Genetics And Sources Of Variation Study Question

Genetics And Sources Of Variation Study Question

Transmission Genetics and Sources of Variation Study Guide

First off, be sure to review the genetics worksheets. It IS worth your time as I am gonna ask some questions from it. This includes the terms, and outcomes of the basic monohybrid and dihybrid crosses.

Identify which of Mendels’ laws (Law of dominance, Law of segregation, and Law of independent assortment) applies to these situations:

For the genotype Aa, half of the gametes will carry A, half will carry a.

The genotypes AA and Aa have the same phenotype

In the genotype AaBb, half of the gametes that carry A will also carry B (these are gametes that are AB), and half of the gametes that carry A will also carry b (these are gametes that are Ab).

Some alleles are dominant, while others are recessive. Other relationships between alleles include incomplete dominance, and codominance. For the following crosses, tell me the relationship between the alleles.

— If black is crossed to white and the offspring are all black.

— If black is crossed to white, and the offspring are ‘salt and pepper’.

— What if black is crossed to white and the offspring are grey?

What is the ‘central dogma of molecular biology’? There is a historically (and biologically) more accurate way to say it or simply diagram it.

What are the 2 principle steps of gene expression.

Define transcription and translation. Be sure to not confuse these!

What are codons and anticodons.

What is the ‘genetic code’?

Darwin was challenged that the very act of natural selection in populations will reduce variation in a population. Why might that be an issue for the future of natural selection in the population?

How do populations restore genetic variation? There are several … Name some. Some have to do with ways that mutations are introduced. Others with how sexual reproduction combines mutant alleles in novel ways.

Carp (a kind of fish) have exactly 100 pairs of chromosomes in their diploid cells. How many combinations of chromosomes are possible due to independent assortment?

Viruses and bacteria and eukaryotes of course replicate their genomes as they reproduce. But an RNA virus is many times more likely to change a given base in its genome when it replicates than will many bacteria, and many times more likely to have a base change at a given position than a eukaryote. What does this mean in terms of accuracy in genome replication in RNA viruses versus bacteria versus eukaryotes?

Despite that previous point, a eukaryote will often have many more mutations in its genome than will a virus after a single round of DNA replication. Your cells average about 30 base pair changes each time one of your cells replicates. How is it that we carry more mutations in our genomes than do viruses, even though our rate of mutation is much lower? [The answer is really simple].

When one inspects diversity in natural (and large) populations, what does one generally see in their genetic diversity?

Some species have become critically endangered due to habitat loss or hunting. This is often seen to effect genetic diversity in what way?

When we say ‘mutations are random’, what do we really mean?

Explain the Luria-Delbruck experiment. Lets walk through it.

What were they testing?

What would they see if bacteria were induced to be resistant by the presence of viruses?

What would they see if bacteria were resistant at various times before exposure to viruses?

What was the result of their experiment — what hypothesis was supported?

-1 The Genetics of Populations Study Guide

This portion leads to a review of Hardy-Weinberg equilibrium (H.W.E.)

The late 1800’s and early 1900’s saw the emergence of two scientific revolutions in biology: evolutionary biology and genetics. Clearly these two sciences needed to not conflict with each other but at first they did! What was the nature of this conflict? How was it eventually resolved?

What are ‘polymorphisms’ in traits? Here are examples of variations. Can you pick out which one is a polymorphism?

(a) Plant bugs differ in the length of their proboscis, in a continuous, graded series. The cover slide of the PowerPoint file over this material shows the common shows wild pigeons. (b) Some birds have a solid grey back, and others have a grey and white back.

In humans, individuals with a straight hairline are homozygous for a recessive allele (ww). Individuals with a widows’ peak hairline have a dominant allele of the same gene, so they are either WW or Ww. MOST people have a straight hairline, so lets say 90% of us are ww, and only 10% of us carry the W allele. So the phenotypic ratio is 9 straight : 1 widows’ peak. If NOTHING else happens but random mating, no mutation, no migration, no selection, etc, what should happen to this phenotypic frequency over time? Should it stay 9:1, or will it gradually change to a 3:1 ratio? Why?

Who demonstrated that allele frequencies stay constant unless something works to change it? (this will be two people).

The condition where allele frequencies stay constant in populations under certain conditions is called

Define evolution in terms of frequencies of alleles / genes.

There are several conditions required for true Hardy-Weinberg equilibrium (HWE). Name several of them.

If ANY of these above conditions are not met, what happens to allele frequencies in the population?

If allele frequencies change in a population for any reason, we say the population is e-……………………. (I know I am being redundant. I just really want you to know this forwards and backwards)!

Define ‘population’ in formal terms.

Tell me what a ‘gene pool’ is in terms of a population.

Suppose there are two alleles of a gene. Describe to me what an ‘allele frequency’ is. It is OK to use % in your description when being a little informal about this.

You should now have the first population genetics worksheet in front of you.

Some background. Most of this is FYI: Mice have this gene called ‘Agouti’. Two common alleles of this gene are A and a, where A promotes yellow pigment and a is a recessive mutation. Mice homozygous for the mutation therefore have the genotype aa, and are black in color because they only make eumelanin and not the yellow pigment phaeomelanin. Mice that are AA or Aa make both yellow and black pigment and are called ‘Agouti’ mice.

What are the two symbols that represent the frequencies of two alleles of a gene?

Suppose you have a population of mice where 75% of the coat color alleles are A, and 25% of the alleles are a. How would you express these frequencies in terms of decimals?

Summarize the meaning of the equation p + q = 1

If you are given the # of individuals with specific genotypes (like BB, Bb, and bb), can you calculate the frequencies of those genotypes in the population?

From this, can you calculate the frequencies of the two alleles (B and b)? There are two ways to do that. I do not care which method you use.

What are the symbols used to express the frequencies of the different genotypes? So when you are given, say, the frequencies of the heterozygotes, what is the symbol for that particular frequency? [Many students don’t get this question. Be sure you know it!]

Summarize the meaning of the equation p2 + 2pq + q2 = 1.

When, and only when, can you use this formula: q = DO NOT USE THIS UNLESS CONDITIONS PERMIT YOU TO DO SO.

If you only have the clue that the frequencies of homozygous recessives are, say, 0.45 (meaning that q2 = 0.45), what is the expected frequency of the recessive allele? What is the frequency of the dominant allele? What is the frequency of homozygous dominants, and frequency of heterozygotes. Assume H.W.E.

IF you have a population, of course it will be true that p2 + 2pq + q2 = 1 for that population even if it is not in H.W.E. That is simply because the frequencies of different genotypes will add up to 100% of the genotypes (duh!). Now, suppose you use that data to calculate the observed frequencies of alleles (the values of p and q). Now suppose you used that to determine the expected genotype frequencies. [I will be showing you how to do these things]. Anyway, what would it mean if the expected frequencies were the same as the observed frequencies? What would it mean if the expected and observed frequencies were not the same?

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