COMPLEX TRAITS

Question 1

what controls complex traits

Answer 1

: Complex traits are governed by a combination of multiple loci and environmental factors, not following simple Mendelian inheritance rules.

Question 2

what is genetic determinism

Answer 2

Genetic determinism is the idea that genes solely determine physical characteristics or behaviors, rather than a combination of genetic and environmental factors.

Question 3

What is an example of how genetic determinism is incorrect?

Answer 3

An example is the colorpoint locus in cats, where enzymes for coat pigmentation are temperature-sensitive, showing that environmental factors (temperature) influence phenotype.

Question 4

PENETRANCE

Answer 4

Penetrance is the proportion of individuals with a given genotype that show the expected phenotype

Question 5

EXPRESSIVITY

Answer 5

Expressivity is the degree to which a gene is expressed, which can be influenced by both internal and external environmental factors.

Question 6

What is the difference between additive and non-additive gene action?

Answer 6

Additive gene action refers to effects where genes contribute equally to the phenotype, while non-additive gene action involves interactions like dominance and epistasis.

Question 7

What is broad sense heritability?

Answer 7

Broad sense heritability is the proportion of phenotypic variation in a population that is due to genetic variation (including all genetic factors).

Question 8

What is narrow sense heritability?

Answer 8

Narrow sense heritability is the proportion of phenotypic variation that is due to additive genetic variance, which is more useful for predicting response to selection.

Question 9

What does QTL mapping involve

Answer 9

used to identify specific regions of the genome (loci) that are associated with quantitative traits—traits that are influenced by multiple genes and show continuous variation, such as height, weight, or yield in crops.

Question 10

How is GWAS different from QTL mapping?

Answer 10

GWAS is used for natural populations without the need for controlled crosses, assessing many alleles at once to identify genomic regions associated with traits.

Question 11

What is linkage disequilibrium?

Answer 11

Linkage disequilibrium refers to the degree to which one genetic variant is inherited or correlated with a nearby genetic variant in a population.

Question 12

What is the consequence of eugenics based on genetic determinism?

Answer 12

Eugenics is a flawed concept where certain groups are prevented from reproducing to create a “fitter” population, wrongly assuming that all human traits are solely controlled by genetics.

Question 13

What does heritability measure in genetics?

Answer 13

Heritability estimates how much of the variation in a trait is due to genetic differences, helping to distinguish genetic from environmental influences.

Question 14

In complex traits, what increases the risk of developing a trait?

Answer 14

Having specific genetic variants increases the risk of developing a trait, but it is not a certainty.

Question 15

What are the different APOE gene variations associated with Alzheimer’s disease (AD)?

Answer 15

E3: No specific association

E2: Reduced risk

E4: Higher risk

Additive effect: Having two copies of E4 increases risk more than having one.

Question 16

What is the function of the APOE gene?

Answer 16

The APOE gene is involved in transporting lipids between cells and tissues.

Question 17

What are SNPs (single nucleotide polymorphisms) and their relevance?

Answer 17

SNPs are the most common type of genetic variation in DNA and can impact health.
They are used as genetic markers to locate genes associated with diseases or traits.

Question 18

What is linkage disequilibrium (LD)?

Answer 18

Linkage disequilibrium is the degree to which one genetic variant is inherited or correlated with a nearby variant in a population.

Question 19

What goes against linkage disequilibrium?

Answer 19

Recombination breaks up genetic associations, going against linkage disequilibrium.

Question 20

What are the causes of linkage disequilibrium?

Answer 20

Physical proximity on a chromosome

Selection (advantageous to keep variants together)

Population history

Genetic drift

Migration

Mutations

Question 21

Why is linkage disequilibrium important?

Answer 21

Identifies genetic variants associated with diseases or traits (GWAS)

Helps map disease-causing genes

Assists in understanding population history

Recognizes recombination hotspots that often show lower LD

Question 22

What is pleiotropy?

Answer 22

Pleiotropy occurs when a single gene influences two or more seemingly unrelated traits.

Question 23

What are the types of pleiotropy?

Answer 23

Direct pleiotropy: A gene affects multiple traits due to its role in different biological pathways.

Indirect pleiotropy: A change in one trait due to a gene causes secondary effects in other traits.

Question 24

What is the evolutionary significance of pleiotropy?

Answer 24

Constraint of evolution: Selection for or against a gene can have unintended consequences.

Adaptation: Pleiotropy can allow organisms to adapt quickly if one gene influences multiple traits.

Complexity in trait inheritance: Adds complexity to how traits are inherited and selected for, making outcomes harder to predict.

Question 25

QTL

Answer 25

How It Works:
Trait Measurement:
You measure the quantitative trait (e.g., plant height, milk production, disease resistance) in a population of organisms (e.g., plants, animals, or humans).

Genetic Markers:
You use genetic markers (specific known locations in the genome) that vary between individuals in the population. These markers could be SNPs (single nucleotide polymorphisms) or microsatellites.

Genotyping:
You genotype (determine the DNA sequence or marker information) of each individual in your population.

Statistical Analysis:
You analyze the relationship between the genetic markers and the measured traits. By comparing which markers are present in individuals that show higher or lower values of the trait, you can identify regions of the genome that are linked to the trait.

QTL Identification:
The regions on the chromosome that are associated with variation in the trait are called Quantitative Trait Loci (QTLs). These are the genetic regions that contribute to the variation in the quantitative trait.