Population Dynamics Humans, Sickle-cell Disease, and Malaria How does a population of humans become resistant to malaria?

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

The Origins of Genetic Variation Offspring of sexual reproduction are genetically different from their parents and from one another. Meiosis Random mutations Crossing over Independent assortment of chromosomes Random fertilization

Meiosis and comparing it to Mitosis

The Origins of Genetic Variation Offspring of sexual reproduction are genetically different from their parents and from one another. Meiosis Random mutations 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., Science (2010) found about 60 mutations, 30 from each parent, that occurred during meiosis. Hemophilia in the Royal Family: Hypothesis - hemophilia allele arose through mutation in gamete of Queen Victoria’s mother or father.

Crossing Over In crossing over, Homologous chromosomes exchange genetic information. Genetic recombination occurs.

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

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

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

Heritable Variation and Patterns of Inheritance - Ch 9 Gregor Mendel Was the first person to analyze patterns of inheritance. Deduced the fundamental principles of genetics.

Figure 9.6a

Monohybrid Crosses A monohybrid cross is a cross between parent plants that differ in only one characteristic.

Mendel developed four hypotheses from the monohybrid cross: There are alternative forms of genes, called alleles. For each characteristic, an organism inherits two alleles, one from each parent. Alleles can be dominant or recessive. Gametes carry only one allele for each inherited characteristic.

Mendel developed four hypotheses from the monohybrid cross: There are alternative forms of genes, called alleles. For each characteristic, an organism inherits two alleles, one from each parent. Alleles can be dominant or recessive. Gametes carry only one allele for each inherited characteristic.

Mendel developed four hypotheses from the monohybrid cross: There are alternative forms of genes, called alleles. For each characteristic, an organism inherits two alleles, one from each parent. Alleles can be dominant or recessive. Gametes carry only one allele for each inherited characteristic.

Mendel developed four hypotheses from the monohybrid cross: There are alternative forms of genes, called alleles. For each characteristic, an organism inherits two alleles, one from each parent. Alleles can be dominant or recessive. Gametes carry only one allele for each inherited characteristic.

Mendel developed four hypotheses from the monohybrid cross: There are alternative forms of genes, called alleles. For each characteristic, an organism inherits two alleles, one from each parent. Alleles can be dominant or recessive. Gametes carry only one allele for each inherited characteristic.

Phenotype Genotype An organism’s physical traits; what it looks like. An organism’s genetic makeup; what genes it has.

Genetic Alleles and Homologous Chromosomes Figure 9.7

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

Figure 9.5

Dihybrid cross Is the mating of parental varieties differing in two characteristics.

Mendel’s law of independent assortment states that Each pair of alleles segregates independently of the other pairs during gamete formation.

Figure 9.23

Using a Testcross to Determine an Unknown Genotype A testcross is a mating between An individual of unknown genotype and a homozygous recessive individual.

Family Pedigrees Shows the history of a trait in a family. Allows geneticists to analyze human traits.

Human Disorders Controlled by a Single Gene

Variations On Mendel’s Laws Some patterns of genetic inheritance are not explained by Mendel’s laws. Incomplete dominance Codominance Pleiotropy Polygenic Inheritance

Incomplete Dominance in Plants In incomplete dominance, F1 hybrids have an appearance in between the phenotypes of the two parents.

Incomplete Dominance in People In incomplete dominance, F1 hybrids have an appearance in between the phenotypes of the two parents.

ABO Blood Type: An Example of Multiple Alleles and Codominance The ABO blood groups in humans are an example of multiple alleles.

The immune system produces blood proteins That may cause clotting when blood cells of a different type enter the body.

Pleiotropy and Sickle-Cell Disease Pleiotropy is the impact of a single gene on more than one characteristic. Sickle-cell disease is an example.

Polygenic Inheritance Polygenic inheritance is the additive effects of two or more genes on a single phenotype.

The Role of Environment Many human characteristics result from a combination of heredity and environment.

The Chromosomal Basis of Inheritance The chromosome theory of inheritance states that Genes are located at specific positions on chromosomes. The behavior of chromosomes during meiosis and fertilization accounts for inheritance patterns.

Figure 9.23

Linked Genes Linked genes Are located close together on a chromosome. May be inherited together.

The Process of Science: Are Some Genes Linked? Using the fruit fly Drosophila melanogaster, Thomas Hunt Morgan determined That some genes were linked based on the inheritance patterns of their traits.

What to expect if the genes follow the rules of independent assortment GL gl gL Gl gl GgLl ggll ggLl Ggll 50% parental phenotypes 50% recombinant phenotypes

Unexpected Results!! Figure 9.24

Linked Genes The “P”, “a”, and “b” genes are linked because they are on the same chromosome.

What to expect if the genes are linked. GL gl GgLl ggll 100% parental phenotypes Figure 9.24

Unexpected Results!! Figure 9.24

Genetic Recombination: Crossing Over Two linked genes Can give rise to four different gamete genotypes because of crossing over!

Figure 9.25

Figure 9.26

Linkage Maps Studies using Drosophila Developed a method for mapping gene loci. Resulted in linkage maps.

If these genes are linked on one chromosome: How far apart are they? Figure 9.24

Figure 9.27

Sex-Linked Genes Sex-linked genes Are any genes located on a sex chromosome. Were discovered during studies on fruit flies.

Sex Determination in Humans and Fruit Flies Sex chromosomes Are designated X and Y. Determine an individual’s sex.

Figure 9.28

Eye color is a sex-linked gene in fruit flies Figure 9.29

Inheritance patterns of a sex-linked gene Figure 9.30

Sex-Linked Disorders in Humans A number of human conditions result from sex-linked (X-linked) genes.

Red-green color blindness Is characterized by a malfunction of light-sensitive cells in the eyes.

Hemophilia Is a blood-clotting disease. Figure 9.32