SCIENCE 10 LIFE SCIENCE: GENETICS Genome British Columbia, 2004

SCIENCE 10

LIFE SCIENCE:

GENETICSGenome British Columbia, 2004 www.genomicseducation.ca

I. How does the genetic code relate to the

assembly of different proteins?

Recall from the unit on the cell that all of its

activities are controlled by a nucleus.

Recall from the unit on the cell that all of its

activities are controlled by a nucleus. This

nucleus contains DNA, deoxyribonucleic acid,

which contains the information necessary to

make a variety of proteins.

assembly of different proteins? (cont.)

Proteins perform many functions in your body,

such as those found in your muscles that

allow you to move or those in your mouth that

breakdown the starch in bread.

Proteins perform many functions in your body,

such as those found in your muscles that

allow you to move or those in your mouth that

breakdown the starch in bread. These

proteins also perform and control many

functions within the cell, but are only made

when needed.

The instructions to make these proteins are

contained in the genetic code.

contained in the genetic code. This code

consists of four different molecules known as

bases that are grouped into triplets.

contained in the genetic code. This code

consists of four different molecules known as

bases that are grouped into triplets. Each

triplet codes for one of twenty amino acids,

the building blocks used to build these

proteins.

Each triplet codes for one of twenty amino

acids, the building blocks used to build these

proteins. The DNA determines what amino

acids, how many of each amino acid, and the

order of these amino acids to use for each

protein.

Each triplet codes for one of twenty amino

acids, the building blocks used to build these

proteins. The DNA determines what amino

acids, how many of each amino acid, and the

order of these amino acids to use for each

protein. It’s like writing sentences with three

letter words from a four letter alphabet.

A gene is a section of DNA that contains the

genetic code for a specific protein, so it can

determine how an organism appears and

functions.

II. How are the principles that govern the

inheritance of traits used to solve problems

involving simple Mendelian genetics?

What is inheritance?

• Inheritance is the transfer of characteristics

from parents to their offspring, such as hair,

eye, and skin colour.

• Inheritance is the transfer of characteristics

from parents to their offspring, such as hair,

eye, and skin colour. This explains why your

traits resemble your parents and brother/sister.

involving simple Mendelian genetics? (cont.)

Who was Mendel?

• Gregor Mendel (1822 – 1868) was an Austrian

monk who experimented with pea plants to

determine how seven different, easily observed

traits are inherited:

Who was Mendel?

• Gregor Mendel (1822 – 1868) was an Austrian

monk who experimented with pea plants to

determine how seven different, easily observed

traits are inherited: seed shape and colour, pod

shape and colour, flower colour and location,

and stem length.

What did we learn from Mendel’s experiments?

• He realized that traits are inherited in

predictable phenotype ratios.

• He realized that traits are inherited in predictable

phenotype ratios. The phenotype are traits of

organism observed in its appearance or

behaviour, which is determined by its genes.

• He realized that traits are inherited in predictable

phenotype ratios. The phenotype are traits of

organism observed in its appearance or

behaviour, which is determined by its genes.

• A trait can have different forms if there are

different forms of a gene at the same position of

DNA, which are known as alleles.

• If an organism has the same allele from each

parent, then it is homozygous and is called a

purebred.

• If an organism has the same allele from each

parent, then it is homozygous and is called a

purebred. However, if it has a different allele

from each parent, then it is heterozygous and is

called a hybrid.

• When he crossed a white–flowered plant with a

purple–flowered plant and then crossed two of

these offspring, he observed the following

results.

results.P generation

results.P generation purebred parents

all purple

results.

F1 generation(first falial)

P generation purebred parents

all purple

results.

F1 generation(first falial)

P generation purebred parents

hybrid offspring

all purple

• When he crossed two of these purple–flowered

hybrid offspring from the F1 generation, he

observed the following results.

F1 generation hybrid offspring

¾ purple¼ white

F2 generation(second falial)

¾ purple¼ white

• These results showed that each parent passed on a

single allele to the offspring, such that the seed and

the pollen only carry one allele each, not both.

• These results showed that each parent passed on a

single allele to the offspring, such that the seed and

the pollen only carry one allele each, not both.

• It also showed that each trait is inherited separately

from each other, such that one trait did not affect

how another trait was inherited.

• Finally, it showed that the dominant purple colour

masked or hid the recessive white colour.

• Finally, it showed that the dominant purple colour

masked or hid the recessive white colour. For the

white colour to be observed, the flower must have

two alleles for the white colour, such that is must be

a purebred for this trait.

How can we predict these results?

• We can use a Punnett square to determine

determined the probability, the chances of a

particular outcome.

• To complete a Punnett square, we use a letter to

represent each trait.

represent each trait. We represent the dominant

allele with a capital letter, and the recessive allele is

given the same letter but in lower case.

given the same letter but in lower case. For the pea

plant flowers, the dominant purple colour = P and

the recessive white colour = p.

the recessive white colour = p. If both parents are

pure bred, then purple coloured parent must be PP

and the white coloured parent must be pp.

the recessive white colour = p. If both parents are

pure bred, then purple coloured parent must be PP

and the white coloured parent must be pp. To

predict the results of a cross, we insert the alleles

from each parent into the Punnett square.

We complete the possible combinations.

p Pp Pp

• These results show that all the F1 offspring are all

purple coloured hybrids.

p Pp Pp

• We can use another Punnett square to predict the

the F2 offspring.

P PP Pp

the F2 offspring.

P PP Pp

the F2 offspring.

P PP Pp

p Pp pp

• The F2 offspring consist of:

1 PP: purple coloured

2 Pp: purple coloured

1 pp: white coloured

¾ purple coloured

1 pp: white coloured ¼ white coloured

¾ purple coloured

1 pp: white coloured ¼ white coloured

• The phenotype ratio for this generation is 3:1.

¾ purple coloured

What are the other patterns of inheritance?

A.Incomplete Dominance

What happens when neither allele is dominant?

• If a parent has straight hair and the other parent

has curly hair, then they may have children with

wavy hair, an intermediate phenotype.

• If a parent has straight hair and the other parent

has curly hair, then they may have children with

wavy hair, an intermediate phenotype.

• This occurs when neither allele in a hybrid is

completely are not completely expressed, such

that neither allele can mask the other allele.

B. Codominance

What happens when both alleles are dominant?

B. Codominance

What happens when both alleles are dominant?• Depending upon what alleles you inherited from

each parent, you can have blood type:

A, B, AB, or O.

B. Codominance

What happens when both alleles are dominant?• Depending upon what alleles you inherited from

each parent, you can have blood type:

A, B, AB, or O.• If you inherited an allele for type A from one

parent and an allele for type B from the other

parent, then you would have type AB blood,

such that you are a hybrid expressing both

alleles.

C. Sex Linkage

Are there any traits related to an individuals sex?

C. Sex Linkage

Are there any traits related to an individuals sex?

• Of your 23 pairs of chromosomes, you have one

pair of sex chromosomes.

C. Sex Linkage

Are there any traits related to an individual’s sex?

pair of sex chromosomes. Females have two X

chromosomes, while males have one X and one

Y chromosome.

C. Sex Linkage

Are there any traits related to an individual’s sex?

pair of sex chromosomes. Females have two X

chromosomes, while males have one X and one

Y chromosome.

• Hemophilia is a disease where blood does not

properly clot and caused by a recessive gene on

the X chromosome.

C. Sex Linkage (cont.)

• If a male inherits a defective allele from his

mother, then he will have hemophilia because he

does not have second X chromosome with a

normal allele to mask this defective allele.

C. Sex Linkage (cont.)

• If a male inherits a defective allele from his

mother, then he will have hemophilia because he

does not have second X chromosome with a

normal allele to mask this defective allele.

• Although he will pass this allele onto his

daughter, she can only get this disease if she

inherits a defective gene from her mother.

III. What are factors that may cause mutation

III. What are factors that may cause mutations?

What is a mutation?

• A change in a DNA sequence that occurs

naturally during cell division or results from an

environmental factor.

What environmental factors cause mutations?

A. Chemical:

A. Chemical: Some toxins, such as PCBs

(polychlorinated biphenals), may react

chemically with DNA and cause cancer.

B. Biological:

B. Biological: Some viruses, such as HIV which

causes AIDS, infect host cells by inserting their

DNA in the host’s DNA.

C. Physical:

C. Physical: Radiation, such as UV light from

sunlight or X-rays from a dentist’s office,

directly damages the structure of DNA.

IV. What are the positive, neutral, and negative

effects of various mutations?

A. Positive:

A. Positive: If a mutation improves an organism’s

ability to survive or compete in its environment,

then this is a positive mutation.

A. Positive: If a mutation improves an organism’s

then this is a positive mutation.

For example, a mutation that allows a western

red cedar tree to grow faster may compete better

against other trees for sunlight.

B. Negative:

B. Negative: If a mutation reduces an organism’s

then this is a negative mutation.

B. Negative: If a mutation reduces an organism’s

then this is a negative mutation.

For example, a mutation that impairs a deer’s

vision will make it harder to see food and prey

clearly.

Another example is an albino, who has white

skin and hair.

Another example is an albino, who has white

skin and hair. Albinos cannot produce melanin,

which is the pigment that gives colour to our

skin, hair, and eyes and protects us from

ultraviolet light.

C. Neutral:

C. Neutral: If a mutation does not change an

organism’s ability to survive or compete in its

environment, then this is a neutral mutation.

Most mutations do not affect an organism

because they do not significantly change the

proteins that are made.

Most mutations do not affect an organism

because they do not significantly change the

proteins that are made.

For example, a mutation that turns a rose’s

colour from red to pink would not affect its

function.

The effects of a mutation are not always

obvious.

The effects of a mutation are not always

obvious. While a western red cedar that grows

faster can get more sunlight, it may be more

likely to suffer damage from strong winds.

V. What are the implications of current and emerging biomedical, genetic, and reproductive technologies?

biomedical, genetics, and reproductive technologies

genetic probes

genetic testing

genetic probes

genetic testing

gene therapy

genetic probes

genetic testing

gene therapy

forensic science

genetic probes

genetic testing

gene therapy

forensic science

drug development

genetic probes

genetic testing

gene therapy

forensic science

drug development

drug production

genetic probes

genetic testing

gene therapy

forensic science

drug development

drug production

cloning

genetic probes

genetic testing

gene therapy

forensic science

drug development

drug production

cloning GMOs

V. What are the implications of currentand emerging biomedical, genetic,and reproductive technologies?

What is genomics and how will it affect my life?

CLICK HERE TO FIND OUT

What are some current genetic research projects in BC?

CLICK HERE TO FIND OUT

THE END

Genome British Columbia, 2004 www.genomicseducation.ca

SCIENCE 10 LIFE SCIENCE: GENETICS Genome British Columbia, 2004

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