Department of Psychology - FSU Genetics of Behavior Daniel Montoya Ph.D. Department of Psychology - FSU

Genetics of Behavior New genes do not simply “appear” in the genome. They are the result of duplication of old genes. They separate, over an evolutionary scale, by mutation, selection and drift

Genetics of Behavior We use the evidence of what remains to figure out how genes drifted and mutated over long periods of time

Genetics of Behavior Example: color vision genes Where does color vision comes from in humans? color vision in reptiles color vision in mammals and man

Visual Coding and the Retinal Receptors The vertebrate retina consist of two kind of receptors: Rods - most abundant in the periphery of the eye and respond to faint light. (120 million per retina) Cones - most abundant in and around the fovea. (6 million per retina) Essential for color vision & more useful in bright light.

Color vision Dichromatic vision is perception of two hues only (blue and yellow) of the normal four primaries, lacking that for red and green and their derivatives. Most mammals posses this system

Color vision Trichromacy or trichromaticism is possessing three independent channels for conveying color information Derived from the three different cone types. Organisms with trichromacy are called trichromats. Reptiles, some monkeys and humans

Color vision Tetrachromacy is possessing four independent channels for conveying color information, or possessing four different types of cone cells in the eye. Organisms with tetrachromacy are called tetrachromats. Turtles, birds

Color vision gene Australian (but not American) marsupials have an ancestral reptilian visual pigment that is lost in the rest of the mammals

Color vision Humans did not retain trichromatic vision from reptiles but rediscovered: Old World Monkeys and apes New World Howler Monkey

Color vision Why is trichromacy so important? Fruit eating: In a green forest, fruit stands out by its color and assist in detecting younger, more succulent leaves

Color vision The colors that we perceive are “labels” for electromagnetic radiations. I.e. “Red” has a wavelength of 700 billionth of a meter

Best fit All eyes in our planet are set to make the best use of the wavelengths of electromagnetic radiation from the sun as is filtered by our atmosphere.

electromagnetic spectrum

Color Vision Some cones are more sensitive toward the red of the spectrum, others toward the blue. The comparison between the cones makes color vision possible

Color Vision Dichromatic animals have only two populations of cones to compare; trichromatic three and tetra- chromatic four. By comparing the firing rates from just three kinds of cones, our brain perceives all color hues

Visual Coding and the Retinal Receptors Photopigments - chemicals contained by both rods and cones that release energy when struck by light. Photopigments consist of 11-cis-retinal bound to proteins called opsins. Light energy converts 11-cis-retinal quickly into all-trans- retinal. Light is thus absorbed and energy is released that activates second messengers within the cell.

Color vision The genes that make our green and red opsins molecules are the same They are located on the X chromosome The gene for blue opsin lies in a non-sex chromosome (chromosome 7)

opsin genes Each opsin type has diverged evolutionarily through gene duplications and/or amino acid substitutions Five types of opsins are considered to have emerged from a common ancestor of vertebrates on the basis of molecular phylogenetic analyses. The five types of opsins are: RH1 (specialized opsin for rod photoreceptor cells [rod opsin, also generaly called "rhodopsin"]), RH2 (green-sensitive cone opsin), SWS2 (blue-sensitive cone opsin), SWS1 (uv-to-blue sensitive cone opsin), and M/LWS (red-green sensitive cone opsin).

Opsin genes

New world monkeys Female Howler monkeys have two X chromosomes (with the chance to have g+r or r+r or g+g) plus the autosomal blue. Some females may be trichromatic Males have the autosomal blue plus either red or green Red and green opsin genes in New World monkeys are an example of polymorphism polymorphism is the simultaneous existence, in a population, of two or more alternative versions of a gene

Polymorphism Example in humans: sickle cell anemia in humans An individual with two copies of the gene (Homozygotes) suffer from the anemia, but Heterozigotes are protected against malaria

Old World monkeys There was a duplication of an opsin gene on the X chromosome the original individual found itself with two copies of the same gene (g+g or r+r) the old world monkeys became trichromatic on subsequent evolution as one of the opsins started to be more sensitive to red

polymorphism vs duplication Gene Duplication X Chromosome genes X Chromosome genes either/ or and Autosomal gene Autosomal gene

Case studies Analyze your case study and come up with the best scenario that will explain that particular gene appearing in that population: either polymorphism or gene duplication.