Category Archives: genetics

Human intervention in evolution

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This fruit is from a genetically modified papaya plant, bred to reduce the risk of disease. How are genetically modified organisms created? (YouTube video, 5.31min)

Quizlet – Flashcards for Chapter 16

While genetic techniques have certainly provided health benefits to our society (disease diagnosis and therapies, production of insulin and increased production of more nutritious and disease resistant foods), there are also community concerns about the ways that these technologies are being used and the future consequences. ABC Splash have some short videos that outline some of the issues of genetic technologies:

The Hardy-Weinberg Principle of Allele Frequencies

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The Hardy-Weinberg Principle is a mathematical law that predicts allelic frequencies, making several assumptions:

  • Large population
  • Random mating
  • No immigration
  • No emigration
  • No natural selection

In nature, these assumptions are extremely unlikely to occur, but it is the deviation from the expected distribution of alleles (according to the HW Principle) that informs us about the action of these natural conditions.

Please complete Activity 13.2 (page 141) Looking at Allele Frequencies – Parts A and B.

Welcome Back – Term 3!

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Year 12 students will be counting down the next 14 weeks until their VCE Biology exam on the morning of Friday 30th October. We will start this term with a review of the structure of DNA, using the GTAC resources, “Exploring the structure of DNA“.

On Wednesday 22nd July we will be heading to the University of Melbourne Genetics Department to complete three practical activities that will contribute to your school-based assessment:

  1. An investigation using a DNA tool and a manipulation technique
  2. An investigation of inheritance in Drosophila melanogaster including a review of meiosis in gamete formation
  3. Meiosis in Drosophila

On Friday 4th September you will have the opportunity to travel to Brauer College and participate in GTAC outreach program, “From Hominoids to Hominins”.

On Tuesday 13th October you will be able to attend a “Get into Genes” program as revision prior to your exam.

Mutants can be beautiful!

 

Both these roses come from the same bush in my garden at home. The one on the left is how the rose normally looks, year after year. This year, on a single branch sprouting to the side, there are about six flowers that look striped, like the one on the right. This article, from the American Rose Society, describes how a genetic mutation can cause this change in pigments.

Stripes may also result from spontaneous or induced mutations. Mutations are sudden changes that occur at a very low frequency in a gene. Spontaneous mutations (popularly known as ‘sports’) alter the existing genes and their expression, resulting in stripes. Induced mutations by irradiation or chemical mutagens also lead to genetically-altered  pigmentation, and the result is stripes. Stripes may develop as a result of the transmission of genes responsible for stripes through hybridization. Viral infection that causes variegation in tulips may also cause stripes in roses. These infections could interfere with physiological functions of pigmentation, giving them a striped appearance.

It is possible that a mutation has occurred during mitosis somewhere at the base of the new branch and all the cells in the new branch carry the mutated gene, which is expressed as a striped phenotype. If this is the case, a cutting from this branch will also produce striped flowers. So, I will take a cutting and propagate this rose, to see if we can produce more of these beautiful mutants!

Human intervention in evolution

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Humans have had an influence on evolutionary processes for much longer than you may have thought – we have tamed wolves and wild cats to become the many breeds of domestic dogs and cats that share our homes today and we have selected cattle, sheep, goats and pigs over many generations for food characteristics. Our main food crops such as rice, corn, wheat, as well as many fruit and vegetables, are very different to their wild ancestors.

Artificial selection, or selective breeding, is the process by which humans breed other animals and plants for particular traits; for example, increased size, fast muscle growth or sweeter taste. This can be a deliberate process, like when farmers choose to breed animals or plants with particular characteristics or it can be accidental. In Asia and Africa, over many centuries, bull elephants with particularly large tusks have been targeted as trophies and for their valuable ivory. As a consequence, individuals with large tusks produce fewer offspring and become less frequent in the population. (Read more about elephant evolution here and here).

In more recent times, due to greater understanding of genetic inheritance and modern gene technology, we have been able to identify specific genes that code for particular characteristics and create new breeds of organisms with beneficial traits – drought tolerance, increased productivity or improved storage life, for example.

Play the videos from ABC Splash “Genetic Engineering of Crops”

Some sites that may be useful for your research project:

Population genetics

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Population genetics is the study of distributions and changes in allele frequency in a population, as the population is subject to the four main evolutionary processes:

  • Natural selection
  • Genetic Drift
  • Mutation
  • Gene flow (by migration or distribution of pollen and seeds)

Variation between individuals and species and polymorphism: In any normal population there is some variation between individuals – a box of apples may have individual apples that are slightly different sizes and shapes with slightly different colour variations, even when they come from the same tree. So, not all variation is caused by genetic differences. It may be environmental differences that result in the variation – for example, the amount of light, temperature or soil nutrients in the case of plants or the nutrition and experiences provided to animals. Some characteristics , such as height or wing length might show continuous variation, while other characteristics can be clearly separated into different categories (discontinuous variation). An example of discontinuous variation in humans might be the ability to roll one’s tongue – you can either do this or you can’t – there is no blending, or in-between characteristic. Polymorphism occurs when two or more clearly defined phenotypes are present in the population. A classic example is the light and dark coloured morphs of the peppered moth. The ABO blood grouping is an example in human populations.

Inherited variationsFrom our Unit 3, Area of Study 2 work, we understand that the DNA molecule, present in every cell of living organisms, codes for proteins that determine the phenotype of an organism. DNA is passed from one generation to the next through reproduction, which can occur asexually or sexually (with the production of gametes (meiosis) and fusion of sperm and egg). So, families of individuals tend to look more alike than non-related individuals due to these inherited characteristics. This was seen in our work with pedigree trees, showing how genetic diseases can be passed on through several generations.

Mutations – sources of variation: The source of these variations is genetic mutations – check pages 371-372 and 477-478 in your textbook “Nature of Biology”. Genetic mutations may be spontaneous or may be induced by exposure to mutagenic agents (X-rays and Gamma rays and some chemicals, such as benzene and mustard gas).

Gene pool, gene flow, genetic drift (by chance): The gene pool is the set of all genetic information in a population, while gene flow describes how genes leave and arrive in a population by death and emigration or births and immigration. Genetic drift is the change of gene frequencies due to random sampling.

Polygenes, polygenetic traits: Polygenes are non-allelic genes that together influence a phenotypic trait – often the precise loci of these genes is unknown to biologists. Examples of polygenetic traits in humans are height, weight and skin colour.

Mitochodrial DNA: Mitochondrial DNA is a single, circular strand of DNA found in the mitochondria of eukaryotic cells. In most species, mitochondrial DNA is inherited solely form the mother. In humans, mitochondrial DNA was the first significant part of the human genome to be sequenced.

Founder and bottleneck effects:The founder effect is the lost of genetic variation that occurs when a new population is established by a small group of individuals from a larger population. The people of Easter Island and Pitcairn Island show limited genetic variability (small gene pools) due to this effect. A similar effect is the bottleneck effect, when large numbers of a population are removed, leaving a small gene pool.  As a species, cheetahs have famously low levels of genetic variation. In fact, cheetahs are so closely related to each other that transplanted skin grafts do not evoke an immune response. This can probably be attributed to a population bottleneck they experienced around 10,000 years ago, barely avoiding extinction at the end of the last ice age. However, the situation has worsened in modern times. Habitat encroachment and poaching have further reduce cheetah numbers, consequently snuffing out even more genetic variation and leaving cheetahs even more vulnerable to extinction.

 

 

Recombinant DNA technologies

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On Monday we had the opportunity to connect with the Gene Technology Access Centre via the video conferencing equipment, Polycom. Nicole and Frazer facilitated a great session about recombinant DNA technology, including a demonstration of gel electrophoresis to determine if genes had been successfully inserted into a plasmid.

Did you know that humans have the same gene sequences as other organisms?

  • 61% similarity to fruit flies
  • 99% similarity to mice
  • 99.9% similarity to chimpanzees

The human genome has 22 pairs of autosomes and 1 pair of sex chromosomes (XX in females and XY in males). Chromosomes exisit in the nucleus (as single strands) and there is also some (maternal – passed down from the mother) DNA in the mitochondria, which is circular. Prokatyotes (bacteria) also have circular DNA called ‘plasmids’.

Sea jellies have a gene that codes for a protein that is luminescent, called a “green fluorescent protein”. This gene is a useful marker, to determine if other genes have been successfully introduced to an organism.

Restriction enzymes (used for ‘cutting’ DNA) are used to open the plasmid, the new gene is inserted and then a DNA ligase is used to stick the ends together. We are using four different restriction enzymes (EcoRY13; BamH1; Nhe1 and Sma1). The DNA sequence at a restriction site is a palindrome – reads the same forwards and backwards. Some restriction enzymes cause ‘sticky’ ends (uneven or with a tail – exposed base pairs) while others cause ‘blunt’ ends (no overhanging base pairs). Once the new gene is inserted, complementary base pairs are joined by hydrogen bonds – or ‘pasted together’ with DNA ligase.

This is the process we will model using the paper cut-outs:

  1. E.coli is a bacteria that can be resistant to various antibiotics (eg. Amp R = ampicillin resistant).
  2. Cut the plasmid using a restriction enzyme.
  3. Insert the gene of interest into the plasmid, stick it together and produce the recombinant plasmid, which should contain the ampicillin resistance gene as well as the “GFP” (green fluorescent protein) gene.
  4. To test if the recombination has been successful, we need to use the restriction enzymes to produce various lengths of DNA. These are then pipetted into ‘wells’ in the gel. Because DNA is a negatively charged molecule, we load the wells at the negative end and attach the positive wire to the other end, so that the pieces of DNA a drawn through the gel matrix to the other side. The longest pieces move more slowly and travel the shortest distance, while the shortest molecules move most quickly through the gel and travel the greatest distance.

Mendel’s Peas

Learning Intention: Students will understand the significance of Gregor Mendel in the history of genetics and be able to use the following terms correctly: dominant, recessive, alleles, genotype, phenotype, homozygous, heterozygous, cross-pollination, self-pollination and F1 generation.

Success Criteria: Students will complete the following three activities and be able to describe what they have learned in a class discussion.

Gregor Mendel (1822-1884) was an Austrian monk who is known as the father of modern genetics due to his experimental work with plant hybridization. It was Mendel who first coined the terms “dominant” and “recessive” and he formulated generalizations that have become known as “Mendel’s Laws of Inheritance”. “Mendel’s Pea Genetics – Experiments that changed the world” is a twenty-five minute documentary that describes his life. Complete the following three activities: