Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Prokaryotic chromosomes consist of a single, circular DNA molecule that is not associated with proteins (often referred to as 'naked' DNA).
Some prokaryotes also contain plasmids, which are small, circular, extra-chromosomal DNA molecules that often carry genes for antibiotic resistance.
Eukaryotic chromosomes are linear DNA molecules associated with histone proteins. The DNA wraps around eight histones to form a nucleosome, which further coils into a fiber.
Homologous chromosomes are pairs of chromosomes that have the same sequence of genes at the same loci, though they may carry different alleles (e.g., allele vs ).
A diploid nucleus () has two sets of chromosomes (one from each parent), whereas a haploid nucleus () has only one set of chromosomes.
The number of chromosomes is a characteristic feature of a species; for example, humans have chromosomes ().
Sex is determined by the pair of chromosomes in humans: results in a female, and results in a male. All other chromosomes are called autosomes.
A karyogram is an image of the chromosomes of an organism, arranged in homologous pairs of decreasing length. It is used to diagnose chromosomal abnormalities such as Trisomy (Down Syndrome).
📐Formulae
💡Examples
Problem 1:
A cell from an organism with a diploid number of undergoes meiosis. Calculate the total number of possible chromosome combinations that can occur in the resulting gametes due to independent assortment.
Solution:
Explanation:
Since , the haploid number is . Using the formula for independent assortment, we calculate , which equals possible combinations.
Problem 2:
Identify the chromosomal abnormality and the sex of an individual whose karyogram shows three copies of chromosome and the sex chromosomes and .
Solution:
Condition: Trisomy (Down Syndrome); Sex: Male.
Explanation:
The presence of three chromosomes at position indicates Trisomy . The presence of one and one chromosome indicates the individual is male ().
Problem 3:
In a human cell (), how many DNA molecules are present during the phase of the cell cycle?
Solution:
DNA molecules.
Explanation:
In humans, the diploid number is . During the phase, DNA replication occurs, doubling the amount of DNA. Therefore, in , there are chromosomes, each consisting of two sister chromatids, resulting in DNA molecules.