Related Experiment Video
Updated: Aug 8, 2026
10:44
Sex Stratified Neuronal Cultures to Study Ischemic Cell Death Pathways
Published on: December 9, 2013
Summary
Anencephaly incidence and sex ratio correlate within and between populations. Data suggest two causal factors for anencephaly: one environmental affecting females, and another possibly genetic or environmental affecting both sexes equally.
Area of Science:
- Reproductive Health
- Developmental Biology
- Epidemiology
Background:
- Anencephaly is a severe birth defect with varying incidence and sex ratios.
- Previous research by Knox (1974) suggested a link between anencephaly sex ratio and incidence.
Purpose of the Study:
- To investigate the relationship between anencephaly sex ratio and incidence.
- To evaluate Knox's hypothesis regarding dizygotic twinning rates.
- To explore potential differing causes of anencephaly.
Main Methods:
- Review of existing epidemiological data on anencephaly.
- Analysis of population-based incidence and sex ratio variations.
- Comparison with dizygotic twinning rates.
Main Results:
- The study supports the correlation between anencephaly sex ratio and incidence.
- Knox's hypothesis on dizygotic twinning rates appears questionable.
- Evidence suggests two distinct causal pathways for anencephaly.
Conclusions:
- Anencephaly may arise from at least two distinct causes.
- One cause appears environmental, primarily affecting female embryos.
- A second cause, potentially environmental or genetic, affects sexes equally, impacting teratogen testing strategies.
Related Concept Videos
01:30Neurulation
Neurulation is the embryological process which forms the precursors of the central nervous system and occurs after gastrulation has established the three primary cell layers of the embryo: ectoderm, mesoderm, and endoderm. In humans, the majority of this system is formed via primary neurulation, in which the central portion of the ectoderm—originally appearing as a flat sheet of cells—folds upwards and inwards, sealing off to form a hollow neural tube. As development proceeds, the anterior...
01:29Nondisjunction
During meiosis, chromosomes occasionally separate improperly. This occurs due to failure of homologous chromosome separation during meiosis I or failed sister chromatid separation during meiosis II. In some species, notably plants, nondisjunction can result in an organism with an entire additional set of chromosomes, which is called polyploidy. In humans, nondisjunction can occur during male or female gametogenesis and the resulting gametes possess one too many or one too few chromosomes.
02:32X 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...
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...
02:45The 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...
Normal male Drosophila has a ratio of one X chromosome to two sets of autosomes. In contrast, normal female Drosophila...
02:57Meiosis vs. Mitosis
Cell division is necessary for growth and reproduction in organisms. Mitosis aids cell growth and development by dividing somatic cells. In contrast, meiosis causes the division of germ cells and plays an essential role in sexual reproduction. Due to their unique functional requirements, mitosis and meiosis differ from each other in multiple aspects.
Before the start of mitosis and meiosis I, the cell synthesizes DNA, resulting in two homologous copies of each chromosome. DNA synthesis is...
Before the start of mitosis and meiosis I, the cell synthesizes DNA, resulting in two homologous copies of each chromosome. DNA synthesis is...
01:21Nondisjunction
Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate correctly and move to the opposite poles of the cells. This produces daughter cells with abnormal chromosome numbers. Nondisjunction is common during anaphase I or anaphase II of meiosis. Mutations in synaptonemal complex proteins that attach homologous chromosomes increase the chances of nondisjunction in anaphase I of meiosis I. In contrast, mutations in topoisomerases and condensins that hold sister...