Linked genes are genes situated close together on the same chromosome. Because they are physically connected, they do not assort independently during meiosis, meaning they are more likely to be inherited as a unit unless separated by crossing over.
162
What is the specific term for a genetic mutation where a single nucleotide base is replaced by a different base?
A substitution mutation occurs when one nitrogenous base in a DNA sequence is replaced by another. This can lead to silent, missense, or nonsense mutations depending on the resulting codon change. Unlike insertions or deletions, substitutions do not typically cause a frame shift unless they affect splice sites.
163
Which chromosomal mutation occurs when a segment of a chromosome breaks off, rotates 180 degrees, and reattaches in the reverse orientation?
An inversion is a type of chromosomal rearrangement where a segment of the chromosome is reversed end-to-end. This change in gene order can affect gene expression and may lead to evolutionary divergence or genetic disorders depending on the location of the breakpoints.
164
What is the result of adding a single chromosome to the normal diploid number (2N+1)?
Trisomy is a specific type of aneuploidy where an individual has three copies of a particular chromosome instead of the usual two. This condition (2N+1) often results from nondisjunction during meiosis, where chromosomes fail to separate correctly, leading to gametes with an extra chromosome.
165
Aneuploidy, a condition characterized by an abnormal number of chromosomes, typically arises from errors during which biological process?
Aneuploidy is primarily caused by nondisjunction, which is the failure of homologous chromosomes or sister chromatids to separate correctly during meiosis. This results in gametes with an incorrect number of chromosomes. When these gametes fuse during fertilization, the resulting zygote will have an abnormal chromosome count, leading to various genetic disorders.
166
What is the standard diploid number of chromosomes found in human somatic cells?
The normal human karyotype consists of 46 chromosomes, arranged in 23 pairs. This includes 22 pairs of autosomes and one pair of sex chromosomes (XX in females and XY in males), which carry the genetic information necessary for human development and function.
167
What is the term for the genetic condition where multiple copies of chromosomes are present?
Duplication refers to a type of mutation where a portion of a chromosome or a whole chromosome is replicated, resulting in extra genetic material. While the term 'polyploidy' is often used for whole sets of chromosomes, 'duplication' is the standard term for the presence of extra copies of genetic segments.
168
What is the term for the highly condensed, transcriptionally inactive region of a chromosome?
Heterochromatin is a tightly packed form of DNA or condensed chromatin that is generally inaccessible to the machinery required for gene expression. Because it remains condensed throughout the cell cycle, it is considered transcriptionally inactive compared to the more loosely packed euchromatin.
169
What is the specific term used to describe the chromosomal aberration where a segment of a chromosome is lost?
Deletion is a type of mutation involving the loss of a chromosomal segment. This loss can result in significant genetic imbalances, as the organism loses specific genes located within the deleted region. It is distinct from addition (duplication), translocation (movement of segments between non-homologous chromosomes), and inversion (reversal of a segment's orientation).
170
What term refers to a permanent alteration in the DNA sequence or chromosomal structure of an organism?
A mutation is a change in the nucleotide sequence of the genome of an organism. Mutations can result from errors during DNA replication or exposure to mutagens. They can involve single base pairs, entire genes, or larger chromosomal segments, and are the primary source of genetic variation.
