Topic 5 - Mutations and Genetic Variation

Question 1

What must occur if there is to be some form of evolution occurring (genetic basis)?

Answer 1

• the traits must be heritable to some genetic basis

Question 2

What is the challenges with genetic and environmental variation? two examples of this?

Answer 2

• genetic and environmental changes can look very similar
• Snow Goose (genetic variation)
• Willow Ptarmigan (environmental variation)

Question 3

Explain what drives the variation of the snow goose and willow ptarmigan.

Answer 3

• these are not examples of genetic differences, rather a genetic difference driven by changing environmental conditions.

Question 4

What are two examples which could resemble Lamarck’s idea, what is his idea again?

Answer 4

• the idea of inheritance of acquired traits
  1. Peach Aphid: effect of the physical environment determines if it has wings or not
  2. Desert locus: epigentic inheritances (based on the maternal genotype) - crowded vs isolated conditions

Question 5

What would explain evolution occurring but no phenotypic traits appearing?

Answer 5

• there may be substantial amounts of unexpressed genetic variation occurring -these differences could evolve
• this genetic variation is not always observed through the phenotype

Question 6

What are the three explanations for observing phenotypic variation?

Answer 6

1. genetic difference
2. environmental difference
3. combination of genetic and environmental interactions

Question 7

Explain how genetic differences can explain when phenotypic variation occurs?

Answer 7

• there could be one or many gene variations occurring

- this could be a result of epigenetic effects (expression of a gene varied by parental origin)

Question 8

Explain what effect environmental differences can have for phenotypic variation, and what is this typically called?

Answer 8

the result of the same genotype presenting different phenotypes in changing environments

• aka phenotypic plasticity
• changes through environmental stimuli and conditions

Question 9

How do genetoype and environmental interactions affect phenotypic variation?

Answer 9

• the environmental affect varies with the genotype

Question 10

Individuals in populations will show high levels of genetic variation, how is this variation maintained?

Answer 10

• this maintenance of variation is driven by Natural Selection selecting for the best genotype in the populations
• if the environmental factor is continuously changing, then these variants would not have been eliminated yet

Question 11

What is the origin of genetic variation, and give two examples of it.

Answer 11

• mutations is the basis for evolutionary change (essential in changing genetic material)
  1. Point mutations (base substitutions)
  2. Structural mutations (deletions, insertions, or chromosomal rearrangement)

Question 12

Review: what two components do organismal genomes include?

Answer 12

• genes (functional DNA which transcribe and translate for a structural product)
• noncoding DNA (which do not contribute to final gene products and do not appear to have a function yet)

Question 13

Of the two origins of genetic variation, explain point mutations.

Answer 13

• aka single base-pair substitutions where one nucleotide base replaces another
• they may occur in coding regions where they affect amino acid sequences

Question 14

Of the two origins of genetic variation, explain structural mutations, and as a result of them occurring what further mutation may occur?

Answer 14

• these include indels: gains or losses of nucleotide bases
• these may be short or long
• result in frameshift where the entire coding region of a whole gene is affected

Question 15

Define microstatellites and their function.

Answer 15

• short (few bases) of repeating DNA sequences

- abundant in eukaryotes, highly variable and may lead to chromosomes to getting longer when the DNA sequences align.

Question 16

What occurred between microsatellites and the fairy-wren?

Answer 16

• mutation changes (in terms of the number of repeats) occurred between the parents and their offspring

Question 17

How do structural mutations occur? DNA rearrangement (3)

Answer 17

• through recombination during meiosis (intragenic recombination)
• when something goes wrong during the crossing-over which leads to new alleles of a gene region
• or their could be UNEQUAL crossing-over during recombination (of meiosis) which leads to either INSERTIONS or DELETIONS

Question 18

What is meant by the statement: structural mutations can be both small scale and large scale?

Answer 18

• these mutations are a consequence of unequal crossing-over during meiosis
• mispairings when chromosomes swap leads to whole gains or loses of a whole gene

Question 19

How would one observe a mutation? in the old days compared to the present? what effect does this phenotypic mutations have?

Answer 19

• before molecular methods, to detect mutations one would have to observe it phenotypically
• challenge is though some phenotypic mutations maybe minimally invasive
• phenotypic mutations occur they can affect fitness, however most are neutral

Question 20

What occurs when a mutation affects the fitness of an organism?

Answer 20

• this may be deleterious

Question 21

What are some limitations of these mutations? new traits?

Answer 21

• mutations occur as RANDOM events
• organisms cannot produce advantageous mutations in response to an environment
• for a new trait to evolve, a mutation must first produce it

Question 22

What occurred in the Joshua and Esther Lederberg experiment?

Answer 22

• this was a replicate plate experiment which showed how a mutation in an E. coli from a T1 phage was present prior to any exposure to a virus - an advantageous mutation occurred without exposure to an environment where this mutation would be advantageous

Question 23

Define chromosomal mutations, and give two examples of what could occur.

Answer 23

• Aneuploidy: a gain or loss of ONE chromosome
• Polyploidy: gain of entire chromosome sets - causing a rearrangement
• these result in eukaryotic organisms: where there is a GAIN, LOSS or REARRANGEMENT of entire chromsomes

Question 24

Explain where polyploidy would occur for eukaryotes?

Answer 24

• polyploidy (common in plants) would occur during either mitosis or meiosis, specifically if the division of the cytoplasm is out of sync with the replication of DNA

Question 25

What can polyploidy result from?

Answer 25

• the production of unreduced (diploid) games during meiosis

- failure of cytoplasmic division during mitosis

Question 26

Explain how a triploid may result from abnormal chromosome behaviour at meiosis.

Answer 26

• when a trios of homologous chromosomes undergo synapsis and unequal numbers separate
• leading to aneuplod gametes

Question 27

What affect do chromosomal mutations have on the order of genes?

Answer 27

• may change the order or number of genes on a chromosome

Question 28

Explain how an Autotetraploid may result from abnormal chromosome behaviour at meiosis.

Answer 28

• when a quartet of chromosomes undergo synapsis but DO NOT separate as two and two, rater three and one
• leading to aneuplod gametes
• will have reduced fertility

Question 29

Explain how an Allotetraploid may result from abnormal chromosome behaviour at meiosis.

Answer 29

• each chromosome pairs with a single homologue from some parental species, with normal segregation
• normal fertility results with viable gametes

Question 30

What are three types of chromosomal rearrangements that can occur?

Answer 30

• inversion, translocations, and fissions/fusions
• this occurs when chromosomes break and rejoin in new configurations, but this may change gene order and chromosome structure itself

Question 31

What consequences arise from chromosome inversions?

Answer 31

• this occurs when a normal and inverted gene leads to gene duplication and losses
• hybrid progeny will not form viable gametes, fertility is reduced being a reproductive barrier

Question 32

What consequences arise from reciprocal translocations?

Answer 32

• this occurs when 2 non homologous chromosomes give rise to a translocation heterozygote, where this heterozygote undergoes meiosis and he products having incomplete gene complements

Question 33

Explain what is so different between the two species of muntjac deer.

Answer 33

• is the case of related species differing in karyotype (visual number of chromosomes)
• they are genetically different but phenotypically different
• this means that chromosomal evolution occurred NOT gene evolution

Question 34

What is non genetic inheritance?

Answer 34

• epigenetic inheritance is heritable but is NOT caused by changes in DNA sequence

Question 35

How are epigenetic inheritance mediated? do paternal genotype affect inheritance in this case?

Answer 35

• through mechanisms such as DNA methylation - preventing expression of a gene being expressed
• maternal effect results where the parents genotype rather than the genotype of the affected individual on which genes were expressed

Question 36

What is an example where the maternal genotype effects the inheritance of the progeny

Answer 36

• the snails coiling direction of the shell is dependent on the individuals mother.