3.1 DNA TRANSMITTER OF GENETIC CODE 1 Science 9 Unit A Section 3.0 ... •Sexual reproduction usually involves ... associated with a process called meiosis. Science 9 Unit A Section

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Science 9 Unit A Section 3.0

1SCI ENCE 9 – UNI T A : SECTI ON 3 .0

DNA IS THE INHERITED MATERIAL RESPONSIBLE FOR VARIATION.

Science 9 Unit A Section 3.0 2

3.1 DNA – TRANSMITTER OF GENETIC CODE

TEXTBOOK PAGES 38 – 45

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GENETICS

• Genetics is the study of how characteristics of living

things are transmitted from one generation of a

species to succeeding generations.

Science 9 Unit A Section 3.0 3#1

CANADIAN CONTRIBUTION TO DNA

• In 1944, Canadian scientist, Oswald Avery,

confirmed that DNA is the material of inheritance.

• He proposed that a

large molecule found in

cells’ nuclei is responsible

for storing information

and passing it on.


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*DNA*

• DNA stands for deoxyribonucleic

acid, and it is the inherited genetic

material found mainly in the nuclei

of the cells of living things.

• All living things contain DNA in their cells.

The DNA contains instructions for an

organisms’ characteristic features (i.e.

nose shape or hair colour, etc.).


DNA IS FOUND IN THE NUCLEUS OF A CELL


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FRANCIS CRICK & JAMES WATSON

• In 1953, JamesWatson and FrancisCrick revealed that the same chemical building blocks carry the instructions needed for the diversity in our living world.

• Awarded the 1962 Nobel Peace Prize for their discoveries of the structure of DNA.


Francis Crick & James WatsonBritish molecular

biologist,

biophysicist, &

neuroscientist

(1916 – 2004)

American

molecular

biologist,

geneticist, &

zoologist

(1928 – )

#3

THE STRUCTURE OF DNA

• The DNA molecule can be compared to a ladder that has been twisted into a continuous spiral.

• The vertical uprights of the twisted molecular ladder are identical all along its length.

• The overall shape of DNA is helical (like the coil binding on a spiral notebook or agenda).


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THE STRUCTURE OF DNA (CONTINUED)

• The ‘rungs’ of DNA vary in composition.

• Each individual rung pairs up just two of the following four chemicals: • guanine (G)

• cytosine (C)

• adenine (A)

• thiamine (T)


THE FOUR CHEMICAL BASES OF DNA:G C A T

• This arrangement forms a code that

cells can read.


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THE STRUCTURE OF DNA (CONTINUED)

• The arrangement of these four chemicals, G, C,

A, and T, forms a code that cells can read.

• The genetic code is based on arranging the four

chemical “letters” into “words,” or instructions,

that describe how to make any particular

organism.

• In other words, all the blueprints for all the

species on Earth are written in the same

language!


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*CHROMOSOMES*

• DNA contains all the instructions for an

organism’s characteristic features, such as

the shape of your nose or the colour of

your hair.

• If the DNA from a typical human body cell was

stretched out, it would be about two metres long!

• To fit such a large amount of DNA into their

cells, organisms arrange their DNA into

packages called chromosomes.


CHROMOSOMES (CONTINUED)

• Each human cell nucleus contains 46 chromosomes,

except for those in the gametes (i.e. sperm and egg

cells), which contain half (23 chromosomes).

• Think of one chromosome as a single book in a series, and

the entire set of chromosomes as the complete series. If you

were missing a single book, you would be missing

information.


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CHROMOSOME PAIRS

• For humans, a complete set has 46 chromosomes.

• In most familiar organisms, the chromosomes are

organized into pairs.

• So the body cells of a human contain 23 pairs of

chromosomes.


23 PAIRS OF CHROMOSOMES= A FULL SET OF 46 CHROMOSOMES


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EXAMPLES IN OTHER ORGANISMS

Dogs have 78 chromosomes, which is 39 pairs.

Cats have 38 chromosomes, which is 19 pairs.


WHY SO IMPORTANT?

• All of our nuclei, except for those in the gametes,

MUST have a complete set of chromosomes.

• Each chromosome is important and provides crucial

instructions for your characteristics.

• For example, chromosome #1 of a dog reads “make round

eye pupil”, whereas chromosome #2 of a cat reads “make

slit-shaped eye pupil”.


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HUMAN GENOME PROJECT

• The $3 billion government-funded Human Genome

Project (HGP) was an international scientific

research project with the goal of determining the

sequence of chemical base pairs which make up

human DNA, and of identifying and mapping all of

the genes of the human genome from both a

physical and functional standpoint.


HUMAN GENOME PROJECT (CONTINUED)

• Planning for the project started in 1984, got underway in 1990, and was declared complete in 2003.• Over 20 universities and research

centers in the United States, United Kingdom, Japan, France, Germany, and China were involved.

• One discovery from the project? There are approximately 20 500 genes in human beings, the same range as in mice.


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SO WHAT CAN GO WRONG?

• One of the reasons scientists felt it was valuable to

identify the human genome was to help us identify

and understand genetic diseases and possible

cures.

• For example, chromosome abnormalities are missing, extra,

or irregular portions of DNA.

• They usually occur when there is an error in cell division

following meiosis or mitosis.


EXAMPLE: DOWN SYNDROME

• Down syndrome is a genetic disorder caused when abnormal cell division results in extra genetic material from chromosome 21.

• It is typically associated with physical growth delays, characteristic facial features, and mild to moderate intellectual disability.

• Occurs in about one per 1000 babies born each year.


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EXAMPLE: TRISOMY 22

• Trisomy 22 is characterized by threecopies of chromosome 22 rather than two.

• It is typically associated with growth delays, unequal development of the two sides of the body, distinctive malformations of the head and facial area, and intellectual disability.

• It is a frequent cause of miscarriage in the first trimester. Progression to the second trimester and livebirth are rare.


EXAMPLE: ALS

• Amyotrophic lateral sclerosis, or ALS, or Lou Gehrig’s Disease, is a nervous system disease that causes muscle weakness and impacts physical function.

• Symptoms include stiff muscles, muscle twitching, and gradually worsening weakness due to muscle wasting.

• The cause is not known in 90 – 95% of cases (associated with head trauma, military service, drug use, contact sports). About 5 – 10% of ALS cases are inherited from a person’s parents. It is associated with a defect on chromosome 21 or mutations of certain enzymes.


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*GENES*

• A gene is an uninterrupted segment of DNA, which

contains coded instructions.

• Genes are located on the chromosomes. Genes

come in pairs and are located on the same spot of

different chromosomes.


THE RELATIONSHIP:CHROMOSOMES, DNA, AND GENES


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*ALLELE*

• Most genes in most

species exist in an

array of possible

forms that differ as to

their exact DNA

sequence. These

possible forms are

known as alleles.

• An allele is a form of

a gene.

• For example, there

are genes for hair

colour, texture, and

length.

• The different hair

alleles, which could

include:

• Red, blonde, brunette

• Straight, curly, wavy

• Short, long


ALLELES: FORMS OF A GENEIN A PLANT


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SUMMARY


• DNA is located in the nucleus of each cell.

• DNA is packaged into 46 chromosomes.

• If you unwind a chromosome and look at a small

section of it, you are looking at a gene.

HOMEWORK!

• Textbook• Check and Reflect

• Page 45

• # 1 – 4, 7, 9, 10

• Read Topic 3.2

• Page 46 – 47


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3.2 CELL DIVISION


CELL DIVISION AND REPRODUCTION

Asexual reproduction

• Associated with mitosis.

Sexual reproduction

• Associated with

meiosis.


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CELL DIVISION AND ASEXUAL REPRODUCTION

• Recall:• Asexual reproduction involves only

one parent. All of the offspring are genetically identical to the parent.

• In single-celled organisms, binary fission enables the parent cell to split its contents equally between two new cells.

• This ‘asexual reproduction’ (only one parent needed) occurs in the cells of multi-cellular organisms and is known as mitosis.


MITOSIS (1:29)


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*MITOSIS*

• In multicellular organisms, mitosis is the process that

produces two new identical daughter cells from

one parent cell with the same number of

chromosomes.

• Mitosis occurs in the body cells of multicellular

organisms and is responsible for the growth and

cellular repair of a multicellular organism.


MITOSIS (CONTINUED)

• In mitosis, the parent cell first duplicates its DNA and

each chromosome is doubled.

• When the split takes place, each new cell receives

a complete exact copy of the DNA from the parent

cell.


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THE BASICS OF MITOSIS


CELL DIVISION AND SEXUAL REPRODUCTION

• Recall:

• Sexual reproduction usually involves two individual

organisms.

• The offspring that are produced from this union have

genetically different characteristics, half from one parent

and the other half from the other parent - making a unique

offspring.

• In multi-cellular organisms, sexual reproduction is

associated with a process called meiosis.


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MEIOSIS (01:48)


*MEIOSIS*

• Meiosis is a type of cell division that produces cells with only

half the DNA of a normal cell.

• Because each gamete has only half the DNA of a normal cell, when the male and female gametes unite, the zygote has a complete set of DNA.


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*MEIOSIS*

• In order for a gamete to contain only one copy of the different chromosomes, cells must divide twice.

• This produces four daughter sex cells from just one parent cell.


MALE GAMETE + FEMALE GAMETE = ZYGOTE

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SPERM EGG ZYGOTE

½ + ½ = 1 whole

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THE BASICS OF MEIOSIS


44

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http://www.youtube.com/watch?v=D1_-mQS_FZ0&feature=related

http://www.youtube.com/watch?v=VlN7K1-9QB0

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EXPLORE ONLINE


http://www.learnalberta.ca/content/secsu/

html/biological_diversity/mitosis/index.html

RECALL: SEXUAL REPRODUCTION

• During sexual reproduction, the specialized sex cells

(gametes) unite to form a zygote, which develops

into the new organism.


http://www.learnalberta.ca/content/secsu/html/biological_diversity/mitosis/index.html

http://www.learnalberta.ca/content/secsu/html/biological_diversity/mitosis/index.html

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GIVE IT A TRY (TEXTBOOK, PAGE 48)

Organism

Number of chromosomes

in a cell at the end of

mitosis

Number of chromosomes in a body cell

Number of chromosomes in a gamete

Number of chromosomes

in a zygote

Number of pairs of

chromosomes

Cabbage 18

Black bear 38

Human 23

Peanut 40


HOMEWORK!


• Page 48

• # 2 – 6

• Read Topic 3.3

• Page 50 – 54


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3.3 PATTERNS OF INHERITANCE


BREEDERS

• Darwin talked to people who bred pigeons for

show, message carrying, or other purposes.

• He realized that breeding works much the same

way as natural selection, and that many of the

same methods that breeders use can also occur in

nature and can explain the way organisms change

in nature.


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*TRAITS*

• Animal breeders have been selecting animals with

the most desirable characteristics, or traits.

• Traits are characteristics of organisms.

• Scientists can now explain the inherited patterns

they discovered in terms of alleles.


“PLAYING GOD” VS. SURVIVAL OF THE FITTEST

• Sometimes, to prevent unwanted outcomes, only

animals or plants with the most desirable traits are

“allowed” to reproduce.

• This is the idea of “controlled breeding”.


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*PUREBRED* VS. *HYBRID*

Purebred Organisms

• A purebred organism

has ancestors all with

the same form of a

trait.

Hybrid Organisms

• A hybrid organism is

produced by crossing

two individuals (usually

purebreds) who carry

different forms of a

trait.


INHERITANCE IN

• Pure-bloods/Muggles:

• Half-bloods:

• “Pure-bloods” are purebred witches and wizards, or muggles; that is, both of their parents are wizards/witches or both muggles!

• “Half-bloods” are half witch/wizard, and half human; that is, one of their parents was a human (muggle).

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EXAMPLE: BREEDING PUREBREDS

• If a purebred female white cat is bred with a

purebred male black cat:

• The offspring would all be hybrids.


*DOMINANT* VS. *RECESSIVE*

Dominant Trait

• Dominant traits are the

outward form observed

when two opposite-

acting alleles are

inherited.

• For example, black coat

colour (fur) dominant trait

in cats.

Recessive Trait

• Recessive traits are the

outward form observed

only when two same-

acting, non-dominant

alleles are inherited.

• For example, white coat

colour (fur) is a recessive

trait in cats.


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EXAMPLE: BREEDING PUREBREDS

• If a purebred female white cat is bred with a

purebred male black cat:

• The offspring would all have black fur, because black is a

dominant trait.

• The offspring would all be hybrids.


PUREBRED & HYBRIDS + DOMINANT & RECESSIVE = …

• Purebred Black + Purebred Black = Purebred Black

• Purebred Black + Purebred White = Hybrid Black


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QUESTION TO THINK ABOUT

• What will the offspring look like if two hybrid black

cats breed?

• Even though the parents both have black fur, remember

that they are hybrids, which means they are ‘carriers’ for

white fur, even though the white fur does not show.


GENOTYPE VS. PHENOTYPE

Genotype

• An organism’s genotypeis the genetic makeup of the organism.• Hint: Genotype = genes

• It is usually written as two letters, which represent a pair of chromosomes.• Capital letters refer to

dominant traits.

• Lower-case letters refer to recessive traits.

Phenotype

• An organism’s phenotype

is its outward appearance

(i.e. a black cat).• Hint: phenotype = physical traits


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GENOTYPE EXAMPLE: FUR COLOUR

• For example, let’s use the letter “b” to refer to coat

(fur) colour in a cat.

• B = black fur (dominant)

• b = white fur (recessive)

i. Since black is a dominant fur coat colour in cats, a

purebred, black cat will have the following genotype: BBii. A purebred, white cat will have the following genotype:

bb

iii. A hybrid black cat will have the following genotype: Bb


PUNNETT SQUARES

• Punnett squares are named for an English geneticist, Reginald Punnett.

• A Punnett square is a chart which predicts all possible gene combinations in a cross of parents (whose genes are known).

Parent 1

Pa

ren

t 2

B B

b

b


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HOW DO WE USE PUNNETT SQUARES?

• If a purebred black cat is bred with a white cat, use a Punnett Square to determine the colour of the offspring (phenotypes).• B – black (dominant)• b – white (recessive)

• All of the offspring produced will be black hybrid kittens.

Parent 1

Pa

ren

t 2


PUNNETT SQUARES EXAMPLE 1

• If two black hybrid cats are bred, use a

Punnett Square to determine the potential phenotypes of the offspring.

• B – black (dominant)

• b – white (recessive)

Parent 1

Pa

ren

t 2


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• If a purebred black cat is bred with a hybrid black cat, use a Punnett Square to determine the % of offspring that would have black coats, and white coats.• B – black (dominant)

• b – white (recessive)

Parent 1

Pa

ren

t 2



• If a white cat is bred with a hybrid black cat, use a Punnett Square to determine the % of offspring that would have black coats, and white coats, and identify the % of offspring that are ‘purebred’ and ‘hybrid’.• B – black (dominant)• b – white (recessive)

Parent 1

Pa

ren

t 2


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THERE’S SOMETHING ABOUT RECESSIVE TRAITS…

• A recessive trait will ONLY appear in the offspring if TWO recessive alleles are inherited, one from the mother, and one from the father.


EXAMPLE: COLOUR BLINDNESS

• Colour blindness is the inability to see or perceive colour differences under normal lighting conditions.

• Colour blindness is a recessive trait and the related gene is carried on the X chromosome. Males have a higher probability of being colour blind.• Females have two X

chromosomes.• Males have one X and one Y

chromosome.

• This means that for a female to be colour-blind, she would have to inherit the gene from both her mother and her father.

• On the other hand, since Y chromosomes can only be passed on from the father, a male would only need to inherit the gene from his mother in order to be colour blind.


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INHERITING COLOUR BLINDNESS


EXAMPLE: COLOUR BLINDNESS


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*INCOMPLETE DOMINANCE*

• When no specific trait is truly dominant or recessive,

this is known as incomplete dominance.

• Incomplete dominance is a pattern of inheritance

seen when two different alleles are present at the

same gene location, but neither is dominant.

• When the alleles are neither dominant, nor

recessive, an intermediate trait will occur

(combining the two traits).


*INCOMPLETE DOMINANCE*

• Example: Snapdragon flowers

• A purebred red flower is crossed with a purebred white flower and the offspring are neither red nor white, and instead, the flowers are pink.


+ =

#20

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SOME EXCEPTIONAL CASES DO EXIST…

• If offspring are unlike either parent, more than one

gene location and more than one allele may be

responsible for specific traits.

• Example: human eye colour or red hair


EXAMPLE: FETAL ALCOHOL SYNDROME

• When a woman drinks alcohol during pregnancy, she risks giving birth to a child who will pay the price — in mental and physical deficiencies — for his or her entire life.

• Characteristics include: developmental delay, behavioural problems, learning difficulties, facial abnormalities, epilepsy, poor coordination, poor socialization skills.


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POSSIBLE REASONS?

• The complex mixing of the possible combinations for

a particular trait may account for the variation of

traits an offspring has.

• Even though genes play a vital role in determining

development, environmental factors can also have

a bearing on how DNA is interpreted and

developed.


EXAMPLE:THALIDOMIDE

• Thalidomide first appeared in Germany on October 1st, 1957.

• It was marketed towards pregnant women to help combat morning sickness.

• It was quickly being prescribed to thousands of women and spread to most corners of the globe. Nobody had any idea of what was to follow.

• The tests on thalidomide were conducted on rodents which metabolize the drug in a different way than humans. Later tests on rabbits and monkeys produced the same horrific side effects as in humans.


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“THALIDOMIDE BABIES”


THALIDOMIDE (CONTINUED)

• In the late 1950s and early 1960s, more than 10 000 children in 46 countries were born with deformities as a consequence of thalidomide use. It is not known exactly how many worldwide victims of the drug there have been, although estimates range from 10,000 to 20,000.

• Thalidomide became available in Canada in late 1959. Although thalidomide was withdrawn from the West German and United Kingdom markets by December 1961, it remained legally available in Canada until March 2, 1962, a full three months later than its ban in other countries.


http://youtu.be/bT4dF3mqvmg

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LEADING MEANINGFUL LIVES:ALVIN LAW, MOTIVATIONAL SPEAKER &

THALIDOMIDE SURVIVOR (4:21)


HOMEWORK!


• Page 54

• # 1, 2, 4 – 6

• Section 3.0 Review Handout


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3.1 DNA TRANSMITTER OF GENETIC CODE 1 Science 9 Unit A Section 3.0 ... •Sexual reproduction usually involves ... associated with a process called meiosis. Science 9 Unit A Section