Nucleic Acids

Nucleic acids are one of the 4 major ________________ found in all living things. A

macromolecule is also known as a ________, which means it is a ______ molecule made

of smaller repeating _______ known as __________. The monomers of nucleic acids

are called _________________.

There are two major classes of nucleic acids:

1) DEOXYRIBONUCLEIC ACID (DNA)

DNA is the chemical basis for the _____, the fundamental unit of ___________ and is

responsible for governing the _________ of the entire cell. DNA is mainly found in the

_________ of cells but is also present in the ______________.

2) RIBONUCLEIC ACID (RNA)

RNA molecules are mainly found in the _________ of cells and perform ___________,

such as acting as structural scaffolds or being chemical messengers. There are a

variety of different forms of RNA including, _____, ______, and ________.

Nucleotides:

A nucleotide consists of three parts:

i) A nitrogenous base

(so called because nitrogen atoms form part of

the rings of the molecule)

There are two types of nitrogenous bases, _______

and _____________.

In DNA, there are two purine bases, ________ and _______ and two pyrimidine bases,

_________ and _________ that are used to make nucleotides.

In RNA, adenine, guanine and cytosine occur, but ______ does not, it is replaced by the

pyrimidine _________.

Pyrimidines

(single ring)

Purines

(double ring)

ii) A 5-carbon sugar (in DNA it is _______________; in RNA it is _________)

iii) A phosphate group

A nucleic acid polymer consists of alternating chains of ______ and ____________,

with a nitrogenous base attached to a deoxyribose (or ribose) sugar. The nucleotide is

held together by __________ bonds that are known as a ______________________.

A molecule of RNA is a ______________ structure that often becomes ______, while

DNA takes on _____________, _____ formation. In DNA, bonds are formed between

nitrogenous base pairs and are held together through ___________ bonding.

The nitrogenous base pairs between the DNA double helix always pair up such that

_________ and _________ are together and _________ and _________ are joined.

Nucleotides are not only important as building blocks of nucleic acids; they also have

important functions in their own right. Most of the energy being put to use at any given

moment in any living organism is derived from the nucleotide ____________________

(ATP).

Deciphering the Genetic Code

Genes and Chromosomes

The ___ is the major functional sub-unit of DNA. Genes are specific sequences of

____ that have the potential to be ____________ and to ________ an organism’s

_________. We often think of genes as the portion of ___________ information that

defines one particular trait of an organism’s physical characteristics.

The sum of the entire _____ including all of the ______ ( _______ - _______ )

within a cell is referred to as the __________.

The specific _______, _____ and _________ of genes are unique to each species, but

even organisms that are only

______________ may carry very

similar genes.

In humans genes are organized

onto ______________. Each

chromosome contains linear

double-stranded molecules. DNA

molecules are held together with

________ called _________. A

chromosome is actually ___

protein, ___ DNA, ___ RNA.

Genes are __________________

along chromosomes. The density of

genes can vary from one

chromosome to another. For

example, in humans:

Chromosome 4 –

Chromosome 19 –

There is no set relationship between the number of genes on a chromosome and the total length of the chromosome

Central Dogma

DNA provides the information that ultimately codes for a specific _______ to be

produced. This is a two-step process of __________, followed by ___________.

Transcription is a process that occurs

within the _______, where the

information from one gene is used as a

________ to produce a

_____________ strand of ____

nucleotides (mRNA) that is then

moved into the ____________.

Translation is the process where the mRNA

transcript is used to generate a sequence of

_________, which will eventually fold into a three-

dimensional structure and become an active protein.

This process occurs in the _________ of cells and

requires a number of ____________________

(_____ and _____).

Information for the genetic code is read as a series

of _____ consecutive _____ or _____. Each codon

ultimately corresponds to a specific _________

that will be added to a growing ______________

chain.

Mutations

A mutation is any type of _______ genetic

change. There are several types of mutations,

some which go _______; others are

_________, while others still may have

serious, ________________ effects.

The following are common mutations that can

occur during replication:

Base Substitution

A different ___________ is substituted.

Examples:

Silent -

Mis-sense –

Non-sense -

Frameshift mutation

Addition or deletion of a _________ can

throw _______________ off

Example:

SEETHEREDCATANDTHEFATDOG

SEEHEREDCATANDTHEFATDOG

Even without exposure to ________, each of

your genes undergoes _________ of

mutations during your life; most of these are

corrected by ___________________.

Cell Division

You are made up of approximately ___________ cells. This is amazing considering that all these cells started from one fertilized egg. Even now cells are dividing in your body! Cell division is needed for:

1. Growth -

2. Repair -

3. Reproduction –

How does cell division occur?

Cell division occurs in three stages:

1. Replication –

The replication process must be relatively ______ and it must be

______ for cells to survive. Remarkably, cells are able to duplicate

their DNA in a few _____, with an error rate of approximately ___ per

___________ nucleotide pair!

2. Mitosis -

3. Cytokinesis -

The end result of these stages are __________________________ from

one original cell.

In order to describe the events of the cell cycle, the process has been

divided into several phases:

INTERPHASE:

The cell is doing its ______

_____ in the form of ___________ –

cannot be seen

Cell __________

At the end of interphase the DNA has

______________

PROPHASE:

_________________ disappears

_____________ disappears

DNA __________ and __________ and

becomes visible - ____________

_____________ form and can be seen

_____________ move apart

METAPHASE:

Chromosomes line up at _______ of cell

Centrioles are located at _______

Spindle fibres attach to ____________ and

centrioles

ANAPHASE:

Centromeres _______ and single-

stranded ___________ move to

opposite poles

Pulled by spindle fibres

TELOPHASE:

Opposite of ___________

_______________ reappears

___________ reappears

_______________ disappears

Chromatid become ______ and

_________ and cannot be seen

(____________)

FINAL RESULT OF CELL DIVISION:

___________ occurs (division of

cytoplasm)

Two _____________________

_______________ cells

Meiosis

Different characteristics are displayed by different people. This variation in

characteristics is shown because each person comes from a different family. Even

within a family there are differences.

Each human cell has __ chromosomes in total or _______ of chromosomes. Each pair of

chromosomes resembles each other in ____, _____ and ___________________. You

receive one member of each pair from your ______ and the other from your _______.

These pairs of chromosomes are called ___________________________. Your genes

are located on these chromosomes.

Meiosis is the process by which a ________ cell (2n) produces ________ (n) gametes

or sex cells.

Meiosis occurs only in the _______________ of most living things:

Spermatogenesis =

Oogenesis =

Plants =

Meiosis Terminology

Diploid

Two sets of _________________ (2n)

Body cells (___________) are diploid cells

Human cells have ___ chromosomes or 2 sets (2n) of ___ chromosomes

Haploid

Single set of ________________ (n)

Sperm or egg (___________) are haploid cells

Human sex cells have ___ chromosomes

Homologous chromosomes (homologues)

Two chromosomes similar in ______ and ______ that carry the _____ genetic

information

Inherit one chromosome from each __________

Zygote

The cell that results when an ______ and a _______ unite (_________________)

Synapsis

The pairing of ______________ chromosomes

Occurs in ______________ of meiosis

Tetrad

Two homologous chromosomes form a loose connection of __________________

Crossing over

The process where the ends of chromosomes (adjacent) become _______ or

_______ together and ______________

The ends of the homologous chromosomes may _________ or ____________

places

Explains why all offspring will be ______________ (except identical twins)

Non-disjunction

During meiosis one chromosome does not get _________ to the proper end of the

cell

One cell may get ____________ chromosomes and others too few

Stages of Meiosis (Interphase occurred first)

Phase Diagram Key events

Prophase I

Same as prophase of mitosis

___________________ and

____________ disappear

____________ become visible

(previously _____________)

______________ appear

_______ occurs as homologous

chromosomes pair up

The ___________ of

information occurs in a process

called ________________

Metaphase I

__________ line up at the

______________ of the cell

Chromosomes align randomly

and differently each time

through meiosis (law of

______________________)

Anaphase I

Tetrads ________ and double

stranded chromosomes move to

the _______ of the cell

Telophase I

Two cells forming, with __ the

number of chromosomes

Each strand is ___________

because of crossing over

Chromosomes still must be

separated into single stranded

chromatid

Prophase II

Same as mitosis prophase

Metaphase II

Double stranded chromosomes

line up at the ___________

Same as mitosis metaphase

Anaphase II

Double stranded

chromosomes _______

into single stranded

_____________

Same as mitosis

anaphase

Telophase II

Four cells with the

___________ number

of chromosomes

Each cell is genetically

different from each

other and different

every time meiosis

occurs

Mendelian Genetics

Early Ideas About Genetics

Aristotle (384-322 BC) Pangenesis - every part of the body was involved in the production of the “seeds” of the

parents; seeds fused to give rise to a new individual.

Anton van Leeuwenhoek (1632-1723) The idea of an “animalcules” in the semen of males – a tiny preformed embryo.

19th Century

Blending theory of inheritance

Charles Darwin Offspring had variations of their parent's characteristics; but he could not explain why.

Gregor Mendel (1822-1884) Developed the fundamental principles that became the modern science of genetics.

Mendel’s Experiments

Gregor Mendel was a monk, whose studies included mathematics and botany. He

conducted a series of experiments on pea plants over an eight-year period.

Mendel used ____ bred (or _____ breeding) pea plants for his experiments, which are

plants that produced ________________________ (Example - tall or short).

Mendel actually studied ________ different traits, each trait that had only ____

possible variations. Mendel obtained pure bred plants through ______________.

Useful terminology:

P generation =

F1 generation =

F2 generation =

Mendel bred pure breeding tall plants with

pure breeding short plants.

All of the offspring were tall. The tall pea

plants were then crossed with each other.

The resulting offspring showed a 3:1 ratio of

tall plants to short plants.

These results led Mendel to conclude that

the trait for ______ plants must be

_______ and the trait for _______ plants to be _______. When both a dominant and

a recessive trait are present, only the __________ one will _________ itself.

Mendel conducted theses experiments many times, using the seven different traits. For

each test, he obtained the same results.

In addition, Mendel came up with the ______________________:

i) The inherited traits (or ______) are determined by pairs of ‘factors’ or ______.

ii) The alleles segregate (or _______) in the formation of ______ (eggs or sperm)

iii) The alleles are ___________ – one from each parent.

Using the information obtained from Mendel’s experiments, we can look at his experiments again from the point of view that every trait is associated with a different allele. Symbols are assigned to the alleles. Capital letters for dominant traits and lower case for recessive. Examples: T = tall and t = short

The _________ are the alleles for a particular trait. The _______________ is how the alleles physically manifest themselves. Genotypes can be either homozygous or heterozygous. __________ means that both of the alleles are the _______ (TT or tt). ____________ means the two alleles are ___________ (Tt).

Punnett Squares

Comparing one trait at a time in breeding experiment is referred to as a monohybrid

cross. The results can be organized in a Punnett square; a way of calculating the

probability of inheriting a particular trait. It is a simple method of illustrating all

possible combinations of gametes from a given set of parents.

Examples:

In guinea pigs, black fur is dominant to white fur. What would the F2 generation look

like if you started with a male homozygous for white fur and a female homozygous for

black fur?

Cross a white furred male with a female from the F1 generation.

Test Cross A test cross is a type of breeding experiment that can be used if the _____________

of an organism is _________, but the _____________ is _____________.

The test cross is always performed between the organism with an unknown genotype

(that carries a dominant allele – __________________ or ____________________)

and an organism that has a _________________________ genotype.

A test cross would NOT be employed to determine human genotypes.

Sample Problem:

Having blue flowers is dominant (B) is a dominant characteristic to the recessive trait of

having pink flowers (b). By performing a test cross with an plant of unknown genotype

that has blue flowers, determine the possible outcomes that could result.

When performing a test cross there are only two possible outcomes that can occur:

1. _____ offspring will appear to have the _____________ trait. This would suggest

that the unknown organism has a genotype that is _________________________.

2. _______ the offspring would have the ___________ trait and ______ would have

the _____________ trait. This would suggest that the unknown organism has a

genotype that must be ___________________.

Test crosses have proven to be a useful tool in the process of ___________________.

Selective breeding is the crossing of ____________ traits from plants or animals to

produce _______________ that have one or several of the desired characteristics.

Selective breeding commonly employs the techniques of either ______________ or

_______________.

______________ is the mating of ___________________ to produce offspring with

desirable characteristics of _______ parents.

______________ is the process by which mating occurs between

____________________ for the purpose of _________________________ certain

characteristics. Inbreeding can often result in

____________________________________ manifesting themselves.

Practice Questions

If you are given a dominant round (R) seed pea plant and you need to know the genotype

of this plant, you need to do a test cross. What pea plant genotype would you cross this

mystery dominant plant with?

In doing this cross, you find that the offspring are all round. What does this indicate

about the mystery parent genotype?

In doing this cross, you find that the offspring show a 1:1 ratio of round:wrinkled. What

does this indicate about the mystery parent genotype?

In corn, the allele for purple kernels is dominant to the alleles for yellow kernels.

Determine the likely genotypes of the parents if the offspring that results from

pollination produce 47 purple kernel producing plants and 14 yellow kernel producing

plants.

This idea of using the phenotypes of offspring to predict the genotypes of parents is

employed when studying human inheritance patterns. This is called _______________.

Pedigree Analysis

Pedigree chart:

From the point of view of individual III - 1, the symbols represent the following relationships:

I - 1 = I - 2 =

II - 1 and II - 2 = II - 3 = II - 4 = II - 5 =

III - 2 = III - 3 =

Practice Problem #1

The following Pedigree shows a family with the trait of shortsightedness. The allele for

shortsightedness (E) is dominant to the allele for normal vision (e). Predict the genotypes for

each individual in the family.

Practice Problem #2

Phenylketonuria (PKU) is a genetic disorder caused by a dominant allele. People with PKU are

unable to metabolize a naturally occurring amino acid, phenylalanine. If phenylalanine

accumulates it inhibits the development of the nervous system, leading to mental retardation.

The symptoms of PKU are not evident at birth, but can develop quickly if the child is not placed

on a special diet. The pedigree chart below shows the inheritance of the defective allele in one

family.

a) How many generations are shown in the pedigree?

b) How many children were born to the parents of the first generation?

c) What are the genotypes of individuals 1 and 2 in generation I?

d) How is it possible that in generation II, some of the children showed symptoms of PKU,

while others did not?

e) Individuals 6 and 7 in generation II had a child without PKU. Does this mean that they

can never have a child with PKU? Explain your answer.

Incomplete Dominance and Codominance

Not all alleles interact under the principle of dominance and recessive. Incomplete

dominance is when both alleles contribute _________ to the ___________ of the

organism, creating a ____________ in a ______________ genotype.

Example:

In four o'clock flowers, red flowers (CR) is incompletely dominant to white (CW). The

heterozygous plants (CRCW) are pink in colour. What are the possibilities for the F2

generation starting with a cross between a red and white flower?

Codominance: Two dominant alleles are expressed at the _______. ________.

Example:

In cattle, red hide colour (R) is codominant to white (W). Cows that are heterozygous

for this trait have a roan hide colour (RW), where the red hair and white hair both

appear on the animal.

Cross two roan cows and determine the chance of getting a white animal.

Sometimes it is a benefit for an individual to inherit two different alleles for the same

trait. This is called ____________________. An example is a person who is

heterozygous for the sickle cell gene; they have some normal red blood cells and are

resistant to ____________.

Dihybrid Crosses 1. What is the frequency of tossing one dice and having it roll the number one?

2. What is the frequency of tossing two dice and having both roll one?

3. What is the frequency of tossing a Yahtzee! Five dice that all roll the number one?

The above examples illustrate that the result of one toss of the dice has no affect on

the outcome of future rolls, that is, one’s dice action is segregated from the others and

independent.

In his studies Gregor Mendel discovered that like the dice, alleles assort independently

from each other. Mendel termed this, ____________________________________.

The law states that:

This simply means that the inheritance of alleles for one characteristic does not affect

the inheritance of alleles for another characteristic (as long as the alleles are on

different chromosomes).

Example:

Whether a human has attached or free earlobes has no effect upon whether or not

their hair is curly or straight. The characteristics are independent from one another.

Mendel came up with the idea for the law of independent assortment while studying the

inheritance of __________________ in crossbreeding (following the same procedures

he had used for studying single traits). This kind of approach is called a ___________

___________.

There are two approaches we can take to determine the probability for each of the

possible outcomes to occur in a dihybrid cross.

Approach #1

You can solve a dihybrid problem by completing two separate monohybrid crosses, one

for each of the characteristics being examined. Then the crosses can be combined to

calculate the probabilities of the dihybrid crosses.

Example:

In garden pea plants the pod colour green (G) is dominant over the recessive allele

yellow (g); while round seed shape (R) is dominant over wrinkled (r). Following mating

between parents with the genotypes GgRr x GgRr, what are the probabilities of

obtaining offspring with the following characteristics:

Green pods and round seeds

Yellow pods and round seeds

Green pods and wrinkled seeds

Yellow pods and wrinkled seeds

Pod Colour Probability Seed Shape Probability Combined

Probability

Green Round

Yellow Round

Green Wrinkled

Yellow Wrinkled

Approach #2

The alternative method to solving dihybrid problems has you come up with all the

possible combinations of alleles that can occur during a cross, and then completing a

giant Punnett square. The first step is to identify the complete genotype of each

organism in the cross (this will include 4 alleles, two for each trait being examined).

Using the previous example of green (G) and yellow (g) pea pods and round (R) and

wrinkled (r) pea seeds :

What is the probability of obtaining a green and wrinkled peas?

Predict the chance of a yellow and round pea from the following parents:

ggRr x Ggrr

Multiple Alleles

Many traits in humans and other species are the result of the inheritance of more than

two alleles for one gene. A gene with more than two alleles is said to have

________________________.

Blood Types In humans a single gene determines a person's ABO blood type. This gene determines

what type of an __________, if any, is attached to the cell membrane of red blood

cells. An antigen protein is a molecule that stimulates the body's __________. The

gene is designated "__" and it has three common alleles: __, __ and __. The different

combinations of the three alleles produce the four different phenotypes of blood.

A & B are dominant to O. A & B are codominant. The possible genotypes for blood typing

are:

IAIA - IBIB -

IAi - IBi -

IAIB - ii -

Examples:

A man with hybrid type A blood and a woman with type AB blood wish to know the

possible blood types for their children.

A rich couple are confronted by a man who claims to be the man's son from a previous

marriage. The son's blood type is "O" and both the man and his ex-wife are hybrid type

A. What is the probability that the young man is telling the truth?

Rh Factor

In addition to the substances that cause A, B, and O blood types there is another

factor called the Rh factor that can be found in blood. The genes for having the Rh

factor are completely dominant to the genes for not having the Rh factor.

For example: Let: R - have the Rh factor

r - absence of the Rh factor

Therefore, RR and Rr produce people that are Rh positive & rr only produce an Rh

negative individual.

What are the possibilities for a man that is pure type B and pure Rh positive with a

woman who is hybrid A and Rh negative?

In addition to the many traits being controlled by one gene with multiple alleles, there

are also many traits that are ________, which means they are controlled by

___________ gene. Examples of polygenic traits include, height, skin colour and eye

colour. These traits tend to exhibit _________________ in which the phenotype

varies gradually from one extreme to another.

Sex Linkage

Linked genes are genes that are on the _________________ and that tend to be

_________________. These genes DO NOT exhibit Mendel's law of independent

assortment and therefore do not follow the Mendelian inheritance patterns that have

been previously discussed.

Sex Determination

Human cells contain __ chromosomes (__ pairs). The first __ pairs are referred to as

________; these chromosomes carry the _________________. Your 23rd pair of

chromosomes are called your _____ chromosomes; these are the ones that determines

your sex, but they also carry ___________________. Males have one X and one Y

chromosome (XY), while females have two X chromosomes (XX).

Sex Linkage

Thomas Hunt Morgan (1866-1945) was an American geneticist who worked with fruit

flies (Drosophila melanogaster) and developed theories on ___________ and

___________________.

Fruit flies are an ideal subject for study in genetics because:

They reproduce rapidly

Offspring can mate shortly after leaving the egg

Females produce over 100 eggs each mating

You can study many generations in a short period of time

They are small – can be housed in a single culture tube

Males can be easily distinguished from females.

Morgan’s Experiment

Morgan explained his experiments by concluding that the X and Y chromosomes contain

different genes, and that in his fruit flies, the Y chromosome does not carry the gene

to determine eye colour.

Morgan called characteristics that are controlled by genes located on the sex

chromosomes as _______________________.

In humans there are numerous sex-linked traits:

Males and females produce the same amount of ______ coded by _______ located on

the X chromosome. However, females have two copies of this chromosome while males

only have one. Experiments have shown that one of the X chromosomes in each female

cell is __________. Which one is inactivated is ____________, and therefore

different X chromosomes are active in different cells. The inactivated X chromosome

is called a __________________.

Sex-Linked Problems

What are the possible offspring for a cross between a normal female and a colour-blind

male?

Let: X - Normal gene for colour-vision male

Xc - Recessive gene for colour-blindness

In humans, baldness is sex-linked and recessive to normal amount of hair. For hair

colour, black is incompletely dominant to blonde, heterozygous have brown hair colour.

Show the possible offspring for a man who is bald and had brown hair and a woman who

is blonde and a carrier for baldness.