Hemizygous

Definition

Hemizygous refers to the state where an individual possesses only one copy of a particular gene or genetic marker, typically on a sex chromosome. This contrasts with the normal diploid state where individuals have two copies of each gene, one inherited from each parent.

5 Must Know Facts For Your Next Test

1. Hemizygosity is most commonly observed on the sex chromosomes, particularly the X chromosome in males.
2. Individuals who are hemizygous for a particular gene or genetic marker will only express one copy of that trait, as they lack a second copy to provide an alternative allele.
3. Hemizygosity can lead to the expression of recessive traits on the sex chromosomes, as there is no masking by a dominant allele.
4. Certain genetic disorders, such as X-linked recessive disorders, are caused by hemizygous mutations on the X chromosome in males.
5. Hemizygosity can also be observed in some cases of chromosomal abnormalities, such as Turner syndrome (45,X), where individuals are missing one of the sex chromosomes.

Review Questions

• Explain how hemizygosity differs from heterozygosity and homozygosity in the context of genetic inheritance.
  • Hemizygosity refers to the state where an individual possesses only a single copy of a particular gene or genetic marker, typically on a sex chromosome. This contrasts with heterozygosity, where an individual has two different alleles of a gene, and homozygosity, where an individual has two identical copies of a gene. Hemizygosity can lead to the expression of recessive traits on the sex chromosomes, as there is no masking by a dominant allele, and is often observed in genetic disorders associated with sex chromosome abnormalities.
• Describe the significance of hemizygosity in the expression of X-linked recessive disorders.
  • Hemizygosity on the X chromosome is particularly important in the expression of X-linked recessive disorders. Since males only have one copy of the X chromosome, any recessive mutations present on that chromosome will be expressed, as there is no second, dominant allele to mask the effect. This means that X-linked recessive disorders, such as Duchenne muscular dystrophy or hemophilia, are more commonly observed in males than females, who would need to inherit the recessive allele from both parents to express the disorder.
• Analyze the potential consequences of hemizygosity in the context of chromosomal abnormalities, such as Turner syndrome.
  • Hemizygosity can also be observed in certain chromosomal abnormalities, such as Turner syndrome, where individuals are missing one of the sex chromosomes (45,X). In this case, the individual is hemizygous for all genes located on the missing sex chromosome, which can lead to a range of developmental and medical issues. The lack of a second copy of the sex chromosome genes can result in the expression of recessive traits, as well as an increased risk of certain conditions associated with the specific chromosomal abnormality. Understanding the implications of hemizygosity in these contexts is crucial for recognizing and managing the associated health concerns.

Related terms

Heterozygous:

Heterozygous describes a genetic condition where an individual has two different alleles of a particular gene, one from each parent.

Homozygous:

Homozygous refers to the state where an individual has two identical copies of a particular gene, one inherited from each parent.

Sex Chromosomes: Sex chromosomes are the chromosomes that determine an individual's biological sex, with females typically having two X chromosomes (XX) and males having one X and one Y chromosome (XY).