Genetics Bit
In these modern times we all know about DNA for various reasons. We also know that genes are a component of DNA, and that these genes contain the specification for their parent organism.

Genes

Dominant - where one gene swamps another, for example RED dominant to WHITE.
Recessive
the opposite where the recessive gene WHITE is recessive to RED.

Chromosomes
Chromosomes occur in pairs usually. In the formation of gametes one of each pair goes to each germ cell at random. When the chromosomes form germ cells genes are interchanged between the two members of a pair. However, although the points at which their interchange take place is again a matter of chance and the genes of each pair go to the germ cells independently of each other, there is a tendency (if they lie close together) for them to keep together as they go to the germ cells. This is known as LINKAGE.

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Science can be thought of as common-sense based on exp[eriment.
Chromosomes with similar numbers will probably cross
Seed - variable germination due to dormancy. Need os some special condition such as pulp fermented - Sow in box, small peebles pushed in, seed drops into cracks.
Damping Off - Pythium de baryanum fungus (Cheshunt Compound (cuprammonium solution)
remember 'dahlia/sunflower' example and the 'blood'
Seed - may need refrigeration to keep or even to activate.
Pollen - is the male gametes, not self-mobile, as in animals, so needs an agent.
The sticky substance on the stigma activates pollen.
Devices to prevent self-fertilisation in some plants - such as different ripening periods for pollen and stigma, or incompatibility factors which prevent pollen fertilising. Most often found in perenials which, being long-lived, can insist on cross-fertilisation. Rogues are a danger to self-fertilised plants as the stock will not remain pure.
Germination - remember epiphyllum seed germinating in fallen fruit in weeks (3) where it took years (3) before. Correct temperature may be important.
Temperature change can kill.


Germ Cells or Gametes
After fertilisation the new cell remains fixed for a time to the tissue producing the female germ cell, and undergoes further development before parting from mit and beginning life on its own.
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Mendel
Any mention of plant breeding should include some reference to Gregor Mendel (1822-1884), an Austrian monk. He embarked on a series of experimental studies on plant breeding involving the edible pea. He conducted various experiments on smooth and wrinkled peas but the best known and influencial one relates to crossing a tall variety of pea with a short one, and observing the ratio of one to the other in the progeny. From this work came his Laws of Heredity.

He found that, in the first generation which became known as F1, that only tall ones appeared. So the story goes, this led Mendel to recognise 'tallness' as the dominant factor, and 'dwarfness' as the recessive factor. It should be noted that his wise choice, the pea, did not involve colour, scent, shape or size, only tall and short.

He bred another generation from that first F1 and obtained a second filial or F2 generation. In this he found that plants were not all tall as in F1, but were in certain ratios for tallness, shortness, and breeding from 'true'. These ratios are usually illustrated by reference to the colours RED and WHITE, but the same holds whatever the factor.

If we symbolise these as R for red and W for white, then crosses become RR for two red crosses, and WW for two white crosses. A red and a white cross would be designated as RW.

From these crosses we get Mendel's Law of Heredity which is widely recognised, and the foundation of genetics and inheritance. His work related to tallness and shortness, remember.

The chart on the left shows that a quarter of them are Red, half are Red/White (=pink), and a quarter are white. These ratios demonstrate that the frequency of Reds and Whites occur by chance as can be demonstrated by tossing coins woth head and tails corresponding to the two choices of Red and White. After ???XX tosses you will get ???. Coming back to the peas, the previous ratios continue in further crosses when the attributes reduce to a quarter of these ratios, or to one sixteenth (a quarter of a quarter). The effect of this is that large numbers of plants (ie hundreds) become involved which is not practical for us amateurs. However, knowing what effects may be expected when crossing two different plants is helpful.

If we cross two plants of the same species, for colour, size and/or shape, we, too, can discover which is the dominant factor. This shows in the F1 generation. Crossing these again in a second or F2 generation the gives the Mendel Ratios of quarters and halves.

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