3- Genetics (Questions)
3.4 List and explain the factors that increase the mutation rate and can cause genetic diseases and cancer, and apply it to the consequences of nuclear bombing of Hiroshima and accident in Chernobyl.
Radiation and mutagenic chemicals increase the mutation rate and can cause genetic diseases and cancer. Radiation: -the high energy wavelengths can have enough energy to cause chemical changes in DNA. Chemical substances: -smoke and mustard gas that possesses chemical can change DNA. -causing thyroid disease after Chernobyl due to release of radioactive iodine. -250% increase in congenital abnormalities -Reduced T cell counts and altered immune functions, leading to higher rates of infection -caused variation in flora and fauna in Chernobyl
3.1 Application: List the number of genes of one plant, one bacterium, one species with more genes and one with fewer genes than a human.
**The number of genes in a species should not be referred to as genome size as this term is used for the total amount of DNA. Estimated number of protein-coding genes in humans is 21 000. Escherichia Coli (Bacteria): less genes than humans ~4 200 Oryza Sativa (Rice): plant, more genes than humans ~38 000 Gallus gallus (Chicken): animal, less genes than humans ~1 700 Daphina pulex (water flea): animal, more genes than humans ~31 000
3.4 Define monohybrid, true breeding, hybrid, F1 and F2.
A monohybrid cross is a genetic cross between two individuals, tracking one gene of interest. True breeding organisms are those that have been bred to have a homozygous genotype. The offspring of a cross between two parent organisms, "first filial." The F2 generation is the result of a cross between two F1 individuals.
3.4 Outline Thomas Morgan's elucidation of sex linked genes with Drosophila.
-Thomas Hunt Morgan studied genetics of fruit flies, Drosophila. -he discovered sex-linked traits; traits that appear to associate differently in males and females. -flies normally have red eyes, but there was a mutant male with white eyes. -this white-eyed male was crossed with a red eyed female (P generation). -all offspring (F1 generation) were red-eyed therefore red is dominant over white. -then, two of the red-eyed offspring were crossed (F1 X F1). -in the offspring (F2), only males had white eyes, -suggesting that the eye-color allele is carried on the X-chromosome.
3.1 Outline the use of a computer software tool to create an alignment of the gene sequences between different species.
-a sequence alignment is a way of arranging DNA sequences -so that similarities and differences between the sequences of different species can be identified. -computer software programs are able to complete alignments quickly and accurately.
3.4 Outline the effects of gene mutations in body cells and gamete cells.
-cell damage and death that result from mutations in somatic cells -occur only in the organism in which the mutation occurred -and are therefore termed somatic or non heritable effects. -cancer is the most notable long-term somatic effect.In contrast, mutations that occur in germ line cells (which become gametes, sperm and egg) -can be transmitted to future generations and are therefore called genetic or heritable effects. -genetic effects may not appear until many generations later.
3.1 State similarities between alleles of the same gene.
-found at the same locus on homologous chromosomes -have mostly the same nucleotide sequence and code for the same general type of protein (for examples the A and B alleles for blood type both code for a membrane embedded protein).
3.1 Explain which gene types are often used to assess the differences in the base sequences of a gene between two species.
-genes that are present in the species being studied must be selected. -for example, the COX1 gene (which codes for a protein involved in cellular respiration) is present in the majority of eukaryotic species so it is a good choice for comparing sequences between species. -additionally, the gene has been sequenced for many species and is therefor accessible in genome databases.
3.4 List three biological research methods pioneered by Mendel.
-large number of replicates to demonstrate reliability of results -repeats of whole experiments. -obtaining quantitative results, not only qualitative descriptions.
3.4 Explain the rarity of genetic diseases.
-often times genetic diseases seem to just "appear" in a family without prior history. -this is usually because the disease is caused by a recessive allele that has been masked by dominant alleles. -if two carriers, who show no disease symptoms, produce offspring, there is a 1/4 change of the offspring showing the disease characteristics. Many genetic diseases have been identified in humans but most are very rare. Most are rare because severe diseases that are caused by homozygous alleles may not survive until reproduction age so they cannot be passed on. Recessive conditions tend to be more common and dominant conditions.
3.4 Describe the cause and effect of red-green color blindness.
-red-green color blindness is caused by a sex linked recessive allele of a gene that -codes for a protein (opsin) in the eye that is sensitive to particular wavelengths of light. -the mutated allele causes red-green color vision defects.
3.1 Outline the consequences of the sickle cell mutation on the impacted individual.
-sickle cells are destroyed rapidly in the bodies of people with the disease -causing anemia, a condition in which there aren't enough healthy red blood cells to carry adequate oxygen to the body's tissues. -anemia results in fatigue and weakness. -the sickle cells also block the flow of blood through vessels -resulting in lung tissue damage that causes acute chest syndrome, pain episodes and stroke. -it also causes damage to the spleen, kidneys and liver.
3.1 State the difference between alleles of the same gene.
-slightly different from each other in the sequence of nucleotides. -they can vary by just one base (i.e. A -->T), called a single nucleotide polymorphism (SNP) or by the insertion or deletion of a base.
3.4 Describe the role of statistical tests in deciding whether an actual result is a close fit to a predicted result.
-such as the chi-square test -allow us to determine the probability of observing a discrepancy between observed (actual results) and expected (predicted results). -in other words, statistics help us determine the chance of getting the observed results given what was expected.
3.4 State the usual cause of one allele being dominant over another.
-the cause of allele dominance is complex and can vary between genes. -in general, the dominant allele codes for a functioning proteins -whereas the recessive allele codes for a less (or non-) functioning protein. -sometimes the recessive allele is the "normal" or "healthy" version of the gene.
3.1 Outline the technological improvement that sped the DNA sequencing process.
-the largest advancement in gene sequencing was the automation of the process with computer-assisted technology. -what used to take humans hours or days can now be done by a computer much more rapidly, more accurately and for less money.
3.4 A mutation in the CFTR gene causes cystic fibrosis. Which protein does this gene code for?
A chloride channel in the mucous membrane; The gene is found on chromosome number 7 and codes for a protein that causes a faulty chloride channel to be embedded in cell membranes. This results in an effect on the secretion of sweat, mucus and digestive juices.
3.4 Define gamete, haploid, and zygote.
A gamete is a reproductive cell, egg or sperm. Gametes are haploid; containing a single set of unpaired chromosomes. Haploid cells contain a single set of unpaired chromosomes and therefore only one allele of each gene. The zygote is the diploid cell that results from the fusion of two haploid gametes during fertilization.
3.1 Define the term gene.
A gene is a heritable factor that consists of a length of DNA and influences a specific characteristic.
3.1 Define gene locus.
A gene locus is the location of a gene on a chromosome. Each chromosome carries many genes.
3.1 Describe a base substitution mutation.
A gene mutation is a change in the nucleotide sequence of a section of DNA coding for a specific trait. The new allele that results from the mutation might result in: Missense - cause one amino acid in the protein coded for by the gene to change Silent - have no effect on the protein coded for by the gene Nonsense - code for an incomplete, non-functioning polypeptide for form.
3.1 Outline the relationship between a gene and a chromosome.
A gene occupies a specific position on a chromosome; this specific position is called locus. Genes can be linked into groups, and each group = one type of chromosome.
3.4 Define "carrier" as related to genetic diseases.
A genetic carrier is an individual that has inherited a recessive allele of a gene but does not display the symptoms of the disease because they also have the dominant (normal functioning) allele. Carriers are heterozygous.
3.4 Define "mutagen", and how it affects cells.
A mutagen is a chemical or physical agent that causes mutations.Mutagens cause mutations in three different ways: 1. Some are mistakenly used as bases when new DNA is synthesized at the replication fork. 2. Some react directly with DNA, causing structural changes that lead to miscopying of the template strand when the DNA is replicated. 3. Some mutagens act indirectly on DNA. They do not themselves affect DNA structure, but instead cause the cell to synthesize chemicals that have a direct mutagenic effect.
3.4 Define "mutation" as related to genetic diseases and cancer.
A mutation is the permanent alteration of the nucleotide sequence of the genome of an organism.
3.4 Outline the conventions for constructing pedigree charts.
A pedigree chart is a diagram that shows the occurrence of a phenotype in generations of a family. Male = square Female = circle Shaded = affected
3.1 Define alleles, and outline how it is formed.
Alleles are the various specific forms of a gene. New alleles are formed by mutation, and they differ from each other by one or only a few bases. Most animal have 2 copies of each type of chromosome, and each copy may have same or different alleles; but only one allele can occupy the locus of a gene on a chromosome.
3.4 State the maximum number of alleles in a diploid zygote.
Alleles are variations of a single gene. Although there usually are multiple alleles for a gene in the population, any single individual can only have a maximum of two alleles of a gene, one allele on each chromosome of a homologous pair.
3.4 Describe patterns that can be seen regarding diseases caused by autosomal dominant, autosomal recessive, and sex linked.
Autosomal dominant: -every affected individual have at least one affected parent -present in every generation -present in both males and females Autosomal recessive: -cases where both parent are not affected -skips generation -present in both males and females Sex linked: -more common in males -can only inherit from parent of opposite gender
3.4 List out genetic diseases that are due to autosomal dominant, autosomal recessive, co-dominant, and sex linked.
Autosomal dominant: Huntington's Disease Autosomal Recessive: cystic fibrosis Co-dominant: Sickle cell anemia ABO Blood groups Sex linked: haemophilia (recessive) red-green color blindness (recessive)
3.4 State the genotype for all 4 types of blood.
Blood A: -homozygous: I^A I^A -heterozygous: I^A i Blood B: -homozygous: I^B I^B -heterozygous: I^B i Blood AB: -ONLY heterozygous: I^A I^B Blood O: -ONLY homozygous: ii
3.4 State two similarities and two differences between male and female gametes
Both egg and sperm are haploid (23 chromosomes in humans) cells produced through meiosis. -the egg and sperm are very different in size and shape. -eggs are large cells; sperm are much smaller. -sperm have flagella, egg do not.
3.4 Explain the causes of cystic fibrosis and Huntington's disease.
Cystic fibrosis is one of the most common genetic diseases. The recessive allele was formed by a mutation in the CFTR gene, which codes for a chloride channel in mucous membranes. The gene has been mapped on chromosome 7 and is involved in the secretion of sweat, mucus and digestive juices. Huntington's disease is a neurodegenerative disorder that usually starts to affect people between 30 and 50 years of age. It is caused by a dominant allele that has developed through the mutation of the HTT gene found on chromosome 4.
3.4 Explain dominant and recessive allele in inheritance.
Dominant alleles mask the effects of recessive alleles but co-dominant alleles have joint effects; which means (pair of) alleles that both affect the phenotype when present in a heterozygote / both alleles are expressed;
3.4 Define "dominant allele.", "recessive allele", and "co-dominant alleles".
Dominant alleles show their effect even if the individual is heterozygous, they can mask the presence of another allele. Recessive alleles only show their effect if the individual has two copies (homozygous recessive), otherwise their presence can be masked by a dominant allele. With codominant alleles, both alleles are expressed equally; there isn't masking of a recessive by a dominant allele.
3.4 Describe the cause and effect of hemophilia.
Hemophilia is caused by a mutated allele of a gene that codes for a essential protein in the blood clotting process. Without proper clotting, hemophiliacs are prone to excessive bleeding.
3.1 Describe the relationship between the number of genes in a species and the species complexity in structure, physiology and/or behavior.
In general, eukaryotes have more genes than prokaryotes. However, within plants and animals there is little correlation between complexity and the number of genes.
3.4 Outline why Mendel's success is attributed to his use of pea plants.
Mendel discovered the principles of inheritance with experiments in which large numbers of pea plants were crossed. -his success was due to him obtaining numerical values, rather than just descriptions of outcomes. -Mendel's use of peas allowed for the observation of easily distinguishable characteristics (i.e. yellow or green pods). -Also, the peas were able to reproduce quickly allowing for many generations of data to be collected. -Lastly, the reproduction could be controlled, so Mendel knew exactly which two parent plants were being bred (either cross-bred or self-pollination). From his experiment he discovered the presence of dominant and recessive alleles through artificial pollination of purebred pea plants.
3.1 Describe an example of a gene with multiple alleles.
Nearly all genes have multiple alleles (multiple versions). For example, in humans the ABO blood type is controlled by a single gene, the isoagglutinogen gene (I for short). The I gene has three common alleles: I^A: codes for antigen type A I^B: codes for antigen type B i: codes for no antigen
3.1 Define "sequence" in relation to genes and/or genomes.
Sequence (noun): the order of the nitrogenous bases in a gene or genome. "The sequence of the gene is ATCCGTA." Sequence (verb): the process of determining the order of the nitrogenous bases in a gene of genome. "We are going to sequence the gene to test for a genetic disease."
3.4 Define sex linkage.
Sex linkage refers to genes located on the sex chromosomes, X or Y. The genes expression, inheritance pattern and effect on the phenotype will differ between males and females.
3.1 Outline the Human Genome Project and its outcome.
The Human Genome Project began in 1990 with the aim of determining the complete sequence of the human genome and identifying every gene that it contains. Gene sequencers is a technique used in gene sequencing. The sanger process is used, and fluorescent markers are used to label the DNA fragments in order to find out the order of the DNA sequences. An optical detector is used to detect the colours of fluorescence along the lane. There is a series of peaks of fluorescence, corresponding to each number of nucleotides, and a computer is used to deduce the base sequences. Outcomes of the HGP: knowledge of location of human genes / position of human genes on chromosomes;knowledge of number of genes/interaction of genes / understanding the mechanism of mutations; evolutionary relationships between humans and other animals; discovery of proteins / understanding protein function / detection of genetic disease; leads to the development of medical treatment/enhanced research techniques; knowledge of the base sequence of genes/study of variation within genome;
3.4 Explain the reason why the outcomes of genetic crosses do not usually correspond exactly with the predicted outcomes.
The actual outcomes of a genetic cross may not exactly match outcomes predicted based on a Punnett square because there is an element of chance in the segregation of alleles and fertilization.
3.1 Explain the causes of sickle cell anemia.
The cause of sickle cell anaemia is due to the base substitution mutation in the DNA. -in DNA sense strand gene that codes for hemoglobin protein, GAG is being mutated to GTG (thymine substituted adenine) -which then codes for valine instead of glutamic acid on the SIXTH amino acid. -this causes a change to the base sequence of mRNA transcribed from it and a change to the sequence of a polypeptide in hemoglobin.
3.1 Outline the definition of genome.
The genome is the whole of the genetic information of an organism. The size of a genome is therefore the total amount of DNA in one set of chromosomes in that species. It can be measured in millions of base pairs of DNA.
3.1 State the size in base pairs of the human genome.
The human genome is composed of about 3.2 billion base pairs divided amongst nucleus chromosomes and mitochondrial DNA.
3.1 State the aim of the Human Genome Project.
The main aims of the Human Genome Project were to determine the sequence of the ≈ 3.2 billion base pairs and identify the location of the ≈ 20-25 thousand genes in the human genome.
3.4 Explain the relationship between meiosis and inheritance.
The two alleles of each gene separate into different haploid daughter nuclei during meiosis. Gametes are haploid so contain only one allele of each gene. Fusion of gametes results in diploid zygotes with two alleles of each gene that may be the same allele (homozygous) or different alleles (heterozygous)
3.1 State the number of genes in the human genome.
There are an estimated 20,000-25,000 genes in the human genome.
3.4 Describe conclusions from Mendel's pea plant experiments.
Through selective breeding of pea plants, Mendel discovered: -that certain traits show up in offspring without blending of the parent's characteristics. Mendel observed seven traits: flower color stem length seed color pod color flower position seed shape pod shape. Mendel concluded: 1. genetic "units" of inheritance are passed from parents to offspring 2. the offspring inherits one "unit" from each parent for each trait. 3. the "unit" may be masked or hidden (i.e. recessive) in an individual but can still be passed on to the next generation.
3.4 State the gametes for sickle cell anaemia alleles.
dominant allele (no sickle cell gene) Hb^A recessive allele (with sickle cell gene) Hb^S co-dominance: Hb^A Hb^S
