Genetics: Chromosomes and Gene Variation

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Questions and Answers

What is the typical organization of the bacterial chromosome?

Linear and not membrane-bound

Linear and membrane-bound

Circular and membrane-bound

Covalently closed circular structure, not membrane-bound (correct)

What is unique about the genetic information storage in eukaryotic cells?

It is only stored in the nucleus

It is not stored in a specific organelle

It is only stored in the mitochondria and chloroplasts

It is stored in both the nucleus and the mitochondria/chloroplasts (correct)

What is the primary function of the regions immediately before or after a gene?

Initiation of replication (correct)

Mutagenesis

Gene expression

Regulation of transcription

What is the name of the project that was started in 1990 to sequence the human genome?

Human Genome Project Signup and view all the answers

What is the approximate number of genes in a human cell?

20,000 to 30,000 Signup and view all the answers

What is the primary function of introns in bacterial genomes?

Interrupting tRNA sequences Signup and view all the answers

What percentage of the mitochondrial genome is coding?

97% Signup and view all the answers

What is the typical organization of chromosomes in human cells?

23 sets of chromosomes (22 autosomes, 1 pair of sex chromosomes) Signup and view all the answers

What is the approximate length of the mitochondrial genome?

17,000 base pairs Signup and view all the answers

What is the primary function of introns?

RNA splicing Signup and view all the answers

What is the main difference between eukaryotic and prokaryotic genomes?

Eukaryotic chromosomes have an elaborate system of DNA packing Signup and view all the answers

What is the approximate length of the nuclear genome?

3.3 billion base pairs Signup and view all the answers

What is the correlation between genome size and organism complexity?

No correlation Signup and view all the answers

What is the primary function of non-coding regions in DNA?

Regulating gene expression Signup and view all the answers

What percentage of the nuclear genome corresponds to genes encoding proteins, introns, and regulatory sequences?

50% Signup and view all the answers

What is the primary difference between prokaryotic and eukaryotic genomes?

Presence of nucleus Signup and view all the answers

What proportion of the human genome is composed of repeated DNA sequences?

50% Signup and view all the answers

What is the primary function of satellite DNA in the human genome?

Chromosomal segregation Signup and view all the answers

What is the term used to describe the variation in the number of repeats at a given minisatellite locus?

Polymorphism Signup and view all the answers

What is the estimated percentage of coding genes in the human genome?

1.5% Signup and view all the answers

What is the name given to the process of identifying individuals based on their minisatellite DNA?

DNA fingerprinting Signup and view all the answers

What is the term used to describe the repetitive, GC-rich sequences found in minisatellites?

Variable Number of Tandem Repeats Signup and view all the answers

What is the main purpose of using minisatellites in forensic science?

Identifying individuals Signup and view all the answers

What is the term used to describe the regions of the genome where satellite DNA is primarily located?

Centromeric and pericentromeric regions Signup and view all the answers

Study Notes

Genome Organization

The number of genes varies between species, with bacteria containing a few thousand genes and human cells containing between 20,000 and 30,000 genes.
The size and number of chromosomes also vary between species, with bacteria having a single circular chromosome and humans having 23 sets of chromosomes (22 autosomes and 1 pair of sex chromosomes).

Prokaryotes vs Eukaryotes

Both prokaryotic and eukaryotic cells contain double-stranded DNA, but their genomes are organized differently.
Eukaryotic chromosomes contain an enormous amount of DNA, which requires an elaborate system of DNA packing to fit all of the cell's DNA into the nucleus.

Prokaryotic Genome

The bacterial chromosome has less associated protein compared to eukaryotes.
The chromosome is typically a covalently closed circular structure.
Prokaryotes may contain one or more extra circular DNA molecules, called plasmids.

Eukaryotic Genome

Eukaryotic genes can be discontinuous.
Eukaryotic genomes contain coding and non-coding DNA, as well as repeated sequences.
Some genetic information is stored in the nucleus and in the mitochondria/chloroplast.

Introns

Until 1993, it was thought that introns were exclusive to eukaryotic genes.
About 25% of sequenced bacterial genomes show the presence of introns.
Introns in bacterial chromosomes do not interrupt protein-coding sequences, but instead interrupt mainly tRNA sequences.

DNA, Chromosomes, Genes, and Complexity

Neither the total length of DNA nor the number of chromosomes correlates strongly with the perceived complexity of an organism.
The correlation between complexity and genome size is poor because most of eukaryotic DNA is non-coding.

Non-coding Regions

DNA contains genes, but also contains other sequences that have purely regulatory functions.
These regions may correspond to areas immediately before or after a gene and function as initiation sites for replication or participate in the regulation of transcription.

Landmarks

1866: Mendel's laws
1869: DNA is discovered by Friedrich Miescher
1953: Watson and Crick describe the DNA structure
1956: The number of human chromosomes is determined
1990: The beginning of the Human Genome Project
2022: The completion of the human genome (Telomere-to-Telomere (T2T) Consortium)

Medical Genetics

Medical genetics is the branch of genetics that studies the implications of the genetic content of an individual on their health, with a particular emphasis on the genetic basis of human diseases.
Applications of medical genetics include clinical diagnosis, gene identification, cancer genomics, disease treatment, and prenatal diagnosis.

The Human Genome

The human genome is distributed between the nucleus (mainly) and the mitochondria.
The mitochondrial genome is a double-stranded circular molecule, 17,000 base pairs long, with 97% of the genome being coding.
The nuclear genome consists of 46 linear chromosomes, 3300 million base pairs long, with 50% of the genome corresponding to genes encoding proteins, introns, and regulatory sequences.

Human Genome Organization

The nuclear genome contains repeated (50%) and non-repeated (50%) sequences.
Repeated sequences include satellite DNA, minisatellites, and microsatellites.
Satellite DNA consists of repetitions (5-171 bp) that cover regions of hundreds of Kb.
Minisatellites are used for DNA fingerprinting due to their high level of polymorphism.

DNA Fingerprinting

DNA fingerprinting is a method for identifying individuals based on their minisatellite DNA.
It was developed in the mid-80s and is widely used in forensics, paternity analysis, and for research purposes.

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Description

This quiz covers the variation in gene numbers and chromosome structure among different species, including bacteria and humans. It also touches on the concept of haploid and diploid cells.