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X and Y Chromosomes

X and Y Chromosomes

Among mammals, the gender of an organism is determined by the sex chromosomes. Humans have two sex chromosomes, X and Y. Every human diploid cell has 22 pairs of autosomes and one pair of sex chromosomes. A human female has two X chromosomes, while a male has one X chromosome and one Y chromosome.
The germline cells such as egg and sperm cells carry only half the number of chromosomes, i.e., 22 autosomes and one sex chromosome. All eggs have an X chromosome, while sperm cells can carry an X or...

Chromosomal Theory of Inheritance

Chromosomal Theory of Inheritance

In 1866, Gregor Mendel published the results of his pea plant breeding experiments, providing evidence for predictable patterns in the inheritance of physical characteristics. The significance of his findings was not immediately recognized. In fact, the existence of genes was unknown at the time. Mendel referred to hereditary units as “factors.”

The Ratio of X Chromosome to Autosomes

The Ratio of X Chromosome to Autosomes

In most organisms, sex is determined by the ratio of X and Y chromosomes. However, in some organisms, such as Drosophila and C.elegans, sex is determined by the ratio of the number of X chromosomes to the number of sets of autosomes. The Y chromosome in Drosophila is active but does not determine sex. It contains genes responsible for the production of sperms in adult flies.
Normal male Drosophila has a ratio of one X chromosome to two sets of autosomes. In contrast, normal female Drosophila...

Lampbrush Chromosomes

Lampbrush Chromosomes

In 1882, Flemming observed lampbrush chromosomes (LBC) in salamander eggs. Later in 1892, Rückert observed LBCs in shark egg cells and coined the term "lampbrush chromosomes" because they looked like brushes used to clean kerosene lamps.
LBCs are made up of two pairs of conjugating homologous chromatids. Each chromatid consists of alternatively positioned regions of condensed-inactive chromatin and loosely placed-active side loops, which can be contracted and extended. The loops resemble the...

Lampbrush Chromosomes

Lampbrush Chromosomes

In 1882, Flemming observed lampbrush chromosomes (LBC) in salamander eggs. Later in 1892, Rückert observed LBCs in shark egg cells and coined the term "lampbrush chromosomes" because they looked like brushes used to clean kerosene lamps.
LBCs are made up of two pairs of conjugating homologous chromatids. Each chromatid consists of alternatively positioned regions of condensed-inactive chromatin and loosely placed-active side loops, which can be contracted and extended. The loops resemble the...

Meiosis I

Meiosis I

Meiosis is a carefully orchestrated set of cell divisions, the goal of which—in humans—is to produce haploid sperm or eggs, each containing half the number of chromosomes present in somatic cells elsewhere in the body. Meiosis I is the first such division, and involves several key steps, among them: condensation of replicated chromosomes in diploid cells; the pairing of homologous chromosomes and their exchange of information; and finally, the separation of homologous chromosomes by a...

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Related Experiment Video

Updated: Jul 5, 2026

An Efficient Method for Quantitative, Single-cell Analysis of Chromatin Modification and Nuclear Architecture in Whole-mount Ovules in Arabidopsis

An Efficient Method for Quantitative, Single-cell Analysis of Chromatin Modification and Nuclear Architecture in Whole-mount Ovules in Arabidopsis

Published on: June 19, 2014

Plant sex chromosomes: molecular structure and function.

M Jamilena¹, B Mariotti, S Manzano

¹Departamento de Biología Aplicada, Area de Genética, Escuela Politécnica Superior, Universidad de Almería, Almería, Spain. mjamille@ual.es

Cytogenetic and Genome Research

|May 28, 2008

Summary

Plant sex chromosome evolution reveals Y chromosomes are not as degenerate as previously thought. Studies show Y-linked genes remain essential, with limited degeneration observed across diverse species.

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Area of Science:

Plant genetics
Evolutionary biology
Molecular biology

Background:

Dioecious plants possess sex chromosomes that evolved from autosomes.
Sex chromosome evolution involves recombination suppression and Y chromosome divergence.
Studies in model plants reveal diverse evolutionary pathways for sex chromosomes.

Purpose of the Study:

To investigate the molecular structure and gene function of sex chromosomes in model dioecious plants.
To understand the evolutionary pathways and divergence of plant sex chromosomes.
To assess the extent of Y chromosome degeneration and its impact on gene function.

Main Methods:

Comparative genomic analysis of sex chromosomes in Asparagus officinalis, Carica papaya, Silene latifolia, Rumex acetosa, and Marchantia polymorpha.
Analysis of DNA sequences, including repetitive elements and gene content.
Examination of gene expression patterns in Y-linked genes.

Main Results:

Y chromosome degeneration varies among species, with some retaining primitive structures and others showing significant divergence.
Repetitive DNA accumulation contributes to Y chromosome size increase and reduced gene density.
Despite low gene density in some Y chromosomes, most Y-linked genes remain essential and are expressed in both sexes, indicating limited functional degeneration.

Conclusions:

Plant Y chromosome degeneration does not appear to have significantly impacted essential gene functions.
Further sequence analysis will elucidate degenerative changes in Y-linked genes during sex chromosome evolution.
Plant sex chromosome evolution presents a unique model for studying genome evolution and gene function maintenance.