DNA and Genetics

Dr André van Wyk

UFS

Somatic cells

•Cells of the “Soma”= Body cells

•Complete number of chromosomes = 2n

•Diploid

4638

48

Somatic cells

•Cells of the “Soma”= Body cells

•Complete number of chromosomes =

•Diploid

2n2n

2n

2n

Growth = 2n – 2n

Mitosis

Mitosis:

2n = 2n

or n – n

this correct?

n

n

n

mitosis

Sex cells = Half of the chromosome number = n

= haploid cells

Reduction of the chromosome number – a must for the survival of the species

n2n

2n

2n

2n – n

Meiosis

n + n = 2n

Haploid + Haploid = DiploidFERTILISATION

The importance of Meiosis:

• The process of meiosis reduces the number of chromosomes by half. • Meiosis is the process through which somatic cells (2n) are changed into sex cells (n).• Meiosis ensures that the number of chromosomes in the species stays the same over generations• Meiosis is important to introduce genetic variation.

http://www.cellsalive.com/cell_cycle.htm

http://www.cellsalive.com/mitosis.htm

DNA –Position in the cell

Nucleus

DNA double helix

Chromosomes

• In each chromosome, the DNA is grouped into "genes." • Your genome contains about 35,000 genes.

In the nucleus of almost every cell in your body is the collection of DNA needed to make you.

DNA in the nucleus is grouped into 23 sets (pairs) of chromosomes that are called your "genome."

• Instructions is called genetic code• The DNA in your genes tells the cell which amino acids (protein building blocks) must combine to make a protein. It also gives instructions in which sequence the amino acids must combine.

• Thus, DNA provides the blueprint of all life in a living body.• Let us investigate how that this happens.

Instructions to make your whole body and keep it working is contained in DNA

DNA STRUCTURE

• DNA molecule – double helix (ladder)• String of repeating molecules units called

nucleotides• Each nucleotide consist out of - Deoxyribose sugar - One phosphate group - One nitrogen containing base (A,G,C and T)• Adenine and Guanine – purine bases• Thymine and Cytosine – pyrimidine

bases

Remember

Did you know : The total length of DNA in mammal cells is 2 metres – in your body 10 billion km

Structure of DNA

T A

G C

Phosphate

Deoxyribose Sugar

Britannica video

It's hard to believe that an alphabet with only four letters can make something as wonderful and complex as a person

DNA Replication

• With cell division -chromosome split in two (mitoses and meiosis )

• DNA must divide • DNA must make exact copies of itself• DNA molecule – unzip• New bases attached themselves in correct place of

each strand• Each strand becomes a double helix• Sometimes mistakes happens – mutation• Mutations is important in evolution

DNA Replication

Unzip into two single strands

DNA replication continue

New bases attached themselves in the correct place of each strand

Free nucleotides in nucleoplasm

Two identical strands are formed

Each strand now becomes a double helix.

Strand 1 Strand 2

Activity 1

• DNA structure and DNA replication• Group work.

– Instructions

- Use the package marked “DNA” and place the pieces together in order to:

• Know the structure of DNA• Use the pieces and demonstrate the DNA

replication process.

Significance of DNA replication:

• Important for growth, reproduction • Mutations can cause variation• The main enzyme that catalyze the process is

DNA polymerases • Forms building block for amino acids that forms

proteins• Three bases provides more than the 20

combinations needed to code amino acids (p23)• The sequence of the three bases is called a

codon.

Activity 2:Extraction of DNA (LO1)

Instructions : Use Worksheet 1

•Step 1

Place ½ teaspoon of ground wheat in a spice jar. Add 10 teaspoons of tap water to the ground wheat and mix non-stop with a wooden stick for 3 minutes

•Step 2

Add ¼ teaspoon of dishwashing liquid to the cells that have been suspended in water in step 1. Mix gently with a wooden stick every ½ minutes for 5 minutes.

Step 3• Remove all foam that may have formed on top

of the mixture with a paper towel.

Step 4• Tilt the jar and slowly add an estimated equal

volume of methylated spirit to the mixture and carefully pouring it down the side of the jar.

Step 5• Use the wooden sticks to fish these “white slimy

threads” out of the spice jar and transfer it to a 10ml pill vial.

Rubric

Assessment of DNA

• Draw and label a diagram of DNA (LO1:AS2)

(manipulate data)

• Make a model of DNA – (LO1:AS3)

( Communicate data/findings)

• Extraction of DNA out of wheat (LO1:AS2)• http://rubistar.4teachers.org (example rubric 1)

1. Identify the above molecule.2. Give labels for parts numbered 1to 53. Describe how the above molecule replicates itself.4. Why is it of significance that this molecule can replicate itself?

Questions on the DNA Molecule

1

2

3

4

5

G

T

• Diabetics need insulin to live

• Diabetes use insulin from pigs and cattle. This is not the same as human insulin and sometimes produces side effects. With genetic engineering, bacteria are used to produce some human insulin

Bacterial DNA - Manufacturing of insulin

1. A string of DNA is taken from a bacterium

2. A piece is cut out using enzymes as ‘chemical scissors’

3. A cell is taken from a human pancreas. The gene for insulin is cut from the chromosome

4. The insulin gene is put into the string of bacteria DNA

5. The bacteria reproduce, making

clones of themselves

6. The insulin is collected and purified ready for use

Structure of RNA

• Single strand

• Sugar is ribose

• Four nitrogen bases

Adenine and Uracil

Guanine and Cytosine

U

G

C

A

Assessment : Make a stick drawing of RNA

Assessment:Tabulate the Differences between DNA and RNA

DNA RNADouble strand Single strand

Deoxyribose sugar Ribose sugar

Thymine and Adenine Thymine and Uracil

Nucleoplasm Nucleoplasm and cytoplasm

Three types of RNA and their functions

1. Messenger RNA (mRNA) which acts as a template for protein synthesis and has the same sequence of bases as the DNA strand that has the gene sequence.

1. Messenger RNA (mRNA)2. Transfer RNA (tRNA)3. Ribosomal RNA (rRNA)

2. Transfer RNA (tRNA), one for each triplet codon that codes for a pecific amino-acid (the building blocks of proteins). tRNA molecules are covalently attached to the corresponding amino-acid at one end, and at the other end they have a triplet sequence (called the anti-codon) that is complementary to the triplet codon on the mRNA.

3. Ribosomal RNA (rRNA) which make up an integral part of the ribosome, the protein synthesis machinery in the cell.

RNA Transcription

• DNA is the template

• DNA manufactures mRNA in nucleus

• Transported out from the DNA of nucleus

into the cytoplasm

• Transcription similar to DNA replication

U

G

C

A

G

U

C

A

mRNA structureRNA bases pairing

TRANSCRIPTION

Crystal structure of tRNA molecules.

AnticodonC C G

G G C

tRNA

mRNA`

CodonmRNA

The single-stranded chain is folded in a 'clover-leaf’

DNA unzip to expose a gene

mRNA copies the gene

mRNA moves to ribosome r RNA

tRNA carries amino acid to ribosome

Amino acids linked up to form protein molecule

The process of translation and protein synthesis

TRANSLATIONTRANSCRIPTION

Protein synthesis in the cell

Free amino acids

tRNA brings amino acid to ribosome

Ribosome incorporating amino acid in protein chain

mRNA being translated

Assessment of RNA (LO2)1. Describe the role of DNA and RNA in the following

1.1 Formation of mRNA by transcription

1.2 Movement of mRNA from the nucleus to cytoplasm

1.3 Translation of mRNA (codon) to form protein using tRNA (anticodon)

2. Determine the sequence of bases in mRNA from DNA molecule.

GTA ATG TGG TTT

3. Give the mRNA sequence that matched the anticodons of the tRNA

PROLINE

G C U

Activity 2

• Transcription and translation.

• Group work.– Instructions

- Use the package marked “Protein synthesis” and imitate the processes of transcription and translation with the pieces in the pack.

Protein synthesis (assessment)

2

5

3

6

1.

4

7

1. Give labels for number 1 to 7

2. Describe the processes that occur at numbers 2,3,5

Part 2 Chromosomes, meiosis and

sex cells

Mitoses

• Revision:• Group work: • Using the clay provided and build a model

of the process of mitoses. The clay must represent the chromosomes.

• Cut pieces of paper to represents the cell structures/stages.

• Especially pay attention to the structure of the chromosomes.

Mitoses

Meiosis

First meiotic division

Prophase 1

Anaphase 1:

Metaphase 1

Two daughter cells

Meiosis IInterphase: Duplication of each chromosome

Prophase I: Paring of homologous Chromosomes - chiasmata – crossing over

Metaphase I: Organisation of two tetrads in the equatorial plane

Anaphase I: Separation of homologous chromosomes

Completion of Meiotic division:Two daughter cells each with two dyads

Crossing over

Significance of crossing over:

Genetic material is exchanged – cause variation

Second meiotic division

Metaphase II

Anaphase II

Four haploid cells, each with two chromosomes known as reproductive cells. (ovum or sperm)

Metaphase II: Each daughter cell from the previous division has two dyads

Second meiotic division

Anaphase II:–Mitotic separation of chromatids of each chromosome

Completion of second meiotic division – four haploid cells, each with two chromosomes known as reproductive cells. (ovum or sperm)

Sex cells

Sperm and Ovum

Activity 3 (LO1)

Each group use the clay and build the process of meiosis

The importance of Meiosis:

• The process of meiosis reduces the number of chromosomes by half• One cell divides into four cells with each the haploid (n) number of chromosomes• The first meiotic division reduces the number of chromosomes• The second meiotic division is actually mitosis which increases the number of cells• Meiosis is the process through which gametes are prepared for fertilisation.• Meiosis ensures that the number of chromosomes in the species stays the same over generations• Meiosis is important to introduce genetic variation.

Assessment

• Use diagrams to identify the different phases • Use one word to describe the paired

chromosomes• What would the chromosome number in each

cell be at the end of meiosis? • Describe the importance of crossing over• Describe the importance of meiosis• Explain why the four cells at the end of meiosis

is not identical

Chromosomes

(p43)

Chromosomes

Homologous pair

Karyogram and karyotype

• Diagram of arrangement of chromosomes

• Chromosomes are paired according to size

• Arrangement is called karyogram

• Set of chromosomes is called a karyotype

• Human karyogram shows the 23 pairs of chromosomes

• Chromosome set 23 indicate the sex of the individual

Karyogram

Normal Male Normal Female

Down syndrome• Down's syndrome is caused by the presence of three copies of the 21st chromosome.• This chromosomal defect is known as Trisomy-21.• Down's syndrome almost always results in mental retardation, though the severity of the retardation varies.

Characteristics of Down syndrome

Small, oblique eyes

Flattened, nasal bridge

Open mouth Protruding tongue Broad neck

Small underdeveloped ears set low on head

Epicanthic fold

Incurved finger

Single palmar (“simian”) crease

Short broad hands

Wide gap between first and second toe

Assessment

• Identify on the karyogram if the individual is female or male?

• Does this individual has an abnormal number of chromosomes?

• Name the genetic disease that the individual suffer from.

Assessment (LO1)Use the table below and draw a graph to show the relation of maternal age to Down syndrome

Relation of Maternal Age to Down Syndrome

Mother’s age (Years)

Risk of Occurrence

20 - 29 1 in 2 000

30 - 34 1 in 750

40 - 44 1 in 100

45 - 49 1 in 40

This is a rare condition of premature ageing that begins in childhood or early adult life and leads to death within a few years

Hutchinson-Gilford progeria syndrome

Albinism

A person or animal whose melanocytes in the skin do not contain any melanin (pigment) is called an albino. This results in a characteristic appearance with snow-white hair, pink or blue eyes, and pinkish-white skin that is very sensitive to sunlight

♂Carrier A a

♀Carrier A a

½ A ½ a ½ A ½ a

¼ AA ¼ Aa ¼ aA ¼ aa

carriers ½

normal phenotype ¾

albino

Albinism is inherited

Part 3Genetics

Genetics is the scientific study of how physical, biochemical, and behavioural traits are transmitted from parents to their offspring

Terminology• Genes - small portions of DNA and protein• Alleles - genes controlling same characteristic example eye

colour• Haploid – half the number of chromosomes• Diploid – full set of chromosomes• Somatic/body cells (containing genes in pairs)• Sex cells/gametes (containing unpaired genes)• Homozygous – has similar genes for specific characteristic• Heterozygous- unlike genes for a specific characteristic• Human genome - the entire genetic blueprint of a human

beings

Father of Genetics

Gregor Mendeldeveloped the principles of heredity while studying seven pairs of inherited characteristics in pea plants. Although the significance of his work was not recognized during his lifetime, it has become the basis for the present-day field of genetics.

Father of Genetics

Mendel – Monohybrid crosses

Stamen -male

Carpel female

Smooth or dented seeds

Green or yellow seeds

Green or yellow pods

White or purple flowers

P1

F1

Parents

Generation 1

YY yy

Yy Yyx

Generation 2

F2

Punnet square

Yy

YY Yy

yy

Father of GeneticsGenetics: Assessment

Female

Male

Punnet Y Y

y Yy Yy

y Yy Yy

Question: Determines the Genotype and the Phenotype, by means of a Punnet diagramme, the F1 and F2 generations when a homozygote yellow coloured plant (Dominant - Y) is crossed with a white one Resssive - y).

male female

P1 zygotes: YY x yy

Meiosis

Gametes: Y Y y y

Fertilisation:

F1: Genotype = Heterozygous 100% Yy

Phenotype = 100% Yellow

F2 generation: male female

female

male

Punnet Y y

Y YY Yy

y Yy yy

P2 zygotes: Yy x Yy

Meiosis

Gametes: Y y Y y

Fertilisation:

F2: Genotype = Homozygous 25% YY

Heterozygous 50% Yy

Homozygous 25% yy

Phenotype = 75% Yellow

25% White

Assessment (LO1)100%

50%

25%

B100%

50%

25%

A 100%

50%

25%

C

Bb bb Bb bb BB

The following histograms represent the percentage of various genotypes that occur in the F1 generation in several monohybrid crosses. For each, predict the genotypes of the parents (P1).

Inheritance and variation

Father

Off spring

Mother

Human traits

Lobed ears

Dark wavy hair

Brown eyes

Straight nose

Projecting chin

Dominant traits

Blue eyes

Blond straight hair

Upturned nose

Receding chin

Unlobed ears

Recessive traits

Inherited traitsBent little finger

Widow’s peak

Dimples

Rolled tongue

Earlobes: Free and Attached

Hitch-hiker’s thumb Mid-digit hair

Activity 4

• Complete the tabel on human traits in your group

• Study the project handed out to you

• Discuss in your group how this project covers LO1, LO2 and LO3 (SAG)

• How can this project help you with assessment.

Sex determination

XX = girl XY = boy

Is it a boy or a girl?

Hallo here am I

Blood types

• The method of classifying human blood on the basis of the inherited properties of red blood cells (erythrocytes) as determined by their possession or lack of the so-called antigens A and B.

• Thus, persons may have type A, type B, type O, or type AB blood. The A, B, and O blood groups were first identified by the Austrian immunologist Karl Landsteiner in 1901.

Blood – multiple alleles

• Four phenotypes A,B,AB and O• Are determined by presence of two out of three

possible alleles namely A,B and O

Phenotype Possible genotype

A AA, AO

B BB, BO

AB AB

O OO

Assessment

In the TV series Days of Our Lives, two good friends, namely, Hope and Lexie each gave birth to a son. These babies were deliberately switched in the hospital. From the following blood types, determine which baby belongs to which parents:

Baby 1 : Type OBaby 2 : Type A

Hope : Type BHope’s Husband : Type AB

Lexie : Type BLexie’s Husband : Type B

Human Pedigrees (p73)

Shows the line of ancestors: the line of ancestors of an individual animal or person.

• Used to trace diseases like Haemophilia, Muscular dystrophy, Cystic fibrosis

Haemophilia

Affected male

Female carrier

•Discuss whether insurance companies should have the right to refuse cover for a child if prenatal tests results indicate that the child will suffer a severe genetic disorder?

•Using the technology available today, suppose that you could learn with certainty, that by the age of 60 you would suffer from a genetic disease. Would you like to know?

• Makae and Sipho want to marry. Show, in a family tree form, all the possible genotypes of a child they intend to have. (Gg xGg) gg = cystic fibrosis.

Assessment of LO 3 – Ethical dilemmas

Genetic counseling

• Genetic counseling, a process where information and advice is given about inherited disorders. Often it is given to a couple who are planning to have a child but who suspect that there is a greater than normal risk of the child being affected by a genetic disorder

Genetic modification

•In genetic modification, scientists use restriction enzymes to isolate a segment of DNA that contains a particular gene of interest (1).

•In this instance, it is a human gene. A plasmid extracted from its bacteria and treated with the same restriction enzyme can hybridize with this fragment’s “sticky” ends of complementary DNA (2).

•The hybrid plasmid is reincorporated into the bacterial cell, where it replicates as part of the cell’s DNA (3).

• A large number of daughter cells can be cultured and studied, and their gene products may be extracted for further use (4).

Examples of Genetic modification

A scorpion venom gene, engineered into a virus, is used as a spray to kill insects

Poultry with modified genes are resistant to salmonella food poisoning bacteria, and lay bigger eggs more often

Genetically modified pigs grow faster, have less fat, and produced cholesterol-free meat

Salmon eggs have genes inserted into them which make them grow ten times faster than normal

Assessment (LO3)

These tomatoes have been given genes from fish which make them frost resistant and fresh for longer. Would you eat them?

Do a survey on the following two questions:

Do people know what genetic modified foods are?

Will they eat genetically modified food?

Design a questionnaire

Use two groups of people

• Group 1: 15 - 30

• Group 2: 30 – 50 years old

Draw bar graph on the results obtained in the two questions – plot both sets of data on the same graph

Draw a Pie chart with the results

Write down a hypothesis for your investigation

Write down your independent and dependant factors

Write down your conclusion for this investigation

LO1 assessment

Extinct zebra

Tracy

Etienne

Interbreeding

• Baby of the thought extinct zebra is in the Cape museum since 1858 – stuffed by taxidermist

• Later Mr Rau curator of the museum decided to send it to be re-stuffed

• They discovered some muscle tissue left on the inside of the skin

• DNA testing show this zebra is related to Equus burchelli (still alive today)

• Special inbreeding programme was started and today we have back the original species

The story of the extinct zebra