Question

I don't understand what this questions means?!?! What does it mean there is genetic variation for a specific behavior? I thought it was talking about how a specific gene can affect specific behaviors? Is that not the same with diseases? How a specific deletion or misense can determine Sickle Cell? How is it not the same with behaviors? That doesn't make sense. What does it mean "genetic variation for a specific behavior"? Also what does it mean "present in strains of species" Are they talking about the nervous system like in the fruit fly? I DON'T UNDERSTAND.

Question:

In chapter 24 we focused on how genes that control the development, structure, and function of the nervous system and interactions with environmental factors produce behavior. At the same time, we found many opportunities to consider the methods and reasoning by which much of this information was acquired. How do we know there is genetic variation for a specific behavior that is present in strains of a species? How do we know that schizophrenia has genetic components?

Answer 1

• Phenotype describes the observable traits of an individual, or an organism (or a cell). It may be depicted as visible features in terms of characteristics including: physical, physiological, anatomical, biochemical, or behavioral. These phenotypic traits are due to expression of the genotype or genetic code inherited by the individual.
• Phenotypic variation is essential for evolution by the process of natural selection. Phenotypic variation may result due to genetic variation, effect of the environment in which the organism exists, or interaction of environment with genetic components.
• Thus, to determine, how much phenotypic variation is due to genetic interactions or allelic variance, and how much is due to environmental factor, quantification is required (quantitative genetics or quantitative trait locus or QTL mapping).
• Phenotype value is designated as P (describing a trait or phenotype), genetic value or genotype by G, and E is environmental deviation (representing effect of environment and interaction of genotype with environment):

P = G + E

Phenotype variation VP = VG +VE

Genotypic value (G) further may be influenced by:

1. Breeding value (A)- measures the effect of genetic makeup on the phenotype.

• When we consider a population, we measure breeding value in terms of evolution of a phenotypic trait, passed to the subsequent generations. The effect on an individual gene, when passed from parental (P), F1, F2 generations and to offspring is considered as additive effect or additive factor.
• Moreover, the change in the allele of the gene, when passed to offspring (determined by the frequency of the gene at different locus), also determines the breeding value. Thus, breeding value is expressed as the average effect (effect on a gene allele measured in terms of locus and generations).

2. Dominance deviation (D) – measures the effect of gene due to dominance of an allele.

3. Epistasis (I)-

• Interaction of non -allelic genes. This factor is influence by the influence of loci on the gene. This value will change, if a single locus controls a gene, or if there is interaction between multiple loci of the gene.
• Epistatic interactions and dominance are non-additive factors.
• Environmental deviation includes environmental effects like climatic variations, nutritional factors. It may be also related to the maternal effect.

Thus, phenotype variation:

VP= VA + VD + VI + VE

• Schizophrenia may considered to have genetic component, by considering heretibility in twins.
• 50% of genes come from father and 50% from mother, which are further influenced by their genetic lineages
• Schizophrenia may considered to have genetic component, by considering heretibility in twins.
• In monozygotic twins- developing from same genes of mother will share 50% of chance to have schizophrenia.
• In dizygotic twins- the fraternal twins will have about 17% chance to share the chance of having schizophrenia.
• Thus, these hereditary similarities in inheritance, indicate schizophrenia having genetic component

• Also there is environmental effect on genes which vary according to its effect on genes of the offspring.