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And : Identifying Genes

37 important questions on And : Identifying Genes

Definition quantitative trait locus

Genes of various effect sizes in multiple genes systems that contribute to quantitative (continuous) variation in a phenotype.

What is allelic association?

It is a correlation between an allele and an trait for individuals in a population

What is continuous phenotype?

Display a range of expression (weight, height) rather than an all-or-none appearance. > can be tested with a linear regression or case study

Definition candidate gene approach

Look at genetic variantion within a pre-specified genes of interest and phenotype or disease states.

What is single nucleotide polymorphism (SNP)?

Involves a mutation in a single nucleotide. SNPs have two alleles.

Which mutation is more damaging?

A mutation that leads to a loss of a base. This leads to frame shifting

What is wrong with repeated sequences?

Very short segments of DNA are repeated after each other, this is unstable and can increase in the next generation. This explains the non-mendelian proces: genetic anticipation.

What are synonymous SNPs?

This are the most SNPs, they don't cause a change in the amino acid sequence. They might have a effect by changing the rate at which mRNA is translated into proteins.

Definition copy number variants (CNVs)

A polymorphism that involves duplication or deletion long stretches of DNA. Might play a role in ASD and schizophrenia.

What is a polygenic score?

Measure of genetic predisposition for complex traits and disease risk.

What is a methode to detect SNPs and microsatellite markers?

PCR

What are the DNA markers and why?

Microsatellite markers and SNPs because they can be identified directly in the DNA itself

The two major strategies for identifying genes for human behavior

Allelic association
Linkage

Definition linkage (behavior traits)

Association within the families. You look at co-inheritance of a DNA marker and a disease.

What is the (dis)advantage of linkage?

It is systematic but not powerful for detecting small effect size.

What is the (dis)advantage of association?

It is more powerful then linkage but until recently it was not systematic and restricted to candidate genes.

Definition affected sib-pair linkage design

It is based on allele sharing for siblings: whether affected siblings share 0,1 or 2 alleles for a DNA marker.

What is the weakness of allelic associtation?

An association can only be detected if a DNA marker is itself the functional gene (direct association) or very close to it (indirect association or linkage disequilibrium)

What are haplotype blocks?

A series of SNPs that are highly correlated and rarely are seperated during recombination.

What is genetic anticipation?

Symptoms appear at an earlier age and with greater successive generations.

What is the HapMap project?

Systematize hapolotype blocks for several ethical groups

What is whole-genome amplification?

The use of few restriction enzymes in PCR to chop up and amplify the entire genome. This makes microarrays possible.

Methods to test a continuous phenotype

Linear regression or case study

Why should we do association studies?

Learn about the disease biology
Predict disease based on the genome
Use genetics to improve epidemiology

What is genetic effect?

The change in average trait value, give a change in the genotype.

What is a genome-wide association study (GWAS)?

Scan the entire genome for common genetic variation. Goal is to identify single nucleotide polymorphisms (SNPs) that are associated with phenotypic traits

What is premutation and fragile X syndrome?

Parents who inherit X chromosomes with a normal number of repeats (5 - 40 repeats) sometimes produce eggs or sperm with an expanded number of repeats (up to 200), called a permutation > does not cause disability in the offspring but is unstable and leads to more expansions in the next generation which do cause disability.

What is whole-genome sequencing?

We can detect every single DNA polymorphism by sequencing each individual's entire genome

What is Polymerase chain reaction (PCR)?

Method to detect SNPs and microsatellite markers. It rapidly makes millions of copies of a specific DNA sample, allowing scientists to take a very small sample of DNA and amplify it to a large enough amount to study it

What is a primer?

A short DNS sequence that marks the starting point for DNA replication. Primers on either side of a polymorphism mark the boundaries of a DNA sequence.

What is a polymerase?

An enzyme that begins the process of copying DNA. It begins to do so on each strand of DNA at the point of the primer

What is a haploid genotype (haplotype)?

The DNA sequence on one chromosome

What is linkage analysis?

A technique that detects linkage between DNA markers and traits, used to map genes to chromosomes

What are single-gene disorders?

The disease is normally inherited on a certain allele. When you inheret the C allele you insert e.g. The Huntington Disease gene. This marker (allele) is not the Huntington gene itself.

What is a candidate gene?

A gene whose function suggests that it might be associated with a trait

What is the linkage disequilibrium?

A violation of Mendel's law of independent assortment. IT is most frequently used to describe how close together DNA markers are on a chromosome; linkage disequilibrium of 1.0 means that the alleles of the DNA markers are perfectly correlated

What are the broad aims of contemporary genetics?3

1. Identify > the specific genetic variants which are related to a phenotype
2. Interpret > the (biological) effects these SNPs have on a trait
3. Predict > for individuals or groups, their risk for disease

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Twin Research in Psychology

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