Chapter 9 - Evolution produces changes across generations

Question 1

Evolution

Answer 1

The gradual change in characteristics of a species overtime. Occurs over many generations

Question 2

Phenotype

Answer 2

The observable characteristic due to genotype

Question 3

genotype

Answer 3

The combination of alleles for a gene

Question 4

How do changes to the alleles present in a population occur

Answer 4

New alleles forming as a result of mutations or being introduced through migration

Question 5

How does the frequency of alleles in the population change

Answer 5

Frequency of alleles may alter because of a selective pressure in natural selection or by chance in genetic drift

Question 6

Population

Answer 6

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

Question 7

Gene pool

Answer 7

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

Question 8

Allele frequencies

Answer 8

How often each allele of a gene occurs in population. Populations that differ in the characteristics they possess are likely to have different frequencies of the various alleles of a gene in their respective gene pools

Question 9

Mutation

Answer 9

A sudden and permanent change in a gene on a chromosome leading to new characteristics in an organism

Question 10

Mutant

Answer 10

An organism with a characteristic resulting from a mutation

Question 11

what are the two main types of mutations

Answer 11

• Gene mutations: changes in a single gene so that the traits normally produced by that gene are changed or destroyed
• Chromosomal mutations: A change to the structure and or number of chromosomes in an organism

Question 12

Mutagens

Answer 12

An environmental agent that increases the rate of mutation. eg, Mustard gas, sulphur dioxide, some antibiotics, ionising radiation (UV, x-rays, cosmic rays, radiation from radioactive waste, fallout from atomic and nuclear explosions)

Question 13

Albinism

Answer 13

Results from one missing protein, marked by an absence of pigment from the hair, skin and eyes

Question 14

how are mutations classified

Answer 14

By a number of different characteristics. It is the some of these characteristics that determines the overall impact the mutation will have on the individual

Question 15

What are the two causes of mutations

Answer 15

• Induced mutations: a mutation caused by a mutagenic agent

- Spontaneous mutations: A mutation that occurs due to an error in a natural biological process (mitosis, meiosis)

Question 16

what are the different ways of classifying mutations

Answer 16

Heritability of the mutation, effects of the medication and the extent of the mutation

Question 17

Somatic mutation

Answer 17

A change occurring in a gene in a body cell. Only the individual with the mutation is affected. Each time the mutant cell divides, mutation is passed onto the daughter cell. As reproductive cells are not affected, once the individual dies, the mutation is lost, not passed on. Somatic mutations involved in many cancerous growth and maybe result of mutagenic agent.

Question 18

Germline mutations

Answer 18

A change in the hereditary material in egg or sperm that becomes incorporated into the DNA of every cell in the body of the offspring. Individual with mutation not usually affected however mutation passed on to next and subsequent generations. Eg, PKU can arise through a mutation during the formation of gametes and can be passed onto offspring

Question 19

Missense mutations

Answer 19

Causes change in an amino acid resulting in a different protein being produced

Question 20

nonsense mutations

Answer 20

Changes base sequence to a STOP codon, producing a shortened peptide chain unlikely to fulfil its function

Question 21

neutral mutations

Answer 21

Causes a change in amino acid but does not change structure of protein enough to change its function

Question 22

silent mutations

Answer 22

Does not change sequence of amino acids and therefore in the protein produced. Possible as most amino acids are coded for by more than one base sequence

Question 23

What are the four ways the effect of a mutation are classified

Answer 23

• Missense mutations
• nonsense mutations
• neutral mutations
• silent mutations

Question 24

Extent of the mutation

Answer 24

Another characteristic used to classify mutations is the amount of DNA affected. Could range from a single base to a whole chromosome. A gene mutation affects only a single gene, a chromosomal mutation affects a number of genes. May change the structure of a chromosome or the number of chromosomes. Chromosomal mutations often cause abnormalities so severe that miscarriage often occurs in early pregnancy

Question 25

Point mutation

Answer 25

A change in just one of the bases of a DNA molecule. may be due to a nucleotide being:

• Inserted: a new nucleotide added to DNA strand
• Substituted: An existing nucleotide is replaced with another one, with a different base
• Deleted: a nucleotide is removed from the DNA strand

Question 26

Frameshift mutation

Answer 26

Some mutations result in a frame shift. A frame shift is a mutation involving an insertion or deletion that results in a change in the way the sequence is read. Will not occur when three bases are added or deleted. In these instances, the DNA will simply code for one more or one less amino acid but the result will be the same

Question 27

What are the five reasons for mutations affecting the largest section of DNA

Answer 27

• Duplication (or insertion): section of chromosome occurs twice
• Deletion: piece of DNA is removed (e.g. cri du chat)
• Inversion: breaks occur in a chromosome and the broken piece joins back in, but the wrong way around
• Translocation: part of a chromosome breaks off and is rejoined to the wrong chromosome
• Non-disjunction: failure of a chromosome pair to separate and so one daughter to cell has an extra chromosome. Referred to as aneuploidy

Question 28

Aneuploidy

Answer 28

A change in the chromosome number as a result of non-disjunction

Question 29

Two diseases causes by gene mutations

Answer 29

• Duchenne muscular dystrophy: Genetic disease resulting in wasting of leg muscles and then arms, shoulders and chest. May arise through mutation in the mother which can then be inherited by her sons or mutation may occur in male zygote. Becomes apparent around the age of 3 to 5, unlikely to live for more than 20 to 25 years. eventually death occurs due to Failure of respiratory muscles
• Cystic fibrosis

Question 30

Diseases cause by chromosomal mutations

Answer 30

• Trisomy: Down syndrome, Patau syndrome, Klinefelter syndrome
• Monosomy: Cri-du-chat syndrome, Turner syndrome

Question 31

Trisomy

Answer 31

Result of non-disjunction. The eggs or sperm formed when non-disjunction occurs have one chromosome to many or one chromosome is missing

Question 32

Partial trisomy

Answer 32

when parts of an extra copy of chromosome 21 is attached to one of the other chromosomes

Question 33

monosomy

Answer 33

Where in individual has only one copy of a chromosome instead of two

Question 34

partial monosomy

Answer 34

Where part of a pair of chromosomes is missing

Question 35

Lethal recessives

Answer 35

A recessive allele that, inherited in the homozygous condition, results in the death of the embryo, foetus or child. EG, Tay sachs

Question 36

Tay sachs disease

Answer 36

Disorder of lipid metabolism that is inherited in an autosomal recessive pattern. It is a lethal recessive condition caused by a mutation in the gene that codes for an enzyme that is responsible for breaking down toxic substances, including fatty substances in the brain and spinal-cord. The missing enzyme results in the accumulation of fatty substances in the nervous system, which destroys the neurons. A baby with two recessive alleles for tay sachs develops normally for the first few months, and then deterioration that causes intellectual and physical disability begins. Death occurs in early childhood

Question 37

Gene flow

Answer 37

The transfer of alleles from one population to another through migration

Question 38

Migration

Answer 38

The movement of people from one area to another with the intention of settling permanently. If immigrants to a certain country bring alleles that are not already in the population, the frequencies for that allele of that gene will be altered

Question 39

What are the two barriers to gene flow

Answer 39

• Geographical barriers: A feature of the landscape that prevents populations from interbreeding. Includes oceans, mountain ranges, larger lake systems, deserts and expensive ice sheets
• Socio-cultural barriers: Barrier to interbreeding that is due to social or cultural factors such as economic status, educational background and social position

Question 40

What is an example of how the distribution of ABO blood groups has been influenced by migration

Answer 40

The change in the frequency of the (I B) allele across Europe and Asia. The inhabitants of East Asia (mongols) have a proportionately higher frequency of the (I B) allele than those living to their west in Europe. It is thought that most western Europeans originally did not have the (I B) allele at all until the mongols Invaded Europe, spreading not only their culture but their genes as well. Today, There is a steady decrease in this area from central Asia to western Europe