Cellular Genetics: Genetic Information, Nuclear Structure, and Karyotyping

Vocabulary practice cards covering the localization of genetic material in unicellular and multicellular organisms, classic grafting and cloning experiments, nuclear ultrastructure, and the principles and methodology of chromosomal karyotyping.

Acetabularia

A unicellular green marine alga measuring $4\text{ to }6\,\text{cm}$ that lives on rocks in warm waters, consisting of a basal rhizoid containing a nucleus, an elongated stalk, and a species-specific cap.

Acetabularia acetabulum

A species of unicellular green alga characterized by having an umbrella-like cap with a smooth, regular border.

Acetabularia crenulata

A species of unicellular green alga characterized by having a cap with a finely serrated or dentate border.

Rhizoid

The basal part of the Acetabularia alga containing the cell nucleus, which is indispensable for cellular survival and full algal regeneration following sectioning.

Acetabularia Nuclear Graft Experiment

A cross-transplantation experiment where exchanging nuclei between the rhizoids of A. crenulata and A. acetabulum causes the regenerated alga to develop the cap morphology of the nucleus donor species.

Gurdon's Experiment (1960)

A scientific investigation by English biologist Gurdon where UV-irradiated, enucleated eggs of wild brown-green Xenopus received transplanted nuclei from albino tadpole intestinal cells, yielding $30$ identical albino adults out of $54$ eggs.

Nuclear Envelope

A double membrane enclosing the spherical nucleus of eukaryotic cells during interphase, perforated by nuclear pores.

Nuclear Pores

Channels perforating the nuclear envelope that permit transport and communication between the nucleoplasm and the cytoplasm.

Chromatin

The nuclear substance carrying genetic and hereditary information during interphase, which condenses into visible filaments called chromosomes during cell division.

Colchicine

A chemical agent added during karyotype preparation to block dividing cultured cells specifically in metaphase.

Osmotic Shock

A karyotyping procedure involving sudden changes in osmotic pressure to burst cultured cells, releasing and spreading stained chromosomes onto a slide.

Karyotype

The classified arrangement of all chromosomes of a cell, organized by pairs, size, centromere location, and banding patterns.

Centromere

The constricted chromosomal region uniting sister chromatids and delineating the chromosomal arms (short arm and long arm).

Diploid ($2n$)

A cellular state where chromosomes exist in homologous pairs, one derived from each parent, such that humans have $2n = 46$ and Drosophila have $2n = 8$.

Autosomes

Non-sex chromosomes that appear in identical homologous pairs across both biological sexes of a diploid species ($44$ autosomes in humans, $6$ autosomes in Drosophila).

Sex Chromosomes

Chromosomes that determine biological sex, designated as $XX$ for females and $XY$ for males in humans and Drosophila.

Human Chromosomal Formula

The notation describing human diploid chromosome complements: $2n = 44 + XX$ for females and $2n = 44 + XY$ for males ($2n = 46$ total).

Drosophila Chromosomal Formula

The notation describing fruit fly (Drosophila) diploid chromosome complements: $2n = 6 + XX$ for females and $2n = 6 + XY$ for males ($2n = 8$ total).

Acetabularia

A single-celled marine green alga measuring $4\text{ to }6\,\text{cm}$ in length that grows on rocks in warm marine waters, consisting of a basal rhizoid with a nucleus, a stalk, and a cap.

Acetabularia acetabulum

A species of unicellular green alga characterized by a smooth umbrella-like cap with an even, regular edge.

Acetabularia crenulata

A species of unicellular green alga distinguished by an umbrella-like cap with a finely dentated (serrated) margin.

Rhizoid (Acetabularia)

The basal part of the Acetabularia alga containing the cell nucleus; it is the only excised fragment capable of regenerating a complete organism.

Acetabularia Nuclear Graft Experiment

A cross-transplantation experiment demonstrating that grafting the nucleus of Acetabularia crenulata into the rhizoid of Acetabularia acetabulum (or vice versa) produces a regenerated cap displaying the phenotype of the donor nucleus.

Gurdon's Experiment (1960)

A genetic study conducted by English biologist Gurdon in which nuclei from intestinal cells of an albino Xenopus tadpole were transplanted into UV-irradiated, enucleated eggs of wild-type brown-green females.

Gurdon's Quantitative Results

Out of $54$ prepared Xenopus eggs injected with albino tadpole intestinal nuclei, $30$ developed into identical, same-sex, completely albino adult toads.

Nuclear Membrane

The double boundary structure delimiting the spherical nucleus of a eukaryotic cell, perforated by nuclear pores.

Nuclear Pores

Perforations or openings across the nuclear membrane that regulate macromolecular transport between the nucleoplasm and cytoplasm.

Chromatin

The dispersed form of genetic material within the interphase nucleus that condenses into visible filamentous chromosomes during cell division.

Karyotype

The ordered arrangement and classification of all chromosomes from a single cell grouped by homologous pairs, size, centromere location, and banding patterns.

Colchicine

A chemical reagent added during karyotype preparation to inhibit mitotic spindle formation and arrest dividing cells specifically at metaphase.

Osmotic Shock (Karyotype Preparation)

The technique of bursting cultured cells in a hypotonic medium following chromosome staining to release the condensed metaphase chromosomes for imaging.

Centromere

The primary constriction of a chromosome that joins sister chromatids and divides the chromosome into short arms and long arms.

Sister Chromatids

Two identical copies of a replicated chromosome joined together at the centromere before being separated during cell division.

Autosomes

Somatic chromosomes that appear in identical pairs in both males and females of a species ($44$ autosomes or $22$ pairs in humans; $6$ autosomes or $3$ pairs in Drosophila).

Sex Chromosomes (Gonosomes)

Chromosomes involved in genetic sex determination, consisting of an $\text{XX}$ pair in females and an $\text{XY}$ pair in males.

Human Chromosomal Formula

The mathematical notation of the human diploid chromosome complement ($2n = 46$), written as $2n = 44\text{A} + \text{XX}$ for females and $2n = 44\text{A} + \text{XY}$ for males.

Drosophila Chromosomal Formula

The mathematical notation of the fruit fly diploid chromosome complement ($2n = 8$), written as $2n = 6\text{A} + \text{XX}$ for females and $2n = 6\text{A} + \text{XY}$ for males.

Diploid ($2n$)

A cellular condition in which chromosomes are present in homologous pairs, one set inherited maternally and the other paternally (e.g., $2n = 46$ in humans, $2n = 8$ in Drosophila).