Genes - Athro Limited, Education on the Web
 Genetics on the molecular level 

DNA and Packaging Genes

Bacteria are normal - mammals are strange.... Two basic designs for DNA packaging Bacteria - 'chromosome' + plastids Everyone else - chromosomes Haploid-Diploid-Polyploid Puzzles of how genes work - [separate page]

Relating heredity and genetics to genetic mechanisms

Mechanism of genetics - level one - genes at loci on chromosomes. Observation - genes seem like particles Explanation - genes are pieces of information stored in DNA Observation - genes come in pairs of copies Explanation - chromosomes come in pairs (note - not from DNA double helix - sense&antisense copies on one strand - other chromosome has second set of sense&antisense) Observation - both parents and children have just one pair of each gene, and children get one of their pair from each parent. Explanation - chromosomes duplicate and split up in meiosis so that gametes each get one of each chromosome. Haploid-diploid. Chromosomes come in pairs. Mitosis - normal cell division, parent and resulting cells both diploid Meiosis - making gametes, parent cells diploid, resulting cells haploid gametes Observation - two different genes, even on the same chromosome tend to be inherited independently Explanation - recombination during meiosis. Observation - most genes act like they are inherited indpendently. The allele one gets for one gene from one parent seems independent of the alleles for any other genes. Paradox - since genes get packaged on chromosomes, how could this be so? Genes on the same chromosome should be inherited all together. Recombination

The answer to this paradox is recombination. Pairs of chromosomes line up during the cell division events that create gametes and switch pieces with each other.

Mitosis and Meiosis To give a specific example of recombination in genetics, if genes for Agouti and Merle (to use Shelties) happened to be on the same chromosome. If one parent were sable and trifactored at the Agouti locus and Merle and not-merle at the merling locus, then that parent should only be able to produce gametes that were sable-merle or tricolor-notmerle, but never gametes that were sable-notmerle. Thus breedings to a bicolor dog that isn't merled should only be able to produce sable merles and tricolors, but never blue merles. But we observe that breeding a trifactored sable merle to a bicolor produces sable merles, trifactored sables, tricolors, bicolors, and blue merles - combinations that couldn't occur if the genes were on the same chromosome.

Genetics mechanisms of heredity: Examples of how genes work

Mechanism of heredity understood at level 2 - DNA stores information, transcribed to RNA, RNA translated to protein. Proteins do things: make structures, help catalyze reactions, regulate other genes. Mutations change gene product. Three kinds of genes at work: 1) Structrural Genes - Type I Collagen. Proteins have shapes. Proteins can assemble in groups to build larger structures. 2) Genes Doing Something - Hemoglobin Proteins don't do it alone. Single base pair changes can alter a protein's function, or not, depending on where they are. Allele can map onto several mutations. 3) Genes Regulating Activity - Genes can regulate other genes.

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Copyright © 2000 Athro, Limited. All Rights Reserved.
Written by Paul J. Morris
Maintained by Athro Limited
Date Created: 2000 July 11
Last Updated: 2000 July 11