Population Genetics and Evolution

All the genetic information in a cell in is contained where?

in the sequence of FOUR subunits along the molecule and DNA

The molecular subunits of DNA are what?

the nucleotides

Name the four nucleotides in DNA

guanine, adenine, thymine, and cytosine (GATC)

The DNA strand forms what?

a template from which the cell manufactures proteins

Proteins consist of what?

chains of up to 20 different types of amino acids

Each nucleotide encodes what

a sequence of three nucleotides

This coding triplet is referred to….

as a codon

Because ___ codons taken three at a time yield 64 different sequences

4

There are only ___ amino acids to encode

20

T/F: there is a considerable redundancy in the genetic code

true

T/F: a change in one of the nucleotides in a DNA codon will not alter the amino acid that is coded for or it may not

false: a change in one of the nucleotides in a DNA codon may alter the amino acid that is coded for or it may not

Change in nucleotides altering amino acid code depends on what

where it occurs and if the resultant changes causes the three-nucleotide codon to actually code for a different amino acid

Such changes are referred to as

substitutions

Substitutions form

one class of changes to the DNA molecule that are referred to collectively as mutations

Mutations can result from

random copying error when the genetic material replicates during cell division by the action of certain chemical agents, or due to the effects of ionizing radiation

Keep in mind, many mutations that occur have either….

deleterious or advantageous effects on the organism in which they occur because they occur in non-coding portions of the DNA sequence

In protein coding sequences, changes at the…..

third codon position are observed with greater frequency than are changes at either of the first two positions

Most mutations are felt to exert….

deleterious effect

Explain how most mutations are felt to exert a deleterious effect

Over the course of evolutionary history, natural selection has operated to weed out most of the deleterious alleles, leaving behind only those alleles that suit the organism to its environment. Any new variant allele resulting from a mutation is likely to disrupt the well-tuned interaction between the organism and its environment. New proteins produced by mutant genes might have different properties from the protein that the mutant is based on. Some of these new mutants might be beneficial, but most are thought to be deleterious. That is, they are felt to most likely decrease the fitness of the individual in some way

Give how genotype can be defined

as the sum total of all the genetic characteristics that determine the structure and functioning of the organism

Define phenotype

physical expression of the genotype in the organism

Phenotype is a combination of

of morphological and physiological characters.

Each gene codes for

a particular protein

These proteins may be structural in nature meaning

they may act in the physical composition of the organism or they may form hormones or enzymes critical to the functioning of the organism

Different sequences of genetic subunits in a particular gene that are caused by mutations are referred to as

alleles

many alleles, or different forms of a given gene, (have/ do not have) an impact on the organisms phenotype

have

many alleles may code for….

some protein product that lends the organism a different appearance such as blue eyes vs brown eyes

Alleles may code for an enzyme that contains

a slightly different composition of amino acids

While this causes no externally visible change, this sort of variation can be profound

ok

perhaps, one allele of the gene for an enzyme_______

has much greater affinity for a certain substrate in an enzymatic reaction

Such allelic products, or alternative forms of a gene confer

some sort of a selective advantage on an organism

diploid organisms have

two copies of all genes that are NOT sex linked

if the two copies of a gene in an organism are identical, then what

the individual is referred to as homozygote

If they are different, that is if the individual has two different alleles, of a gene, it is known as

heterozygote

In heterozygotes individuals, the transcription of a DNA sequence into RNA and the translation of that RNA into protein will produce what?

two different gene products

If one of these gene products completely masks the expression of the other gene, we refer to the allele that coded for that protein as

dominant

The alternative allele is defined as

recessive

These two alleles may results in what

an intermediate phenotype

Review: list the HWE assumptions

large population, random mating, no selection, no mutation,

Is HWE occurs, which is does not, what does that mean

the relative frequencies of homozygotes and heterozygotes will achieve equilibrium proportions

What are these proportions

p2 + 2pq + q2 = 1.0 and subsequently p + q = 1.0

Why is it important to know this?

because deviations from the expected proportions given measured levels of allele frequency are indicative of the effects of selection, nonrandom mating or other factors that influence the genetic makeup of the population

Different phenotypes interact with the environment in slightly different ways. This can lead to

variation in survival and fecundity among individuals in a population

Define fecundity

the rate at which an individual produces offspring

The rate of reproduction of a given phenotype is a measure of what

fitness

when differences in fitness among individuals have a genetic basis, what will that lead to?

those alleles that confer higher fitness will tend to reproduce faster and take over the population

Those phenotypes having the highest fitness are said to be

selected

The change in genotype frequencies resulting from natural selection is referred to as

evolution

Research on selection in english peppered moths was conducted by who

H.D. Kettlewell

Describe H.D. Kettlewell’s experiment

Briefly, there are two color morphs of the English peppered moth, one dark and one light. The light morph had historically been the dominant form with relatively fewer of the dark morphs. It was discovered that in forested areas near centers of industry, there seemed to be a greater number of the dark morphs relative to the light morphs, and in forested areas that were remote from industrial centers, the light morph was still predominant.
Through a fairly elegant series of experiments the English physician H.D. Kettlewell, turned naturalist, determined that the darker morphology conferred a selective advantage on the moth in industrial areas where the trees had darker trunks. Industrial pollution turned normally light-colored tree bark darker which would make a darker morph of the moth harder to see by predators.

In the non-industrial areas, the lighter moths had a selective advantage as tree trunks were lighter in color due to
an absence of excessive industrial pollutants. The agents of the selection in this instance were insectivorous birds that routinely searched the trunks of trees to prey on these moths. Those morphs easiest to observe were taken as prey items in greater numbers. Hence the morph that was more cryptic in a given area was selected for and subsequently had higher fitness. Thus, the increase of the dark morphs in polluted environments

Evolutionary responses often involve traits…..

other than those being selected

There are several traits that are highly integrated into discrete clusters that involve osteology in mice. What are those traits?

1. Cranial features having to do with skull length
2. skull width, body weight, and tail length
3. cranial features having to do with skull width, scapula length and pectoral girdle size
4. limb bones and total body length

Therefore, in mice, if you were to develop a breeding program to select for an increase in body weight, you would along with the desired increase in body wight will see what type of chnages?

changes in skull width and tail length

The message is that natural selection operates through what type of system

through a system of phenotypic compromise that is tempered by the genetic makeup of the organism and the physical linkage of the traits are being selected

Inbreeding and outcrossing is what?

“Everyone Knows that close inbreeding is bad”

Define inbreeding

mating among close relatives; that is mating among siblings or in plants that process of “selfing”

Why is inbreeding bad

most individuals are heterozygous for at least some rare, deleterious, recessive genes

Inbreeding means that the frequency of the allele is…

low in the population at large (rare), that the results of the gene product of this allele are negative in some way (deleterious), and that in a heterozygous condition, the gene product is not expressed (recessive)

The negative consequences of having this rare allele is only expressed….

in the homozygous condition

Most individuals are felt to have ….

at least some of these genes

If an individual that carried the recessive trait in the heterozygous condition were to mate with an individual from the population at large, what is the probability?

the probability would be fairly low that that individual carried the same recessive trait, this depends on the frequency of the allele

What are the results of this?

such a union would be that half of their progeny would be heterozygous for the trait and the other half would not carry the allele at all

T/F: All of the progeny would however be at a disadvantage by simply carrying the trait

false: none of the progeny would however be at a disadvantage by simply carrying the trait

If on the other hand a carrier of the trait reproduced by “selfing”, what will the results be

¼ would be homozygous for the deleterious allele and would suffer a loss in fitness as a consequence

Most species have a variety of mechanisms to….

reduce the frequency of inbreeding

Among these are dispersal of progeny which include

recognition of close relatives, and negative assortative mating (preferential mating among phenotypically unlike partners).

Hermaphroditic species of plants (those in which individuals bear both male and female sexual organs) have additional mechanisms to prevent “selfing”, such a

self-incompatibility, temporal separation of male and female function, and elaborate flower structures designed to make “selfing” difficult

Genetic changes in small populations: in small populations, the frequencies of alleles and genotypes may change because…

of random variations in birth and death rates that are due to chance events even in the absence of selection

because of random variations in birth and death rates that are due to chance events, even in the absence of selection, this phenomenon is referred to as

genetic drift

________ events can also have a profound impact upon the genetic structure of a population

founder

Founder event occurs when

a few individuals from a larger population colonize a new habitat

What is the significance of founder effect

these new populations have a reduced sample of total genetic variation fround in the parents

Hence, drift and inbreeding can result in

the fixation of alleles that were at a relatively reduced frequency in the population as a whole. This can and does lead to considerable population subdivision and heterogeneity