Genetic diversity and adaptation

Question 1

What is a mutation?

Answer 1

• Any change to the quantity or the base sequence of the DNA of an organism is known as a mutation

Question 2

What is a gene mutation?

Answer 2

• Any change to one or more nucleotide bases or a change in the sequence of the bases, in DNA is known as a gene mutation

Question 3

Can mutations be inherited?

Answer 3

• Mutations occurring during the formation of gametes may be inherited, often producing sudden and distinct differences between individuals.

Question 4

What is a substitution mutation and how does it effect the organism?

Answer 4

• The type of gene mutation in which a nucleotide in a DNA molecule is replaced by another nucleotide that has a different base is known as a substitution.
• This may cause the codon to code for another amino acid which will change the polypeptide produced will differ as it will effect the tertiary structure of the final protein, then the replacement amino acid may not form the same bonds.
• The protein may be a different shape and not function properly.

Question 5

Why can some mutations have no effect on the organism?

Answer 5

• As the code is degenerate, the change in base my make a triplet that codes for the same amino acid, so mutations may not have an effect.

Question 6

What is a deletion mutation and how does it effect the organism?

Answer 6

• A gene mutation by deletion arises when a nucleotide is lost from the normal DNA sequence.
• This will cause the amino acid sequence to be entirely different so the polypeptide can’t function properly.
• This is because bases are read in triplets. One deleted nucleotide causes all triplets in a sequence to be read differently because each has been shifted to the left by one.

Question 7

What are chromosome mutations?

Answer 7

• Changes in the structure or number of whole chromosomes are called chromosome mutations

Question 8

What are the two forms that chromosome mutations can arise spontaneously?

Answer 8

• Changes in whole sets of chromosomes
• Changes in the number of individual chromosomes

Question 9

What is meant by changes in whole sets of chromosomes?

Answer 9

• Occur when organisms have three or more sets of chromosomes rather than the usual two. This condition is called polyploidy and occurs mostly in plants.

Question 10

What is meant by changes in the number of individual chromosomes?

Answer 10

• Sometimes individual homologous pairs of chromosomes fail to separate during meiosis.
• This is known as non-disjunction and usually results in a gamete having either one more or one fewer chromosome.
• On fertilisation with a gamete that has the normal complement of chromosomes, the resultant offspring have more or fewer chromosomes than normal in all their body cells.

Question 11

Why is meiosis important?

Answer 11

• Meiosis produces 4 daughter cells that are genetically different from each other.
• Meiosis produces gametes which are haploid sex cells so that when two gametes fuse together the zygote will have a diploid number of chromosomes.
• This provides genetic variation

Question 12

What are the two nuclear divisions in meiosis?

Answer 12

• First division (meiosis 1) -> homologous chromosomes pair up and their chromatids wrap around each other. Equivalent portions of these chromatids may be exchanged in a process called crossing over. By the end of this division the homologous pairs have separated, with one chromosome from each pair going into one of the two daughter cells.
• Second meiotic division (meiosis 2) -> the chromatids move apart. At the end of meiosis 2, four cells gave usually been formed. In humans, each of these cells contains 23 chromosomes.

Question 13

Describe the process of meiosis I

Answer 13

PROPHASE I
- nuclear envelope + nucleolus disintegrate
- chromosomes condense and become visible
- Centrioles move to opposite poles of the cell + spindle fibres start to form
METAPHASE I
- Homologous chromosomes line up along the equator due to spindle fibres
- Crossing over can occur between homologous pairs as they have the same genes in the same locus to form recombinant chromosomes
- The alleles for these genes can very so genetic variety increases
ANAPHASE I
- Spindle fibres contract, pulling the homologous chromosomes apart to opposite poles of cell.
TELOPHASE I
- Nuclear envelope and nucleolus reform
- Chromosome become invisible
CYTOKINESIS
- Cytoplasm divides into 2

Question 14

Describe the process in meiosis II

Answer 14

PROPHASE II
- Nuclear envelope and nucleolus disintegrate
- Chromosomes condense and become visible
- Centrioles move to opposite poles (rotated 90) and spindle fibres start to form
METAPHASE II
- Chromosomes line up along the equator
ANAPHASE II
- Spindle fibres contract, pulling sister chromatids apart. Chromosomes move to opposite poles of cells
TELEPHASE II
- Nuclear envelope and nucleolus reform
- chromosomes become invisible
CYTOKINESIS II
- Cytoplasm divides

Question 15

How can meiosis produce genetic variation?

Answer 15

• Independent assortment of chromosomes -> the production of different combinations of alleles in daughter cells due to the random alignment of homologous pairs along the equator of the spindle during metaphase I
• Crossing over -> Sections of DNA are swapped between the chromosomes in a pair

Question 16

What is genetic diversity?

Answer 16

The number of different alleles of genes in a popualtion

Question 17

What is population?

Answer 17

A group of individuals of the same species that live in the same place and can interbreed

Question 18

What is a species?

Answer 18

One or more populations. A group of similar organisms that can breed together to produce fertile offspring

Question 19

What is allele frequency?

Answer 19

The number of times an allele occurs in a gene pool

Question 20

What is a gene pool?

Answer 20

The total number of alleles in a particular population at a specific time.

Question 21

Describe the process of natural selection

Answer 21

• Within any population of a species there will be a gene pool containing a wide variety of alleles
• Random mutations of alleles with this gene pool may result in a new alleles of a gene which in most cases will be harmful
• However, in certain environments, the new allele of a gene might give its possessor an advantage over other individuals in the population.
• These individuals will be better adapted and therefore more likely to survive in their competition with others
• These individuals are more likely to obtain available resources and so grow more rapidly and live longer
• As a result, they gave a better chance of breeding successfully and producing more offspring.
• Only those individuals that reproduce successfully will pass on their alleles to the next generation.
• Therefore it is the new allele that gave the parents an advantage in the competition for survival that is most likely to survive and so reproduce successfully.
• Over many generations, the number of individuals with the new advantageous allele will increase at the expense of the individuals with the less advantageous alleles
• Over time, the frequency of the new advantageous allele in the population increases while that of the non-advantageous ones decreases