Variation & Selection

Question 1

what is a mutation?

Answer 1

a spontaneous change in the sequence of DNA, number or structure of chromosomes in an organism

Question 2

what are mutagens?

Answer 2

agents in the external environment that greatly increase that rate of mutation

Question 3

what are some examples of mutagens?

Answer 3

• ultraviolet light
• alpha, beta, gamma radiation

Question 4

what causes the sickle shape in sickle cell anemia mutation?

Answer 4

1. alteration in the sequence of DNA coding for the β-globin chain, leading to a change in amino acid sequence in the polypeptide
2. mutated gene produces haemoglobin molecule S instead of haemoglobin molecule A
3. HbS is insoluble in water due to an exposed region, and less efficient in carrying oxygen
4. at low oxygen concentration, HbS molecules crystallize into rod-like structures from hydrophobic interactions, deforming into a sickle shape

Question 5

how does the sickle shape of the red blood cell impact an individual?

Answer 5

1. red blood cells are deformed into a sickle shape, thin blood vessels become blocked, interfering with blood circulation and depriving organs of oxygen
2. organs become damaged, leading to death, while the spleen enlarges as more red blood cells die from its shorter life span

Question 6

what type of genetic disorder is the sickle cell anemia?

Answer 6

homozygous recessive disorder

Question 7

what genetic copies do individuals with the sickle cell trait have?

Answer 7

one copy of the sickle cell allele and normal allele each

Question 8

what causes a chromosomal mutation?

Answer 8

the failure of pairs of homologous chromosomes or of chromatids to separate during anaphase I or anaphase II of meiosis respectively

Question 9

what chromosome is responsible for Down syndrome?

Answer 9

chromosome 21

Question 10

what causes the symptoms of Down syndrome?

Answer 10

the abnormal extra genetic material from an extra chromosome 21

Question 11

what are the two types of variation?

Answer 11

continuous and discontinuous variation

Question 12

what are the traits of discontinuous variation?

Answer 12

• clear-cut phenotypes without intermediates
• not affected by the environment
• brought about by one or a few major genes

Question 13

what are the traits of continuous variation?

Answer 13

• complete gradation of phenotypes from one extreme to the other without break
• controlled by a combination of a number of genes
• affected by the environment
• frequency distribution is a normal distribution curve

Question 14

what is natural selection?

Answer 14

the tendency of organisms that possess favorable adaptations to their environment to survive and become parents of the next generation
evolution occurs when natural selection results in changes in allele frequency in a population

Question 15

what is adaptive radiation?

Answer 15

process where one species evolves into two or more species as a result of different populations becoming reproductively isolated from one another, when they adapt to different environments

Question 16

why are heterozygote individuals with the sickle cell trait at a selective advantage in areas common with malaria?

Answer 16

• malaria parasite spends part of its life in the red blood cell
• parasite is less able to survive in red blood cells with HbS molecules

Question 17

how do heterozygotes have similar phenotypes to homozygotes in relation to the sickle cell mutation?

Answer 17

• heterozygotes still exhibit traits of sickle cell without any severe symptoms
• red blood cells only sickle when blood oxygen concentration is low

Question 18

how do bacteria gain resistance to antibiotics from natural selection?

Answer 18

1. bacteria is exposed to mutagens, causing changes to their genetic material
2. bacteria produce proteins that gives them resistance to antibiotics
3. when exposed to the antibiotic, sensitive bacteria are killed, while resistant bacteria survive
4. if amount of antibiotic taken is insufficient to kill all bacteria, resistant bacteria multiply, passing down the gene for antibiotic resistance to the next generation
5. the next generation of bacteria is even more resistant, and the same antibiotics no longer work on them

Question 19

why is inbreeding detrimental to future generations?

Answer 19

• accumulation of recessive alleles
• recessive alleles not expressed in heterozygotes are more likely to be passed down to offspring
• if recessive allele codes for a genetic disease, the offspring becomes homozygous recessive for the gene and suffers from the disease