Human Bio Ch 9

Question 1

What is a population?

Answer 1

A group of organisms of the same species living together in a particular place at a particular time

Question 2

What is a gene pool?

Answer 2

The sum of all the alleles carried by the members of a population

Question 3

What is allele frequency?

Answer 3

How often each allele of a gene occurs in a population

Question 4

What is a mutation and what are the 2 types?

Answer 4

Mutation is a change in a gene or chromosome leading to new characteristics in an organism. 2 types:
1. Gene mutation - an alteration to a single gene
2. Chromosomal mutation - a change to the structure and/or numbers of chromosomes in an organism

Question 5

What are examples of mutagens?

Answer 5

When exposed to what is known as mutagen mutations can occur, examples are:
1. mustard gas
2. formaldehyde
3. sulfur dioxide
4. some antibiotics
5. ultraviolet light
6. X-rays
7. gamma rays

Question 6

What are the 2 types of causes for mutations?

Answer 6

1. Induced mutation - mutagens in the environment
2. Spontaneous mutation - random error or biological process

Question 7

What are the 2 main ways a mutation is classified for heritability?

Answer 7

1. Somatic - a change occurring in a gene in a body cell (only this individual is affected)
2. Germline - a change in the hereditary material in the egg or sperm that becomes incorporated into the DNA of every cell in the body (can be passed down generations)

Question 8

What are the 4 main effects of a mutation?

Answer 8

1. Missense - cause a change in the amino acid, and therefore in the protein produced.
2. Nonsense - change the base sequence to the code to stop. This means that the synthesis of the protein will stop, and so a shorter protein is produced that is unlikely to be ubel to fulfil its function.
3. Neutral - cause a change in the amino acid, however the amino acid is of the same type and does not change the structure of the protein enough to change its function.
4. Silent - do not cause any change in the amino acid, and therefore in the protein produced, This is possible as most amino acids are coded for more than one base sequence.

Question 9

What is a point mutation and how does it occur?

Answer 9

A point mutation is a change in just one of the bases in a DNA molecule (nucleotide). These changes may be due to a nucleotide being:
1. inserted - a new nucleotide is added to the DNA strand
2. substituted - an existing nucleotide is replaced with another one, with a different base
3. deleted - a nucleotide is removed from the DNA strand

Question 10

What is a frameshift mutation?

Answer 10

Is a mutation involving an insertion or deletion that results in a change in the way that the sequence is read.

Question 11

What are examples of larger mutations that affect a larger section of DNA?

Answer 11

1. duplication - a section of a chromosome occurs twice
2. deletion - a piece of DNA is removed
3. inversion - breaks occur in the chromosome and the broken piece joins back in, but the wrong way around
4. translocation - part of a chromosome breaks off and is rejoined to the wrong chromosome
5. non-disjunction - during meiosis a chromosome pair does not separate and so one daughter cell has an extra chromosome and one daughter cell has one less. Referred to aneuploidy (a change in chromosome number) can be seen as down syndrome.

Question 12

What conditions can a gene mutation cause?

Answer 12

Duchenne muscular dystrophy - a genetic disease resulting in wasting of leg muscles and then arms, shoulders and chest. This may arise through a mutation in the mother which can then be inherited by her sons. Usually becomes apparent around 3-5 y/o and the lifespan is up to 20 -25 y/o.

Cystic Fibrosis - mucus-secreting glands in the lungs and pancreas become fibrous and produce abnormally thick mucus resulting in, among other things, chest infections. This mutation occurs on a huge gene on chromosome number 7. Mutant allele is recessive so must inherit from both parents.

Question 13

What conditions can a chromosomal mutation cause?

Answer 13

1. Trisomy - is a result of non-disjunction. Extra chromosome. Results in Trisomy 21 (down syndrome), the child will have 3 of chromosome 21 instead of 2. People with down syndrome have a characterised facial expression, intellectual disability and weakened muscles. Many symptoms of down syndrome can still occur even if only part of an extra chromosome is attached. This is called partial trisomy.
   Patau Syndrome can also occur when there is an extra chromosome on chromosome 13 which causes intellectual disability, an extra finger, cleft palate and malformations of ears and eyes. The extra chromosome can come from either the mothers egg cell of fathers sperm cell. Can affect sex chromosomes, with an extra X/Y chromosome have Klinefelter syndrome and have small testes, do not produce sperm, breasts are enlarged and body hair is sparse
2. Monosomy - missing a chromosome. If a chromosome is completely missing, monosomy usually results in severe malformations and miscarriage. If only part of the chromosome is missing than it is said to be partial monosomy. An example of partial monosomy is Cri-du-chat syndrome, genetic disorder due to a missing portion of chromosome 5, causes the cry of an infant to sound like a cat meowing due to problems with larynx and nervous system. Can also affect sex chromosomes females with only one X chromosome have Turner Syndrome and are short in stature, lack secondary sexual characteristics and are infertile.

Question 14

What is a lethal recessive mutation and what is an example?

Answer 14

Lethal recessive - a recessive allele that is inherited in the homozygous condition, results in the death of the embryo, foetus or child.

Tay-Sachs disease - a genetic disorder caused by a missing enzyme that results in fatty substances accumulating in the nervous system. There is a mutation on the HEXA gene that codes for the enzyme beta-hexosaminidase which is responsible for breaking down toxic substances including fatty substances called GM2 ganglioside in the brain and spinal cord. Death usually occurs in early childhood.

Question 15

What is migration?

Answer 15

The movement of people from one area to another with the intention of settling permanently.

Question 16

What is gene flow?

Answer 16

The transfer of alleles from population to another through migration.

Question 17

What are the 2 main barriers to gene flow?

Answer 17

1. Geographical barriers - oceans, mountain ranges, large lakes, desserts etc. (feature of the landscape that prevents populations from interbreeding)
2. Sociocultural - economic status, educational background, social position etc. (social or cultural factors that lead to a barrier in interbreeding)

Question 18

What is natural selection and what was Darwin’s 3 observations?

Answer 18

The process by which a species becomes better adapted to its environment, those individuals with favourable characteristics have a survival advantage and so pass those characteristics onto subsequent generations.

Observations:
1. Variation - all members of a species vary. Variations were passed onto offspring.
2. Birth rate - living organisms were reproducing at a rate far greater than what their food supplies and resources could handle.
3. Nature’s balance - although birth rate was high, species maintained a relatively constant population.

Question 19

What does survival of the fittest mean?

Answer 19

Thos with favourable survived, while many of those with unfavourable characteristic died before they had the opportunity to reproduce.

Question 20

What are some examples of natural selection?

Answer 20

1. Body stature
   - inuits (long body, short limbed) smaller surface area in relation to body volume and lose less heat in cold environments and therefore have a survival advantage.
   - africans (short body, long limbs) larger surface area to lose more heat in hot environments and therefore have a survival advantage.
2. Sickle cell anaemia - an inherited disease causing early death results from the inheritance of 2 alleles of sickle cell anaemia. RBC’s are of a crescent shape, die early, inflexible and can become stuck in the blood vessels causing a blockage.
   Homozygous normal - no sickle cell anaemia susceptible to malaria
   Homozygous recessive - have sickle cell anaemia
   Heterozygous advantage - have sickle cell anaemia trait survive against malaria (show no symptoms unless oxygen is in low supply)
3. Tay-Sachs disease - lethal conditions that causes a build up of fatty substance in the CNS due to the absence of the enzyme beta-hexosaminidase.
   Homozygous recessive - die before in early childhood therefore do not reproduce (have tay-sachs)
   Homozygous normal - have no tay-sachs but are susceptible to contract tuberculosis and possibly die before reproducing.
   Heterozygous advantage - survive tuberculosis and pass on both alleles.
4. Thalassemia - alters the structure of of haemoglobin.
   Alpha thalassemia - due to a mutation on the HBA gene on Chr 16 (reduces alpha globin in haemoglobin)
   Beta thalassemia - due to mutation of the HBB gene on Chr 11 (reduces level of beta globin in haemoglobin)
   More common in areas affected by malaria. Have less haemoglobin in their red blood cells and therefore cannot carry as much oxygen around the body. Severity of disorder varies depending the number of genes affected.

Question 21

What is genetic drift?

Answer 21

The occurrence of characteristics in a population as a result of chance rather than natural selection, occurs only in small populations. Random, non-directional change in allele frequency that occurs by chance.

Question 22

What are 2 examples of genetic drift?

Answer 22

1. Founders effect - a new population is formed by a small number of individuals, small sample size can cause marked deviations in allele frequencies from the original population. An example of this is the Ashkenazi Jews and their high frequency of Tay-sachs disease. They have isolated themselves and only marry within their community this created a founder effect as the tay-sachs disease which is normally a 1 in 300 chance in non ashkenazi jews is now a 1 in 27 chave in ashkenazi jews.
2. Bottleneck effect - occurs when the size of a population is significantly reduced due to a sudden event such as a natural disaster. The allele frequency of the survivors may not reflect that of the original population. An example is when a typhoon reduced the population of Pingelap (island in Micronesia) to only 20. One of these people was heterozygous for the total color blindness disease and passed that gene on.

Question 23

What is speciation and what are the steps involved?

Answer 23

Speciation is the process of new species developing.
A species is the basic unit of biological classification, members of a species are capable of interbreeding and producing fertile offspring.

The steps include:
1. variation - there is variation between individuals of a species
2. Isolation - populations of the same species are isolated without gene flow
3. selection - each population is subjected to different selective agents
4. speciation - the allele frequencies change until they become so different they are no longer able to interbreed.

Question 24

Explain Speciation in more depth?

Answer 24

1. a range of variations exist within a population, which shares a common gene pool
2. a barrier has formed dividing the population into 2. No interbreeding occurs between the 2 populations. Each population has a separate gene pool .
3. different selection pressures act on each of the 2 populations over a number of generations. This brings about a change in the gene frequencies of each gene pool. Such changes lead to evolution of separate subspecies.
4. over a long period of time the changes in the gene frequencies may be great enough to prevent the production of fertile offspring by interbreeding between the 2 populations from ever occurring again. When this happens, 2 species exist.