Population Dynamics Humans and malaria Science (2010), v.328:841

Global Map of Malaria Malaria

“…a far more urgent task: reducing the horrific toll of malaria in central Africa, where five countries account for 50% of all global deaths from the disease and elimination is not possible.” Science (2010), v.328:849

Malaria is large threat to human health in equatorial regions of the Earth Malaria life cycle http://www.cdc.gov/malaria/about/index.html

http://www.who.int/topics/malaria/en/

But some human populations show resistance to the disease. How??

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Natural Selection • Overproduction • Environmental pressure/competition • Pre-existing individual variation • Heritable traits • Happens over generations (time) • Happens in populations (not single individuals) • Offspring must be viable and fertile

Human Population Growth The History of Global Population Growth

Darwin’s Inescapable Conclusion – Fact 1: Potential for overproduction and competition for existence – Fact 2: Individual variation

Evidence for humans?

– The inescapable conclusion: Unequal reproductive success • Darwin called this process natural selection. • The result of natural selection is evolution when a population has adapted to its environment.

Darwin’s Inescapable Conclusion – Fact 1: Potential for overproduction and competition for existence – Fact 2: Individual variation – The inescapable conclusion: Unequal reproductive success

Evidence for humans?

• Darwin called this process natural selection. • The result of natural selection is evolution when a population has adapted to its environment.

The Modern Synthesis: Darwinism Meets Genetics

Populations as the Units of Evolution – A population

– The modern synthesis is the fusion of genetics with evolutionary biology.

• Is a group of individuals of the same species living in the same place at the same time. • Is the smallest biological unit that can evolve.

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Genetic Variation in Populations – Population genetics • Focuses on populations as the evolutionary units. • Tracks the genetic makeup of populations over time.

Sources of Genetic Variation in sexually reproducing organisms

– Individual variation abounds in populations. • Not all of this variation is heritable. • Only the genetic component of variation is relevant to natural selection.

– Hemophilia • Is a blood-clotting disease.

– Mutations • Are changes in the DNA of an organism.

– Sexual recombination • Crossing over • Independent assortment of chromosomes • Random fertilization

Intergenerational Mutation Rate • By how many mutations does your genome differ from your parents genome? • Roach et al (2010) found about 60 mutations, 30 from each parent, that occurred during the formation of egg and sperm (meiosis).

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Sickle-cell allele: genotype, phenotype, and resistance to malaria

Sickle-cell Allele

Malaria infection causes cells to sickle. Sickled cells, along with parasite, are killed.

from The Human Evolution Coloring Book, 2nd Ed.

Biochemistry of sickle-cell disease

Sources of Genetic Variation in sexually reproducing organisms – Mutations • Are changes in the DNA of an organism.

– Sexual recombination • Crossing over • Independent assortment of chromosomes • Random fertilization

from Steinberg, M.H., (2006), Trends Pharm. Sci., 27(4):204-210.

Meiosis, The Basis of Sexual Reproduction – Sexual reproduction depends on • Production of gametes through Meiosis. • Fertilization.

Gametes and the Life Cycle of a Sexual Organism – The life cycle of a multicellular organism is the sequence of stages leading from the adults of one generation to the adults of the next.

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– Fertilization

– Humans are diploid organisms.

• Is the fusion of sperm and egg. • Creates a zygote, or fertilized egg.

• Their cells contain two sets of chromosomes • Their gametes are haploid, having only one set of chromosomes

– Sexual life cycles involve an alternation of diploid and haploid stages. Figure 8.14

Eukaryotic Chromosomes – Each eukaryotic chromosome contains one very long DNA molecule, • Typically bearing thousands of genes.

– The number of chromosomes in a eukaryotic cell • Depends on the species.

Meiosis is the process where the two sets of homologous chromosomes are separated into different cells - egg or sperm.

Homologous Chromosomes – Homologous chromosomes are matching pairs of chromosomes. –Humans have •Two different sex chromosomes, X and Y. •A female has XX •A male has XY •Twenty-two pairs of matching chromosomes, called autosomes.

Meiosis is the process where the two sets of homologous chromosomes are separated into different cells - egg or sperm.

Start with one cell with 2 sets of homologous chromosomes End with 4 cells with 1 set of homologous chromosomes How does this happen?

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The Process of Meiosis – In meiosis, • • •

Haploid daughter cells are produced in diploid organisms. Two consecutive divisions occur, meiosis I and meiosis II, preceded by interphase. Crossing over occurs.

From movie folder play: MeiosisOverview.html Interphase.html ProphaseI.html MetaphaseI.html AnaphaseI.html

TelophaseICytokin.html ProphaseII.html MetaphaseII.html AnaphaseII.html TelophaseIICytokin.html Figure 8.16.1

Figure 8.16.2

Figure 8.16.3

Review: Comparing Mitosis and Meiosis – All the events unique to meiosis occur during meiosis I.

Figure 8.17

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The Origins of Genetic Variation – Offspring of sexual reproduction are genetically different from their parents and from one another.

Independent Assortment of Chromosomes – In independent assortment, every chromosome pair orients independently of the others during meiosis.

– Independent assortment of chromosomes – Random fertilization – Crossing over – Random mutations

Crossing Over

Random Fertilization – The human egg cell is fertilized randomly by one sperm, leading to genetic variety in the zygote.

– In crossing over, • Homologous chromosomes exchange genetic information. • Genetic recombination occurs.

From the movie folder play: - CrossingOver.html

When Meiosis Goes Awry

How Accidents During Meiosis Can Alter Chromosome Number

– What happens when errors occur in meiosis?

– In nondisjunction, • The members of a chromosome pair fail to separate during anaphase. • Gametes with an incorrect number of chromosomes are produced.

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– The result of nondisjunction

Figure 8.20

Down Syndrome: An Extra Chromosome 21

– The incidence of Down Syndrome increases with the age of the mother.

– Down Syndrome • Is a condition where an individual has an extra chromosome 21. • Is also called trisomy 21.

Abnormal Numbers of Sex Chromosomes – Nondisjunction • Also affects the sex chromosomes.

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