genetics- quantitative traits

quantitative traits overview

traits that are measurable

• rely on multiple genes

• variation in traits

• lots of possible phenotypes

• slight changes in phenotypes

continuous variation of traits

quantitative traits

display continuous variation

measured and described in quantitative terms (quantitative inheritance)- multiple genes

range of different phenotypes

display continuous variation

polygenic

input for multiple genes

multiple genes control phenotype

varying phenotypes result from input of many genes

multifactorial traits

result of both gene action and environmental influences

phenotype relies on genetic genetic input (alleles) and environment (cellular and/ or outside environment)

quantitative patterns

mendelian factors could not account for the range of phenotypes seen in quantitative patterns of inheritance

multiple-gene hypothesis

multiple alleles

more certain types of alleles —> change phenotype

many contribute to phenotype in a cumulative/ quantitative way

discontinuous traits (discrete)

simple pheno and geno relationship

show only a few distinct phenotypes

Aaco

continuous traits

hegight mass, measurable traits- lots of variety and different outcomes

DO NOT follow mendel’s laws and principles

so many possible phenotypes b/c polygenic (multiple alleles, not environment) or multifactoral (genes and environment)

medicine

disorders are characterized by variation

many disorders caused by multiple genetic/environmental factors

goood to understand for

• prevention

• genetic counseling

• treatments

agriculture and farming

bigger and BETTA food

economics

breeding programs

crops

livestock

big torkey

polygenetic traits

multiple genes

measured in large samples bc need large sample size to rep a population for #good stats

mode

value most frequently observed

3,3,3,5,6,6,7

mode is 3

median

middle value of set of values

if even take mean of two middle values

3,3,3,5,6,6,7

median is 5

mean

average

sum of values divided by number of samples

variance

distribution of measured values in relation to the mean

covariance

measures the shared variation of two traits by an individual

measures how much two random variables change together

• do they both increase

• does one increase and the other decreases

correlation coeficcient r

measure of how traits are associated

varies from -1 to 1

closer to 1 = better related/correlated

CORRELATION DOES NOT EQUAL CAUSATION

r values

quantitative traits are described by

a frequency distrubution (histogram)

bins make it possible to see bellcurve

WE WANT DA BELLCURVE

PROBELM with pheno disribution on chart

hard to make geno and pheno distinguish bc of overlap

pheno can only be within a certain range, depends on trait being analyzed

what is distinctive abt polygenic inheritance

mean of F1 is intermediate to the means of two parents

but F2 shows greater standard deviation and range

polygene hypothesis

phenotypes result from input of many genes

each gene locus may be occupied by either an additive allele or a nonadditive allele

phenotype is based on how many additive alleles you havea

additive allele

contributes equally to the phenotype

nonadditive allele

does not contribute to the phenotypedi

difference between additive alleles and incomplete dominance

more of a range of phenotypes

additive allele practice probelm

Two genes in corn, each with two alleles, contribute to ear length

• allele L contributes to long ears; allele l does not

• allele T contributes to long ears; allele t does not

to find proportions of phenotypes in the F2, if the trait is quantitative and follows the polygenic hypothesis

(a+b)ⁿ

n is total # of alleles in a genotype

a is a nonadditive allele, b is an additive allele

figure dis out