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.