1. Introduction
In a previous tutorial in this 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.
Mutations are random changes in a nucleotide sequence (or in an entire chromosome, though that’s beyond the scope of what we’ll be discussing below). For a review of the types of mutations, their effects, and their causes, click here.
2. Mutations can have three consequences
2a. Mutations are mostly harmful
Firstly, as is the case with sickle cell anemia, a mutation might take a working protein and make it stop working. This is especially true if the mutation results in a 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 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 here: the 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 kinds 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.
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%.
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 the 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 on 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 the 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
- The impact of mutations on phenotype
- Heterozygote advantage
- Mutation and Variation
The quiz that follows assumes that you’ve mastered the material in a previous tutorial about mutation, in addition to what’s immediately above. If you need to review mutation, click here.
[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==[Qq]
[c]IG11dGF0 aW9uLg==[Qq]
[c]IHJlY29tYmluYXRpb24=[Qq]
[f]IE5vLiBXaGlsZSDigJh0cmFuc2Zvcm1hdGlvbuKAmSBpcyByb3VnaGx5IHN5bm9ueW1vdXMgd2l0aCDigJhjaGFuZ2Us4oCZIHRoZXJl4oCZcyBhIGJldHRlciBtYXRjaCBmb3IgdGhlIGRlZmluaXRpb24gYWJvdmUuIEFkZGl0aW9uYWxseSwgdGhlcmXigJlzIGEgc3BlY2lhbCBiaW9sb2dpY2FsIGRlZmluaXRpb24gb2Yg4oCYdHJhbnNmb3JtYXRpb2464oCZIHB1dHRpbmcgbmV3IEROQSBpbnRvIGEgY2VsbC4gTmV4dCB0aW1lLCBjaG9vc2UgYW5vdGhlciB0ZXJtLg==[Qq]
[f]IFRoYXTigJlzIGNvcnJlY3QuIEEgbXV0YXRpb24gaXMgYSBjaGFuZ2UgaW4gdGhlIG51Y2xlb3RpZGUgc2VxdWVuY2Ugb2YgYSBnZW5lLg==[Qq]
[f]IFJlY29tYmluYXRpb24gZG9lcyBpbnZvbHZlIGNoYW5nZXMgaW4gRE5BLCBhcyBETkEgZnJvbSBkaWZmZXJlbnQgc291cmNlcyBpcyBtaXhlZCB0b2dldGhlci4gQnV0IHRoZXJl4oCZcyBhIGJldHRlciB0ZXJtIHRvIG1hdGNoIHRoZSBkZWZpbml0aW9uIGFib3ZlLg==
Cg==[Qq]
[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=[Qq]
[c]IEZh bHNl[Qq]
[f]IE5vLiBNdXRhdGlvbnMgYXJlIHJhbmRvbS4gRXZvbHV0aW9uYXJ5IGFkYXB0YXRpb24gaXMgYWJvdXQgcHJldmlvdXNseSBleGlzdGluZyB2YXJpYXRpb25zIGJlaW5nIHNlbGVjdGVkIGJ5IHRoZSBlbnZpcm9ubWVudCwgYW5kIGFsbGVsZSBmcmVxdWVuY2llcyBzaGlmdGluZyBpbiByZXNwb25zZS4=[Qq]
[f]IFRoYXTigJlzIGNvcnJlY3QuIE11dGF0aW9ucyBhcmUgcmFuZG9tLiBFdm9sdXRpb25hcnkgYWRhcHRhdGlvbiBpcyBhYm91dCBwcmV2aW91c2x5IGV4aXN0aW5nIHZhcmlhdGlvbnMgYmVpbmcgc2VsZWN0ZWQgYnkgdGhlIGVudmlyb25tZW50LCBhbmQgYWxsZWxlIGZyZXF1ZW5jaWVzIHNoaWZ0aW5nIGluIHJlc3BvbnNlLg==
Cg==[Qq]
[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[Qq]
[c]IG11dGF0 aW9uLg==[Qq]
[c]IGdlbmUgYWx0ZXJhdGlvbi4=[Qq]
[f]IE5vLiBXaGlsZSB0aGUgbnVjbGVvdGlkZSBzZXF1ZW5jZSBoYXMgY2hhbmdlZCwgdGhlcmXigJlzIGEgYmV0dGVyIHRlcm0gdGhhbiDigJhzaGlmdOKAmSB0byBkZXNjcmliZSB3aGF0IGhhcHBlbmVkLg==[Qq]
[f]IFRoYXTigJlzIGNvcnJlY3QuIEEgbXV0YXRpb24gaXMgYSBjaGFuZ2UgaW4gdGhlIG51Y2xlb3RpZGUgc2VxdWVuY2Ugb2YgYSBnZW5lLCB3aGljaCBpcyB3aGF0IHlvdSBzZWUgYWJvdmUu[Qq]
[f]IE5vLiBXaGlsZSB0aGUgY2hhbmdlIGFib3ZlIHdvdWxkIGFsdGVyIGEgZ2VuZSwgdGhlcmXigJlzIGEgYmV0dGVyIHRlcm0gdG8gZGVzY3JpYmUgd2hhdCBoYXBwZW5lZC4=
Cg==[Qq]
[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=[Qq]
[c]IGRlbGV0aW9uIG11dGF0aW9uLg==[Qq]
[c]IHNpbGVudCBt dXRhdGlvbi4=[Qq]
[c]IGZyYW1lc2hpZnQgbXV0YXRpb24u[Qq]
[f]IE5vLiBBbiBpbnNlcnRpb24gbXV0YXRpb24gd291bGQgYWRkIGEgbmV3IG51Y2xlb3RpZGUgc29tZXdoZXJlIGluIHRoZSBudWNsZW90aWRlIHNlcXVlbmNlLCBhbmQgcHVzaCBhbGwgdGhlIG90aGVyIG51Y2xlb3RpZGVzIG92ZXIgb25lIHBvc2l0aW9uLiBUaGUgbWFpbiBjb25zZXF1ZW5jZSBvZiB0aGlzIGlzIHRoYXQgaXQgY2hhbmdlcyB0aGUgcmVhZGluZyBmcmFtZSwgYW5kIGNoYW5nZXMgZXZlcnkgY29kb24gZG93bnN0cmVhbSBvZiB0aGUgbXV0YXRpb24uIE5leHQgdGltZSwgY2hvb3NlIGEgdHlwZSBvZiBtdXRhdGlvbiB3aXRoIGEgbGVzcyBkcmFzdGljIGVmZmVjdC4=[Qq]
[f]IE5vLiBBIGRlbGV0aW9uIG11dGF0aW9uIHdvdWxkIHJlbW92ZSBhIG51Y2xlb3RpZGUgc29tZXdoZXJlIGluIHRoZSBudWNsZW90aWRlIHNlcXVlbmNlLCBhbmQgcHVsbCBhbGwgdGhlIG90aGVyIG51Y2xlb3RpZGVzIG9uZSBwb3NpdGlvbiBmb3J3YXJkLiBUaGUgbWFpbiBjb25zZXF1ZW5jZSBvZiB0aGlzIGlzIHRoYXQgaXQgY2hhbmdlcyB0aGUgcmVhZGluZyBmcmFtZSwgYW5kIGNoYW5nZXMgZXZlcnkgY29kb24gZG93bnN0cmVhbSBvZiB0aGUgbXV0YXRpb24uIE5leHQgdGltZSwgY2hvb3NlIGEgdHlwZSBvZiBtdXRhdGlvbiB3aXRoIGEgbGVzcyBkcmFzdGljIGVmZmVjdC4=[Qq]
[f]IEV4YWN0bHkuIEEgc2lsZW50IG11dGF0aW9uIGNoYW5nZXMgdGhlIEROQSBidXQgZG9lc27igJl0IGNoYW5nZSB0aGUgYW1pbm8gYWNpZHMgdGhhdCB0aGUgc2VxdWVuY2UgaXMgY29kaW5nIGZvci4=[Qq]
[f]IEEgZnJhbWVzaGlmdCBtdXRhdGlvbiByZXN1bHRzIGZyb20gZWl0aGVyIGluc2VydGluZyBvciBkZWxldGluZyBhIGJhc2UuIFRoZXNlIGluc2VydGlvbnMgY2hhbmdlIHRoZSByZWFkaW5nIGZyYW1lIGR1cmluZyB0cmFuc2xhdGlvbiBhbmQgY2F1c2UgbWFueSBvZiB0aGUgYW1pbm8gYWNpZHMgaW4gdGhlIHByb3RlaW4gdGhhdCB0aGUgZ2VuZSBjb2RlcyBmb3IgdG8gYmUgY2hhbmdlZC4gSW4gdGhlIGV4YW1wbGUgYWJvdmUsIHdoYXQgd2UgaGF2ZSBpcyBhIHNpbXBsZSBzdWJzdGl0dXRpb24gYW5kIG9uZSB0aGF0IGRvZXNu4oCZdCBjaGFuZ2UgZXZlbiBvbmUgYW1pbm8gYWNpZC4gQ2hvb3NlIGFub3RoZXIgYW5zd2VyIG5leHQgdGltZS4=
Cg==[Qq]
[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[Qq]
[c]IFRoZSBtdXRhdGlvbiB3aWxsIGNhdXNlIGEgc2VyaWVzIG9mIGNoYW5nZXMg aW4gdGhlIGFtaW5vIGFjaWRzIHRoYXQgdGhlIGdlbmUgY29kZXMgZm9yLg==[Qq]
[c]IFRoZSBtdXRhdGlvbiB3aWxsIGNhdXNlIG5vIGNoYW5nZSBpbiB0aGUgcmVzdWx0aW5nIHByb3RlaW4u[Qq]
[f]IE5vLiBJZiBhIHNpbmdsZSBudWNsZW90aWRlIGlzIGRlbGV0ZWQgbmVhciB0aGUgc3RhcnQgb2YgYSBnZW5lLCB0aGVuIHRoZSDigJhyZWFkaW5nIGZyYW1l4oCZIGZvciBhbGwgc3Vic2VxdWVudCBjb2RvbnMgd2lsbCBiZSBzaGlmdGVkLiBBbG1vc3QgYWxsIHRoZSBjb2RvbnMgd2lsbCBiZSBpbmNvcnJlY3RseSByZWFkLCBjaGFuZ2luZyBtYW55IGFtaW5vIGFjaWRzIGluIHRoYXQgcHJvdGVpbi4=[Qq]
[f]IFRoYXTigJlzIHRoZSBtb3N0IGxpa2VseSByZXN1bHQuIElmIGEgc2luZ2xlIG51Y2xlb3RpZGUgaXMgZGVsZXRlZCBuZWFyIHRoZSBzdGFydCBvZiBhIGdlbmUsIHRoZW4gdGhlIOKAmHJlYWRpbmcgZnJhbWXigJkgZm9yIGFsbCBzdWJzZXF1ZW50IGNvZG9ucyB3aWxsIGJlIHNoaWZ0ZWQuIEFsbW9zdCBhbGwgdGhlIGNvZG9ucyB3aWxsIGJlIGluY29ycmVjdGx5IHJlYWQsIGNoYW5naW5nIG1hbnkgYW1pbm8gYWNpZHMgaW4gdGhhdCBwcm90ZWluLg==[Qq]
[f]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
Cg==[Qq]
[q topic= “gene_pools_and_mutation”]Insertion or deletion of a single nucleotide in a DNA sequence results in a
[c]IGZyYW1lc2hpZn QgbXV0YXRpb24u[Qq]
[c]IHNpbGVudCBtdXRhdGlvbi4=[Qq]
[c]IHBvaW50IG11dGF0aW9uIHRoYXQgZG9lc27igJl0IGNoYW5nZSB0aGUgcmVhZGluZyBmcmFtZS4=[Qq]
[f]IFRlcnJpZmljISBJbnNlcnRpb25zIG9yIGRlbGV0aW9ucw==wqA=aW4gdGhlIG51Y2xlb3RpZGUgc2VxdWVuY2UgZWl0aGVyIHB1c2ggYWxsIHRoZSBudWNsZW90aWRlcyBkb3duIG9yIHB1bGwgdGhlbSBhbGwgZm9yd2FyZC4=wqA=VGhlIG1haW4gY29uc2VxdWVuY2Ugb2YgdGhpcyBpcyB0aGF0IGl0IGNoYW5nZXMgdGhlIHJlYWRpbmcgZnJhbWUsIGFuZCBjaGFuZ2VzIGV2ZXJ5IGNvZG9uIGRvd25zdHJlYW0gb2YgdGhlIG11dGF0aW9uLg==[Qq]
[f]IE5vLiBBIHNpbGVudCBtdXRhdGlvbiBjaGFuZ2VzIHRoZSBETkEsIHdpdGhvdXQgY2hhbmdpbmcgYW55IG9mIHRoZSBhbWlubyBhY2lkcyB0aGUgZ2VuZSBjb2RlcyBmb3IuIEluc2VydGlvbnMgb3IgZGVsZXRpb25zIGluIHRoZSBudWNsZW90aWRlIHNlcXVlbmNlIGVpdGhlciBwdXNoIGFsbCB0aGUgbnVjbGVvdGlkZXMgZG93biBvciBwdWxsIHRoZW0gYWxsIGZvcndhcmQuwqA=VGhlIG1haW4gY29uc2VxdWVuY2Ugb2YgdGhpcyBpcyB0aGF0IGl0IGNoYW5nZXMgdGhlIHJlYWRpbmcgZnJhbWUsIGFuZCBjaGFuZ2VzIGV2ZXJ5IGNvZG9uIGRvd25zdHJlYW0gb2YgdGhlIG11dGF0aW9uLiBTZWUgaWYgeW91IGNhbiBmaW5kIGEgY2hvaWNlIHRoYXQsIGluIGEgc2luZ2xlIHdvcmQsIGNhcHR1cmVzIHdoYXQgaGFwcGVucyB3aXRoIGluc2VydGlvbnMgb3IgZGVsZXRpb25zLg==[Qq]
[f]IE5vLiBUaGUga2V5IHBvaW50IGhlcmUgaXMgdGhhdCBpbnNlcnRpbmcgb3IgZGVsZXRpbmcgYSBudWNsZW90aWRlIGZyb20gYSBETkEgc2VxdWVuY2Ugc2hpZnRzIGV2ZXJ5IG51Y2xlb3RpZGUgZm9yd2FyZCBvciBiYWNrd2FyZC4gVGhpcyBkb2VzIGNoYW5nZSB0aGUgcmVhZGluZyBmcmFtZS4gTmV4dCB0aW1lLCBjaG9vc2UgYW5vdGhlciBhbnN3ZXIu
Cg==[Qq]
[q topic= “gene_pools_and_mutation”]Which type of mutation is most likely to be acted upon by natural selection?
[c]IEEgc2lsZW50IG11dGF0aW9uICh3aGljaCBvbmx5IGNoYW5nZXMgdGhlIEROQSk=[Qq]
[c]IEFuIGFjdGl2ZSBtdXRhdGlvbiAod2hpY2ggY2hhbmdlcyB0aGUg RE5BLCBhbmQgdGhlIHByb3RlaW4gdGhlIEROQSBjb2RlcyBmb3Ip[Qq]
[f]IE5vLiBTaWxlbnQgbXV0YXRpb25zIGhhdmUgbm8gZWZmZWN0IG9uIGFuIG9yZ2FuaXNt4oCZcyBwaGVub3R5cGUuIFNpbmNlIG5hdHVyYWwgc2VsZWN0aW9uIG9ubHkgYWN0cyBvbiB0aGUgcGhlbm90eXBlLCBzaWxlbnQgbXV0YXRpb24gY2Fu4oCZdCBiZSBhY3RlZCBvbiBieSBuYXR1cmFsIHNlbGVjdGlvbi4=[Qq]
[f]IFRoYXTigJlzIGNvcnJlY3QuIEFjdGl2ZSBtdXRhdGlvbnMgY2hhbmdlIHByb3RlaW4sIHdoaWNoIGNoYW5nZXMgYW4gb3JnYW5pc23igJlzIHBoZW5vdHlwZS4gU2luY2UgbmF0dXJhbCBzZWxlY3Rpb24gYWN0cyBvbiBhbiBvcmdhbmlzbeKAmXMgcGhlbm90eXBlLCBhY3RpdmUgbXV0YXRpb25zIGJlY29tZSB0YXJnZXRzIGZvciBzZWxlY3Rpb24u
Cg==[Qq]
[q topic= “gene_pools_and_mutation”]The most common consequence of an active mutation is for there to be
[c]IGltcHJvdmVtZW50IG9mIHRoZSBwcm90ZWluLCBtYWtpbmcgaXQgbW9yZSBlZmZlY3RpdmUgYW5kIGluY3JlYXNpbmcgYW4gb3JnYW5pc20mIzgyMTc7cyBwcm9iYWJpbGl0eSBvZiBzdXJ2aXZhbC4=[Qq]
[c]IG5vIGltcGFjdCBvbiB0aGUgb3JnYW5pc23igJlzIHBoZW5vdHlwZS4=[Qq]
[c]IGRhbWFnZSB0byBhIGZ1bmN0aW9uaW5nIHByb3RlaW4sIHJlc3VsdGluZyBpbiBk aXNlYXNlIGZvciB0aGUgb3JnYW5pc20gdGhhdCBiZWFycyB0aGUgbXV0YXRpb24u[Qq]
[f]IE5vLiBXaGlsZSB0aGlzIGlzIHBvc3NpYmxlLCBhbmQgYW4gaW1wb3J0YW50IHBhcnQgb2YgZXZvbHV0aW9uLCBpdOKAmXMgdmVyeSB1bmxpa2VseS4gTXV0YXRpb25zIGFyZSByYW5kb20gY2hhbmdlcywgYW5kIHJhbmRvbSBjaGFuZ2VzIGFyZSBtb3JlIGxpa2VseSB0byBicmVhayB0aGluZ3MgdGhhbiB0byBmaXggdGhlbS4=[Qq]
[f]IE5vLiBCeSBkZWZpbml0aW9uLCBhbiBhY3RpdmUgbXV0YXRpb24gaXMgY2hhbmdpbmcgYSBwcm90ZWluLiBQcm90ZWlucywgb24gc29tZSBsZXZlbCwgYXJlIHdoYXQgbWFrZSB1cCBhbiBvcmdhbmlzbeKAmXMgcGhlbm90eXBlIChlaXRoZXIgZGlyZWN0bHksIG9yIHRocm91Z2ggZW56eW1lcyB0aGF0IGNvbnRyb2wgZGV2ZWxvcG1lbnQpLg==[Qq]
[f]IFllcy4gTXV0YXRpb24gaXMgdGhlIGNhdXNlIG9mIG1hbnkgZ2VuZXRpYyBkaXNlYXNlcy4gVGhlIG1vc3QgbGlrZWx5IGltcGFjdCBvZiBhIG11dGF0aW9uIGlzIHRvIHRha2UgYSBwcm90ZWluIHRoYXTigJlzIHdvcmtpbmcgYW5kIGRpbWluaXNoIG9yIGRlc3Ryb3kgaXRzIGZ1bmN0aW9uLg==
Cg==[Qq]
[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=[Qq]
[c]IGhldGVyb3p5Z290 ZSBhZHZhbnRhZ2Uu[Qq]
[c]IGFsbGVsZSBzZWxlY3Rpb24u[Qq]
[f]IE5vLiBXaGlsZSB0aGlzIHdpbGwgYWx0ZXIgdGhlIGZyZXF1ZW5jeSBvZiBhbGxlbGVzIGluIHRoaXMgcG9wdWxhdGlvbiBpbiBmYXZvciBvZiB0aGUgbGV0aGFsIGFsbGVsZSwgdGhhdOKAmXMgbm90IHRoZSBuYW1lIHRoYXTigJlzIHVzZWQuIFRoaW5rIGFib3V0IHdoaWNoIGdlbm90eXBlIGhhcyB0aGUgc3Vydml2YWwgYWR2YW50YWdlLg==[Qq]
[f]IFllcy4gVGhpcyBzaXR1YXRpb24sIHdoZXJlIGhldGVyb3p5Z290ZXMgc3Vydml2ZSBhdCBoaWdoZXIgcmF0ZXMsIGV2ZW4gdGhvdWdoIHRoZXkgY2FycnkgYSBsZXRoYWwgYWxsZWxlLCBpcyBjYWxsZWQgaGV0ZXJvenlnb3RlIGFkdmFudGFnZS4=[Qq]
[f]IE5vLiBPbiBhIHBvcHVsYXRpb24gZ2VuZXRpYyBsZXZlbCwgdGhlIGxldGhhbCBhbGxlbGUgd2lsbCB3aW5kIHVwIHdpdGggYSBtdWNoIGhpZ2hlciBmcmVxdWVuY3kgdGhhbiB3b3VsZCBiZSBleHBlY3RlZCBmb3IgYSBsZXRoYWwgYWxsZWxlLiBCdXQgdGhhdOKAmXMgbm90IHRoZSBuYW1lIGZvciB0aGlzIHBoZW5vbWVub24uIFRoaW5rIGFib3V0IHdoaWNoIGdlbm90eXBlIGhhcyB0aGUgc3Vydml2YWwgYWR2YW50YWdlLg==
Cg==[Qq]
[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[Qq]
[c]IHNzLCBTUyzCoFNz[Qq]
[c]IFNTLCBzcyzCoFNz[Qq]
[c]IFNzLC BTUyw=wqBzcw==[Qq]
[f]IE5vLiAmIzgyMjA7U1MmIzgyMjE7IGlzIHRoZSBub3JtYWwgaGVtb2dsb2JpbiBnZW5vdHlwZSwgYnV0IGluZGl2aWR1YWxzIHdpdGggdGhpcyBnZW5vdHlwZSBzdWZmZXIgZnJvbSBtYWxhcmlhLiBZb3XigJlyZSBjb3JyZWN0IGluIHB1dHRpbmcgJiM4MjIwO3NzJiM4MjIxOyBsYXN0IHNpbmNlIGl0IHJlc3VsdHMgaW4gc2lja2xlIGNlbGwgYW5lbWlhLCBhIHNlcmlvdXMgZGlzZWFzZS4gVGhpbmsgYWJvdXQgd2hpY2ggZ2Vub3R5cGUgcHJvZHVjZXMgYSBwaGVub3R5cGUgdGhhdCBkb2VzIGJlc3QgaW4gbWFsYXJpYS1hZmZlY3RlZCBhcmVhcywgYW5kIGNob29zZSBhbm90aGVyIHNlcXVlbmNlLg==[Qq]
[f]IE5vLiAmIzgyMjA7c3MmIzgyMjE7IGlzIGZvciBzaWNrbGUgY2VsbCBhbmVtaWEsIGEgc2VyaW91cyBkaXNlYXNlLiB3aXRoIGEgbG93IHN1cnZpdmFsIHJhdGUuICYjODIyMDtzcyYjODIyMTsgc2hvdWxkIGdvIGxhc3QuICYjODIyMDtTUyYjODIyMTsgaXMgdGhlIG5vcm1hbCBoZW1vZ2xvYmluIGdlbm90eXBlLCBidXQgaW5kaXZpZHVhbHMgd2l0aCB0aGlzIGdlbm90eXBlIHN1ZmZlciBmcm9tIG1hbGFyaWEuIFRoaW5rIGFib3V0IHdoaWNoIGdlbm90eXBlIHByb2R1Y2VzIGEgcGhlbm90eXBlIHRoYXQgZG9lcyBiZXN0IGluIG1hbGFyaWEtYWZmZWN0ZWQgYXJlYXMsIGFuZCBjaG9vc2UgYW5vdGhlciBzZXF1ZW5jZS4=[Qq]
[f]IE5vLiAmIzgyMjA7U1MmIzgyMjE7IGlzIHRoZSBub3JtYWwgaGVtb2dsb2JpbiBnZW5vdHlwZSwgYnV0IGluZGl2aWR1YWxzIHdpdGggdGhpcyBnZW5vdHlwZSBzdWZmZXIgZnJvbSBtYWxhcmlhLiAmIzgyMjA7c3MmIzgyMjE7IGlzIGZvciBzaWNrbGUgY2VsbCBhbmVtaWEsIGEgc2VyaW91cyBkaXNlYXNlIHdpdGggaGlnaCBtb3J0YWxpdHkgKCYjODIyMDtzcyYjODIyMTsgc2hvdWxkIGdvIGxhc3QpLg==wqA=VGhpbmsgYWJvdXQgd2hpY2ggZ2Vub3R5cGUgcHJvZHVjZXMgYSBwaGVub3R5cGUgdGhhdCBkb2VzIGJlc3QgaW4gbWFsYXJpYS1hZmZlY3RlZCBhcmVhcywgYW5kIGNob29zZSBhbm90aGVyIHNlcXVlbmNlLg==[Qq]
[f]IEV4Y2VsbGVudC4gSGV0ZXJvenlnb3RlcyBoYXZlIHRoZSBhZHZhbnRhZ2UgYW5kIHN1cnZpdmUgYXQgdGhlIGhpZ2hlc3QgcmF0ZS4gJiM4MjIwO1NTJiM4MjIxOyBpcyBmb3Igbm9ybWFsIGhlbW9nbG9iaW4sIGJ1dCB0aGUgbm9ybWFsIHBoZW5vdHlwZSBpcyB2dWxuZXJhYmxlIHRvIG1hbGFyaWEsIGEgdmVyeSBzZXJpb3VzIGRpc2Vhc2UgdGhhdCBjYW4gYmUgZGVhZGx5LiBXaGlsZSAmIzgyMjA7c3MmIzgyMjE7IGlzIG5vdCBleGFjdGx5IGxldGhhbCwgaXQgcmVzdWx0cyBpbiBzaWNrbGUgY2VsbCBhbmVtaWEsIGEgZGlzZWFzZSB3aXRoIGxvd2VyZWQgc3Vydml2YWwgcmF0ZXMu
Cg==[Qq]
[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==[Qq]
[c]IE11dGF0aW9ucyBoYXZlIG9ubHkgbmVnYXRpdmUgZWZmZWN0cyBvbiBhIHBvcHVsYXRpb27igJlzIGdlbmUgcG9vbC4=[Qq]
[c]IFBvcHVsYXRpb25zIGVuY291cmFnZSBtdXRhdGlvbnMgaW4gb3JkZXIgdG8gcmVzcG9uZCB0byBlbnZpcm9ubWVudGFsIGNoYWxsZW5nZXMu[Qq]
[f]IFllcy4gV2hpbGUgb24gYW4gaW5kaXZpZHVhbCBiYXNpcywgbXV0YXRpb25zIGFyZSBtb3N0bHkgaGFybWZ1bCwgb24gYSBwb3B1bGF0aW9uIGxldmVsIG11dGF0aW9ucyBhcmUgYW4gaW1wb3J0YW50IHNvdXJjZSBvZiB0aGUgdmFyaWF0aW9uIHRoYXQgbWFrZXMgYWRhcHRhdGlvbiBwb3NzaWJsZS4=[Qq]
[f]IE5vLiBXaGlsZSBvbiBhbiBpbmRpdmlkdWFsIGJhc2lzLCBtdXRhdGlvbnMgYXJlIG1vc3RseSBoYXJtZnVsLCBvbiBhIHBvcHVsYXRpb24gbGV2ZWwgbXV0YXRpb25zIGFyZSBhbiBpbXBvcnRhbnQgc291cmNlIG9mIHRoZSB2YXJpYXRpb24gdGhhdCBtYWtlcyBhZGFwdGF0aW9uIHBvc3NpYmxlLg==[Qq]
[f]IE5vLiBNdXRhdGlvbnMgYXJlIGNvbXBsZXRlbHkgcmFuZG9tLiBOZWl0aGVyIGluZGl2aWR1YWxzIG5vciBwb3B1bGF0aW9ucyBoYXZlIGFueSBjb250cm9sIG92ZXIgd2hlbiBtdXRhdGlvbnMgaGFwcGVuLCBhbmQgd2hldGhlciB0aG9zZSBtdXRhdGlvbnMgd2lsbCBiZSBoYXJtZnVsIG9yIGJlbmVmaWNpYWwu
Cg==[Qq]
[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==[Qq]
[c]IFBvcHVsYXRpb24gQg==[Qq]
[f]IFllcy4gVmFyaWF0aW9uIGlzIHRoZSByYXcgbWF0ZXJpYWwgdGhhdCBuYXR1cmUgYWN0cyB1cG9uIHRvIHNlbGVjdCBuZXcgYWRhcHRhdGlvbnMuIFBvcHVsYXRpb24gJiM4MjIwO0EsJiM4MjIxOyB3aXRoIGl0cyBtYW55IGZpeGVkIGFsbGVsZXMsIHNlZW1zIHRvIGhhdmUgbGl0dGxlIHZhcmlhYmlsaXR5LiBBZGFwdGluZyB0byBlbnZpcm9ubWVudGFsIGNoYW5nZSB3aWxsIGJlIHZlcnkgZGlmZmljdWx0Lg==[Qq]
[f]IE5vLiBWYXJpYXRpb24gaXMgdGhlIHJhdyBtYXRlcmlhbCB0aGF0IG5hdHVyZSBhY3RzIHVwb24gdG8gc2VsZWN0IG5ldyBhZGFwdGF0aW9ucy4gUG9wdWxhdGlvbiAmIzgyMjA7QiwmIzgyMjE7IHdpdGggdHdvIG9yIG1vcmUgYWxsZWxlcyBmb3IgbWFueSBnZW5lcywgd2lsbCBoYXZlIG1vcmUgdmFyaWF0aW9uLCBlbmFibGluZyBpdCB0byBoYXZlIGEgYmV0dGVyIGNoYW5jZSBvZiBhZGFwdGluZyB0byBjaGFuZ2VzIGluIGl0cyBlbnZpcm9ubWVudC4=[Qq]
[x]
[restart]
[/qwiz]
Links
- Genetic Drift, The Founder Effect, and Population Bottlenecks (the next tutorial in this population genetics module).