Genetics

Genes shape traits and populations through inheritance, variation, and evolution. An organism’s phenotype, or physical traits, comes from its genotype, which is the set of alleles, or gene variants, inherited from its parents. Genes can also interact with one another and with environmental factors to produce traits in different ways.

Allele and trait patterns in a population are not fixed. Natural selection, migration, and random genetic drift can all change how common certain alleles are over...

Genetic crosses help scientists study how traits are passed from one generation to the next. In a genetic cross, two organisms are mated on purpose so researchers can follow how parental DNA is recombined in the offspring. This makes it possible to infer gene function, gene interactions, and gene location.

Genetic crosses also played a key role in the development of Mendel's three laws of inheritance. Those laws form the basis of modern genetics. The video then focuses on tetrad analysis, a...

Genetic screens are tools scientists use to reveal gene function and study gene interactions. They work by changing genes and then checking the organism for a trait, or phenotype, that can be seen or measured. This makes them useful for linking a DNA change to a biological effect.

One common approach is a forward genetic screen. In a forward screen, mutations are made at random, and researchers look for organisms with a phenotype of interest. This method can help identify unknown genes that...

Genetic variations can play a major role in human disease. Some mutations are inherited from one generation to the next. Others appear during a person’s life and can contribute to diseases such as cancer.

Medical geneticists study these changes to understand how disease develops. Their work has a long history, and it focuses on key questions about how genetic alterations affect health. Researchers use this knowledge to improve diagnosis and expand treatment options for patients.

Several tools...

SNPs, or single nucleotide polymorphisms, are the most common form of genetic variation in humans. They are changes at a single DNA base. In many cases, these differences do not directly affect gene expression. Even so, they can help scientists locate disease-associated genes or support patient diagnosis.

This page explains how SNPs are identified, or genotyped. Several common methods are used for this purpose. These include direct hybridization, PCR-based methods, fragment analysis, and...

Karyotype analysis focuses on chromosomes and their number and structure. A karyotype is the direct view of a cell’s chromosomes, and it can reveal chromosomal abnormalities linked to disease.

Chromosomes in a karyotype can be stained with different dyes to create unique banding patterns. These patterns help scientists compare chromosomes and look for changes in structure. The video also explains newer cytogenetics methods, including comparative genomic hybridization and fluorescence in situ...

Gene expression is the process cells use to turn genetic information into functional products. In many cases, that product is a protein made from amino acids. This process is controlled at several stages, and mistakes in control can contribute to diseases such as cancer.

The study of gene expression has also grown through major historical discoveries. One key advance was learning how specific combinations of DNA bases encode the amino acids that build proteins. That discovery helped explain...

Microarrays let scientists compare gene expression by measuring how strongly genes are turned on in a sample. They rely on complementary binding, which means matching nucleic acid strands stick to each other. In this method, probes attached to a glass chip bind to nucleic acids taken from samples.

With microarrays, researchers can evaluate the expression of thousands of genes at the same time. That makes the method useful for spotting broad patterns in cells and tissues. Scientists can also...

RACE, or Rapid Amplification of cDNA Ends, is a PCR-based method used to find the full length of an mRNA transcript. It extends cDNA to either the 3' end or the 5' end, even when the full sequence is not already known. Because it focuses on one end of a transcript, it is also called one-sided or anchored PCR.

RACE starts with reverse transcription, which converts mRNA into single-stranded complementary DNA, or cDNA. The reaction then uses one gene-specific primer and one generic primer. The...

RNA-seq measures gene expression by sequencing RNA from a sample. It is a high-throughput method, which means it can read many RNA molecules at once. It is especially useful because it can be analyzed without prior genomic information.

In RNA-seq, RNA isolated from samples of interest is first used to build a DNA library. A DNA library is a prepared collection of DNA fragments made from the RNA. That library is then amplified and sequenced. The resulting data can show which genes are...

Epigenetic tags can change how genes work without changing the DNA sequence itself. In genetics research, scientists have long seen heritable traits that are not explained by changes in the nucleotide sequence of DNA. These differences are linked to chemical and protein-based controls that act on genes.

One common mechanism is DNA methylation, which adds methyl groups to cytosine bases in DNA. Another involves histones, the proteins around which DNA is wrapped. Chemical groups added to...

DNA methylation is a DNA change that can help turn genes on or off. It happens most often at CpG dinucleotides, which are places where a cytosine is followed by a guanine in the DNA sequence. Methyl groups added at these sites may affect gene expression and are often studied near promoters and other gene control regions.

Clusters of these methylation sites are called CpG islands. When CpG islands near a promoter become methylated, they may help keep a gene silent in a stable way. This matters...

Histones help package DNA in eukaryotic nuclei. DNA wraps around these proteins to form chromatin, the compact structure that organizes the genome. Histones can also carry chemical changes, and those changes can affect gene expression.

Scientists use chromatin immunoprecipitation, or ChIP, to find which DNA regions are linked to specific histone modifications or other gene regulatory proteins. An antibody is used to isolate the protein of interest. The DNA that remains attached to that protein...

Genetic engineering changes an organism’s DNA on purpose. It is used to build research tools, create model organisms, and support agricultural applications. Scientists also study it for future uses such as stress tolerance in crops and gene therapy for human disease.

The field grew as researchers confirmed that DNA is the genetic material. Those discoveries led to tools that can modify DNA. This page also traces the history of genetic engineering and shows how those tools became part of modern...

Homologous recombination is a key method for DNA engineering in modern biology. It lets scientists change DNA by using matching stretches of sequence between different DNA molecules. This approach helps overcome limits of standard molecular cloning with restriction enzymes, which can be less useful for large or complex DNA constructs.

Recombineering uses homologous recombination to edit DNA more efficiently. It depends on recombination-competent organisms and genomic libraries such as...

Genome editing uses DNA repair to make targeted changes in the genome. It works by creating a double-strand break in DNA with an engineered nuclease. The nuclease is guided to a chosen genomic site by a protein or an RNA that recognizes a specific sequence.

After the break, the cell tries to repair the damage. During that repair process, mutations can be introduced into the targeted DNA region. This makes genome editing a useful way to modify specific sequences without relying only on gene...