genetics discussion 1 (genetic diversity, evolution, meiosis, chromosomes)

Question 1

1a. Large numbers of offspring ensured selection of the fittest in any particular species. With birth control are humans limiting their chances for creating diversity to survive environmental change?

Answer 1

danilla
Actually not sure it is.

Yes, as birth control decreases the opportunity for mutation and genetic recombination events, it therefore limits genetic variation. As evolutionary changes take place via changes in the frequency of alleles between one generation and the next, a lack of natural selection may slow down chances of survivability traits against a rapidly changing environment.

Unfortunately we are changing the world must faster than nature does so we are unable to evolve fast enough to keep up with the pace of this change.

Question 2

1b. Why do we potentially face a crisis with many vegetable and fruit types due to our intervention in enabling mass food production?

Answer 2

Mass food production decreases genetic variation in our food as they are all clones of one another. This means there is no variation in disease exposure making humans less likely to build up their immunity. An example would be the Cavendish banana

This decreases the biodiversity across our crops, which does not allow variety in the genetic pool to fight against viruses etc.

Question 3

Why is the current concern about global warming linked to the concept of natural selection?

Answer 3

Natural selection is when species of animals and plants are best adapted to their environment survive and are best suited to reproduce.

The current concern about global warming is linked to the concept of natural selection by ensuring only the fittest survive to pass their genes on to the next generation. The species that are able to survive the changes in the environment are most likely to adapt and evolve to the climate changes and therefore are more likely to pass on their genes. However climate change is occurring faster than many species ability to evolve, thus many species may become extinct.

Further note: Some may say that our greatest selection pressure at this time is indeed our own human species, more specifically human-induced climate change. If we can’t first accept, and secondly put in place major changes to adapt to these threats we face, we will be among the 150-200 species of plant/insect/bird/mammal going extinct every day.

Question 4

3. We have said that the brightly coloured male always gets the birds. How is it then, that more than one male gets to mate?

Answer 4

Darwin’s theory states that there are two selective pressures, sexual selection (competition for mates between the same sex) and ecological selection (competition for food and avoiding predators). Although males with bright feathers have mating success, males with feathers that aren’t as bright may have survived longer and be good at getting meals.

Possibly. Another reason is that the alpha male can’t be in multiple places at once. So a smart male will steal an opportunity when they can!

Question 5

Latest findings from genetic research suggests that over 70% of mental illness due to depression, schizophrenia and bipolar disorder are due to genetic causes. How could this be possible in a person who has no family history of mental illness? (I’m looking for an answer that does involve genetic code).

Answer 5

The mechanism behind genetic aetiology of mental illness is poorly understood as it is thought to involve complex interactions between many genes. However, epigenetics is a growing field of research that may help to explain varying expressions of genetic code that cause these mental illnesses.

Change in DNA methylation is one of many epigenetic mechanisms that can alter the activity and expression of a gene, without affecting its code.

Therefore, two people with the same genotype may have different phenotypes if exposed to different environmental conditions (e.g. hyper/hypo-methylation). A person with a mental illness who has no family history of mental illness may simply be expressing a gene differently than the rest of their family.

Question 6

Explain how a chromosome changes through DNA recombination and how this is different from mutation in a nucleotide.

Answer 6

mutation in a nucleotide can change a single base in the gene which may or may not change the protein sequence. Compared to a single base deletion mutations are as harmful. Mutations can introduce new alleles into a population which causes genetic variation, but is accidental.

Recombination occurs when two molecules of DNA exchange pieces of genetic material with one another. This also produces new combinations of alleles however is purposely done by the body.

Include also that crossover occurs during meiosis and this introduces the opportunity for mistakes to occur.

Question 7

6*. Chimpanzees have 24 pairs of chromosomes, humans have 23. How could they have a possible common ancestor?

Answer 7

It is believed by scientists that the chromosome 2 in humans is a fusion of two chimpanzee chromosomes. The fusion would have occurred once in a single individual and every single human being on earth would have to be a descendant of that one individual.

Question 8

Give a reason why the 98% of our DNA, called junk DNA, couldn’t possibly be junk DNA.

Answer 8

Junk DNA or “Non-Coding DNA” refers to the DNA that does not encode protein sequences, however, it does play a vital role in encoding the telomeres on our chromosomes, along with also having areas for regulation proteins to turn on and off transcription such as the example of the antibodies produced during the third line of our defense.

Question 9

8*. Why does A nearly always bind to T and G nearly always bind to C?

Answer 9

Binding of A-T and G-C pairings are formed on the basis of their ability to form hydrogen bonds. Therefore, A-T bind due to having 2 hydrogen bonds, and G-C pair as they both have 3 hydrogen bonds. It is occurrences where DNA will bind incorrectly (A-C) that DNA mutations can occur.

Question 10

9*. DNA is called the double helix. Why does it need to separate at times?

Answer 10

DNA double helix needs to seperate at some times so that our cells can replicate our DNA strands. New DNA is needed every time cells divide so that the original number of chromosomes is preserved in each daughter cell.

Question 11

10*. Why are there 23 pairs of chromosomes rather than 46 non-paired chromosomes?

Answer 11

One chromosome from each pair is inherited from each biological parent. Our diploid number is 46 and our haploid number is 23.

Question 12

Why are bands visible on the chromosomes in many photographs of actual chromosomes?

Answer 12

Chromosomes are treated with stains to reveal patterns of horizontal bands whilst also pairing and ordering all the chromosomes (karyotyping). This is called G-banding.

Darker bands visible are of adenine and thymine (A-T) and lighter bands consist of guanine and cytosine (G-C). The bands are then numbered on each arm of the chromosome, allowing any particular band to be precisely identified. Bands form an identical pattern on homologous chromosomes, giving them a distinctive appearance. Banding is used to find any chromosomal abnormalities, such a translocations, chromosome deletions through lost segments, and chromosome duplications through surplus segments. These abnormalities would disrupt the pattern of light and dark bands unique to each set of chromosomes.

Question 13

12*. How do the chromosomes differ in male and female cells?

Answer 13

Chromosomes differ in male and female cells as females have two of the same kind of sex chromosomes (XX) whereas males have two different kinds of sex chromosomes (XY). Females are therefore called the homo-gametic sex whilst the males are known as the hetero-gametic sex. The Y chromosome also appears to be shorter in shape in comparison to the X chromosome

Question 14

Why are telomeres important in understanding malignant cancer?

Answer 14

Telomeres are crucial for the survival of cancer cells. They are maintained by an enzyme called telomerase in the vast majority of tumors. The mechanisms underlying telomere length (TL) maintenance and telomerase expression involve transcriptional, post-transcriptional and epigenetic regulation, and in-depth understanding of these mechanisms may provide novel biomarkers and targets for early detection of disease, determination of disease prognosis, and the development of therapeutics.

Question 15

What is the purpose of meiosis?

Answer 15

To halve the number of chromosomes so that gametes can be produced. When an egg and sperm unite, the original number of chromosomes is restored. Also there is an important step of chromosome cross over so that there is genetic mixing to enable genetic variety in the offspring.

The purpose of meiosis is related to reproduction, with the objective of increasing diversity in offspring.
The crossing over of chromosomes that results in genetic variability in phenotypes within the same species
A means for increasing chances of survival
The process of reducing the gamete diploid number to 4 daughter cells - with 23 chromosomes each

Question 16

Polymorphs have a short life span of around a month. How does the body ever produce enough if apoptosis limits the number of times polymorphs can divide?

Answer 16

Neutrophils are produced for progenitor stem cells which originate in the bone marrow. 1011 neutrophils are produced every day through this process . From here, neutrophils enter the blood where they circulate until they leave into tissues (where they are called polymorphs). Once polymorphs reach the end of their short lifespan within tissues, they are cleared through phagocytosis. Despite the rapid turnover, the number of neutrophils in circulation remains relatively constant due to the large numbers being produced in the bone marrow.

Question 17

How could you describe A, B and O blood types from a genetic point of view (you must use the word allele in your answer)?

Answer 17

There are 3 versions or “alleles” of a person’s blood type: A, B and O. A person’s blood type is determined by which allele they inherit from each parent.

Both the A and B alleles are dominant over O. therefore an individual who has an AO genotype will have an A phenotype. If both an A and B allele are inherited, both are expressed. O is a recessive allele, therefore individuals who are type O have OO genotypes, thus they inherited a recessive O allele from both parents

Question 18

17*. A haploid cell can be found in which types of tissue in the body?

Answer 18

A haploid cell can be found in egg or sperm cells, as the contain 23 single chromosomes

Question 19

Give two important aspects that makes meiosis different from mitosis.

Answer 19

1. Meiosis involves two divisions whereas mitosis involves only one.
2. Meiosis also produces 4 daughter cells that are genetically varied (due to cross-over of chromosomes) compared to their parent cell, whereas mitosis produces 2 daughter cells that are genetically identical to their parent cell (provided there is no mutations).

Question 20

Using meiosis explain why children may have characteristics of both their maternal grandparents, even though only one copy of mum’s gene is present in the children.

Answer 20

A child receives 50% of their DNA from their mother, this 50% contains a combination of maternal grandparent DNA. The relationship between a mother and her child involves a single meiosis event, the one that formed the egg that made the child. When a mother’s cell undergoes meiosis, it recombines the grandparent chromosomes to produce a unique set of chromosomes to pass on to a child. This recombination is produced by the process of crossing over in meiosis 1, where pairs of homologous chromosomes (one from each pair is maternal and one is paternal) exchange segments between non-sister chromatids which results in new allele combinations in the haploid daughter cells. One of these daughter cells is the eggs cells which will eventually fuse will the sperm cell from the father to make the child. This means that although the child does not get an even 1/4 of DNA from each grandparent, there will be genes from each of their maternal grandparents in their DNA.

Question 21

Explain what Trisomy is and give an example of a human syndrome resulting. Why do all humans with this syndrome have different presenting symptoms and different levels of disability?

Answer 21

Trisomy is the result of nondisjunction (an error in cell division) which can lead to an extra chromosome or part thereof causing Down syndrome (of which there are three different types) (21), Edward syndrome(18) or Patau syndrome(13).

The level of disability varies due to amount of chromosome being affected (was it a whole or part). Age of the mother can be a risk factor for Down syndrome.

Question 22

21*. If round and wrinkled pea seed alleles were co-dominant, what do you think the offspring’s seed shape would be?

Answer 22

The offspring would express a blend of both the wrinkled and round shape as it would acquire a dominant round shape allele and a dominant wrinkled shape allele.

Question 23

22*. How is telomerase important in understanding skin cancer?

Answer 23

Telomerase protects the telomeres from getting shortened (replicates them by adding TTAGGG repeats). The shortening of the telomeres acts as a signal that the cell is getting older and will trigger apoptosis, however skin cells have telomerase present which prevents this from happening. Therefore the skin cells are more prone to mutating and becoming cancerous as they don’t undergo apoptosis, are constantly replicating and are exposed to the external environment.