Biology IB HL - 3.4 Inheritance Part 3

The formation of a blood clot is controlled by a cascade of coagulation factors whose genes are located on the X chromosome

When one of these factors becomes defective, fibrin formation is prevented - meaning bleeding continues for a long time

Different forms of haemophilia can occur, based on which specific coagulation factor is mutated (e.g. haemophilia A = factor VIII)

Red-green colour blindness is a genetic disorder whereby an individual fails to discriminate between red and green hues

This condition is caused by a mutation to the red or green retinal photoreceptors, which are located on the X chromosome

A gene mutation is a change to the base sequence of a gene that can affect the structure and function of the protein it encodes

Mutations can be spontaneous (caused by copying errors during DNA replication) or induced by exposure to external elements

radiation

chemical

biological agents

e.g. UV radiation from the sun, gamma radiation from radioisotopes, X-rays from medical equipment

Chemical – e.g. reactive oxygen species (found in pollutants), alkylating agents (found in cigarettes)

Biological Agents – e.g. bacteria (such as Helicobacter pylori), viruses (such as human papilloma virus)

Agents which increase the rate of genetic mutations are called mutagens, and can lead to the formation of genetic diseases

Mutagens which lead to the formation of cancer are more specifically referred to as carcinogens

The nuclear bombing of Hiroshima and accident at Chernobyl are two examples of a catastrophic release of radioactive material

The nuclear bombing of Hiroshima (and Nagasaki) occurred in August 1945, during the final stages of World War II

The Chernobyl accident occurred in April 1986, when an explosion at the reactor core caused the release of radioactive material

The Chernobyl meltdown involved far more fissionable material and produced different isotopes with much longer half-lives

The Hiroshima nuclear bomb was detonated above ground and radiation was dispersed, resulting in less irradiation of the soil

An increased incidence in cancer development (with a strong correlation between dose of radiation and frequency of cancer)

Reduced T cell counts and altered immune functions, leading to higher rates of infection

A wide variety of organ-specific health effects (e.g. liver cirrhosis, cataract induction, etc.)

Some of the consequences of radiation exposure are specific to the incident due to the types and amounts of radiation released

Thyroid disease was a common consequence of the Chernobyl accident due to the release of radioactive iodine

There was no significant increase in birth defects following the Hiroshima bombing, but an estimated 250% increase in congenital abnormalities following the Chernobyl meltdown

There is anecdotal evidence to suggest that radiation levels around Chernobyl have caused variation to local flora and fauna

The presence of residual radiation in the environment can become concentrated in organisms via bioaccumulation

There is anecdotal evidence to suggest that radiation levels around Chernobyl have caused variation to local flora and fauna

The presence of residual radiation in the environment can become concentrated in organisms via bioaccumulation

A pedigree is a chart of the genetic history of a family over several generations

Males are represented as squares, while females are represented as circles

Shaded symbols mean an individual is affected by a condition, while an unshaded symbol means they are unaffected

A horizontal line between man and woman represents mating and resulting children are shown as offshoots to this line

Generations are labelled with roman numerals and individuals are numbered according to age (oldest on the left)

If both parents are affected and an offspring is unaffected, the trait must be dominant (parents are both heterozygous)

If both parents are unaffected, all offspring must be unaffected (homozygous recessive)

All affected individuals must have at least one affected parent

If both parents are unaffected and an offspring is affected, the trait must be recessive (parents are heterozygous carriers)

If both parents show a trait, all offspring must also exhibit the trait (homozygous recessive)

It is not possible to confirm sex linkage from pedigree charts, as autosomal traits could potentially generate the same results

However certain trends can be used to confirm that a trait is not X-linked dominant or recessive

If a male shows a trait, so too must all daughters as well as his mother

An unaffected mother cannot have affected sons (or an affected father)

X-linked dominant traits tend to be more common in females (this is not sufficient evidence though)

If a female shows a trait, so too must all sons as well as her father

An unaffected mother can have affected sons if she is a carrier (heterozygous)

X-linked recessive traits tend to be more common in males (this is not sufficient evidence though)