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?