| 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.
Sources:
Part of the Athro, Limited web site.
Copyright © 2000 Athro, Limited. All Rights Reserved.
Written by Paul J. Morris mole@morris.net
Maintained by Athro Limited
Date Created: 2000 July 11
Last Updated: 2000 July 11
Biology