Podcast
Questions and Answers
What is the purpose of X-inactivation in humans?
What is the purpose of X-inactivation in humans?
What does the Lyon hypothesis explain?
What does the Lyon hypothesis explain?
Which chromosomal condition is known to be incompatible with life, except for the X chromosome?
Which chromosomal condition is known to be incompatible with life, except for the X chromosome?
In individuals with XXX or XXXX chromosomal patterns, what occurs with their X chromosomes?
In individuals with XXX or XXXX chromosomal patterns, what occurs with their X chromosomes?
Signup and view all the answers
What is the primary function of X chromosome inactivation in XX embryos?
What is the primary function of X chromosome inactivation in XX embryos?
Signup and view all the answers
Which type of chromatin contains active genes and appears light in color during staining?
Which type of chromatin contains active genes and appears light in color during staining?
Signup and view all the answers
What distinguishes facultative heterochromatin from euchromatin?
What distinguishes facultative heterochromatin from euchromatin?
Signup and view all the answers
Which condition arises from a failure to inactivate an extra chromosome?
Which condition arises from a failure to inactivate an extra chromosome?
Signup and view all the answers
What happens to the inactive X chromosome in terms of its chromatin structure?
What happens to the inactive X chromosome in terms of its chromatin structure?
Signup and view all the answers
Study Notes
Sex Chromosomes, Barr Body and Lyon Hypothesis
- Sex is determined at fertilization
- Sex differences appear in the 7th week of development
- Sex is influenced by genetics and environment
- Females (generally XX) do not have a Y chromosome
- Males (generally XY) have a Y chromosome
- Diploid germ cells (XX in females, XY in males) undergo meiosis to form gametes (eggs and sperm)
- X chromosomes carry more genes than Y chromosome
- Females possess two X chromosomes (XX), while males have one X and one Y chromosome (XY)
Objectives
- Understand X inactivation
- Determine the number of Barr bodies in a human cell
- Explain the Lyon hypothesis
- Recognize the advantages of Barr body determination
Matters of Sex
- Aneuploidy: Having too many or too few chromosomes compared to a normal genotype
- Monosomy: Possessing only one copy of a particular chromosome
- Monosomy for most chromosomes is incompatible with life; an exception is the X chromosome
X Chromosome Dosage
- Females (XX) have twice as many X-linked genes as males (XY).
- X inactivation is the process of silencing one X chromosome in females to equalize the amount of gene products between males and females
- X inactivation occurs to compensate for unequal gene dosage
X Chromosomes
- X inactivation can be observed by culturing cells with different karyotypes, determining the levels of enzymes encoded by the X chromosome.
X Linked Gene
- G6PD (glucose-6-phosphate dehydrogenase), carried on the X chromosome, codes for an enzyme that breaks down sugar
- Females produce the same amount of G6PD enzyme as males.
- Individuals with extra X chromosomes (e.g., XXY, XXX) produce the same amount of G6PD as individuals with a normal X chromosome complement.
Conclusion
- Only one X chromosome is active in any given cell; the other is inactivated.
- X inactivation can be paternal or maternal in any given cell
- The process of X inactivation ensures that both males and females have equivalent expression from genes present on the X chromosome
- In XX and XXXX individuals, two or four X chromosomes are inactivated
Three types of Chromatin:
- Euchromatin: true chromatin, containing active genes.
- Heterochromatin: stains darker, consists of highly repetitive DNA. Found near telomeres and centromeres.
- Facultative Heterochromatin: a type of heterochromatin that can become euchromatin (or active) under specific conditions
Facultative Heterochromatin
- Facilitates the inactivation of a portion of an entire chromosome to control gene expression.
- One part of the X chromosome functions as facultative heterochromatin
Demonstration of Barr Body
- In epithelial cells (e.g., buccal smear), Barr body appears as a darkly stained mass in the nuclear membrane (30-50% of the cell in normal females)
- In blood leukocytes, sex chromatin appears as a drumstick attachment to the nucleus in 3% of female neutrophils.
Significance of Barr Body
- Barr body staining can diagnose:
- Genetic sex in doubtful cases of hermaphroditism
- Abnormalities of sex chromosomes
- Abnormal sexual development and maturation
- Infertility, including primary amenorrhea and spontaneous abortions
- Fetal sex using cells from amniotic fluid
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
This quiz explores the complexities of sex chromosome inheritance, including the Lyon hypothesis and the concept of Barr bodies. Learn about the genetic and environmental factors influencing sexual development, aneuploidy, and the implications of X chromosome dosage. Test your understanding of these critical biological concepts.
