Genetics Chapter 28: Complex and Quantitative traits

Exam 2 material

What are complex traits? What are quantitative traits?g

Given the description or data regarding a trait, be able to identify it as a quantitative trait or otherwise. Are such traits usually influenced by the environment? Is it possible to define such traits numerically?

What is continuous variation? What are meristic traits?

Define polygenic inheritance.

Given two sets of crosses from P generation to F2 generation be able to identify single gene cross such as Mendel’s experiment for a single character from crosses that represent quantitative traits.

Be able to explain the major points embodied in the multifactorial or multigene hypothesis explaining quantitative variations.

Do Mendel’s law of equal segregation and independent assortment continue to be obeyed in inheritance of quantitative traits?

Be able to describe the details of Nilsson-Ehle experiment in which the quantitative variation of hull color in wheat was observed. What was the proportions of offspring showing the extreme phenotypes?

crossed true breeding red w true-breeding white and he got intermediate red. Incomplete dominance? no! when the intermediates were crossed they produced 5 diff shades of red! (1:4:6:4:1)

What does it suggest about the number of genes controlling this trait in the above experiment?

Given two sets of experimental data showing traits controlled by one or more
genes, predict whether there was a strong influence of the environment in
determining the trait. Similarly for polygenic inheritance. If a quantitative trait
controlled by many different genes (eg 10 genes) and also influenced by
environment was studied and plotted, what would the approximate frequency
distribution of this trait appear as?

Given the ratios of the F2 expressing either extreme phenotype, be able to
estimate the number of gene involved in determining the quantitative trait.

Given the number of distinct phenotypic classes estimate the number of gene
pairs or vice versa if both parents are heterozygotes.

Given genotype of parents (need not be heterozygotes at each gene pair) that
control a quantitative trait, be able to predict maximum and minimum number
of additive alleles within gametes, number of different kinds of gametes based on number of additive alleles, as well as range of phenotypes in offspring as well as
number of phenotypic classes.

What are QTLs or quantitative trait loci? What is a general scheme for mappin

Continuous traits

quantitative traits that do not fall into discrete categories

meristic traits

can be expressed in whole numbers

Threshold traits

inherited due to contributions of many genes (most diseases)

Frequency distribution

traits do not naturally fall into a small number of discrete categories used to represent quantitiative traits

Normal distribution

trait of interest falls in a symmetrical way around the average value

polygenic inheritance

transmission of traits influenced by two or more genes

True or false: most quantitative traits are polygenic

true

Why are polygenic traits difficult to categorize into discrete genotypic categories?

The number of genes controlling the trait increases; 3 or more and the influence of the environment increases
( Punnett square cannot be used to analyze them)

How do you determine the number of gene pairs if the proportion of individuals in th eextremes are known?

¼ raised to n where n = gene pairs involved

How do you calculate the number of distinct F2 phenotypic classes?

2n + 1 (only if both parents are hetero at all pairs)