription until it is removed by excision repair pathway (xeroderma pigmentosum defect)

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Induced mutations can be initiated by:

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chemical mutagens (base analogs, base modifiers, intercalating agents) Radiation (UV) breaks bons, results in dimerization of bases

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Transition

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Purine to purine or pyramidine to pyramidine.

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Transversion

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purine to pyrimidine or vice versa

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silent mutation

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no effect. Same AA

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missense mutation

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different AA

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non sense mutation

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premature stop codon

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frameshift mutation

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deletion or insertion of size that is not a factor of 3

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haploinsufficiency

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when 50% of a normal protein is not sufficient for normal function

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germinal mutation

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occurs in cells destined to produce gametes. Typically not expressed in the person containing the mutation. Can be passed to offspring.

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Germline mosaicism

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a form of masaicism foncinfed to the germ and germline cells- should come to mind when an affected child has two unaffected parents

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Somatic mutations

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occur in the body (soma) cells of an organism, cannot be passed on to children. Can affect a number of cells in the body, while the rest are normal (termed "Mosaicism"

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Polyploidy occurs in cells and organisms when there are more than two paired (homologous) sets of chromosomes.

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Aneuploidy is an abnormal number of chromosomes, and is a type of chromosome abnormality.