TOPIC 4: GENETICS

4.1: Chromosomes, genes, alleles and mutations

4.1.1 Eukaryotic chromosomeSTATE: Eukaryotic chromosomes are made of DNA and proteins

4.1.2: GeneDefine gene: A heritable factor that controls a specific characteristic. It is a section of DNA that codes for making one or more polypeptides.

4.1.2: AlleleDefine allele: One specific form of a gene, differing from other alleles by one or a few bases only and occupying the same gene locus as other alleles of the same gene.

4.1.2: GenomeDefine genome: The whole of the genetic information of an organism

4.1.3: Gene MutationDefine mutation: A change in the base sequence of a gene

4.1.4:Sickle cell anaemia

CCU GUG GAG

amino proline VALINE glutamic acid acids

4.1.4:

4.1.4

Explain the causes of sickle-cell anemia. [8] M11/4/BIOLO/HP2/ENG/TZ2/XX

caused by gene mutation;(sickle-cell anemia) due to a base substitution (mutation);changes the code on the DNA;which leads to a change in transcription / change in mRNA;DNA changes from CTC to CAC/GAG toGTG / mRNA changes from GAG to GUG;(accept DNA changes from CTT toCAT/GAA to GTA / mRNA changesfrom GAA to GUA)which (in turn) leads to a change in translation / change in polypeptide chain/protein;(the tRNA) adds the wrong amino acid to the polypeptide chain;glutamic acid replaced by valine;produces abnormal hemoglobin;causing abnormal red blood cell/erythrocyte shape / sickle shape;which lowers the ability to transport oxygen;sickle-cell allele is codominant;homozygote/HbS HbS have sickle cell anemia/is lethal / heterozygote/HbS HbA hasthe sickle trait/is carrier (and is more resistant to malaria);

Explain the cause of sickle cell anemia and why it has been selected through natural selection. [8] M08/4/BIOLO/SP2/ENG/TZ1/XX+

Explain the effect of base substitution mutation in sickle cell anemia.[3] N07/4/BIOLO/HP2/ENG/TZ0/XX+

One homologous pair of chromosomes in their non-duplicated form

Two homologous pairs of chromosomes. Chromosomes are shown in their duplicated form.

DNA Replication

Define: Homologous chromosomes: matching pairs of chromosomes

4.2: Meiosis

STATE: Meiosis is a reduction division of a diploid nucleus to form haploid nuclei

Diploid: # of chromosomes in a body (somatic) cell (2n)

Haploid: # of chromosomes in a sex cell (n)

Prophase I of Meiosis I

Homologous chromosomes pair up forming a synapsis and crossing over occurs

Nuclear membrane breaks down

Chromosomes condense and supercoil

Spindle microtubules develop from the centrioles.

Metaphase I of Meiosis I

Microtubules attach to chromosomes. Homologous chromosomes are “pushed and pulled” by microtubles to the equator of the cell.

Anaphase I of Meiosis I

Homologous chromosomes separate and are pulled to opposite poles.

Chromosomes are still in their duplicated form.

Cytokinesis occurs

Telophase I of Meiosis I

Chromosomes arrive at the poles

Chromosomes number is reduced by half.

Chromosomes uncoil

New nuclear membrane reforms.

Microtubules break down

Prophase II of Meiosis II

Nuclear membrane breaks down

Chromosomes supercoil

Centrioles move to the poles and spindle microtubules develop

Metaphase II of Meiosis II

Spindle microtubules attach to chromosomes and move chromosomes to the equator of the cell

Anaphase II of Meiosis II

Sisiter chromatids separate (and are now are called chromosomes) are pulled towards opposite poles

Telophase II of Meiosis II

Chromosomes uncoil

Nuclear membrane reforms

Cytokinesis

Meiosis: Type of nuclear division in which one parent diploid

nucleus divides into four daughter haploid nuclei, each

genetically different to each other.

DNA replication in the S-phase of interphase

Homologous chromosomes separate in meiosis I

Sister chromatids separate in meiosis II

A a

A a

A

a

A a

A

a

AA Aa

aaAa

4.2.1: Meiosis

4.2.2: Homologous Chromosomes

4.2.3: Process of Meiosis

4.2.3: Crossing over

4.2.3: Stages of Meiosis

4.2.4: Non-disjunction

Fertilization following Meiosis II error:

What should happen

Trisomy 21: Down syndrome

Non-disjunction

http://www.biostudio.com/d_%20Meiotic%20Nondisjunction%20Meiosis%20II.htm

http://www.biostudio.com/d_%20Meiotic%20Nondisjunction%20Meiosis%20I.htm

4.2.5: KaryotypingSTATE: In karyotyping, chromosomes are arranged in pairs according to their size and structure

Normal Male

Normal Female

Chromosomes in their duplicate form

Gorilla Karyotype

Dog Karyotype

Sheep Karyotype

What is wrong here?

Down Syndrome

Describe the causes of Down syndrome. [5] M11/4/BIOLO/HP2/ENG/TZ2/XX

Down syndrome is caused by non-disjunction;occurs during meiosis;chromosome pairs fail to separate in meiosis I / chromatids in meiosis II /anaphase II;some gametes have an extra chromosome;can lead to zygotes/individuals with an extra chromosome / individual has47 chromosomes;in Down syndrome this would be trisomy 21/extra chromosome 21;increased probability with increased age of mother/ages of parents; [5 max]

The karyotype below shows the chromosomes from a person with Down syndrome. M11/4/BIOLO/SP2/ENG/TZ2/XX

(a) State the evidence provided by the karyotype that shows this person has Down syndrome. [1]

(b) Outline how Down syndrome occurs due to meiosis. [2](c) Determine, giving a reason, the sex of the person in the karyotype. [1](d) Explain briefly why males are more likely to inherit colour blindness than females. [2]

Explain how an error in meiosis can lead to Down syndrome. [8] M10/4/BIOLO/HP2/ENG/TZ2/XX+

non-disjunction; chromosomes/chromatids do not separate / go to same pole; non-separation of (homologous) chromosomes during anaphase I; due to incorrect spindle attachment; non-separation of chromatids during anaphase II; due to centromeres not dividing; occurs during gamete/sperm/egg formation; less common in sperm than egg formation / function of parents' age; Down syndrome due to extra chromosome 21; sperm/egg/gamete receives two chromosomes of same type; zygote/offspring with three chromosomes of same type / trisomy / total 47 chromosomes; [8 max] Accept the above points in an appropriately annotated diagram.

What’s wrong?

What’s wrong here?

Klinefelter’s Syndrome

What’s wrong?

Patau’s Syndrome

Chronic Myelogenous Leukemia (CML)

Triploid Karyotype

What’s the problem?

What are the Symptoms of Edwards Syndrome?

• About 25% of Edward's syndrome victims die before they are one

month old, • 10% live for one year. Symptoms *Growth deficiency *Breathing difficulties *Developmental delays

4.2.6:

STATE: Karyotyping is performed using cells collected by chorionic villus sampling or amniocentesis, for pre natal diagnosis of chromosome abnormalities.

4.3: Theoretical Genetics

4.3.1:Genotype / Phenotype

Genotype: The combination of alleles an individual has for a particular characteristic

Phenotype: The physical appearance of a feature

4.3.1:Dominant / Recessive Alleles

Dominant allele: an allele that has the same effect on the phenotype whether it is present in the homozygous or heterozygous state.

Recessive allele: an allele that only has an effect on the phenotype when present in the homozygous state.

brown eyes brown eyes blue eyes

4.3.1: Co-dominant alleles

Codominant alleles: pairs of alleles that both affect the phenotype when present in a heterozygote.

4.3.1: Locus

Locus: The particular position on homologous chromosomes of a gene.

4.3.1:Homozygous / Heterozygous

Homozygous: Having two identical alleles of a gene.

Heterozygous: Having two different alleles of a gene.

4.3.1:Carrier

Carrier: an individual that has one copy of a recessive allele that causes a genetic disease in individuals that are homozygous for this allele.

4.3.1:Test Cross

Test cross: testing a suspected heterozygote by crossing it with a known homozygous recessive.

4.3.2: Punnett Grid

4.3.3 and 4.3.4: Multiple Alleles and Blood groups

STATE: Some genes have more than two alleles (multiple alleles)

4.3.5: Sex chromosomes

4.3.6: Sex linkage. Genes carried on the sex chromosomes

STATE: Some genes present on the X chromosome are absent from the shorter Y chromosome

4.3.7: Sex linkage

STATE: A human female can be homozygous or heterozygous with respect to sex-linked genes.

4.3.8: Sex linked diseases

Sex Linked disease

Explain, using an example, how females but not males can be carriers of somerecessive alleles. [4] M11/4/BIOLO/SP2/ENG/TZ1/XX

M10/4/BIOLO/HP2/ENG/TZ2/XX+4. (a) Explain why carriers of sex-linked (X-linked) genes must be heterozygous.[2]

(c) Describe the inheritance of colour blindness in humans.M09/4/BIOLO/HP2/ENG/TZ2/XX

4.3.12: Pedigree Chart

4.4 Genetic Engineering and Other Aspects of

Biotechnology

4.4.1: PCR (polymerase chain reaction)

4.4.2: Gel Electrophoresis

State: that, in gel electrophoresis, fragments of DNA move in an electric field and are separated according to their size.

Person A Person B

DNA cut with restriction enzyme

3 fragments 2 fragments

4.4.3 and 4.4.4: DNA ProfilingSTATE: Gel electrophoresis of DNA is used in DNA profiling

Explain the methods and aims of DNA profiling. [8] M10/4/BIOLO/HP2/ENG/TZ1/XX

4.4.5: DNA profile

The diagram below represents the results of a paternity investigation. Track A is theprofile of the mother of a child, track B is the profile of the child and track C is the profileof a man who might be the father. M11/4/BIOLO/SP2/ENG/TZ1/XXExplain, using evidence from the diagram, whether this man is the father or not. [3]M11/4/BIOLO/SP2/ENG/TZ1/XX

N07/4/BIOLO/SP2/ENG/TZ0/ The diagram below shows a DNA profiling of a family with five children. Segments of theDNA inherited by some members of the family are shown as two dark bands in each column.The DNA fragments are labelled A to F.

(a)State two properties of the fragmented pieces of DNA which allow them to be separated in gel electrophoresis.b. Determine which DNA fragment Son 2 inherited from his mother and which fromhis father.From his mother: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . From his father: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . c. Identify the child that genetically most resembles one of the grandparents. [1]d. Apart from determining family relationships, outline one other application forDNA profiling.[1]

4.4.6: Human Genome Project (HGP)

4.4.6: Possible Advantages to the HGP (know three of these)

Improves our ability to conduct genetic screening for genetic disorders.

Improves our ability to develop new drugs for genetic diseases. (Molecular medicine).

Improves our ability to use DNA in the study of evolution and human dispersal out of Africa.

Match organ donors with recipients in transplant programs.

Elucidating the function of the large proportion of DNA we know little about.

4.4.7: Gene Transfer

4.4.7: Transfer of Genetic Material Across Species

(b) (i) Label the diagram below which shows a basic gene transfer. [2]

(ii) State two general types of enzymes used in gene transfer.[1]

(a) Gene transfer to bacteria often involves small circles of DNA into which genes can beinserted. State the name of a small circle of DNA, used for DNA transfer, in bacteria.(b) The diagram below shows a cut circle of DNA into which a gene is being inserted. Beforeit can be transfered into a bacterium, the ring must be altered, using an enzyme.M10/4/BIOLO/SP2/ENG/TZ1/XX

Outline what must be done next to complete the process of gene insertion into theDNA circle, including the name of the enzyme that is used.[2](c) Discuss the potential benefit and possible harm of one named example of gene transfer between species.

4.4.7: Transfer of Genetic Material Across Species

State: That, when genes are transferred between species the amino acid sequence of polypeptides translated from them is unchanged- because the genetic code is universal.

4.4.8: Gene Transfer

State: that, when genes are transferred between the amino acid sequence of polypeptides translated from them is unchanged- because the genetic code is universal.

The diagram below shows a cut circle of DNA into which a gene is being inserted. Before it can be transferred into a bacterium, the ring must be altered, using an enzyme. M10/4/BIOLO/SP2/ENG/TZ1/XX

Outline what must be done next to complete the process of gene insertion into theDNA circle, including the name of the enzyme that is used. [2]

Discuss the potential benefit and possible harm of one named example of gene transferbetween species. [3]

Outline a basic technique for gene transfer involving plasmids. [6] M08/4/BIOLO/HP2/ENG/TZ2/XX

4.4.9: State two examples of Genetically Modified Crops or Animals

GOLDEN RICE

BT CORN

Golden rice is a variety of rice that has been genetically modified to produce beta-carotene (a precursor of vitamin A). Golden rice has the potential to prevent blindness or death in populations with vitamin A deficiency.

BT corn is a variety of corn that has been genetically modified to produce a bacterial toxin. The toxin is not harmful to people but it kills caterpillars. The advantage of BT corn is that it doesn't need to be sprayed with pesticides.

4.4.10: Benefits/Harmful Effects of GMOs

Advantages of Genetically Modified corn are: 1) it increases profits for farmers by saving them the expense of spraying pesticides; 2) it keeps the price of corn lower for consumers; and 3) it saves the environment from toxic pesticides, which can pose heath risks to people and can kill non-target species that with important roles in the ecosystem.

Disadvantages are: 1) insect pests may develop resistance to the GM corn because continual exposure to the toxins will speed up the rate of natural selection; and 2) GM corn may produce toxic pollen, release it into the air, and harm beneficial species like the monarch butterfly(although recent studies do not support this claim).

Genetic modification involves the transfer of DNA from one species to another. Discussthe potential benefits and possible harmful effects of one example of genetic modification in a named organism. [8] M07/4/BIOLO/SP2/ENG/TZ1/XX

Two examples of genetically modified crops or animals1. Bt Maize2. Golden rice

Potential Benefits of Bt Maize Possible harmful effects of Bt Maize

Describe the genetic modification to produce Bt Maize

4.4.11: Clone: Genetically identical organisms or a group of cells derived from a single parent cell.

4.4.12: Outline a techniques for cloning using differentiated animal cells

4.4.12: Cloning using Differentiated Cells

4.4.13: Ethical Issues in Therapeutic Cloning in Humans

Therapeutic cloning is the creation of an embryo to supply embryonic stem cells for medical use.

4.4.13: Discuss ethical issues of therapeutic cloning in humans

What is therapeutic cloning?

Arguments for therapeutic cloning Arguments against therapeutic cloning