AR103 - Readings pgs. 82-91 - Week 7 Notes - Oct. 29, 2011.
Chapter Four: Heredity and Evolution
Pages # 82 - 91
- Each mitochondrial contains several copies of a ring-shaped DNA molecule, or chromosome.
- While mitochondrial DNA (mtDNA) is distinct from chromosomal DNA, its molecular structure
and functions are the same. The entire molecule has been sequenced and is known to contain
around 40 genes that direct the conversion of energy within the cell.
- Like the DNA in a cell’s nucleus, mtDNA is subject to mutations, and some of these mutations
cause certain genetic disorders that result from impaired energy conversion,
- Animals of both sexes inherit all their mtDNA and mitochondrial traits from their traits.
- Meiosis and recombination don’t occur since mtDNA is only inherited from only one parent
- Meaning that all the variation in mtDNA among individuals is caused by mutation, which
makes mtDNA extremely useful for studying genetic change over time.
Modern Evolution Theory
- Merging of the two theories, Darwin and Wallace’s natural selection + Mendelians mechanism
for inheritance and the theory of mutation.
The Modern Synthesis
- 1920’s-1930’s biologists realized that mutation and natural selection weren’t opposing
processes, but instead they both contributed to biological evolution.
- What is now called modern synthesis.
- Deﬁning evolution as a 2 stage process:
- 1. The production and redistribution of variation (inherited differences among
- 2. Natural selection acting on this variation, whereby inherited differences, or variation,
among individuals differentially affect their ability to successfully reproduce.
A Current Deﬁnition of Evolution
- Deﬁnes evolution as a change in allele frequencies from one generation to the next.
- Allele frequency is in a population, the percentage of all the alleles at a locus accounted for
by one speciﬁc allele.
- Indicators of the genetic makeup of a population, the members of which share a gene
- Population is within a species, a community of individuals where mates are usually
- Gene pool are all of the genes shared by the reproductive members of a population.
- Microevolution are small changes occurring within species, such as changes in allele
- Microevolution are changes produced only after many generations, such as the appearance
of a new species.
- Also called speciation.
- Genetic variation must ﬁrst be produced by mutation, and then it can be acted on by natural
Factors that Produce & Redistribute Variation
- If one allele changes to another - that is if the gene itself is altered - a mutation has happened.
In fact alleles are the results of mutation.
1 AR103 - Readings pgs. 82-91 - Week 7 Notes - Oct. 29, 2011.
- The substitution of one single DNA base for another, called a point mutation, can cause the
allele to change.
- Point mutations have to occur in sex cells if they’re going to have evolutionary
- Because the mutation must be passed from one generation to the next for
evolution to occur. Must occur in gamete cells.
- Its rare for evolution to take place solely because of mutations. However, when mutation is
combined with natural selection, evolutionary changes not only can occur, but they can occur
- Mutation is the only way to create new genes, its role in the production of variation is key to the
ﬁrst stage of the evolutionary process.
- Gene ﬂow is the exchange of genes between populations.
- This exchange of genes between groups can only happen if the migrants interbreed. Or
even if the individuals move temporarily and have offspring in the new population, they
don’t necessarily stay there.
- In humans mating patterns are mostly determine by social factors
- Human population movements have reached previously unheard of proportions, and very few
breeding isolates remain.
- Migration on a smaller scaled has been consistent feature of human evolution since the
ﬁrst dispersal of our genus, and gene ﬂow between populations helps explain why
speciation has been rare during the past million years or so.
Genetic Drift and Founder Effect
- Genetic drift is the evolutionary change(s) in allele frequencies, that are produced by random
factors in small populations. Genetic drift is a result of small population size.
- If an allele is rare in a small population composed of only a few hundred individuals,
then there’s a chance it simply may not be passed on to offspring. If this happens the
allele may completely disappear from the population.
- Founder Effect is a type of genetic drift in which allele frequencies are altered in small
populations that are taken from, or are remnants of, larger populations.
- It is seen in many modern human and non-human populations.
- Occurs when a small band of “founders” leaves its parent group and forms a colony
somewhere else. Termed colonization.
- Over time, a new population will be established, and as long as mates are
chosen only from within its population, all of its members will be descended
from the small original group of founders.
- All the genes in the expanding group will have come from original
- If a rare allele from the founder’s parent population was carried
by even one of the founders, it can eventually become common
among the founder’s descendants.
- Founder effect can also occur do to, small founding groups that may be the survivors of
a larger group that was mostly wiped out by some disaster.
- The small group of survivors becomes a founder population, possessing only a
sample of alleles that were present in the original population.
2 AR103 - Readings pgs. 82-91 - Week 7 Notes - Oct. 29, 2011.
- The outcome of a lo