Presentation on theme: "TOPIC 4: GENETICS. 4.1: Chromosomes, genes, alleles and mutations."— Presentation transcript:
TOPIC 4: GENETICS
4.1: Chromosomes, genes, alleles and mutations
4.1.1 Eukaryotic chromosome STATE: Eukaryotic chromosomes are made of DNA and proteins
4.1.2: Gene Define 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: Allele Define 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: Genome Define genome: The whole of the genetic information of an organism
4.1.3: Gene Mutation Define 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
Explain the causes of sickle-cell anemia.  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 to GTG / mRNA changes from GAG to GUG; (accept DNA changes from CTT to CAT/GAA to GTA / mRNA changes from 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 has the 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. M08/4/BIOLO/SP2/ENG/TZ1/XX+
Explain the effect of base substitution mutation in sickle cell anemia.  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.
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
Aa A a
Aa A a AA Aa aa Aa
4.2.2: Homologous Chromosomes
4.2.3: Process of Meiosis
4.2.3: Crossing over
4.2.3: Stages of Meiosis
Fertilization following Meiosis II error: What should happen Trisomy 21: Down syndrome
4.2.5: Karyotyping STATE: In karyotyping, chromosomes are arranged in pairs according to their size and structure
Chromosomes in their duplicate form
What is wrong here?
Describe the causes of Down syndrome.  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 has 47 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.  (b)Outline how Down syndrome occurs due to meiosis.  (c) Determine, giving a reason, the sex of the person in the karyotype.  (d) Explain briefly why males are more likely to inherit colour blindness than females. 
Explain how an error in meiosis can lead to Down syndrome.  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 here?
Chronic Myelogenous Leukemia (CML)
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 some recessive alleles.  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. 
(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 APerson B DNA cut with restriction enzyme 3 fragments2 fragments
4.4.3 and 4.4.4: DNA Profiling STATE: Gel electrophoresis of DNA is used in DNA profiling
Explain the methods and aims of DNA profiling.  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 the profile of the mother of a child, track B is the profile of the child and track C is the profile of a man who might be the father. M11/4/BIOLO/SP2/ENG/TZ1/XX Explain, using evidence from the diagram, whether this man is the father or not.  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 the DNA 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 from his father. From his mother:........................................................ From his father:......................................................... c. Identify the child that genetically most resembles one of the grandparents.  d. Apart from determining family relationships, outline one other application for DNA profiling.
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.  (ii) State two general types of enzymes used in gene transfer.
(a) Gene transfer to bacteria often involves small circles of DNA into which genes can be inserted. 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. Before it 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 the DNA circle, including the name of the enzyme that is used.  (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 the DNA circle, including the name of the enzyme that is used.  Discuss the potential benefit and possible harm of one named example of gene transfer between species. 
Outline a basic technique for gene transfer involving plasmids.  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. Discuss the potential benefits and possible harmful effects of one example of genetic modification in a named organism.  M07/4/BIOLO/SP2/ENG/TZ1/XX
Two examples of genetically modified crops or animals 1. Bt Maize 2. Golden rice Potential Benefits of Bt MaizePossible 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 cloningArguments against therapeutic cloning