Variation and Classification

REVIEW ANGIOSPERM SEXUAL CYCLE:
 

• SPOROPHYTE (THE 'PLANT'' OAK TREE OR GARDEN SQUASH) PRODUCES - MEGA- (OVULE) AND MICROSPORANGIA (ANTHER)

• ALL SPOROPHTIC TISSUE IS DIPLOID AS ARE MEGA- AND MICROSPORE 'MOTHER' CELLS WHICH DIFFERENTIATE WITHIN THE SPORANGIA - THESE UNDERGO MEIOSIS TO PRODUCE HAPLOID MEGA- AND MICROSPORES WHICH UNDERGO NUCLEAR DIVISIONS TO PRODUCE (WITHIN THE SPORE WALL - ENDOSPORIC) MEGA- AND MICRO GAMETOPHYTES THAT REMAIN IN THE SPORANGIA (8-NUCLEATE MEGAGAMETOPHYTE IN THE OVULE AND 3-NUCLEATE [2 SPERM, 1 GENERATIVE] IN THE POLLEN GRAINS OF THE ANTHER).

• POLLEN GRAINS (MICROSPORE WITH MICROGAMETOPHYTE INSIDE) ARE MOVED (VECTORS) TO AN APPROPRIATE (SAME SPECIES) GYNOECIUM, GAMETOPHYTES EMERGE THROUGH (USUALLY PORES) THE MICROSPORE WALL AND GROW THROUGH THE STYLE TO THE OVULE 'POINT OF ENTRY' (MICROPYLE) WHERE THE TWO SPERM (DOUBLE FERTILIZATION) FUSE WITH THE MEGAGAMETOPHYTE EGG NUCLEUS (SYNGAMY) TO PRODUCE A ZYGOTE (RETURN TO DIPLOIDY - EMBRYO)- AND EMBRYO AND ENDOSPERM

VARIATION:

TERMS:  GENOME = [HAPLOID SET OF CHROMOSOMES] - OURS (H. sapiens) IS COMPOSED OF HOW MANY CHROMOSOMES? - 23 (or full genome = 22 autosomes plus X and Y)

EACH CHROMOSOME CARRIES CODED INFORMATION [GENES] THAT CAN OCCUR IN DIFFERENT FORMS [ALLELES].  IF THE SAME ALLELE IS PRESENT IN BOTH GENOMES WHEN COMBINED [SPOROPHYTE] THE GENE IS HOMOZYGOUS [TRUE BREEDING], IF DIFFERENT ALLELES = HETEROZYGOUS

EXAMPLE:  FLOWER COLOR - WHITExWHITE=WHITE, REDxRED=RED, REDxWHITE=PINK[F₁], PINKxPINK=RATIO OF PROGENY[F₂] 1WHITE,1RED,2PINK

PUNNET SQUARE FOR F₁  (Aa x Aa) CROSS if 'a' allele is not fully recessive (maybe partially inhibits pigment production):
 
 

IF THE RED ALLELE ('A') IS DOMINANT, (maybe allele 'a' blocks pigment production but only if homozygous) THEN 3RED:1WHITE
 

EVOLUTION - CHANGE THROUGH TIME - BASE MECHANISM = NATURAL SELECTION - 1859 - DARWIN - BASIC NOTIONS:

1.  THERE IS VARIATION IN EVERY GENE POOL
[GENE POOL] = POPULATIONS CAPABLE OF HYBRIDIZATION

2.  MOST OF THIS VARIATION IS GENETICALLY BASED [PASSED ON FROM ONE GENERATION TO THE NEXT - later (after Darwin) defined by Mendel] - although PHENOTYPIC PLASTICITY - ENVIRONMENTAL [NOT GENETIC] VARIATION

3.  ALL PROGENY OF A GENE POOL DO NOT SURVIVE TO PRODUCE PROGENY

4.  INDIVIDUALS CARRYING ADAPTIVE GENES ARE MORE LIKELY TO SURVIVE TO PRODUCE PROGENY THAN OTHERS IN THE POPULATION
 - USE UNUSUAL - CULTURAL - EXAMPLES:  ANTIBIOTIC RESISTANCE [PENICILLEN, PESTICIDES, HERBICIDES]

5.  THUS, ALLELIC [DEFINE] FREQUENCIES AT MANY GENES [DEFINE] WILL CHANGE THROUGH TIME - EVOLUTION

 STABLIZING/DIRECTIONAL VS. DISRUPTIVE SELECTION

ARTIFICIAL VS. NATURAL SELECTION:  MAN CONTROLS THE FATE OF PROGENY - CULTURALLY DIRECTED - RECENT - MAJOR MORPHOLOGICAL CHANGES

AGAIN - BELL CURVE - NOTE DEBATE ON DIRECTIONAL [PHYLETIC] VS. DISRUPTIVE [BI-DIRECTIONAL] PHYLOGENETIC RESULTS OF ARTIFICIAL SELECTION

SUCCESS IN EVOLUTION - INCREASE NUMBERS OF INDIVIDUALS/POPULATIONS AND INCREASE GEOGRAPHIC RANGE - I.E., INCREASE THE AMOUNT, DIVERSITY, DISTRIBUTION OF 'HOME' DNA

VARIATION - MUTATION [MINOR, LONG-TERM] - MAJOR INPUT IS FROM GENETIC RECOMBINATION - THE MORE ALLELES PER GENE THE BETTER - CAN ONLY HAVE 2 ALLELES PER GENE PER INDIVIDUAL.  THUS, POPULATIONS WITH VARIABLE INDIVIDUALS ARE PREFERRED

TRADITIONAL AGRICULTURE [EXP. NATIVE AMERICAN] - FIELDS WITH MANY CULTIVARS MUCH GENETIC VARIATION

WESTERN AGRICULTURE - IN THE PAST - HAS PLACED UNIFORMITY AS A HIGH PRIORITY [ASTHETICS, MECHANICAL PROCESSING] - NOW AN INCREASED INTEREST IN 'BIODIVERSITY' - STABILITY - [F₁ MAIZE - LEAF WILT DISEASE OF THE 70s]

Domestication - An evolutionary process that involves changes in gene frequencies through time.  The process produces domesticated SPECIES.  Non domesticated plant species can be cultivated and domesticated species can grow wild.

Summary from:  Charles Darwin (Origin of Species, Chapter 1 Variation Under Domestication:  (see whole chapter 1 and index for full document)

"To sum up on the origin of our Domestic Races of animals and plants. I believe that the conditions of life, from their action on the reproductive system, are so far of the highest importance as causing variability. I do not believe that variability is an inherent and necessary contingency, under all circumstances, with all organic beings, as some authors have thought. The effects of variability are modified by various degrees of inheritance and of reversion. Variability is governed by many unknown laws, more especially by that of correlation of growth. Something may be attributed to the direct action of the conditions of life. Something must be attributed to use and disuse. The final result is thus rendered infinitely complex. In some cases, I do not doubt that the intercrossing of species, aboriginally distinct, has played an important part in the origin of our domestic productions. When in any country several domestic breeds have once been established, their occasional intercrossing, with the aid of selection, has, no doubt, largely aided in the formation of new sub-breeds; but the importance of the crossing of varieties has, I believe, been greatly exaggerated, both in regard to animals and to those plants which are propagated by seed. In plants which are temporarily propagated by cuttings, buds, &c., the importance of the crossing both of distinct species and of varieties is immense; for the cultivator here quite disregards the extreme variability both of hybrids and mongrels, and the frequent sterility of hybrids; but the cases of plants not propagated by seed are of little importance to us, for their endurance is only temporary. Over all these causes of Change I am convinced that the accumulative action of Selection, whether applied methodically and more quickly, or unconsciously and more slowly, but more efficiently, is by far the predominant power."