A pair of sex chromosomes can decide the sex of humans and other mammals. Males have XY chromosomes, while females have XX chromosomes. X and Y chromosomes are not homologous. They also don’t carry the same genes. Y chromosome is shorter and it carries a small number of genes compared to the X chromosome. The genes on the X chromosome are known as X linked genes. Similarly, the genes located on the Y chromosome are known as Y linked genes or holandric genes. Both X linked and Y linked genes are commonly known as sex linked genes.
1. Overview and Key Difference
2. What is a Holandric Gene
3. What is a Sex Linked Gene
4. Similarities Between Holandric and Sex Linked Gene
5. Side by Side Comparison – Holandric vs Sex Linked Gene in Tabular Form
What is a Holandric Gene?
Holandric gene is a gene located in the Y chromosome. Therefore, holandric genes are present only in males. These genes are hemizygous, and they have only one allele. Holandric genes are also known as Y linked genes. They are a form of sex linked genes. Holandric genes are inherited from father to sons (holandric inheritance). Y linked genes are fewer in number, so they are difficult to detect.
Studies show that there are about 200 holandric genes on the Y chromosome. Not all holandric genes are sex-determining. ASMTY, TSPY, IL3RAY, SRY, TDF, SOX21 and BPY2 are several holandric genes. Y chromosome rarely undergoes recombination. Moreover, the deletions occurring in Y chromosome can cause male infertility.
What is a Sex Linked Gene?
Sex linked gene is a gene located on sex chromosomes, either in X or Y chromosomes. However, sex linked genes or traits are mainly referred to as X linked genes. This is because X chromosome is large and there are many more genes on it than the Y chromosome. Generally, there are about 1098 genes on the X chromosome.
Males are affected largely by the sex linked diseases because they have only one X chromosome, and the mutations in X chromosome are not masked by another healthy X chromosome, as in females. Sex linked genes not only determine the sex-related traits, but they also code for some other characteristics. Haemophilia, Duchenne muscular dystrophy, fragile-X syndrome, high blood pressure, congenital night blindness, G6PD deficiency, and red-green colour blindness, which is the most common human genetic disorder, are several non-sex-related characteristics that are coded by X linked genes.
When considering X linked and Y linked genes, males get Y linked genes while both male and female get X linked genes.
What are the Similarities Between Holandric and Sex Linked Gene?
- Holandric gene is a form of sex linked gene.
- They are found on sex chromosomes.
- Most of these genes are sex-determining.
What is the Difference Between Holandric and Sex Linked Gene?
Holandric gene is a gene located on the Y chromosome in males while sex linked gene is a gene located on a sex chromosome. So, this is the key difference between holandric and sex linked gene. Furthermore, holandric genes are found on the Y chromosome while sex linked gene is found in both X and Y chromosomes. Besides, males have holandric genes, while both male and females have sex linked genes.
Moreover, another difference between holandric and sex linked gene is the zygosity. Holandric genes are hemizygous while sex linked genes can be homozygous, heterozygous or hemizygous.
Summary – Holandric vs Sex Linked Gene
Twenty third chromosome pair of the human genome is the sex chromosome pair, which determines whether the human is a male or a female. The genes present on sex chromosomes are commonly known as sex linked genes. They can be X linked genes or Y linked genes. Y linked genes are present only in the Y chromosome of males, and they are also known as holandric genes. Holandric genes are hemizygous, having only one allele. X linked genes of females are not hemizygous. They can be homozygous or heterozygous, having two similar or different alleles, respectively. Thus, this summarizes the difference between holandric and sex linked gene.
1. “Sex-linked inheritance” By GYassineMrabetTalk✉This W3C-unspecified vector image was created with Inkscape. – Own work (CC BY-SA 3.0) via Commons Wikimedia
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