Chapter 18 Bio
What is not true regarding "heritability"?
1. Heritability is the measure of whether a trait can be passed from parents to offspring in a given population. 2. A heritability of 100% means that a certain trait―if present in the parental generation―will always be observed in the progeny. 3. A heritability of 0% means that any variation observed for a trait in a given population is the result of genetic―not environmental―factors. 4. If the heritability of a given trait in a population is 100%, then the heritability of that trait for all populations will be 100% (i.e., heritability is constant across different populations for the same trait).
_____________________ is defined as the percentage of cases in which both members of a pair of twins show the trait when it is known that at least one member shows it.
Concordance
A concordance of 50% for a trait occurring in identical twins only provides evidence for the role of nature or genes in the development of this trait, and does not yield any information regarding the role of nurture or environment in this trait.
False
All genotypes are equally susceptible to the effects of a high-fat diet.
False
All of the genes involved in a complex trait contribute equally to the manifestation of that trait.
False
An example of "regression toward the mean" would be if the offspring of two short parents had an average height equal to the average height of the parents―not of the population as a whole.
False
Genetic and environmental influences do not interact or contribute to the phenotypic outcomes in precise ways.
False
Genetic differences are always more important than environmental differences for determining phenotypic outcomes.
False
Heritability in non-scientific terms means "the capability of being inherited or being passed on by inheritance"; this is a very accurate description of the inheritance of a complex trait.
False
In a study of concordance, a sample of identical twins was evaluated for adult-onset diabetes. The data below were collected for this trait: (1) in 36 identical twin pairs, both showed adult-onset diabetes (2) in 40 identical twin pairs, only one showed adult-onset diabetes (3) in 336 identical twin pairs, neither showed adult-onset diabetes The data above imply that the environment is not an important component of adult-onset diabetes.
False
Nilsson-Ehle studied the effects of a small number of genes on a particular trait about a century ago, and found that the Mendelian laws of inheritance did not apply.
False
Only by studying identical twins raised in separate environments can scientists uncover the role of genes vs. environment in the development of a specific trait. Comparing the occurrence of the trait in identical vs. fraternal twins yields little usable data.
False
Several genes involved in human cholesterol levels can be found on the X chromosome in humans.
False
Similar to single-gene traits, traits determined by multiple genes also show the expected 3:1 ratio of phenotypes in the progeny between two heterozygotes.
False
Single gene traits are more likely to be influenced by the environment.
False
The magnitude of heritability is an intrinsic property of a trait.
False
You may know that certain forms of dwarfism are the result of mutations in the Sox9 gene. Thus, Sox9 is considered to be the major height determining gene in humans.
False
____________ of a trait in a population can be measured and is the proportion of the total variation in the trait (phenotypic variation) that is due to genetic differences among individuals.
Heritability
Imagine that one of your good friends comes from a tall family. You measure the height of your friend and her two brothers. What would you expect of the average height of your friend and her siblings?
The average height of your friend and her siblings will be higher than the mean height of the population as a whole, but will be lower than the average height of your friends' parents.
A trait with high heritability responds rapidly to selection pressures, whereas a trait with a low heritability responds slowly or not at all.
True
Clustering of genes with related functions on the same chromosome reflects the fact that many genes arose through the process of duplication of a single gene, followed by divergence.
True
If all of the variation in a trait in the population is due to differences in the environment, then the mean phenotype of the offspring would be independent of parental phenotype and would be identical to the mean phenotype of the population.
True
If all of the variation in a trait in the population is due to differing genotypes, then the mean phenotype of the offspring would be identical to the parental mean.
True
In a study of concordance, a sample of identical twins was evaluated for adult-onset diabetes. The data below were collected for this trait: (1) in 36 identical twin pairs, both showed adult-onset diabetes (2) in 40 identical twin pairs, only one showed adult-onset diabetes (3) in 336 identical twin pairs, neither showed adult-onset diabetes Items (1) and (2) can be used to calculate concordance as follows: 36/(36 + 40)x 100 = 47%
True
Two-thirds of the American population suffers from disorders determined by multiple genes and environmental factors.
True
When studying phenotypic variations due to the environment, it is necessary to compare organisms with identical genotypes. In addition, it is necessary to use identical environments when studying variation in genotypes.
True
Twin studies have been used to assess the relative importance of "nature" versus "nurture" in determining variation among individuals for complex traits. Which of the following statements is not correct?
Twin studies show that autism and clinical depression are not significantly influenced by genotype.
For which of the following traits would the difference between the concordance rates seen in fraternal and identical twins be the greatest?
autism
For which of the following traits do genetic factors not play a major role in the development of the trait?
cancer (at nonspecific sites)
Traits that are influenced by multiple genes and the environment are called ____________ traits.
complex
Fraternal twins arise from two different fertilized eggs and are called ________________ twins.
dizygotic
If the concordance rate for a given trait is 10% for both identical and fraternal twins, this means that:
genes play a (relatively) minor role in the development of this trait, whereas environment plays a major role in the appearance of this trait.
Lindsay and Joy are twins that share the same genetic material and appear so similar that their teachers cannot tell them apart. Lindsay and Joy are:
identical and monozygotic twins.
Sometimes a fertilized egg, after a few of rounds of division, separates into two embryos that results in identical, or ________________________, twins.
monozygotic
Imagine that a researcher discovers a new gene that plays a role in determining human height, weight, and hand shape. This gene would be considered to be:
pleiotropic
Although more than 50 genes contribute to the level of HDL (high-density lipoproteins), LDL (low-density lipoproteins), or triglycerides, it has also been shown that a single gene within this population of genes can affect two or three of these types of molecules. This single gene with its multiple effects is said to show:
pleiotropy.
If genetically identical strains of corn are grown in different environments, then differences in height would be due to the environment and:
the heritability measure would be 0%.
If genetically different strains of corn are grown in a greenhouse and subject to identical environmental conditions, then differences in height would be due to genetic differences and:
the heritability measure would be 100%.
Down syndrome, the most common type of birth anomaly due to an extra chromosome, is also known as _________ 21.
trisomy
