Sl Genetics

Front 1

State that eukaryote chromosomes are made of DNA and proteins

Back 1

Eukaryote chromosomes are made of DNA and proteins.

Front 2

Define gene, allele and genome

Back 2

Gene: A heritable factor that controls a specific characteristic.
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 gene.
Genome: The whole of the genetic information of an organism.

Front 3

Define gene mutation

Back 3

Gene mutation: A change in the sequence of bases in a gene

Front 4

Explain the consequence of a base substitution mutation in relation to the processes of transcription and translation, using the example of sickle-cell anemia

Back 4

Sickle cell anemia is a disorder that affects the red blood cells, it is caused by a mutation in one of the haemoglobin genes. An amino acid called glutamic acid has been replaced by one called valine. The triplet GAG in the gene has mutated to GTG and the triplet in the opposite strand, CTC becomes CAC. This is the triplet that is transcribed, so in the mRNA GAG becomes GUG. GAG would have been translated in to glutamic acid, but GUG is translated into vaeline. As a result, haemoglobin molecules do not form properly, causing the red blood cells to be rigid and have a sickle shape.

Front 5

State that meiosis is a reduction division of a diploid nucleus to form haploid nuclei

Back 5

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

Note:
Diploid: two sets of chromosomes in nucleus, the chromosomes are in pairs, each parent contributed one of the pair.
Haploid: one set of chromosomes in a nucleus, only one member of each pair of chromosomes.

Front 6

Define homologous chromosomes

Back 6

Homologous chromosomes have the same genes as each other, in the same sequence, but not necessarily the same alleles of those genes.

Front 7

Outline the first part of the process of meiosis, including prophase 1, metaphase 1, anaphase 1, telophase 1 and cytokinesis 1

Back 7

Prophase 1: supercoiling of chromosomes, replcated chromosomes pair up in their homologous pairs to form a bivalent (this is called synapsis), crossing over may occur, spindle fibre network of microtubules start to form, nuclear envelope begins to break down.
Metaphase 1: spindle fibre network complete, bivalents line up along the equator in a random way, centromeres attach to microtubules.
Anaphase 1: Microtubules contract separating homologous pairs to opposite poles, centromeres do no split.
Telophase 1: chromosomes uncoil, spindle microtubules break down, nuclear envelope re-forms.
Cytokinesis 1: two separate cells.

Front 8

Draw diagrams to depict the prophase 1, metaphase 1, anaphase 1, telophase 1 and cytokinesis 1 stages of meiosis

Back 8

.

Front 9

Outline the process of crossing over

Back 9

This process may occur during prophase 1. Chromatids within the homologous pair may touch, break and re-join in a different way. This means parts of the maternal and paternal chromosomes cross over, and this mixes the genes, causing variety
.
.
.
.
.
.

Front 10

Draw diagrams to depict the prophase 2, metaphase 2, anaphase 2, telophase 2 and cytokinesis 2 stages of meiosis

Back 10

.

Front 11

Outline the second part of the process of meiosis, including prophase 2, metaphase 2, anaphase 2, telophase 2 and cytokinesis 2

Back 11

Prophase 2: supercoiling of chromasomes, spindle microtubules start to form, nuclear envelope breaks down.
Metaphase 2: chromosomes move to the equator, microtubule network complete, microtubules attach to centromeres.
Anaphase 2: centromeres split, microtubules contract, chromosomes pulled to opposite poles.
Telophase 2: chromosomes uncoil, spindle microtubules break down, nuclear envelope re-forms.
Cytokinesis 2: four cells from one original cell, each with one chromosome from each homologous pair, these are haploid cells, one or more may now undergo differentiation into gametes.

Front 12

Explain that non-disjunction can lead to changes in chromosome number, illustrated by reference to Down syndrome (trisomy 21)

Back 12

.

Front 13

State that, in karyotyping, chromosomes are arranged in pairs according to their size and structure

Back 13

In karyotypinc, chromosomes are arranged in pairs according to their size and structure

Front 14

State that karyotyping is performed using cells collected by chorionic villus sampling or amniocentesis, for pre-natal diagnosis of chromosome abnormalities

Back 14

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

Front 15

Analyse a human karyotype to determine gender and whether nondisjunction has occurred.

Back 15

Karyotyping can be used to determine gender of a fetus and look for chromosome abnormalities such as non-disjunction. The gender can be deduced by looking at the sex chromosomes. Females will have two X chromosomes while males have one X and one Y. We can distinguish between X and Y with karyotyping as the Y chromosome is smaller than the X. As for non-disjunctions we can see if a chromosome is missing or if their is an extra one by looking at the number of chromosomes. If There should only be two of each chromosome. Each 23 chromosomes should have a pair resulting in 46 chromosomes in total. For example, if we notice that there are three chromosomes 21 then we can conclude that a non-disjunction occurred. In this case, the non-disjunction results in Down’s syndrome. (trisomy 21)

Front 16

Define genotype, phenotype, dominant allele, recessive allele, codominant alleles, locus, homozygous, heterozygous, carrier and test cross

Back 16

Genotype: the alleles of an organism.
Phenotype: the characteristics of an organism.
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.
Codominant alleles: pairs of alleles that both affect the phenotype when present in a heterozygote.
Locus: the particular position on homologous
chromosomes of a gene. Homozygous: having two identical alleles of a gene.
Heterozygous: having two different alleles of a gene.
Carrier: an individual that has one copy of a recessive allele that causes a genetic disease in individuals that are homozygous for this allele.
Test cross: testing a suspected heterozygote by crossing it with a known homozygous recessive.

Front 17

Determine the genotypes and phenotypes of the offspring of a monohybrid cross using a Punnett grid

Back 17

.

Front 18

Describe ABO blood groups as an example of codominance and multiple alleles

Back 18

Codominance means that both alleles have an effect on the phenotype. Multiple alleles means there are many alleles of a gene.

In the ABO blood grouping there are three alleles - I, I, and i. Alleles I and I are codominant. This results in four different phenotypes or blood groups.
.
.
.
.
.
.

Front 19

Explain how the sex chromosomes control gender by referring to the inheritance of X and Y chromosomes in humans

Back 19

Two chromosomes determine the gender of a child. These are called sex chromosomes. The X chromosome is relatively large and carries many genes. The Y chromosome is smaller, and only carries a few genes. If two X chromosomes are present in a human embryo, and no Y chromosome, it develops into a girl. If one Y chromosome and one X chromosome are present, a human embryo develops into a boy. When women reproduce, they pass on one X chromosome in the egg. When men reproduce, they pass on either one X or one Y chromosome in the sperm. So, the gender of the child depedns on whether the sperm that fertilizes the egg is carrying an X or a Y chromosome.

Front 20

State that some genes are present on the X chromosome and absent from the shorter Y chromosome in humans

Back 20

Some genes are present on the X chromosome and absent from the shorter Y chromosome in humans.

Front 21

Define sex linkage

Back 21

Sex linkage is the association of a characteristic with gender, because the gene controlling the characteristic is located on a sex chromosome.

Front 22

Describe the inheritance of colour blindness and hemophilia as examples of sex linkage

Back 22

1. Colour blindness – the gene for the ability to see green and red colour as separate colours is found on the X-chromosome. The recessive allele produces red-green colour blindness. If a male has the recessive allele on the X-chromosome then he will be colour blind. A female must have recessive alleles on both the X-chromosomes and this is very unlikely to occur.
Possible genotypes and phenotypes:
.
.
.
.
.

2. Haemophilia - a genetic disease that is caused by a lack of factor VIII or factor IX in the blood, which slows down the normal clotting of blood. The gene for the factor VIII/IX protein is found on the X-chromosome. Women who carry the defective gene on one of their X-chromosomes are called ‘carriers’. If a male inherits the defective allele he will be a haemophiliac. It is virtually unknown for a female to contract haemophilia, as she would have to be homozygous recessive.
Possible genotypes and phenotypes:
.
.
.
.
.

Front 23

State that a human female can be homozygous or heterozygous with respect to sex-linked genes

Back 23

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

Front 24

Explain that female carriers are heterozygous for X-linked recessive alleles

Back 24

A female carrier must be heterozygous, as one X chromosome has the dominant allele, and the other has the recessive allele. X X. The dominant allele will mask the recessive characteristic. Therefore, the female carries the gene, but does not express it.

Front 25

Predict the genotypic and phenotypic ratios of offspring of monohybrid crosses involving any of the above patterns of inheritance

Back 25

.

Front 26

Deduce the genotypes and phenotypes of individuals in pedigree charts

Back 26

Pedigrees are used to represent individuals in a family tree. Usually circles represent females and squares represent males. The children are linked by horizontal lines and are linked to parents and their offspring by vertical lines.
.
.
.
.
.
.
.
.

Front 27

Outline the use of polymerase chain reaction (PCR) to copy and amplify minute quantities of DNA

Back 27

The polymerase chain reaction copies and amplifies minute quantities of nucleic acid.
1. A solution which contains: DNA to be copied, heat resistant DNA polymerase, all 4 types of nucleotides and primers is heated to separate the DNA strands.
2. Cooled to allow primers to bind by hydrogen bonding to the ends of the target sequences.
2. DNA polymerase adds nucleotides to ends of primers using the long DNA strands as templates.
3. This is repeated until enough DNA is produced

Front 28

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

Back 28

In gel electrophoresis, fragments of DNA move in an electric field and are separated according to their charge and size

Front 29

State that gel electrophoresis of DNA is used in DNA profiling

Back 29

Gel electrophoresis of DNA is used in DNA profiling

Front 30

Describe the application of DNA profiling to determine paternity and also in forensic investigations

Back 30

- Paternity - sometimes there question of the father of a baby is raised. DNA profiling from a mouth swab is used to determine the father.
- Forensic investigations - often, tiny samples of DNA can be found such as a drop of blood, saliva, a hair follicle, scrapings under a finger nail, and the DNA can be amplified using the PCR before profiling.
- Family relationships for immigrants
- Identification of people who died a long time ago.

Front 31

Analyse DNA profiles to draw conclusions about paternity or forensic investigations

Back 31

Satellite DNA is short sequences of DNA repeated many times. It varies between individuals, and it is impossible for individuals having the same satellite DNA. Great care must be taken not to contaminate the DNA. DNA is cut into fragments with restriction enzymes. Gel electrophoresis separates the DNA fragments and the banding patterns are compared.

Front 32

Outline three outcomes of the sequencing of the complete human genome

Back 32

1. Improved knowledge of how human genes function.
2. Improved diagnosis of genetic disease.
3. Increased potential for gene therapy.
4. Increased potential to design drugs to combat genetic malfunctions.

Front 33

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

Back 33

When genes are transferred between species, the amino acid sequence of polypeptides translated from them is unchanged because the genetic code is universal

Front 34

Outline a basic technique used for gene transfer involving plasmids,a host cell (bacterium, yeast or other cell), restriction enzymes (endonucleases) and DNA ligase

Back 34

1. The plasmid is removed from the prokaryotic cell (which is used as a vector).
2. The plasmid is cut with a specific restriction enzyme to produce sticky ends (a short sequence of unpaired bases at the end of the DNA).
3. The desired gene is cut with the same restriction enzyme to produce corresponding sticky ends.
4. The loose ends are joined with ligase.
5. The recombinant plasmid (contains the plasmid genes plus the inserted gene) is inserted into the host cell.
6. The host cell is cloned, producing the desired gene.

Front 35

Discuss the potential benefits of one example of genetic modification

Back 35

Synthesis of Bt toxin in cotton
Benefits:
-. Bacillus thuringiensis is a bacterium that produces a toxin which kills caterpillars that consume the bacteria and Bt cotton contains the bacterial gene that codes for the toxin.
- The cotton bollworm is a serious pest in the major cotton-growing countries of the world.
- Control by chemicals was expensive, damaging to the environment and to human helath.
- Insects also became resistant to the chemical pesticides quickly, requiring more toxic or damaging substances.
- Bt cotton specifically targets those insects feeding on the cotton, so no others are harmed.
- Long term studies have shown no resistence yet.
- Cotton yields have increased significantly.

Front 36

Define clone

Back 36

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

Front 37

Discuss the possible harmful effects of one example of genetic modification

Back 37

Synthesis of Bt in cotton
Possible harm:
- The gene may spread to other plant species,however, all studies so far have showed this has not occured.
- Exposure of soil organisms to Bt toxin leached from dead plant material is potentially harmful.
- The gene could sread to wild species of cotton, however its use is banned in countries where wild cotton grows.

Front 38

Outline a technique for cloning using differentiated animal cells

Back 38

This procedure shows how Dolly the Sheep was cloned:
1. Udder cell removed from sheep 1.
2. Egg removed from sheep 2.
3. Nucleus removed from egg.
4. Udder cell and enucleated egg fused.
5. Cell stimulated to divide, forming embryo.
6. Embryo implanted into receptive ewe.
7. Dolly!
.
.
.
.
.
.
.

Front 39

Discuss the ethical issues of therapeutic cloning in humans

Back 39

NEED INFO