DNA is the inherited material responsible for variation

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DNA – Transmitter of Genetic Code

DEOXYRIBONUCLEIC ACID (DNA) :

Genetic material found mainly in the nuclei of cells of living things

  • DNA acts as a “blueprint” for offspring giving each offspring a complete set of instructions
  • DNA is the inherited material responsible for variation
  • Canadian scientist, Oswald Avery helped discover DNA as the large molecule responsible for storing information and passing it on

DNA History

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  • DNA was 1st discovered in 1869 but little was known about its role
  • 1944 – Avery confirmed DNA was the material of inheritance.
  • James Watson and Francis Crick unraveled the structure of DNA and showed how the same chemical building blocks could carry out a wide range of instructions

DNA STRUCTURE

  • Like a ladder spun around in a continuous spiral
  • The rungs vary in composition
  • Each rung has a pair of the following:
    • guanine
    • cytosine
    • adenine
    • thymine
  • Think G-CAT , guanine and cytosine are always paired together as are adenine and thymine
  • The arrangement of these forms a code the cells can read (like the alphabet where the letters can be arranged into millions of different words)

GENETIC CODE :

Arrangement of 4 chemical “letters” on a DNA molecule that can be arranged into “words” that form instructions for making an organism


Chromosomes

SCIENTISTS USE FLORESCENT MARKERS ON HUMAN CHROMOSOMES TO CREATE A FALSE COLOR IMAGE

SCIENTISTS USE FLORESCENT MARKERS ON HUMAN CHROMOSOMES TO CREATE A FALSE COLOR IMAGE

CHROMOSOMES: 

Organisms arrange the DNA into packages whose contents are neatly put together into structures that easily fit into the cell

  • DNA in a human cell stretches out to about 2m long which is more than 1 million times longer than the cell itself
  • Humans have 46 chromosomes or 23 pairs of chromosomes
  • DNA is like a set of encyclopedias and a chromosome is one volume
  • Every cell in the human body has 46 chromosomes except the gametes which have 23
  • Dogs have 78 chromosomes (39 pairs), cats have 38 chromosomes(19 pairs)

Genes:

An uninterrupted segment of DNA, which contains coded instructions responsible for the inheritance of an organism’s characteristic features

Research is done with fruit flies and that has been able to tell us:

  • Genes are located on chromosomes
  • Each chromosome contains numerous gene locations
  • Like chromosomes, genes come in pairs
  • Both genes in a pair carry DNA instructions for the same thing
  • Same gene occupy matching locations but may not be exactly the same in both locations

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ALLELES :

Possible 'forms' of a gene

Ex. Alleles for brown eyes and blue eyes. 

 

 

Ex: “ A hairy coat” in dogs varies. You could have straight, curly, short, long, coarse, fine, and the colour that are all different possibilities for “hairy coats”

Therefore:

  1. "A hairy coat" is more than one characteristic, it is a combination of several characteristics
  2. More than one gene pair may be involved in determining individual characteristics of a dog’s “hairy coat”
  3. Could be several alleles for each gene pair

 

Human Genome


Cell Division

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Cell Division and Asexual Reproduction

  • Before binary fission, the unicellular organism (ex. Paramecium) makes an exact copy of its DNA – eachChromosome doubles
  • When the cell divides, each new cell has a complete set of DNA
  • In multicellular organisms the process that produces 2 new cells with the same number of chromosomes is called mitosis
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MITOSIS :

Type of cell division that produces two identical daughter cells from one parent cell. Responsible for growth and cellular repair of a multicellular organism


Cell Division - Sexual Reproduction in Plants and Animals

  • Two gametes unit to form a zygote → male provides male gamete and female provides female gamete
  • If the gametes had the same number of chromosomes as every other cell in the body, (ex. 46 in humans) then the zygote would have twice the DNA (92 chromosomes) it needs
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MEIOSIS :

Type of cell division that produces cells with only ½ the DNA of a normal cell

  • When the 2 gametes unit (23 chromosomes each) you get a complete set of DNA (46 chromosomes)
  • Meiosis involves two cell divisions
  • Gametes contain only one copy of each different chromosome

 


Patterns of Inheritance

TRAIT :

A characteristic of an organism

PUREBREED :

A referring to a plant or animal that has ancestors with all the same form of a trait (ex. White cats whose ancestors have produces only white offspring for several generations)

- “True-breeding” ex. Black cat x Black cat

HYBRID :

An organism produced by crossing two purebred individuals for different forms of a trait ex. Black cat x White cat


Dominant VS. Recessive

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DOMINANT TRAIT :

The outward form observed when two opposite acting alleles are inherited

(ex. Long leg fruit flies – an offspring with one short leg allele and one long leg allele will grow long legs – the short leg allele is recessive because it has no influence if the dominant, long leg allele is present) (figure 3.13 p. 50)

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RECESSIVE TRAIT :

 Out ward form observed when two same acting, non-dominant alleles are inherited

If we take hybrid black offspring and cross breed…

3 offspring are black and 1 is white (75% black, 25% white)

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Possibilities:

  • (i) Black from mother (B) and Black from father (B) = Black (BB) offspring (2 dominant alleles)
  • (ii) Black from mother (B) and white from the father (b) = Black (Bb) offspring (1 dominant and one recessive allele)
  • (iii) White from mother (b) and black from the father (B) = Black (Bb) offspring (1 dominant and one recessive allele)
  • (iv) White from mother (b) and white from father (b) = White (bb) offspring (2 recessive alleles)

 

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INCOMPLETE DOMINANCE :

The pattern of inheritance seen when 2 different alleles are present at the same gene location , but neither is dominant (ex. Red snap dragons and white snap dragons produce pink snap dragons)

  • A child with wavy hair as a result of one parent's curly hair and the other's straight hair.
  • If a red tulip and a white tulip are cross pollinated they result is a pink tulip
  • For eye colour, hair colour, and skin pigment it is much more complex than simply dominant and recessive or incomplete dominance

 

Environmental factors can also influence traits

  • Ex. FAS – Fetal Alcohol Syndrome or
  • Ex. Thalidomide given to pregnant women produced offspring with abnormally developed limbs
  • Ex. Epigenetics

Human activity affects biological diversity

Reduction of Biological Diversity

- Species and ecosystems and their processes are being stressed by urbanization, agriculture, and forestry

EXTINCTION :

Disappearance of every individual of a species from the entire planet

  • Scientists estimate that 99% of all species that have ever existed are now extinct
  • Can happen by catastrophic events or over a long period of time

EXTIRPATION :

A local extinction or disappearance of a species from a particular area (ex. Grizzly bear on the prairies) 

See table on p. 59


Natural Causes of Extinction and Extirpation

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Causes of Extinction

  • Catastrophic events (volcanic eruptions, floods, fire, etc.)
  • Lack of food due to over population
  • Disease

OVER SPECIALIZATION :

Species has adaptations for a small set of environmental conditions, which leaves it vulnerable to extinction (Ex. Giant Panda eats only bamboo that is disappearing)


Human Causes of Extinction and Extirpation

How humans manage to disturb ecosystems:

  • Habitat destruction (construction, agriculture, development, logging, damming of rivers, etc.)
  • Pollution – pesticides, herbicides, fertilizers that can damage environments and cause birth defects
  • Over-hunting (ex. Plains bison, passenger pigeons, prairie dogs)
  • Introduction of non-native species (Bio-invasion)

Ex. Horses & cattle brought by European settlers – compete with native species for resources

Bottom line is that extinction and extirpation reduce biological diversity


Selecting Desirable Traits

ARTIFICIAL SELECTION (Selective Breeding): 

Breeding by humans of plants and animals with desirable traits to produce offspring with those desirable traits (ex. Horse and dog breeding)

  • Can be used in food (ex. Corn) to “weed out” undesirable traits
  • Many of our plants no longer resemble wild species due to artificial selection for over 10000 years

 

BIOTECHNOLOGY :

The use of living things to make agriculture, industrial or medical products (ex. Seeds from best corn plants planted by Native peoples to get the best yield)

  • Takes many generations to get a full crop/herd with desired traits
  • Can be “high tech” or “low tech”
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CLONES :

A genetically identical copy of an entire organism or its cells or genes; cloning is the process of creating a clone (ex. Cuttings of plants)

Cells are now removed from plant with desired traits and placed in a Petri dish with nutrients and hormones they need.  They then develop into seedlings


ARTIFICIAL INSEMINATION :

Artificial collection and injection of sperm from a male into a female; used in livestock breeding (ex. Bull sperm inserted into many cows)

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INVITRO FERTILIZATION :

Fertilization that happens outside the body, usually in a Petri dish; used in livestock breeding (ex. Prize cow eggs with bull sperm and embryos are implanted into other cows)

GENETIC ENGINEERING:

The intentional altering of DNA of an organism or population of organisms (ex. Inserting a gene from one species into another species – human insulin producing gene into bacteria) 

- All of these technologies, although beneficial to humans, can put species at risk of disease due to their similarities or resistance (ex. Weeds in crops to herbicides)


Reducing our Impact on Biological Diversity

- 1992 - United Nations Convention on Biological Diversity

- 1995 – Canadian Biodiversity Strategy

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IN-SITU CONSERVATION: 

The maintenance of wild organisms within their functioning ecosystem (Ex. National Parks)

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  • Linking protected sites with corridors
  • Restoring land to natural states (ex. Wetlands) through private and corporate donations (examples on p. 73-74)
  • Any species classified as endangered or threatened is protected by law from hunting, capture, picking, or transplanting
  • Species are assessed by the Committee On The Status Of Endangered Wildlife In Canada (COSEWIC)
    • Nationally – Species at Risk
    • Alberta – Endangered Species Conservation Committee (ESCC)

EX-SITU CONSERVATION :

The maintenance of organisms outside of their ecosystems or natural habitats; an endangered species maintained in a zoo is an example or seed banks

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