Genetic Variation in Crops: Explaining Pre-Existing Characters

[gracy]

I am not getting one line from my textbook.Can someone please explain.That line is as follows:
In many crops genetic variations are available as pre-existing characters in wild relatives of the crop.

My attempt for this is -i think it means if any crop shows any variations it means remaining closest members would also show these variations
.I don't think it is right.
please explain.

 

[Simon Bridge]

Without the nroader context, it is tricky.
Domestic crops will show genetic variation.
The specific variations from the domestic crop norm are also present in wild relatives.

 

[Doug Huffman]

Crops as highly sorted mono-cultures are a relatively recent technological development. Look to legacy cultivars for genetic variations visible in the field. Contrast corn-maize in which I am amazed seeing miles of stalks, each one with the first leaf at precisely the same height above the soil.

 

[gracy]

Without the nroader context, it is tricky.
Domestic crops will show genetic variation.
The specific variations from the domestic crop norm are also present in wild relatives.

Here,pre-existing character and wild relatives means?give me some hint.

 

[jim mcnamara]

This is why the USDA's Federal Seed Storage laboratory exists - Norway has a comparable facility. Both wild and all available varieties of most crop plants are preserved at the facility.

Plants grown as crops are genetically identical, and are therefore less resistant to disease and insect pests.

The idea is to have a broad spectrum of traits for one kind of plant available. No single plant can have all of them at one time - which is what the sentence in your textbook is trying to say. A lot of wild traits are "undesirable", but really good ones can be mixed in there, too.

Example good/bad:
Soybeans are prone to hard seed. This means if you plant a hard seed in the Spring it won't germinate, probably for 10-20 years. This is bad if you want to sell soybeans in the Fall. So if you find soybeans that do not have hard seed, then you would prefer that. This is good.

In 1970 when corn blight became a major problem in the US, the "Texas male sterile" gene was the culprit. So a world-wide search was undertaken to find corn (Zea mays if you are European, corn has a dichotomous meaning.) that had male strilty traits. One such trait was found in Czechoslovakia. The US imported thousands of tons of seed from there.

 

[gracy]

Here,pre-existing character means?

A lot of wild traits are "undesirable", but really good ones can be mixed in there, too.

will you mind explaining what is wild trait?what is wild relatives?does it mean commonly available,i.e not rare with no variations.right?

 

[Vagn]

will you mind explaining what is wild trait?what is wild relatives?does it mean commonly available,i.e not rare with no variations.right?

Wilds means undomesticated, so the grey wolf is the wild relative of the dog. Similarly, many crops have ancestors which are still prevalent in an undomesticated state, these crops may have characteristics which a farmer may want to introduce into their own crop such as being more resistant to a pest.

 

[gracy]

This is why the USDA's Federal Seed Storage laboratory exists - Norway has a comparable facility. Both wild and all available varieties of most crop plants are preserved at the facility.

Plants grown as crops are genetically identical, and are therefore less resistant to disease and insect pests.

The idea is to have a broad spectrum of traits for one kind of plant available. No single plant can have all of them at one time - which is what the sentence in your textbook is trying to say. A lot of wild traits are "undesirable", but really good ones can be mixed in there, too.

Example good/bad:
Soybeans are prone to hard seed. This means if you plant a hard seed in the Spring it won't germinate, probably for 10-20 years. This is bad if you want to sell soybeans in the Fall. So if you find soybeans that do not have hard seed, then you would prefer that. This is good.

In 1970 when corn blight became a major problem in the US, the "Texas male sterile" gene was the culprit. So a world-wide search was undertaken to find corn (Zea mays if you are European, corn has a dichotomous meaning.) that had male strilty traits. One such trait was found in Czechoslovakia. The US imported thousands of tons of seed from there.

in my sentence pre-existing characters means?does it mean already available characters?

 

[jim mcnamara]

Pre-exist means it already existed somewhere before the present time

Example: many humans have brown eyes, humans had brown eyes 75 years ago. Brown eyes is a pre-existing trait.

 

[gracy]

Pre-exist means it already existed somewhere before the present time

Example: many humans have brown eyes, humans had brown eyes 75 years ago. Brown eyes is a pre-existing trait.

does it mean it should be still present?

 

[jim mcnamara]

Pre-exist implies:
1. it existed before now
2. it exists right now

 

[gracy]

Pre-exist implies:
1. it existed before now
2. it exists right now

sorry,but one more question.it existed before,it exists right now and what about in between?

 

[jim mcnamara]

Traits cannot come and go like members of an audience. They persist, so that means that pre-existing implies (from a perception, how-we-see-it point of view) it was and ever since it was seen it has been. Scientists do not like to make statements like this generally because a lot of the time nobody is writing down every day 'I observed trait #6412 today'

So we assume if I see it now and you saw it a year ago, it did not magically go away for a few weeks in between. This follows the principle of the simplest available good explanation is the best. Sometimes called 'Ockham's Razor' which you can google for.

 

[gracy]

these crops may have characteristics which a farmer may want to introduce into their own crop such as being more resistant to a pest.

these crops -which crops?crops of ancestors which are still prevalent in an undomesticated state or crops of descendants ?

into their own crop

own crop-which crop ?can be any crop or has to be related with the crop from which farmer wants characters to be transferred?
sorry for being too specific but all 'crop terms' are messed-up.

 

[mes314159]

Domesticated crops have been bred for many many generations. While they have plenty of genetic variation, they presumably won't have the broader range of variation found in their wild ancestors since the whole point of domestication is to standardize the plant for certain desirable (to farmers) properties. However, during many generations of breeding for domestication, new random mutations will also arise and either be fixed if they are desirable or else just distribute randomly. So wild relatives of a domestic crop may not have all of the variation in the domestic variety, although as noted they are expected to be more diverse. That reduction in diversity is why domestic varieties are often hit hard when new pathogens (new varieties of those pathogens, more likely) arise. Wild varieties having greater diversity are more likely to include at least some plants resistant to that pathogen, if those plants can be found, the resistance can be bred "into" the domesticated variety. There is however no guarantee that a wild population of relatives will have such resistance genes. But eliminating biodiversity certainly risks the loss of such resistance genes, which may come back to bite us in the future of course.

 

[gracy]

Wild varieties having greater diversity are more likely to include at least some plants resistant to that pathogen,

why wild relatives are thought to be more diverse?and why greater diversity corresponds to resistance to pathogen?

 

[mes314159]

Wild relatives are not automatically more diverse, and there are examples of wild populations with reduced diversity (African cheetahs apparently). They are usually more diverse simply because they are not under human selection for a limited range of traits. Greater genetic diversity simply means that there is more chance of some individuals being resistant to any particular pathogen - it's no guarantee. But for example there are certain genetic variants found originally in some african humans, which increase their resistance to HIV. The genes involved are being studied for possible new anti-viral medicines.