Molecular Genetics and Linkage Analysis Quiz

Molecular Genetics and Linkage Analysis

• Topics covered in the lecture include PCR, gel electrophoresis, Sanger sequencing, next-generation sequencing (NGS), VNTRs, X-linked inheritance, and genetic linkage analysis.
• These techniques are essential in studying genetic variation, diagnosing diseases, and understanding inheritance patterns.

PCR Overview

• PCR (Polymerase Chain Reaction) is an automated DNA replication process performed in a test tube.
• The process involves denaturation, primer annealing, and primer extension steps.
• Taq polymerase is a heat-stable enzyme that synthesizes new DNA during PCR.
• Each PCR cycle doubles the number of DNA copies, producing billions of copies after 30 cycles.

Sanger DNA Sequencing

• Sanger sequencing involves in vitro DNA replication to read DNA nucleotide sequences.
• Dideoxynucleotides halt DNA synthesis, producing fragments of various lengths.
• Each dideoxynucleotide is labeled for detection during sequencing.
• Fragments separated using gel electrophoresis reveal the DNA sequence.
• The Human Genome Project used Sanger sequencing to determine the sequence of ~22,000 genes.

Gel Electrophoresis

• Gel electrophoresis separates DNA fragments based on size, allowing visualization.
• Molecular-weight markers help determine fragment sizes in base pairs.
• Smaller DNA fragments move faster through the gel compared to larger fragments.
• This technique is used to analyze PCR products.
• Gel electrophoresis is used to compare alleles in codominant inheritance.

VNTR Markers

• Variable Number Tandem Repeats (VNTRs) are repeating DNA sequences that vary between individuals.
• PCR amplifies VNTR regions for genetic comparison in forensic and paternity tests.
• VNTRs are codominantly inherited, meaning both alleles are detectable.
• VNTRs create unique genetic profiles useful for identification purposes.

X-Linked Inheritance

• X-linked inheritance patterns involve genes located on the X chromosome.
• Males are more commonly affected by X-linked recessive disorders, as they only have one X chromosome.
• Females can be carriers of X-linked recessive disorders.

Genetic Linkage Analysis

• Researchers study families with a history of a disorder to map the location of the mutation on a chromosome.
• The number of repeats of a specific sequence correlates with the severity and onset of the disorder.
• This technique helps predict disease onset and severity in family members carrying the mutation.

Next-Generation Sequencing (NGS)

• NGS allows for massively parallel sequencing of DNA fragments.
• DNA is fragmented, and clusters of identical DNA strands are amplified for sequencing.
• Fluorescently labeled nucleotides identify the sequence as DNA is synthesized.
• NGS is faster and cheaper than Sanger sequencing, and produces billions of base pairs in a day.

Third-Generation Sequencing (TGS)

• TGS reads long stretches of DNA in real time.
• This technique does not require DNA amplification.
• PacBio and Oxford Nanopore are key TGS technologies.
• Nanopores detect electrical signals generated by nucleotides passing through.

Autosomal Inheritance

• Autosomal inheritance patterns involve genes located on non-sex chromosomes.
• Both males and females are equally likely to inherit autosomal traits.

Autosomal Dominant Inheritance

• Only one copy of a dominant allele is needed to express the associated phenotype.
• Affected individuals typically have one affected parent.
• Autosomal dominant disorders typically do not skip generations.
• Huntington's disease is an example of an autosomal dominant disorder.

Autosomal Recessive Inheritance

• Both copies of the recessive allele are necessary to express the associated phenotype.
• Affected individuals typically have parents who are carriers.
• Autosomal recessive disorders can skip generations.
• Cystic fibrosis is an example of an autosomal recessive disorder.

X-linked Recessive Inheritance

• Genes located on the X chromosome.
• Males more commonly affected since they only have one X chromosome.
• Affected males inherit trait from mothers.
• Carriers are females who have one normal and one affected X chromosome.

X-Linked Dominant Inheritance

• Genes located on the X chromosome.
• Traits equally seen in both males and females.
• Affected males pass trait to all daughters, but not sons.
• Affected females pass trait to both sons and daughters.

Y-Linked Inheritance

• Genes located on the Y chromosome.
• Only males are affected.
• Traits are passed directly from father to son.