Chapter 25

What is implied by a relativly high value of H^2?

High value indicates that the environment had a relatively low impact on phenotypic variation

How can we ascertain the number of polygenes involved in the inheritance of a quantitative trait?

-(2n+1), where (2n+1) is the number of possible phenotypes and n equals the number of additive loci -1/4^n, where n=the number of polygenes if the ratio of F2 individuals resembling either of the two extreme P1 phenotypes can be determined

How do we know that threshold traits are actually polygenic even though they may have as few as two discrete phenotypic classes?

-Environmental factors have a considerable impact on polygenic system, and therefore, on expression of threshold traits. -Polygenic conditions involving thresholds occur if a range of expression is possible, but the trait is either expressed or not expressed.

What are the major points in the multi-gene hypothesis?

-Together, the genes controlling the trait under study produce a wide range of phenotypic variations. -Analysis of multiple-gene traits requires the study of large numbers of progeny. -Each additive allele contributes roughly equally to the phenotype. -nonadditive alleles do not contribute quantitatively to the phenotype

What is the formal expression used to examine the relative importance of genetic vs environmental factors?

Broad-sense heritabiliy index (H^2)= VG/VP

Quantitative inheritance involves the interaction of a number of gene loci. The pattern of genetic transmission typical of quantitative inheritance is:

Continuous variation of phenotypic expression

How do we know that monozygotic twins are not identical genotypically as adults?

Difference in inherited disease status

All EXCEPT which of the following statements are major points in the multiple-gene hypothesis?

Each gene locus involved in the phenotype may be occupied by either an additive allele, which contributes to the phenotype, or a nonadditive allele, which offsets the additive alleles.

What findings led geneticists to postulate the multiple-factor hypothesis that invoked the idea of additive alleles to explain inheritance patterns?

Experimental results involving pigmentation in wheat showed that a number of additive alleles acting in Mendelian fashion could explain continuous variation.

T or F: Traits such as height, general body structure, skin color, and some behavioral traits are probably caused primarily by genes that behave codominantly or epistatically.

False

T or F: Concordance refers to the frequency with which members of a twin pair express a different trait.

False, concordant alleles are alleles that are the same in twins

Bell shaped distributions produced by plotting results of F2 and F3 crosses are typical of which type of inheritance?

Multiple factor inheritence

In the analysis of quantitative traits, positions on chromosomes called quantitative trait loci (QTLs) are often discussed. In the same context, restriction fragment length polymorphisms (RFLPs) are also discussed. What is the relationship between QTLs and RFLPs?

RFLPs serve as reference points in mapping QTLs.

Define the term broad-sense heritability.

Refers to the degree which phenotypic variation is due to genetic factors.

T or F: The multifactor hypothesis suggests that many factors or genes contribute to the phenotype in cumulative or quantitative manner.

True

(s^2)= S(Xi-X)^2 / n-1 is the formula for calculating what statistical value?

Variance

Broad sense heritability equation

Vp= VE + VG + VGE

How do we assess environmental factors to determine if they impact the phenotype of a quantitatively inherited trait?

by heritability estimation