Unit 3:genetics

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reduction division

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the first division of meiosis in which the number of chromosomes is reduced to half the original number.

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diploid

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. an organism or cell having double the basic haploid number of chromosomes.

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Haploid

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an organism or cell having only one complete set of chromosomes, ordinarily half the normal diploid number.

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synapses

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Specialised junctions at which a neuron communicates with a target cell. At classical synapses, a neuron's presynaptic terminal releases a chemical transmitter stored in synaptic vesicles which diffuses across a narrow synaptic cleft and activates receptors on the postsynaptic membrane of the target cell. The target may be a dendrite, cell body, or axon of another neuron, or a specialised region of a muscle or secretory cell. Neurons may also communicate through direct electrical connections which are sometimes called electrical synapses; these are not included here but rather in gap junctions

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independent assortment

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formation of random combinations of chromosomes in meiosis and of genes on different pairs of homologous chromosomes by the passage at random of one of each diploid pair of homologous chromosomes into each gamete independently of each other pair

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Locus

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the chromosomal position of a gene as determined by its linear order relative to the other genes on that chromosome.

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gene

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the basic physical unit of heredity; a linear sequence of nucleotides along a segment of DNA that provides the coded instructions for synthesis of RNA, which, when translated into protein, leads to the expression of hereditary character

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allele

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any of the alternative forms of a gene that may occur at a given locus

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homologous pairs

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one set having come from its mother while the other set has come from its father

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, dominant, recessive

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One parent has a single, faulty dominant gene (D), which overpowers its normal counterpart

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, phenotype

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This is the "outward, physical manifestation" of the organism. These are the physical parts, the sum of the atoms, molecules, macromolecules, cells, structures, metabolism, energy utilization, tissues, organs, reflexes and behaviors; anything that is part of the observable structure, function or behavior of a living organism.

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genotype

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This is the "internally coded, inheritable information" carried by all living organisms. This stored information is used as a "blueprint" or set of instructions for building and maintaining a living creature. These instructions are found within almost all cells (the "internal" part), they are written in a coded language (the genetic code), they are copied at the time of cell division or reproduction and are passed from one generation to the next ("inheritable"). These instructions are intimately involved with all aspects of the life of a cell or an organism. They control everything from the formation of protein macromolecules, to the regulation of metabolism and synthesis

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homozygous

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having identical pairs of genes for any given pair of hereditary characteristics

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, heterozygous

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Having two different alleles for a single trait.

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monohybrid cross

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Also called monohybrid cross. a genetic cross made to examine the distribution of one specific set of alleles in the resulting offspring.

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test cross

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The crossing of an organism, with an unkown genotype, to a homozygous recessive organism (tester). A cross between an individual of unknown genotype or a heterozygote (or a multiple heterozygote) to a homozygous recessive individual.

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Law of Segregation

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the principle, originated by Gregor Mendel, stating that during the production of gametes the two copies of each hereditary factor segregate so that offspring acquire one factor from each parent.

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Law of Independent Assortment

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the principle, originated by Gregor Mendel, stating that when two or more characteristics are inherited, individual hereditary factors assort independently during gamete production, giving different traits an equal opportunity of occurring together

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incomplete dominance

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the appearance in a heterozygote of a trait that is intermediate between either of the trait's homozygous phenotypes.

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codominance

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Genetics. of or pertaining to two different alleles that are fully expressed in a heterozygous individual

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epitasis

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That part which embraces the main action of a play, poem, and the like, and leads on to the catastrophe; opposed to protasis.

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pleiotropy

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the phenomenon of one gene being responsible for or affecting more than one phenotypic characteristic.

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polygenic inheritance

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the heredity of complex characters that are determined by a large number of genes, each one usually having a relatively small effect.

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linkage

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an association between two or more genes on a chromosome that tends to cause the characteristics determined by these genes to be inherited as an inseparable unit.

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inactivation

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to stop the activity of (certain biological substances

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non-disjunction

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The failure of one or more pairs of chromosomes to separate at the miotic stage of karyokinesis, with the result that both chromosomes are carried to one daughter cell and none to the other.

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deletion

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a type of chromosomal aberration in which a segment of the chromosome is removed or lost.

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duplication

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a type of chromosomal aberration in which a region of the chromosome is repeated.

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translocation

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a chromosomal rearrangement in which a segment of genetic material from one chromosome becomes heritably linked to another chromosome

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semiconservative replication

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The normal process of DNA synthesis, in which the two original strands of the molecule separate, and each acts as a template on which a new complementary strand is laid down.

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helicase

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enzyme, molecular biology> A prokaryote enzyme that uses the hydrolysis of ATP to unwind the DNA helix at the replication fork, to allow the resulting single strands to be copied. Two molecules of ATP are required for each nucleotide pair of the duplex.

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replication fork

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a Y-shaped part of a chromosome that is the site for DNA strand separation and then duplication

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Okazaki fragments

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short fragments of newly synthesised dna strands produced during dna replication. All the known dna polymerases can only synthesis dna in one direction, the 5' to 3' direction. however as the strands separate, replication forks will be moving along one parental strand in the 3' to 5' direction and 5' to 3' on the other parental strand.

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Mutations

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deletion, substitution, insertion, frame shift

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Protein Synthesis

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one-gene-one-enzyme hypothesis, one-gene-one-polypeptide hypothesis

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DNA Organization

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chromatin, histone proteins, nucleosomes, euchromatin, heterochromatin, transposons

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bacteriophages

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A virus that infects and lyses certain bacteria

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retroviruses

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any of a family of single-stranded RNA viruses having a helical envelope and containing an enzyme that allows for a reversal of genetic transcription, from RNA to DNA rather than the usual DNA to RNA, the newly transcribed viral DNA being incorporated into the host cell's DNA strand for the production of new RNA retroviruses: the family includes the AIDS virus and certain oncogene-carrying viruses implicated in various cancers.

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reverse transcriptase

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a retrovirus enzyme that synthesizes DNA from viral RNA, the reverse of the usual DNA-to-RNA replication: used in genetic engineering to clone genes from RNA strands.

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Plasmids

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A circular, double-stranded unit of DNA that replicates within a cell independently of the chromosomal DNA. Plasmids are most often found in bacteria and are used in recombinant DNA research to transfer genes between cells.

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conjugation

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the reproductive process in ciliate protozoans in which two organisms of different mating types exchange nuclear material through a temporary area of fusion.

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transduction

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the transfer of genetic material from one cell to another by means of a virus

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regulation of gene expression

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operons