LECTURE 11 - Quantitative Inheritance

Question 1

2 TYPES of GENETIC TRAITS

+ difference in terms of…

• discrete or continuous?
• described or measured by?
• effect of environment
• controlled by how many genes?

Answer 1

1. Quantitative
   - continuous
   - described using measurable units
   - largely affected by the environment
   - controlled by multiple genes
2. Qualitative
   - discrete (has this trait or not) / categorical
   - classified on either-or bases
   - less affected by environment
   - controlled by 1-2 genes

Question 2

what do you call a pattern of inheritance where a single gene controls a trait?

what type of genetic trait is this expressed?

what is its opposite?

Answer 2

Mendelian Inheritance

or

Monogenic Inheritance

in QUALITATIVE GENETIC TRAITS

r
in quantitative genetic traits, it s called POLYGENIC INHERITANCE

Question 3

3 TYPES of Quantitative Traits - Polygenic Inheritance

Answer 3

1. Meristic Trait
   - discrete
   - counted as not measurable
   - controlled by many genes
2. Threshold Trait
   - traits are either present or absent
   - controlled by many genes
3. Continuous Trait
   - traits are measured (may decimal)
   - controlled by many genes

Question 4

POLYGENIC INHERITANCE

• how many genes affect a single trait?
• each ____ will contribute _____ & ____ to the trait

Answer 4

• multiple genes
• allele
• additively and equally

*more dark skin alleles will result n a darker shade

Question 5

PHENOTYPIC VARIANCE

• the variance observed across a ____ due to ___
• denoted by ____
• formulas (2)?

Answer 5

• population
• phenotype
• Vp

1.) Vp = Vg + Ve + Vgxe

Vg - variance due to genotypic differences

Ve- variance due to environmental factors

Vgxe - variance due to interaction of genotype and environment

2.) variance formula so Vp of F1 = variance of all raw quantitative data of F1 phenotype

Question 6

PHENOTYPIC VARIANCE

• can this be estimated?

Answer 6

It is DIFFICULT TO ESTIMATE but can be assumed to be equal to 0

Question 7

GENOTYPIC VARIANCE

• formula?

Answer 7

Vg = Va + Vd + Vi

Va = variance due to additive gene effects

Vd = variance due to dominance gene effects

Vi = = variance due to epistatic gene effects (alleles at different loci)

Question 8

GENOTYPIC VARIANCE

• can this be measured?

Answer 8

It is DIFFICULT TO MEASURE but can be assumed to be equal to 0

UNLESS given in the problem

Question 9

DETERMINE THE AUTHOR

• continuous variation is due to MULTIPLE GENES

Answer 9

Yule (1906)

Question 10

DETERMINE THE AUTHOR

• every gene has a small effect on the character

Answer 10

Yule (1906)

Question 11

DETERMINE THE AUTHOR

• studied grain color in wheat is a continuous variable
• found that as NO. OF INDEPENDENT GENES ARE INCREASED, distribution follows a normal curve

Answer 11

Herman Nilsson-Ehle

Question 12

DETERMINE THE AUTHOR

• proposed the term “polygenes”

(group of genes that influence the expression of a quantitative trait in an additive manner”

Answer 12

mather (1943)

Question 13

example of polygenes (5)

Answer 13

kernel color

skin color

corolla length

IQ

crop yield

Question 14

Metric vs Economic characters

*types of quantitative traits

Answer 14

METRIC CHARACTERS
- distributed in a continuous manner
- measurable
(weight, height, head size, limb length)

ECONOMIC CHARACTERS
- grain yield
- seed size
- meat yield

Question 15

are quantitative traits polygenic

Answer 15

yes

Question 16

are quantitative traits influenced by environmental factors?

+ examples (2)?

Answer 16

yes

IQ is affected by nutritous diet + good health + good education

YIELD is affected by soil, climate, and fertilizer

Question 17

BASIC ASSUMPTIONS for POLYGENIC INHERITANCE

(7)

Answer 17

1. genes do not have individually recognizable phenotypic effects
2. a series of genes control the trait
3. genes have cumulative effect
4. dominance of allele is ordinarily absent**

**instead a series of genes create an additive effect for phenotype

5. F1 is intermediate of parents
6. there is appreciable influence of environment
7. classification of trait is thru measurable units

Question 18

when will Vp = Ve?

Vp = phenotypic variation
Ve = environmental variation

+ formula for Ve

Answer 18

Vp = Ve will only be for P1, P2, and F1

this is because 100% of all individuals in this generation have the SAME genotype…. so, they’re variation would only be based on environmental factors

thus… from the formula Vp = Vg + Ve + (Vgxe)….

Vg = 0

so

Vp = Ve

thus… the value of Ve can be ESTIMATED by (Vp1+Vp2+Vf1) / 3

Question 19

formula for Vp, Vg, and Va of F2 generation?

Answer 19

Vf2 = Vg + Ve

Vg = Vf2 - Ve

Va = 2(Vf2 - VBC1)

Question 20

refers to the proportion of a POPULATION’S (not an individual) phenotypic variation that is attributable to genetic factors

+ 2 types + difference

Answer 20

heritability

*used to examine the relative contributions of genes and environments to variation in a specific trait

OR “measures amount of phenotypic variation in a population due to genetic factors”

1.) broad sense - measures full contribution of genetic variation to phenotypic variation

2.) narrow sense - measures only contribution of additive alleles to phenotypic variation

Question 21

HERITABILITY

interpret the ff values of heritability:

• 0
• 0.5
• 1

Answer 21

• 0 = none can be attributed to genotypic variation (only due to environment)
• 0.5 = 50% of observed phenotypic variation among individuals is due to genotypic variation
• 1 = 100% of observed phenotypic variation among individuals is due to genotypic variation

Question 22

FORMULA of:

broad sense heritability vs narrow sense heritability

Answer 22

BS: h²B = (Vg / Vp)

NS: h²N = (Va / Vp)

Question 23

why is narrow sense heritability more useful to animal and plant breeders?

Answer 23

bc narrow sense only takes into consisderation ADDITIVE GENES which are predictable and consistent when passed from gen to gen

broad sense takes into account the FULL CONTRIBUTION of genetic variation (which includes additive, dominance, and epistatic genes) wherein the latter 2 are inconsistent and cannot be predicted

Question 24

is heritability fixed for a trait?

Answer 24

no.,.. it is dependent on genetic make up and environment

SO varies across generations

Question 25

FORMULA for determining the phenotypic contribution of EACH ALLELE for a quantitative trait? + check lec vid for practice problems

Answer 25

contributory effect per allele = [(largest phenotype - smallest phenotype) / 2n] wherein n = number of gene pairs controlling the trait *largest phenotype: homo dominant *smallest phenotype: homo recessive

Question 26

FORMULA for the number of gene pairs controlling a quantitative trait

Answer 26

n = [log (total # of progeny / frequency of extreme phenotype)] ----- [log 4] *extreme phenotype can EITHER be the biggest or smallest amount of individuals with a specific phenotype

Question 27

FORMULA for the quantitative phenotype based from genotype

Answer 27

Phenotype = [(no. of contributory alleles x CEPA) + basal phenotype --- Contributory alleles = dominant alleles Basal phenotype = the lowest phenotype (homozygous recessive or all: aaaaa)

Question 28

how many contributory alleles in here: AAAAa AAaaa

Answer 28

1.) 4 2.) 2

Question 29

2 ways to determine the GENOTYPIC PHENOTYPIC ratio of F2 + notes to remember

Answer 29

1. Binomial expansion - study solving *first and last term has 1 as its coefficient *in (a+b)^[2n] a = A (contributory / dominant) b = a (non-contributory / recessive) * a = 2n to 0 * b = 0 to 2n 2. Pascal's triangle - study solving

Question 30

FORMULA for phenotype for F1 or F2

Answer 30

phenotype of homo recessive parent + (number of dominant alleles x contributory effect per allele)

Question 31

PROBLEM SOLVING: GIVEN: AAAA = 100 g aaaa = 20 g number of gene pairs = 4 find the: 1. contributory effect per allele 2. phenotype of F1 3. phenotype of F2 4. frequencies of F2

Answer 31

1.) (100 g / 20 g) / (2*4) = 10g / allele -- 2.) 20g + (4) (10g) = 60g -- 3.) use binomial / pascal OR use same formula as number 2 OR manually do the phenotypes, wherein at: 0 contributory alleles = 20g 1 contributory allele = 30g 2 contributory alleles = 40g .... 20g is lowest phenotype so it occurs at phenotype with 0 contributory / dominant alleles 4.) use coefficient based on binomial / pascal triangle

Question 32

what is LARGEST and SMALLES phenotype? + what do u call this both?

Answer 32

*largest phenotype: homo dominant *smallest phenotype: homo recessive both are considered as "extreme phenotypes"

Question 33

CRITERIA for n to be a valid estimate (3)

Answer 33

1. Alleles must have equal and additive effects. 2. Genes assort independently. 3. Original parents are homozygous.

Question 34

EFFECT of the ff to quantitative traits: 1. dominance 2. epistasis

Answer 34

1. average phenotype of F1 is closer to the dominant parent 2. graph is asymmetric and skewed towards one parent

Question 35

FORMULA for finding the no of gene pairs (2)

Answer 35

1.) extreme phenotype = 1/(4^n) 2.) n = (D^2) / (8*Vg) wherein D = difference of the MEAN of P1 and P2 Vg = genotypic variance of F2 (Vg = Vf2 - Ve)

Question 36

ROUNDING OFF RULES 9.49 9.50

Answer 36

9.49 = 9 9.5 = 10 *round off based on first decimal place

Question 37

is QTL associated with environmental factors and quantitative traits?

Answer 37

yes

Question 37

WHAT IS a map location for a chromosomal region that is associated with a trait

Answer 37

Quantitative Trait Loci (QTL)

Question 38

used for studying presence of specific genes

Answer 38

QTL

Question 39

aims to localize chromosomal regions that affect variation of quantitative traits in a population

Answer 39

QTL mapping

Question 40

statistical method that links phenotypic and genotypic data to explain genetic basis of variation in complex traits

Answer 40

QTL analysis

Question 41

what is used to map the position of QTL?

Answer 41

molecular markers - since it is associated consistently associated with inheritance of a trait - unlikely to affect trait of interest

Question 41

3 examples of molecular markers

Answer 41

DNA MARKERS 1. single nucleotide polymorphisms 2. simple sequence repeats 3. restriction fragment length polymorphisms

Question 41

TRAITS of longest-lived people in blue zone?

Answer 41

1. Move Naturally every 20 minutes 2. Life Outlook (time for happy hours, emotional wellbeing, dreams and goals) - 15% lower risk of dying + live up to 7 years 3. Diet - wine: 2-4 glasses per day - plant-based diet - max 80% full 4. Connections (relationships) : live up to 4 to 14 years longer

Question 41

Danish Twin Studies - author? - results on life span of twins?

Answer 41

- Dan Buettner - 20% genetics ; 80% lifestyle and environment

Question 41

CASE STUDY - Twins - how many twins were studied? - BROAD sense heritability value of propensity for divorce?

Answer 41

- 1500 + parents + spouses - 52% (goes up by 6x in identical twins; max 2x for fraternal)