Chapter 2: PROPAGATION – LIFECYCLE & GENETICS
LIFECYCLE
Annual:
“Well, my body is insignificant, what matters is my progeny and offspring. Life is short. Live fast die young. I’m going to invest in lots and lots of seeds that go into the ground for next year.”
Evolved in places where there are yearly cycles of light and dark, hot and cold periods.
Biennial:
“The first year, I’m just saving and saving – energy and body mass. Ya know, it takes a lot of energy to make fancy flowers, make baby seeds and all. Its not easy, not cheap. So save one year, hunker down. Hopefully the year after, I can make a go of it.”
Evolved in places where the plant probably wishes the season was longer and there was more sun, so that it could get it all done in just one sitting. But no, it just ain’t so.
Perennial:
Herbaceous deciduous (leaves die back to the ground):
“Yeah the earth is a pretty good insulator. I can sit tight here while the cold and snow come around. Still alive and holding steady down in the roots. But the leaves they kinda tender, just can’t take it. So I will sacrifice ‘em and grow some new ones when the warm weather come around again.”
Herbaceous evergreen:
“Its okay. I can take it. The cold, the wind, the sun low in the sky. I got leaves short low to the ground. Stiff little things all covered with waxes and hairs for blankets. I’ll be alright. I’ll see you next year, and the year after that, and the year after that.”
Woody deciduous:
“So I have figured out a few ways to survive all through the cold winter months. But still, the leaves – they are a liability. They are cheap to manufacture. As long as I got my trunk and branches and roots down in the ground going every which way. As long as I got all that stored food and energy just in case one of them late winter early spring storm snaps come through… It’s gonna be okay.”
Woody evergreen:
“You don’t gotta worry about me. I am most of the northern and southern forests all over the planet. I shed snow when it piles on thick. Wind pollinated so I don’t ask for insect pollination help. Oh, I’m also in the tropics too where its always 12 hours of daylight and steady wet dry seasons. So… I kinda rule around here. Not braggin or nuthin, just sayin.”
The two life cycle styles:
Seed germination – grow grow grow (vegetative period or adolescence) – reproduce and set seed, disperse seed (adult) – old age and death, repeat and repeat through generations & generations.
Seed germination – grow grow grow – reproduce through cloning yourself – disperse clones – old age and death, repeat.
Asexual life styles:
Citrus apomixis:
“I did not get any suitors this season. So I made my own seeds from my own cells. They are all me. Sometimes like four sprouts coming outa one seed kinda embryo.”
Nopales Opuntia cutting
“So coyote was chasing roadrunner and hahahaha bumped right up against me. Knocked me a pad loose. So the pad (me) was sitting there on the desert sands. It just felt right ya know. Mama papa over there, me in my own spot. So I sunk some roots and there you go.”
Willow stick cutting
“I was there minding my own business by the river bank when that son of a gun beaver come around again. Beaver don’t usually chew on me but this particular individual… must have been hungry or did not recognize me or something. A bunch of willow branches got cut and floated downstream. Luckily they (I) collected in a little log jam by the side of a muddy river turnaround and when I touched the riverbank soil I was like, whew, I’m here. Still alive. Might as well send down some roots.”
Oxalis bulbs
“This the funniest thing. Again, I’m not harming anybody, just hanging out. Here comes this person full of anger starts yanking on my leaves and flowers, digging everywhere. So I just gave it up to him. Yup gave him my fat bulb of a storage organ. He was so mad about me said the bulb couldn’t even go in the compost I was so evil. He bagged up the bulb in a plastic bag and threw me in the trash. Well, the funniest part is that I had thirty little bulbs all just attached too, just a little deeper and easily broken off. So now, I have, I mean I am, thirty young bulbs growing up in a nicely cultivated soil medium. Yippee. I’ll keep growing if the timing is right and theres still spring sun and moisture. Otherwise, next year… Can’t wait!”
Leopard lily bulbils
“That is a cool account, Oxalis, I got a different strategy. I put my little bulbils in between the leaves on the stem, at the axis, and let em fall to the ground when mature. They pretty much have little roots already. So I got it all covered above ground – seeds and fruit from the flowers, and little clones all the way down. Yes real nifty.”
Agave pups
“This is cute, my clones are. My main body dies after it flowers. Its really is just too much effort. I give it my all. Caput thats it. Have you seen my inflorescence stalk?! How tall it gets?! And the flat little black discs of seeds all in them capsules? Well, but I don’t die so easy though. I got little baby pups, offsets, that reach around the bottom off to the sides. So you think I am dead, brown leaves skeleton like, but just watch and wait, watch and wait.”
GENETICS
Inheritance can pass in a top down high to low style, as well as a side to side style
High low is like momma poppa plants each give their bit, and you have a baby plant
you can trace ancestry up the chain back to common relatives
one hundred, two hundred million years ago
You can watch as the family tree branches and intermingles with others
some limbs dying out, others persevering and adapting through the ages
or
you can observe the changes in a clan or an individual as time flows downstream
down through the generations, moving mating and mixing
Side to side is common to bacteria and other ancient basic looking life forms
so you got two bacteria hanging out together
one is round and chunky, the other one is more long and skinny
the round one, people tried to kill it with antibiotics, but it lived
now it has seen the enemy, it is resistant
it knows all its receptors and enzymes and chemical sleight of hands
the round one has a piece of plasmid DNA that codes for resistance
it gives the long skinny bacteria a piece of that and boom
the long skinny one is resistant as well now
‘thanks for that’
‘no problems, we are in this together’
The DNA can also move between individuals
with the help of a virus or a feeding bug or a human grafting scions
the new and foreign DNA could turn out badly for the recipient
like immobilize you mutate you and kill you
or the new DNA might turn out to be beneficial
making you tougher stronger with functions you never thought possible
Genes move vertically between generations of organisms
genes move horizontally between organisms caught in the same time and space
Very cool stuff
PLANT GENETICS
BASICS
Plants animals fungus algae and amoebas
have got a code that determines who and what they are
The code is given to you by your parents
Your mom gives you half of her code
And dad gives you the other half of your code
So you are a mix of the two, complete
Lets say that you are inside of a pine seed, you are a pine embryo
sittin around, getting ready to sprout in the warm sun
you get one sex cell from your mom, that is the sex cell egg inside the ovary
and you get one sex cell from your dad, that is sperm or the pollen
the stuff that makes people go ahhhchhhhooooo
the wind carried the pollen from dad
dropped it down
to the young pine cone of mom
egg + sperm = a fertilized egg = embryo
okay so far so good
you get half your chromosomes from mom
and half your chromosomes from dad
nice, complete set of chromosomes
CHROMOSOMES
So the genetic code
is a large folded up mass
of a spiraling coiled ladder chain
of thing called DNA
strands of DNA make structures called chromosomes
the chromosomes condense into sausage like shapes
like two bratwurst links with a twist in the middle
and later decondense into squiggly masses again
depending on the situation
The chromosomes are in every cell of the creature
they are tucked inside the center of the cell
in the nucleus
ready to split apart and replicate duplicate
to be passed on to the next generation
Chromosomes come in pairs
like a matching set
mom gives you a set
dad gives you a set
more or less the same code, but slightly different instructions
kinda like
two cookbooks with the same list of recipes
but slightly distinct ingredients and ways to combine them
humans have 23 pairs of chromosomes
making that 46 total chromosomes
in each cell nucleus
46 chromosomes in every regular body cell
where a body cell is a bone cell or a muscle cell or a skin cell or a tendon cell or an organ cell
the list goes on
except in the sex cells or the gamete cells –
where there are only half the number of chromosomes
23, not 46
the sex cells are the sperm or the egg, of a male or a female
Some creatures have fewer chromosomes than us
cats and pigs have 38, northern leopard frogs got 26, corn has 20, flatworm Planaria has 16
some organisms have more than us
potatoes have 48, dogs got 78, hermit crabs got 254, adder’s tongue fern has 1,440
DIVERSITY
Mixing it up
the cool thing about the combinations
from different individuals
is that there is going to be variation and exchange
this leads to a wide range of characteristics and traits that will lead to
flexibility and diversity over time
this enables plants to
survive in conditions from wet humid dank to dry parched winds
live in whitened snowfields and high altitude mountains
have tiny waxy leaves that take the glare of the sun
possess humongous fleshy leaves that are happy in the shade of tall trees
and so on and so forth
giving rise to a wide range of possibilities, the ability to adapt and overcome
climatic shifts, uplift of mountains, changing sea levels, movement of glaciers, meteor strikes
The sex cell chromosomes come from body cells with the proper amount of chromosomes
When the chromosomes get ready to be passed on
parts of the chromosome pairs break off, and swap a bit of their codes with each other
and mix it up
I’ll give you some of mine if you give me some of yours
crossing over is what they call it
dancing the do si do, lets see what happens kind of an outcome
Then afterwards
the chromosomes split, and they line up randomly
they get stirred up this way
it is like shuffling the deck of cards a bunch of times
throwing the dice a thousand rounds
or the back and forth motion of mah jong tiles, face down, going in circles and circles
some facing this way, others facing that way
then off to your own corner again
independent assortment is what they call this randomness
the cell started off duplicated, so it divides once, then twice
until the one cell is now four cells
the four cells are all sex cells
sperms and eggs
plant sperm cells are pollen that came in on an air current, or stuck to a hummingbirds feather
egg cells are gamete cells sex cells that are inside of an embryo sac, inside of an immature seed called an ovule
the ovules are along the placenta, arranged neatly inside the immature fruit called the ovary
whew lotta layers, gotta protect the babies
pollination and fertilization – the two sex cells join together
this is outcrossing, recombination, giving and receiving information
you can imagine that in this fashion
variation is the norm
and diversity is encouraged at every step of the game
SELECTION
Early on
people hungry
go to collect plants to eat
so say there was a wild population of grasses
you’d go get the ripe seeds to eat with a beater and a basket
seeds you’d later roast over a fire or smash up in a pestle
some of them grasses no good
some seeds too small no carbs
some seeds would shatter and fall to the ground right when you touched em
some seeds were spiky and pinchy
some seeds after you ate them, would give you a stomach ache or kill ya
these seeds were not selected for
these did not become part of the human diet
people would choose the grasses with fat seeds that would stay together when gathered
seeds that were yummy and nutritious
over time
if you collected these seeds, stored them, and planted the best of the batch next year
you will have domesticated a wild strain, and begun the course of agriculture and settled civilization
corn, wheat, barley, rice, sorghum, millet…
Observation is the key
once you figured out the male and female parts of a plant
you could start to mix and match, mate and breed
different plants, different strains, different species
sometimes they would not mate if they were too distant kin –
no progeny no offspring would result
other times breeding would create a new plant
something in between, a plant with characteristics of both the mother and the father plant
with vigor and improved qualities…
the new plant would, say for example, have
huge numerous seeds and a short sturdy stalk to support it
superior resistance to all forms of disease, and drought tolerance
super fast growth cycle, bunch of crops a year and be a strong competitor against weeds
a better, stronger, larger plant
more food, happier people
with food secure, there is time to do other things
SELECTION GOALS
In plant breeding and genetics
the goal is often the establishment of pure strain creatures
with consistent performance traits
that keep these same features
year after year after year
the goal is not
random outcross outbred populations with variable ‘performance’
this is hit and miss, and not worthwhile for harvesting, processing, storage and consumption
the goal is
pure line of individuals that are all more or less exactly alike
breeders commonly inbreed these plants
and ‘fix’ the creature into dependable sameness uniformity homogeneity
this has been the fate of grass seeds like rice, wheat, corn
this can take five, ten generations or more of
selfing, crossing back with the same line, being reproductively
isolated from another strain through distance and geography
With animals
inbreeding can become disastrous over time
the genes start tweaking and malfunctioning, mutating
disease and disorders set in, causing birth defects and reduced fertility
this is sometimes the case of purebred lines of dogs
with plants, over time
they too can succumb to problems
resulting from the repetition of the same identical genetic lines
generation after generation
resulting in the loss of fitness and degradation of immune systems
at that time, plant breeders will often seek out wild relatives
strong, unusual, and special
to breed back into that uniform monoculture of grains or fruits
or, plant breeders may breed two pure lines together, cross them
the result is a hybrid, oftentimes with the best characteristics
of both the mother and the father
this is why
in general
outcrossing is healthy
for most life forms
PHENO AND GENO TYPES
The code that underlies it all –
the sequence, structures and the way it all interacts
is called genotype
what the code reveals on the surface, on the outside,
what it shows is the appearance –
the color of the flower, the shape of the leaves, the kind of hairs on the stem –
that is the phenotype, the physical characteristics expressed
okay
PLOIDY
Back track a little bit
in humans, with 46 chromosomes in 23 pairs
each pair or set is given the letter n
n is the haploid number
in humans, 2n=46, n =23, and
2n is the diploid number
you get 23 chromosomes from mom (one haploid egg cell)
23 chromosomes from dad (one haploid sperm cell)
that makes 46, and you are on your way
whew
in honey bees
where there is a female queen and female workers
2n = 32, n= 16
the queen and the female workers both have 32 chromosomes per cell
a reasonable diploid
but the drone bee, the male
is basically an egg cell that never got fertilized, a male
that is – a total momma’s boy
a male that has only 16 chromosomes per cell
haploid male
almost like some kind of male clone of the mother
whew
now keep in mind
this is nature we are talking about here
there is endless variation and interaction
and there is still much that we are not totally clear about
or maybe experts only, situations that deny simplification
we are just giving some examples
so that you can begin to understand the breadth and complexity of the system
and appreciate and marvel at the ingenuity and diverse strategies for survival
back to ploidy
in cone bearing plants
it is relatively simple
haploid gamete meets another haploid gamete makes a zygote
plus the seed has a little bit of food tucked in for the baby zygote
the bit of food is another haploid female cell
one more time – the embryo is mama and papa
the food feeding the embryo in the beginning, the endosperm, is all mama
in flowering plants
plants with flowers and fruits, not cones for reproductive structures
repeat
dry fruits, fleshy fruits
fruits, not cones
in flowering plants
one haploid sperm cell fertilizes the haploid egg cell
resulting in a zygote, diploid
and another haploid sperm cell joins two haploid female cells to make
food for the baby embryo
the resulting food, endosperm, is triploid
so in plants
unlike in animals
it is actually common
for individuals to have more than two sets of chromosomes
plants can be more than just diploids
this seems to make them more adaptable and stable over time
and self correct chromosomes gone awry
more than two sets
is called polyploidy
this can happen through natural means
cause nature is nature
and sometimes she is sloppy and prone to mistakes that turn out to be gifts
in other cases, humans alter genomes and create polyploids
with a chemical such as colchicine
making a 2n plant a 4n plant, with 2n sperm and egg cells
colchicine comes from the colchicum plant meadow crocus
the poisonous look alike of the saffron crocus
Example
Mom was a natural tetraploid (four sets)
dad was a natural tetraploid (four sets)
the sex cells combine, but somehow the cells don’t separate and divide well
rather than getting half and half so that you turn out with four sets
you get all of moms and all of dads sets
you get eight sets yeehawww you become an octoploid
The polyploid progeny
may have difficulty reproducing
if it has an odd number of sets -3, 5, 7
because when it tries to produce its sex cells
when its time to do the hoe down and shuffle around and find your partner
it is threes company
and that don’t go well on the dance floor
it just does not split up and combine in a proper fashion
the triploid progeny are sometimes aborted as zygotes
or they live, but are sterile and can’t make more progeny of their own
In the seedless watermelon
a tetraploid and a diploid parent are crossed (4 and 2 sets)
the result is a triploid (3 sets)
it lives but is sterile
later, in the field, the triploid is planted out with the diploid melon vines
the diploid contributes the pollen and causes the fruit to grow
but there was no fertilization, no seeds form
fruit still develops, this is parthenocarpy
the fruit is seedless, sweetened by the sun, and costs a lil extra at the market
Another case of triploidy
occurs in the cultivated banana
except in this case, it is the result of two fertile diploid parents
musa acuminata and musa balbisiana
not sure which mama or which papa
gave two sets of chromosomes
but the progeny, the hybrid, the banana we eat
is a triploid, and it is sterile
and the fruits, like the watermelon, develop without seed, parthenocarpicly
have you ever seen a banana seed?