Lecture 8: Nucleic Acids and Chromosome Structure

These flashcards cover key concepts related to nucleic acids, chromosome structure, DNA packaging, chromatin types, gene linkage, and recombination mapping.

What are the nucleotide bases found in DNA?

Adenine (A), Thymine (T), Cytosine (C), and Guanine (G).

What are the two types of DNA supercoiling?

Positive supercoiling (over-wound) and negative supercoiling (underwound).

What is the function of topoisomerase enzymes?

They mediate supercoiling of DNA in the cell.

What are the two main types of chromatin in eukaryotic cells?

Euchromatin (decondensed and available for transcription) and heterochromatin (condensed and not involved in transcription).

What is a nucleosome?

A structure where the DNA double helix is coiled around a core of eight histone proteins.

What proteins are commonly associated with eukaryotic chromatin?

Major types of histones: H1, H2A, H2B, H3, and H4.

What are the main roles of histone acetylation and methylation?

Histone acetylation loosens histone-DNA interactions to allow transcription; histone methylation condenses nucleosomes for tighter packing.

What are centromeres and their role during cell division?

They are regions of heterochromatin that connect sister chromatids and are sites for kinetochore assembly during cell division.

What are telomeres and their function?

Sequence repeats at the ends of linear chromosomes that protect chromosome ends and buffer against shortening during replication.

What is linkage in genetics?

When linked genes do not segregate independently due to proximity on the same chromosome, leading to lower recombination rates.

How can recombination frequencies be utilized in genetics?

They can be used to determine the relative positions of genes on chromosomes and create genetic maps.

What does one map unit represent in genetic mapping?

One map unit equals a 1% recombination rate, measured in centiMorgans (cM).

What is the significance of double crossovers in linkage mapping?

They can lead to underestimating map distances between genes that are far apart on the same chromosome.

What is interference in genetics?

The phenomenon where one crossover event inhibits additional crossing-over events in the same chromosomal region.

What does the coefficient of coincidence measure?

The ratio of observed double crossovers to expected double crossovers.