1. Mutations, DNA, and Protein

In a previous module, we examined how natural selection can increase the frequency of helpful alleles within a gene pool, and decrease the frequency of harmful alleles. But evolution isn’t only about the increase or decrease of already existing alleles. Through mutation, new alleles can enter gene pools.

A mutation is a random change in a nucleotide sequence (or in an entire chromosome, though that’s beyond the scope of what we’ll be discussing below). For example, examine this nucleotide sequence.

 

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DNA Nucleotides ATG GTG CAC CTG ACT CCT GAG GAG AAG TCT GCC GTT ACT
Amino Acid START Val His Leu Thr Pro Glu Glu Lys Ser Ala Val Thr

The As, Ts, Cs, and Gs on the row labeled “DNA nucleotides” represent the nitrogenous bases which carry genetic information in DNA. The three letters on the amino acid row represent one of the twenty amino acids, or some genetic code “punctuation,” such as “start.” The numbers on top organize the nucleotides into triplets, reflecting the way that the genetic code uses groups of three nucleotides to code for one amino acid. The 13 triplets shown above code for the start of hemoglobin (the same oxygen-carrying protein we discussed in a previous tutorial in relationship to ice fish).

Now examine the wild type hemoglobin sequence and the mutated (changed) hemoglobin sequence below it. Before reading on, try to find the mutation.

Original (wild type) Sequence for Hemoglobin

 

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DNA Nucleotides ATG GTG CAC CTG ACT CCT GAG GAG AAG TCT GCC GTT ACT
Amino Acid START Val His Leu Thr Pro Glu Glu Lys Ser Ala Val Thr

Mutated Sequence for Hemoglobin

 

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DNA Nucleotides ATG GTG CAC CTG ACT CCT GTG GAG AAG TCT GCC GTT ACT
Amino Acid START Val His Leu Thr Pro Val Glu Lys Ser Ala Val Thr
Effects of sickle cell mutation. Source: National Institutes of Health, http://www.nhlbi.nih.gov/health/health-topics/topics/sca

It doesn’t seem like much: just one nucleotide in the 7th triplet, with the triplet GAG changed to GTG. However, that one change results in the 7th  amino acid being Valine instead of Glutamic Acid. And the effects of that change are catastrophic. Because valine is a non-polar amino acid and glutamic acid is ionic, the substitution changes hemoglobin’s chemical and physical properties. The mutation causes adjacent mutated hemoglobin molecules to weakly bond with one another, especially when the mutated hemoglobin is exposed to a low oxygen environment – something that can be brought on whenever blood oxygen levels drop. As a result, running, climbing stairs, or any other kind of exertion causes the mutant hemoglobin to crystallize into long fibers. This changes the shape of the red blood cells. Instead of smooth and roughly doughnut shaped, they become spiky and sickle shaped. This shape causes them to clog up in small blood vessels, damaging the tissue on the other side of the blockage, and causing debilitating pain.

Note that the way that biologists use the word “mutation” can be confusing. In the case of sickle cell anemia, the mutation happened long ago, and, for reasons we’ll soon see, rose to a relatively high frequency in certain human gene pools. In other words, the phrase “sickle cell mutation” is essentially the same as the phrase “sickle cell allele.”

 

In my DNA Rap, I explain this as follows. See if you can drag the right words into the right place.

[qwiz qrecord_id=”sciencemusicvideosMeister1961-Pop-gen: Mutation Interactive Lyrics”]

[q labels = “top”]

Hundreds of bases spell one __________ piece
Hundreds of A’s, G’s, __ and Cs
The gene starts CAC-GTG-CAC
Then TGA-GGA-CTC-CTC 

The key is these bases are ____________
For hemoglobin’s function and conformation
Hundreds of bases, in a predetermined ________
A single change brings on a major disorder

Change T to A in one _________ spot
This little point _________ might not seem like a lot
Thymine to Adenine might not seem that big to ya’
But baby that’s the cause of ________ cell anemia!

[l]hemoglobin

[fx] No, that’s not correct. Please try again.

[f*] Good!

[l]information

[fx] No. Please try again.

[f*] Correct!

[l]mutation

[fx] No, that’s not correct. Please try again.

[f*] Great!

[l]order

[fx] No, that’s not correct. Please try again.

[f*] Correct!

[l]sickle

[fx] No. Please try again.

[f*] Correct!

[l]single

[fx] No, that’s not correct. Please try again.

[f*] Excellent!

[l]Ts

[fx] No, that’s not correct. Please try again.

[f*] Excellent!

[/qwiz]

2. Mutations can have three types of consequences

2a. Mutations are mostly harmful

Firstly, as in the example of sickle cell anemia, a mutation might take a working protein and make it stop working. This is especially true if the mutation results in STOP codon being inserted anywhere in the protein, or if the mutation shifts the reading frame. Then either part or all of the protein won’t be made (in the case of a stop codon), or it will be made with many incorrect amino acids. In the both cases, the mutation causes the loss of a functioning protein.

On account of this, the most likely thing that a mutation will do is cause genetic disorders. Cystic fibrosis, the most common genetic disorder among Americans of European descent, is caused by a deletion of three nucleotides in a gene that codes for a very large membrane protein (to learn more about cystic fibrosis, click herethe link will open in new tab). Tay Sachs disease (discussed in a previous tutorial) is caused by a variety of mutations. The one most common in Jews of Eastern European descent involves a four base insertion in the gene for an enzyme. The insertion causes a change in the reading frame, making the resulting enzyme completely non-functional (click here to read more about Tay Sachs).

2b. Mutations can be silent

Secondly, the mutation might change the DNA, but not the amino acid being coded for. This can happen because the genetic code has a lot of redundancy. For example, the DNA triplets ACT, ACC, ACA, and ACG all code for the amino acid threonine. These kind of mutations, which change DNA but not the protein being coded for, are known as silent mutations. Because they have no effect on the phenotype, they won’t be acted upon by natural selection.

2c.Mutations can be beneficial

Thirdly, the mutation might improve the protein. It might, for example, improve the efficiency with which an enzyme binds to its substrate. Or, as Sean Carroll points out in his book The Making Of The Fittest, it might change a light receptor in an animal’s eye so that it can see a slightly different frequency of light energy, making it able to perceive prey that others without this mutation can’t see.

Frequency of sickle cell anemia allele in Africa. Areas in blue have the highest frequency, then gray, then green, then white

The beneficial nature of some mutations explains why the allele for sickle cell anemia is in such high frequency in parts of sub-Saharan Africa. In Nigeria, for example, up to 2% of newborns are affected by this disease. The disease is caused by a recessive allele, and over 10% of the Nigerian population may be carriers (heterozygotes).You can see this in the map on the left: areas shaded represent populations where the allele frequency for sickle cell anemia exceeds 10%.

Incidence of malaria in Africa. Darker colors have higher incidence. Compare with the sickle cell incidence map.

The high frequency of the disease is explained by the fact that this area is also a central region for malaria, a serious blood disease caused by a parasite that is carried from person to person by mosquitoes. While heterozygotes are, when viewed from outside, mostly symptom free, on the inside (in their blood cells), the presence of the mutated hemoglobin disrupts the life cycle of the malaria causing parasite. In other words, having the allele, if you’re a heterozygote, will be selected for, even while being a homozygote is selected against. You can see the incidence of malaria in the map to the right. Compare it with the map on the left to see how the incidence of malaria correlates with the frequency of the sickle cell allele.

This phenomenon, where harmful recessive alleles are in higher-than expected frequency because having one copy of the allele is a selective advantage, is called heterozygote advantage (the link takes you to a Wikipedia article in a new tab). Heterozygote advantage is well established as an explanation for the high frequency of the sickle cell allele in parts of Africa with malaria. It has also been proposed to explain the high frequency of the cystic fibrosis allele in European populations, where approximately 1 in 25 people is a carrier. The idea is that being heterozygous for the cystic fibrosis allele confers a possible survival advantage in the face of the bacterial diseases cholera and tuberculosis, though this idea is controversial. No known heterozygote advantage has been identified for Tay-Sachs disease, which is carried by about 1 in 27 Jews of European descent.

Heterozygote advantage is a specific example of a wider theme: how variation is the raw material that natural selection acts upon to make populations adapted. While mutations are mostly harmful, on the vast timescale of evolution, they play a role of increasing variation in a gene pool, which increases a population’s ability to adapt.

3. Checking Understanding

The key concepts in this module were

  1. What mutations are
  2. The impact of mutations on phenotype
  3. Heterozygote advantage
  4. Mutation and Variation

If you feel that you understand these concepts well, take this brief quiz. If not, carefully re-read the material above, and then take the quiz.

[qwiz qrecord_id=”sciencemusicvideosMeister1961-Pop-gen: Gene Pools and Mutation”]

[h]Gene Pools and Mutation

[q topic= “gene_pools_and_mutation”]A change in a nucleotide sequence of a gene is called a (n)

[c]IHRyYW5zZm9ybWF0aW9uLg==

[c]IG11dGF0 aW9uLg==

[c]IHJlY29tYmluYXRpb24=

[f]IE5vLiBXaGlsZSDigJh0cmFuc2Zvcm1hdGlvbuKAmSBpcyByb3VnaGx5IHN5bm9ueW1vdXMgd2l0aCDigJhjaGFuZ2Us4oCZIHRoZXJl4oCZcyBhIGJldHRlciBtYXRjaCBmb3IgdGhlIGRlZmluaXRpb24gYWJvdmUuIEFkZGl0aW9uYWxseSwgdGhlcmXigJlzIGEgc3BlY2lhbCBiaW9sb2dpY2FsIGRlZmluaXRpb24gb2Yg4oCYdHJhbnNmb3JtYXRpb2464oCZIHB1dHRpbmcgbmV3IEROQSBpbnRvIGEgY2VsbC4gTmV4dCB0aW1lLCBjaG9vc2UgYW5vdGhlciB0ZXJtLg==

[f]IFRoYXTigJlzIGNvcnJlY3QuIEEgbXV0YXRpb24gaXMgYSBjaGFuZ2UgaW4gdGhlIG51Y2xlb3RpZGUgc2VxdWVuY2Ugb2YgYSBnZW5lLg==

[f]IFJlY29tYmluYXRpb24gZG9lcyBpbnZvbHZlIGNoYW5nZXMgaW4gRE5BLCBhcyBETkEgZnJvbSBkaWZmZXJlbnQgc291cmNlcyBpcyBtaXhlZCB0b2dldGhlci4gQnV0IHRoZXJl4oCZcyBhIGJldHRlciB0ZXJtIHRvIG1hdGNoIHRoZSBkZWZpbml0aW9uIGFib3ZlLjwvcD4KPHAgY2xhc3M9InAxIj4=

[q topic= “gene_pools_and_mutation”]True or false? When the environment changes, a population will evolve new mutations in order to be able to adapt.

[c]IFRydWU=

[c]IEZh bHNl

[f]IE5vLiBNdXRhdGlvbnMgYXJlIHJhbmRvbS4gRXZvbHV0aW9uYXJ5IGFkYXB0YXRpb24gaXMgYWJvdXQgcHJldmlvdXNseSBleGlzdGluZyB2YXJpYXRpb25zIGJlaW5nIHNlbGVjdGVkIGJ5IHRoZSBlbnZpcm9ubWVudCwgYW5kIGFsbGVsZSBmcmVxdWVuY2llcyBzaGlmdGluZyBpbiByZXNwb25zZS4=

[f]IFRoYXTigJlzIGNvcnJlY3QuIE11dGF0aW9ucyBhcmUgcmFuZG9tLiBFdm9sdXRpb25hcnkgYWRhcHRhdGlvbiBpcyBhYm91dCBwcmV2aW91c2x5IGV4aXN0aW5nIHZhcmlhdGlvbnMgYmVpbmcgc2VsZWN0ZWQgYnkgdGhlIGVudmlyb25tZW50LCBhbmQgYWxsZWxlIGZyZXF1ZW5jaWVzIHNoaWZ0aW5nIGluIHJlc3BvbnNlLjwvcD4KPHAgY2xhc3M9InAxIj4=

[q topic= “gene_pools_and_mutation”]A nucleotide sequence changes from

TGAGGTCTCCTC

to

TGAGGCCTCCTC

Of the terms below, this change is best described as a

[c]IG51Y2xlb3RpZGUgc2hpZnQu

[c]IG11dGF0 aW9uLg==

[c]IGdlbmUgYWx0ZXJhdGlvbi4=

[f]IE5vLiBXaGlsZSB0aGUgbnVjbGVvdGlkZSBzZXF1ZW5jZSBoYXMgY2hhbmdlZCwgdGhlcmXigJlzIGEgYmV0dGVyIHRlcm0gdGhhbiDigJhzaGlmdOKAmSB0byBkZXNjcmliZSB3aGF0IGhhcHBlbmVkLg==

[f]IFRoYXTigJlzIGNvcnJlY3QuIEEgbXV0YXRpb24gaXMgYSBjaGFuZ2UgaW4gdGhlIG51Y2xlb3RpZGUgc2VxdWVuY2Ugb2YgYSBnZW5lLCB3aGljaCBpcyB3aGF0IHlvdSBzZWUgYWJvdmUu

[f]IE5vLiBXaGlsZSB0aGUgY2hhbmdlIGFib3ZlIHdvdWxkIGFsdGVyIGEgZ2VuZSwgdGhlcmXigJlzIGEgYmV0dGVyIHRlcm0gdG8gZGVzY3JpYmUgd2hhdCBoYXBwZW5lZC48L3A+CjxwIGNsYXNzPSJwMSI+

[q topic= “gene_pools_and_mutation”]A mutation causes a nucleotide sequence to change from

TGAGGTCTCCTC

to

TGAGGCCTCCTC

Both sequences code for the same amino acid sequence.

This type of mutation is known as a(n)

[c]IGluc2VydGlvbiBtdXRhdGlvbi4=

[c]IGRlbGV0aW9uIG11dGF0aW9uLg==

[c]IHNpbGVudCBt dXRhdGlvbi4=

[c]IGZyYW1lc2hpZnQgbXV0YXRpb24u

[f]IE5vLiBBbiBpbnNlcnRpb24gbXV0YXRpb24gd291bGQgYWRkIGEgbmV3IG51Y2xlb3RpZGUgc29tZXdoZXJlIGluIHRoZSBudWNsZW90aWRlIHNlcXVlbmNlLCBhbmQgcHVzaCBhbGwgdGhlIG90aGVyIG51Y2xlb3RpZGVzIG92ZXIgb25lIHBvc2l0aW9uLiBUaGUgbWFpbiBjb25zZXF1ZW5jZSBvZiB0aGlzIGlzIHRoYXQgaXQgY2hhbmdlcyB0aGUgcmVhZGluZyBmcmFtZSwgYW5kIGNoYW5nZXMgZXZlcnkgY29kb24gZG93bnN0cmVhbSBvZiB0aGUgbXV0YXRpb24uIE5leHQgdGltZSwgY2hvb3NlIGEgdHlwZSBvZiBtdXRhdGlvbiB3aXRoIGEgbGVzcyBkcmFzdGljIGVmZmVjdC4=

[f]IE5vLiBBIGRlbGV0aW9uIG11dGF0aW9uIHdvdWxkIHJlbW92ZSBhIG51Y2xlb3RpZGUgc29tZXdoZXJlIGluIHRoZSBudWNsZW90aWRlIHNlcXVlbmNlLCBhbmQgcHVsbCBhbGwgdGhlIG90aGVyIG51Y2xlb3RpZGVzIG9uZSBwb3NpdGlvbiBmb3J3YXJkLiBUaGUgbWFpbiBjb25zZXF1ZW5jZSBvZiB0aGlzIGlzIHRoYXQgaXQgY2hhbmdlcyB0aGUgcmVhZGluZyBmcmFtZSwgYW5kIGNoYW5nZXMgZXZlcnkgY29kb24gZG93bnN0cmVhbSBvZiB0aGUgbXV0YXRpb24uIE5leHQgdGltZSwgY2hvb3NlIGEgdHlwZSBvZiBtdXRhdGlvbiB3aXRoIGEgbGVzcyBkcmFzdGljIGVmZmVjdC4=

[f]IEV4YWN0bHkuIEEgc2lsZW50IG11dGF0aW9uIGNoYW5nZXMgdGhlIEROQSwgYnV0IGRvZXNu4oCZdCBjaGFuZ2UgdGhlIGFtaW5vIGFjaWRzIHRoYXQgdGhlIHNlcXVlbmNlIGlzIGNvZGluZyBmb3Iu

[f]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

[q topic= “gene_pools_and_mutation”]What’s the most likely effect of a mutation that deletes one nucleotide near the start of a gene?

[c]IFRoZSBtdXRhdGlvbiB3aWxsIGNhdXNlIGEgc2luZ2xlIGFtaW5vIGFjaWQgdG8gYmUgY2hhbmdlZCBpbiB0aGUgcHJvdGVpbiB0aGF0IHRoaXMgZ2VuZSBjb2RlcyBmb3Iu

[c]IFRoZSBtdXRhdGlvbiB3aWxsIGNhdXNlIGEgc2VyaWVzIG9mIGNoYW5nZXMg aW4gdGhlIGFtaW5vIGFjaWRzIHRoYXQgdGhlIGdlbmUgY29kZXMgZm9yLg==

[c]IFRoZSBtdXRhdGlvbiB3aWxsIGNhdXNlIG5vIGNoYW5nZSBpbiB0aGUgcmVzdWx0aW5nIHByb3RlaW4u

[f]IE5vLiBJZiBhIHNpbmdsZSBudWNsZW90aWRlIGlzIGRlbGV0ZWQgbmVhciB0aGUgc3RhcnQgb2YgYSBnZW5lLCB0aGVuIHRoZSDigJhyZWFkaW5nIGZyYW1l4oCZIGZvciBhbGwgc3Vic2VxdWVudCBjb2RvbnMgd2lsbCBiZSBzaGlmdGVkLiBBbG1vc3QgYWxsIHRoZSBjb2RvbnMgd2lsbCBiZSBpbmNvcnJlY3RseSByZWFkLCBjaGFuZ2luZyBtYW55IGFtaW5vIGFjaWRzIGluIHRoYXQgcHJvdGVpbi4=

[f]IFRoYXTigJlzIHRoZSBtb3N0IGxpa2VseSByZXN1bHQuIElmIGEgc2luZ2xlIG51Y2xlb3RpZGUgaXMgZGVsZXRlZCBuZWFyIHRoZSBzdGFydCBvZiBhIGdlbmUsIHRoZW4gdGhlIOKAmHJlYWRpbmcgZnJhbWXigJkgZm9yIGFsbCBzdWJzZXF1ZW50IGNvZG9ucyB3aWxsIGJlIHNoaWZ0ZWQuIEFsbW9zdCBhbGwgdGhlIGNvZG9ucyB3aWxsIGJlIGluY29ycmVjdGx5IHJlYWQsIGNoYW5naW5nIG1hbnkgYW1pbm8gYWNpZHMgaW4gdGhhdCBwcm90ZWluLg==

[f]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

[q topic= “gene_pools_and_mutation”]Insertion or deletion of a single nucleotide in a DNA sequence results in a

[c]IGZyYW1lc2hpZn QgbXV0YXRpb24u

[c]IHNpbGVudCBtdXRhdGlvbi4=

[c]IHBvaW50IG11dGF0aW9uIHRoYXQgZG9lc27igJl0IGNoYW5nZSB0aGUgcmVhZGluZyBmcmFtZS4=

[f]IFRlcnJpZmljISBJbnNlcnRpb25zIG9yIGRlbGV0aW9uczxzcGFuIGNsYXNzPSJBcHBsZS1jb252ZXJ0ZWQtc3BhY2UiPsKgPC9zcGFuPmluIHRoZSBudWNsZW90aWRlIHNlcXVlbmNlIGVpdGhlciBwdXNoIGFsbCB0aGUgbnVjbGVvdGlkZXMgZG93biwgb3IgcHVsbCB0aGVtIGFsbCBmb3J3YXJkLjxzcGFuIGNsYXNzPSJBcHBsZS1jb252ZXJ0ZWQtc3BhY2UiPsKgPC9zcGFuPlRoZSBtYWluIGNvbnNlcXVlbmNlIG9mIHRoaXMgaXMgdGhhdCBpdCBjaGFuZ2VzIHRoZSByZWFkaW5nIGZyYW1lLCBhbmQgY2hhbmdlcyBldmVyeSBjb2RvbiBkb3duc3RyZWFtIG9mIHRoZSBtdXRhdGlvbi4=

[f]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

[f]IE5vLiBUaGUga2V5IHBvaW50IGhlcmUgaXMgdGhhdCBpbnNlcnRpbmcgb3IgZGVsZXRpbmcgYSBudWNsZW90aWRlIGZyb20gYSBETkEgc2VxdWVuY2Ugc2hpZnRzIGV2ZXJ5IG51Y2xlb3RpZGUgZm9yd2FyZCBvciBiYWNrd2FyZC4gVGhpcyBkb2VzIGNoYW5nZSB0aGUgcmVhZGluZyBmcmFtZS4gTmV4dCB0aW1lLCBjaG9vc2UgYW5vdGhlciBhbnN3ZXIuPC9wPgo8cCBjbGFzcz0icDEiPg==

[q topic= “gene_pools_and_mutation”]Which type of mutation is most likely to be acted upon by natural selection?

[c]IEEgc2lsZW50IG11dGF0aW9uICh3aGljaCBvbmx5IGNoYW5nZXMgdGhlIEROQSk=

[c]IEFuIGFjdGl2ZSBtdXRhdGlvbiAod2hpY2ggY2hhbmdlcyB0aGUg RE5BLCBhbmQgdGhlIHByb3RlaW4gdGhlIEROQSBjb2RlcyBmb3Ip

[f]IE5vLiBTaWxlbnQgbXV0YXRpb25zIGhhdmUgbm8gZWZmZWN0IG9uIGFuIG9yZ2FuaXNt4oCZcyBwaGVub3R5cGUuIFNpbmNlIG5hdHVyYWwgc2VsZWN0aW9uIG9ubHkgYWN0cyBvbiB0aGUgcGhlbm90eXBlLCBzaWxlbnQgbXV0YXRpb24gY2Fu4oCZdCBiZSBhY3RlZCBvbiBieSBuYXR1cmFsIHNlbGVjdGlvbi4=

[f]IFRoYXTigJlzIGNvcnJlY3QuIEFjdGl2ZSBtdXRhdGlvbnMgY2hhbmdlIHByb3RlaW4sIHdoaWNoIGNoYW5nZXMgYW4gb3JnYW5pc23igJlzIHBoZW5vdHlwZS4gU2luY2UgbmF0dXJhbCBzZWxlY3Rpb24gYWN0cyBvbiBhbiBvcmdhbmlzbeKAmXMgcGhlbm90eXBlLCBhY3RpdmUgbXV0YXRpb25zIGJlY29tZSB0YXJnZXRzIGZvciBzZWxlY3Rpb24uPC9wPgo8cCBjbGFzcz0icDEiPg==

[q topic= “gene_pools_and_mutation”]The most common consequence of an active mutation is for there to be

[c]IGltcHJvdmVtZW50IG9mIHRoZSBwcm90ZWluLCBtYWtpbmcgaXQgbW9yZSBlZmZlY3RpdmUgYW5kIGluY3JlYXNpbmcgYW4gb3JnYW5pc20mIzgyMTc7cyBwcm9iYWJpbGl0eSBvZiBzdXJ2aXZhbC4=

[c]IG5vIGltcGFjdCBvbiB0aGUgb3JnYW5pc23igJlzIHBoZW5vdHlwZS4=

[c]IGRhbWFnZSB0byBhIGZ1bmN0aW9uaW5nIHByb3RlaW4sIHJlc3VsdGluZyBpbiBk aXNlYXNlIGZvciB0aGUgb3JnYW5pc20gdGhhdCBiZWFycyB0aGUgbXV0YXRpb24u

[f]IE5vLiBXaGlsZSB0aGlzIGlzIHBvc3NpYmxlLCBhbmQgYW4gaW1wb3J0YW50IHBhcnQgb2YgZXZvbHV0aW9uLCBpdOKAmXMgdmVyeSB1bmxpa2VseS4gTXV0YXRpb25zIGFyZSByYW5kb20gY2hhbmdlcywgYW5kIHJhbmRvbSBjaGFuZ2VzIGFyZSBtb3JlIGxpa2VseSB0byBicmVhayB0aGluZ3MgdGhhbiB0byBmaXggdGhlbS4=

[f]IE5vLiBCeSBkZWZpbml0aW9uLCBhbiBhY3RpdmUgbXV0YXRpb24gaXMgY2hhbmdpbmcgYSBwcm90ZWluLiBQcm90ZWlucywgb24gc29tZSBsZXZlbCwgYXJlIHdoYXQgbWFrZSB1cCBhbiBvcmdhbmlzbeKAmXMgcGhlbm90eXBlIChlaXRoZXIgZGlyZWN0bHksIG9yIHRocm91Z2ggZW56eW1lcyB0aGF0IGNvbnRyb2wgZGV2ZWxvcG1lbnQpLg==

[f]IFllcy4gTXV0YXRpb24gaXMgdGhlIGNhdXNlIG9mIG1hbnkgZ2VuZXRpYyBkaXNlYXNlcy4gVGhlaXIgbW9zdCBsaWtlbHkgaW1wYWN0IG9mIGEgbXV0YXRpb24gaXMgdG8gdGFrZSBhIHByb3RlaW4gdGhhdOKAmXMgd29ya2luZywgYW5kPHNwYW4gY2xhc3M9IkFwcGxlLWNvbnZlcnRlZC1zcGFjZSI+wqA8L3NwYW4+dG8gZGltaW5pc2ggb3IgZGVzdHJveSBpdHMgZnVuY3Rpb24uPC9wPgo8cCBjbGFzcz0icDEiPg==

[q topic= “gene_pools_and_mutation”]In a population, a specific gene has two alleles, ‘A’ and ‘a.’ Individuals with genotype ‘aa’ die in early childhood. Individuals with genotype ‘Aa’ have a higher rate of surviving and reproducing than individuals with genotype ‘AA.’ This phenomenon is called

[c]IG11dGF0aW9uIHNlbGVjdGlvbi4=

[c]IGhldGVyb3p5Z290 ZSBhZHZhbnRhZ2Uu

[c]IGFsbGVsZSBzZWxlY3Rpb24u

[f]IE5vLiBXaGlsZSB0aGlzIHdpbGwgYWx0ZXIgdGhlIGZyZXF1ZW5jeSBvZiBhbGxlbGVzIGluIHRoaXMgcG9wdWxhdGlvbiBpbiBmYXZvciBvZiB0aGUgbGV0aGFsIGFsbGVsZSwgdGhhdOKAmXMgbm90IHRoZSBuYW1lIHRoYXTigJlzIHVzZWQuIFRoaW5rIGFib3V0IHdoaWNoIGdlbm90eXBlIGhhcyB0aGUgc3Vydml2YWwgYWR2YW50YWdlLg==

[f]IFllcy4gVGhpcyBzaXR1YXRpb24sIHdoZXJlIGhldGVyb3p5Z290ZXMgc3Vydml2ZSBhdCBoaWdoZXIgcmF0ZXMsIGV2ZW4gdGhvdWdoIHRoZXkgY2FycnkgYSBsZXRoYWwgYWxsZWxlLCBpcyBjYWxsZWQgaGV0ZXJvenlnb3RlIGFkdmFudGFnZS4=

[f]IE5vLiBPbiBhIHBvcHVsYXRpb24gZ2VuZXRpYyBsZXZlbCwgdGhlIGxldGhhbCBhbGxlbGUgd2lsbCB3aW5kIHVwIHdpdGggYSBtdWNoIGhpZ2hlciBmcmVxdWVuY3kgdGhhbiB3b3VsZCBiZSBleHBlY3RlZCBmb3IgYSBsZXRoYWwgYWxsZWxlLiBCdXQgdGhhdOKAmXMgbm90IHRoZSBuYW1lIGZvciB0aGlzIHBoZW5vbWVub24uIFRoaW5rIGFib3V0IHdoaWNoIGdlbm90eXBlIGhhcyB0aGUgc3Vydml2YWwgYWR2YW50YWdlLjwvcD4KPHAgY2xhc3M9InAxIj4=

[q topic= “gene_pools_and_mutation”]For this question, let ‘S’ represent the normal hemoglobin allele, and ‘s’ represent the sickle cell allele. In areas affected by malaria, which of the following sequences of genotypes correctly shows which genotype has the highest survival rate, followed by the second highest, followed by the lowest survival rate.

[c]IFNTLCBTcyzCoHNz

[c]IHNzLCBTUyzCoFNz

[c]IFNTLCBzcyzCoFNz

[c]IFNzLCBTUyw8c3BhbiBjbGFzcz0iQXBwbGUtY2 9udmVydGVkLXNwYWNlIj7CoHNzPC9zcGFuPg==

[f]IE5vLiDigJhTU+KAmSBpcyB0aGUgbm9ybWFsIGhlbW9nbG9iaW4gZ2Vub3R5cGUsIGJ1dCBpbmRpdmlkdWFscyB3aXRoIHRoaXMgZ2Vub3R5cGUgc3VmZmVyIGZyb20gbWFsYXJpYS4gWW914oCZcmUgY29ycmVjdCBpbiBwdXR0aW5nIOKAmHNz4oCZIGxhc3QsIHNpbmNlIGl0IHJlc3VsdHMgaW4gc2lja2xlIGNlbGwgYW5lbWlhLCBhIHNlcmlvdXMgZGlzZWFzZS4gVGhpbmsgYWJvdXQgd2hpY2ggZ2Vub3R5cGUgcHJvZHVjZXMgYSBwaGVub3R5cGUgdGhhdCBkb2VzIGJlc3QgaW4gbWFsYXJpYS1hZmZlY3RlZCBhcmVhcywgYW5kIGNob29zZSBhbm90aGVyIHNlcXVlbmNlLg==

[f]IE5vLiDigJhzc+KAmSBpcyBmb3Igc2lja2xlIGNlbGwgYW5lbWlhLCBhIHNlcmlvdXMgZGlzZWFzZS4gd2l0aCBhIGxvdyBzdXJ2aXZhbCByYXRlLiDigJhzc+KAmSBzaG91bGQgZ28gbGFzdC4g4oCYU1PigJkgaXMgdGhlIG5vcm1hbCBoZW1vZ2xvYmluIGdlbm90eXBlLCBidXQgaW5kaXZpZHVhbHMgd2l0aCB0aGlzIGdlbm90eXBlIHN1ZmZlciBmcm9tIG1hbGFyaWEuIFRoaW5rIGFib3V0IHdoaWNoIGdlbm90eXBlIHByb2R1Y2VzIGEgcGhlbm90eXBlIHRoYXQgZG9lcyBiZXN0IGluIG1hbGFyaWEtYWZmZWN0ZWQgYXJlYXMsIGFuZCBjaG9vc2UgYW5vdGhlciBzZXF1ZW5jZS4=

[f]IE5vLiDigJhTU+KAmSBpcyB0aGUgbm9ybWFsIGhlbW9nbG9iaW4gZ2Vub3R5cGUsIGJ1dCB0aGlzIGluZGl2aWR1YWxzIHdpdGggdGhpcyBnZW5vdHlwZSBzdWZmZXIgZnJvbSBtYWxhcmlhLiDigJhzc+KAmSBpcyBmb3Igc2lja2xlIGNlbGwgYW5lbWlhLCBhIHNlcmlvdXMgZGlzZWFzZSB3aXRoIGhpZ2ggbW9ydGFsaXR5ICjigJlzc+KAmSBzaG91bGQgZ28gbGFzdCkuPHNwYW4gY2xhc3M9IkFwcGxlLWNvbnZlcnRlZC1zcGFjZSI+wqA8L3NwYW4+VGhpbmsgYWJvdXQgd2hpY2ggZ2Vub3R5cGUgcHJvZHVjZXMgYSBwaGVub3R5cGUgdGhhdCBkb2VzIGJlc3QgaW4gbWFsYXJpYS1hZmZlY3RlZCBhcmVhcywgYW5kIGNob29zZSBhbm90aGVyIHNlcXVlbmNlLg==

[f]IEV4Y2VsbGVudC4gSGV0ZXJvenlnb3RlcyBoYXZlIHRoZSBhZHZhbnRhZ2UsIGFuZCBzdXJ2aXZlIGF0IHRoZSBoaWdoZXN0IHJhdGUuIOKAmFNT4oCZIGlzIGZvciBub3JtYWwgaGVtb2dsb2JpbiwgYnV0IHRoZSBub3JtYWwgcGhlbm90eXBlIGlzIHZ1bG5lcmFibGUgdG8gbWFsYXJpYSwgYSB2ZXJ5IHNlcmlvdXMgZGlzZWFzZSB0aGF0IGNhbiBiZSBkZWFkbHkuIFdoaWxlIOKAmHNz4oCZIGlzIG5vdCBleGFjdGx5IOKAmGxldGhhbCzigJkgaXQgcmVzdWx0cyBpbiBzaWNrbGUgY2VsbCBhbmVtaWEsIGEgZGlzZWFzZSB3aXRoIGxvd2VyZWQgc3Vydml2YWwgcmF0ZXMuPC9wPgo8cCBjbGFzcz0icDEiPg==

[q topic= “gene_pools_and_mutation”]Which of the following statements about the role of mutation in a population’s gene pool is most correct?

[c]IE11dGF0aW9ucyBjYW4gYWRkIHZhcmlhdGlvbiB0byBhIHBvcHVsYXRpb27igJlzIGdlbmUgcG9v bCwgbWFraW5nIHRoYXQgcG9wdWxhdGlvbiBtb3JlIGFibGUgdG8gYWRhcHQgdG8gY2hhbmdlLg==

[c]IE11dGF0aW9ucyBoYXZlIG9ubHkgbmVnYXRpdmUgZWZmZWN0cyBvbiBhIHBvcHVsYXRpb27igJlzIGdlbmUgcG9vbC4=

[c]IFBvcHVsYXRpb25zIGVuY291cmFnZSBtdXRhdGlvbnMgaW4gb3JkZXIgdG8gcmVzcG9uZCB0byBlbnZpcm9ubWVudGFsIGNoYWxsZW5nZXMu

[f]IFllcy4gV2hpbGUgb24gYW4gaW5kaXZpZHVhbCBiYXNpcywgbXV0YXRpb25zIGFyZSBtb3N0bHkgaGFybWZ1bCwgb24gYSBwb3B1bGF0aW9uIGxldmVsIG11dGF0aW9ucyBhcmUgYW4gaW1wb3J0YW50IHNvdXJjZSBvZiB0aGUgdmFyaWF0aW9uIHRoYXQgbWFrZXMgYWRhcHRhdGlvbiBwb3NzaWJsZS4=

[f]IE5vLiBXaGlsZSBvbiBhbiBpbmRpdmlkdWFsIGJhc2lzLCBtdXRhdGlvbnMgYXJlIG1vc3RseSBoYXJtZnVsLCBvbiBhIHBvcHVsYXRpb24gbGV2ZWwgbXV0YXRpb25zIGFyZSBhbiBpbXBvcnRhbnQgc291cmNlIG9mIHRoZSB2YXJpYXRpb24gdGhhdCBtYWtlcyBhZGFwdGF0aW9uIHBvc3NpYmxlLg==

[f]IE5vLiBNdXRhdGlvbnMgYXJlIGNvbXBsZXRlbHkgcmFuZG9tLiBOZWl0aGVyIGluZGl2aWR1YWxzIG5vciBwb3B1bGF0aW9ucyBoYXZlIGFueSBjb250cm9sIG92ZXIgd2hlbiBtdXRhdGlvbnMgaGFwcGVuLCBhbmQgd2hldGhlciB0aG9zZSBtdXRhdGlvbnMgd2lsbCBiZSBoYXJtZnVsIG9yIGJlbmVmaWNpYWwuPC9wPgo8cCBjbGFzcz0icDEiPg==

[q topic= “gene_pools_and_mutation”]The gene pools of two populations of the same species are compared. For the genes studied, almost all of the genes for all the alleles in population ‘A’ are fixed. Population ‘B’ has many more genes with two or more alleles. Which population will have difficulty adapting to environmental change?

[c]IFBvcHVsYX Rpb24gQQ==

[c]IFBvcHVsYXRpb24gQg==

[f]IFllcy4gVmFyaWF0aW9uIGlzIHRoZSByYXcgbWF0ZXJpYWwgdGhhdCBuYXR1cmUgYWN0cyB1cG9uIHRvIHNlbGVjdCBuZXcgYWRhcHRhdGlvbnMuIFBvcHVsYXRpb24g4oCYQSzigJkgd2l0aCBpdHMgbWFueSBmaXhlZCBhbGxlbGVzLCBzZWVtcyB0byBoYXZlIGxpdHRsZSB2YXJpYWJpbGl0eS4gQWRhcHRpbmcgdG8gZW52aXJvbm1lbnRhbCBjaGFuZ2Ugd2lsbCBiZSB2ZXJ5IGRpZmZpY3VsdC4=

[f]IE5vLiBWYXJpYXRpb24gaXMgdGhlIHJhdyBtYXRlcmlhbCB0aGF0IG5hdHVyZSBhY3RzIHVwb24gdG8gc2VsZWN0IG5ldyBhZGFwdGF0aW9ucy4gUG9wdWxhdGlvbiDigJhCLOKAmSB3aXRoIHR3byBvciBtb3JlIGFsbGVsZXMgZm9yIG1hbnkgZ2VuZXMsIHdpbGwgaGF2ZSBtb3JlIHZhcmlhdGlvbiwgZW5hYmxpbmcgaXQgdG8gaGF2ZSBhIGJldHRlciBjaGFuY2UgYXQgYWRhcHRpbmcgdG8gY2hhbmdlcyBpbiBpdHMgZW52aXJvbm1lbnQu

[x]

[restart]

[/qwiz]

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