Genetics Ch. 5

Difference among siblings

Due to both genetic & environmental factors

Monozygotic (MZ)

Genetically identical twins derived from a single fertilization involving one egg & one sperm. Share all their genes.

Environmental Variance

The phenotypic variance of a trait in a population that is attributed to differences in the environment.

Genetic Variance

The phenotypic variance of a trait in a population that is attributed to genotypic differences.

Genetic contribution

to phenotypic variation can be estimated.

Regression to the Mean

Averaging out the phenotype

Phenotypes

Can be discontinuous or continuous

No

Can intelligence be measured objectively (like height or weight)?

Haplotypes

Genes associated with reading disability (dyslexia) & cognitive ability have been discovered by comparing ____________.

Identical Twins

Have 100% of their genes in common (correlation coefficient= 1.0)

Polygenic System

Parents with extreme differences in phenotype, tend to have offspring that exhibit a phenotype that is the average of the two parental phenotypes.

Discontinuous Variation

Phenotypes that fall into two or more distinct, non overlapping classes (Ex: Mendel's peas)

Continuous Variation

Phenotypic characters that are distributed from one extreme to another in an overlapping fashion (Ex: Height in humans)

Polygenic Inheritance

Traits are usually quantified by measurement rather than counting. Two or more genes contribute to the phenotype. Phenotypic expression varies across a wide range.

Polygenic Traits

Traits controlled by 2 or more genes. Patterns of inheritance that can be measured quantitively

Dizygotic (DZ)

Twins derived from two separate & nearly simultaneous fertilizations, each involving one egg & one sperm. These twins share about 50% of their genes.

Multifactorial Traits

Variations in expression of polygenic traits often are due to the action of environmental factors.

Single Nucleotide Polymorphisms (SNPs)

allows the association between haplotypes and phenotypes.

General Cognitive Ability

an expanded definition of intelligence. Ex: verbal & spatial abilities, memory & speed of perception, and reasoning.

Human Diseases

are controlled by the action of several genes.

Early studies

believed that physical dimensions of regions of the brain were a measure of intelligence.

Concordance

can be converted to heritability by statistical methods.

IQ tests

can't be equated with intelligence. Relative contributions of genetics, environment, social & cultural influences can't be measured.

Heritability

can't be used to estimate genetic variation between populations.

ob gene

encodes the weight-controlling hormone leptin in mice.

Genetic & Environmental

factors that make important contributions to intelligence.

Skin Color

is a characteristic of a polygenic trait.

Spina Bifida

is a common birth defect involving the nervous system.

Multifactorial Phenotypes

the risk of recurrence is predicted to decline as the degree of relatedness of the individuals declines.

Genetic Variability

within a population is greater than the variability between any two populations.

Concordance

Agreement between traits exhibited by both twins.

Additive Model of Polygenic Inheritance

As the number of genes involved increase, the number of phenotypic classes increases.

Nutrition (especially folate)

has a significant impact on the frequency of occurence.

Multifactorial Traits

have environmental, social, & cultural impacts.

Skin Color

is controlled by 3-4 genes & environmental factors leading to a wide range of phenotypes.

Complex Traits

Determined by the cumulative (additive) effects of genes & the influence of environment.

Five

How many basic eye colors fit a model with two genes, each with two alleles?

Human Obesity Genes

In humans, mutations in the gene for Leptin (LP) of the Leptin receptor (LEPR) account for about 5% of all cases of obesity. Other factors cause the recent explosive increase in obesity.

Phenotype

Interactions with the environment often participate in creating the ____________.

Environment

Many traits are determined by many gene pairs as well as the ___________.

Height

New technologies allow researchers to survey the genome to detect associations with phenotypes such as?

Multifactorial Traits

Polygenic traits resulting from interactions of 2 or more genes & one or more environmental factors. Each gene makes a small contribution. Results in continuous phenotypic variation.

Intelligent Quotient (IQ) Test

Psychological measurements & the ability to perform specific tasks as a function of age led to the development of?

Heritability of a Trait

The degree of phenotypic variation produced by a genotype in a specific population can be estimated by calculating the ________ __ __ ________.

Polygenic Inheritance

The distribution of polygenic traits through the population follows a bell-shaped (normal) curve.

Correlation Coefficient

The fraction of genes shared by two relatives.

Environmental Influence

When raised in separate environments identical twins provide an estimate of the degree of ____________ __________ on gene expression.

Skin Color

is controlled by 3-4 genes, plus environmental factors.

Phenotypic Variation

is derived from two sources: Genetic Variation & Environmental Variance

Intelligent Quotient (IQ)

measurements that have a significant heritable component

Heritability

measures only variation within a population at the time of measurement.

What are complex traits?

multifactorial traits

Twin studies

of obesity show a strong heritability component (about 70%)

Multifactorial Traits

or complex traits are polygenic traits with a strong environmental component.

Armadillos

produce litters of 2-6 genetically identical, same-sex offspring by embryo splitting, the same way identical multiple births can occur in humans.

ob gene

produced by fat cells that signal the brain & ovary. As fat levels become depleted, secretion of leptin slows and eventually stops.

Twin studies

provide an insight into the interaction of genotypes & environment.

db gene

receptors in the hypothalamus are controlled by the?

Twin studies

show a significant genetic component.

Haplotype

specific combinations of SNPs located close together on a chromosome that are likely inherited as a group.

Twin studies

the degree of concordance for a trait is compared in MZ and DZ twins reared together or apart. The greater the difference, the greater the heritability.