The aim of this chapter is not to outline general concepts of classical, Mendelian genetics or techniques of molecular sciences. These should be found in any introductory textbook of undergraduate biology. Nevertheless, a few terms and definitions of general genetics shall be recapitulated first. After that we are going to discuss behavioral genetics in a general way, followed by an outline of the importance of genetic relatedness in the evolution of animal societies, as a background for population genetical consideration. This will be followed by some studies on heritability and selection experiments for behavioral traits, and a few examples for monogenic heredity. A few comments on human behavioral genetics are included in this. Finally, the importance of population genetics, particulary genetics of small populations for wildlife management and conservation biology, shall be outlined.
The term 'heritability' already is one of those that are often used in an incorrect way. Genetically speaking, heritability of a certain trait means that a certain percentage of 'variation' between members of the same generation and population is genetically determined. We shall see that most behavioral traits have heritabilities of <50%, often around 30% or lower. That means that 'within' a population, 30-50% of variance in these traits is influenced by genetics. The rest are maternal effects, pre-and postnatal environment, learning, etc. This is a different definition from the term 'innate behavior' of classical ethology, which meant that a certain behavioral trait is more or less exclusively determined by genetical factors. Modern behavioral biology tends not to use this term any longer, because of the many inaccuracies of the concept (e.g., regarding prenatal influences).
Some more genetical terms should also be defined here. A gene is the part of the genome that determines the sequence of one polypeptide. This has to be kept in mind - there never can be a gene for a certain behavior, only for a certain protein that somehow affects behavior, be it as a hormone, receptor, receptor antagonist, transmitter, etc.
Should there be more than one form of a gene, we are talking of alleles. Should an individual carry two identical alleles of a certain gene, we call it homozygous, should it have two different alleles, heterozygous. The term heterozygosity (H) refers to the percentage of gene loci that are heterozygous in an average individual of a given population. Heterogenity (P) however means the percentage of gene loci that have more than one allele in a population.
Hybrids are offspring of parents of different races, subspecies, etc. The P-generation is the parental generation, the animals which were used to start a breeding experiment, etc., with. In population and conservation genetics, they are also called founders.
Fx-generation (F1, F2, F3,...) are offspring of the P-generation. A backcrossing is the breeding of a member of a filial generation with a member of the P-generation.
Lethal factors, for example, some color factors in pet rodents such as chinchilla or dwarf hamsters, are genes which in a homozygous situation cause the death of the individual (regardless of the developmental stage in which it occurs). Now coming to multiple alleles, this is a situation where more than two alleles of the same gene locus are present in the population. A well-known example is of human blood groups: both A and B are co-dominant, O is recessive. That means that the O allele is only effective when the other chromosome also carries a O.
Should there be more than one trait ofthe phenotype being influenced by one gene, we talk of pleiotropy. An example for pleiotropy in behavioral genetics is the following: in Drosophila, the so-called per gene both influences circadian rhythms and certain characters of male courtship 'songs' (wing vibrations).
Epistasis is the situation where one gene influences the expression of another. An example is that mice with a recessive combination of a certain gene cc are always without any pigment. Should there be at least one dominant gene C, they get pigmentation. But if another gene determines coat color, then B (dominant) causes black, b (recessive) causes brown fur. Polygeneous, contrary to this, means that several genes simultaneously influence the trait. In human beings, skin color is simultaneously influenced by at least three genes, each of them in a dominant or recessive allele. Whenever we find an array of intensities in a certain trait, such as fur color, this is a strong hint at polygeneity.
Mutations are spontaneous or induced changes somewhere in the genome. They can afflict the caryotype as a whole (e.g., a missing or superfluous chromosome), parts of the genome (e.g., a missing arm of a certain chromosome), or individual genes (e.g., by changes in nucleotide sequences). In natural situations, a spontaneous rate of mutation of about 1:105 to 1:106 is to be expected.
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