Ch. 7 Flashcards
Multifactoral Traits
controlled by more than one gene, as well as environmental influences
Polygenic Traits
controlled by more than one gene
Epigenetic modification
heritable changes to DNA that regulate gene expression without altering the DNA sequence
Heritability
estimates the proportion of variation in a complex trait due to genetics in a particular population at a certain time
degree of variation in a trait due to genetics (<1.0 = variability is completely the result of gene action)
Higher the number = higher genetics play a role, lower the number = outside factors
Dizygotic Twins
shared environment and 50% of genes
Monozygotic Twins
identical genotype and shared environment
Twins Raised Apart
shared genotype but not environment
Adopted Individuals
Shared environment but not genes
Genome-Wide Association Studies (GWAS)
compares many genetic markers across the genome between two large groups of people (includes SNP’s and copy number variants (CNV’s) )
Single Nucleotide Polymorphisms (SNP’s)
sites in a genome where the DNA base varies in at least 1% of the population, span the genome rather than define a single gene, can be anywhere among base pairs
GWAS must include at least 100k markers
Some inherited disorders (such as Down syndrome) are associated with unusual fingerprint ridge patterns.
genes; Inherited disorders such as Down syndrome are influenced by genes.
Fingerprint patterns are altered when a fetus touches fingers and toes to the walls of the amniotic sac
environment; When a fetus touches fingers and toes to the walls of the amniotic sac, the environment is influencing the phenotype.
Height is affected by diet
environment
Certain patterns of SNPs are common in individuals who experience a period of rapid height increase
genes; SNPs, or single nucleotide polymorphisms, are sites in the genome, so the influence of SNPs on human height is a genetic factor.
A certain allele of the E4 gene, which encodes apolipoprotein E, increases the risk of a heart attack in people who smoke but not in people who do not smoke
genes & environment; An allele is a genetic influence. Smoking or not smoking, however, is an environmental factor. In this example, an allele of the E4 gene is interacting with the environment (smoking or non-smoking), so both genes and the environment are influencing the risk of heart disease in this example.
Exercise decreases the risk of heart disease
environment
Exposure to the sun increases melanin synthesis
environment
If a trait is determined entirely by genes, not by the environment, then the heritability of the trait is 0.
False; If a trait is determined entirely by genes, then its heritability is 1.0.
Heritability is defined as the proportion of the phenotypic variance for a trait that is due to genetic differences in a population at a certain time
True
The heritability of a single-gene trait is always 1.0
False; Single-gene traits may be influenced by the environment, so their heritability is not always 1.0.
The heritability of a trait changes when the environment changes.
True
If the heritability of a trait is very high, then all siblings will have the same phenotype
False; If the heritability of a trait is high, then 50% of siblings will have the same phenotype because siblings share 50% of their alleles.
Genetic variance for a polygenic trait is due mainly to the additive effects of dominant alleles of different genes
False; Genetic variance is due mainly to the additive effects of recessive alleles of different genes, not dominant alleles.
Identical twins are also called ___ twins.
monozygotic
Among pairs of twins in whom at least one has a particular trait, the ___ of the trait is equal to the percentage of pairs in which both twins express the trait.
concordance
Concordance is the percentage of twin pairs in which both twins express a trait among twin pairs in which at least one twin expresses the trait.
Twins who differ in a trait are ___ for the trait.
discordant
Diseases caused by single genes that approach 100 percent penetrance approach ___ concordance in monozygotic twins.
100%
Among dizygotic twins, concordance is usually around ___ for a dominant trait.
50%
Among dizygotic twins, concordance is usually around ___ for a recessive trait.
25%
For a polygenic trait with little or no environmental influence, the concordance value for monozygotic twins will be ___ the concordance value for dizygotic twins.
greater than
To assess the genetic component of a complex trait, it would be most appropriate to study ___
monozygotic twins separated at birth
Fertility in humans is a trait that is controlled by multiple genes, and which has environmental influences, such as the health and nutrition of the potential parents.
What terms describe fertility as a trait?
polygenic, complex, multifactoral
Monogenic or Mendelian traits are single-gene traits. Since fertility is controlled by multiple genes, these do not apply. Instead, fertility is a polygenic trait, because it is controlled by more than one gene. It is also a complex, or multifactorial trait, because it is influenced by an environmental factor.
Which best describes use of polygenic risk scores in making illness/disease predictions in populations?
Single nucleotide base changes in multiple genes from a genome wide association (GWAS) study of an illness/disease risk of one population are used to make predictions of illness using algorithms in another group.
