genetics 6: chromosomes and replication

What mechanism ensures equal expression of X-linked genes in both sexes?
A. Gene amplification
B. X-inactivation
C. Y-transcription enhancement
D. DNA methylation

X-inactivation

What is a Barr body?
A. An autosomal satellite body
B. The condensed Y chromosome
C. An inactivated X chromosome
D. A chromatin loop domain

An inactivated X chromosome

When during development does X inactivation occur?
A. Zygote stage
B. Immediately after fertilization
C. At 500–1000 cell stage
D. After organogenesis

At 500–1000 cell stage

Which of the following best describes dosage compensation in humans?
A. Tripling autosomal genes in males
B. Equalizing gene expression by silencing one X chromosome in females
C. Doubling Y gene expression in males
D. Repressing Z chromosomes in both sexes

Equalizing gene expression by silencing one X chromosome in females

What causes cells in female mammals to have different gene expression patterns despite identical DNA?
A. Random mutation
B. Unequal crossing over
C. Random X-inactivation
D. Alternative splicing

Random X-inactivation

Which of the following comprises the largest proportion of the nucleus by volume?
A. DNA
B. RNA
C. Proteins
D. Water and salts

Water and salts

What is the primary function of chromatin organization?
A. Enhance mutation rates
B. Facilitate DNA degradation
C. Enable DNA to fit inside the nucleus
D. Enable gene duplication

Enable DNA to fit inside the nucleus

Which of the following best describes linker DNA?
A. A segment of RNA connecting histones
B. The DNA directly bound to histones
C. The ~40 bp segment between core particles
D. The DNA replicated during mitosis

The ~40 bp segment between core particles

Which protein complex facilitates DNA loop formation in higher-order structure?
A. Topoisomerase
B. Condensin
C. Telomerase
D. Cohesin

Condensin

What is the basic structural unit of chromatin?
A. Histone octamer
B. DNA polymerase
C. Nucleosome
D. Replication fork

Nucleosome

What is Giemsa staining used for?
A. Detecting telomerase activity
B. Visualizing gene expression
C. Identifying chromosomal banding patterns
D. Measuring DNA concentration

Identifying chromosomal banding patterns

What distinguishes euchromatin from heterochromatin?
A. DNA sequence type
B. Chromosome location
C. Degree of compaction and gene content
D. Presence of RNA

Degree of compaction and gene content

A. Loosely packed and gene-rich
B. Highly compact and gene-poor
C. Found only in mitochondria
D. Inactive in both mitosis and meiosis

Highly compact and gene-poor

What is the function of telomeres?
A. Promote histone binding
B. Ensure chromosome end stability
C. Anchor chromosomes to the spindle
D. Initiate DNA replication

Ensure chromosome end stability

Which enzyme counteracts chromosome shortening during DNA replication?
A. Helicase
B. Primase
C. Ligase
D. Telomerase

Telomerase

What repeat sequence is commonly found in human telomeres?
A. AATTCC
B. TATAAA
C. TTAGGG
D. CGGTTG

TTAGGG

Why do chromosomes shorten each replication cycle?
A. Exonuclease activity at ends
B. DNA polymerase cannot replace primers at 3' ends
C. Lack of histones at the tips
D. Repeated cutting by condensins

DNA polymerase cannot replace primers at 3' ends

What describes a kinetochore?
A. Transcription site
B. DNA-protein structure at telomeres
C. Spindle-attachment complex at centromeres
D. Looping protein for compaction

Spindle-attachment complex at centromeres

Centromeres are typically rich in which base pair composition?
A. GC
B. AT
C. UG
D. CU

AT

What protein complex holds sister chromatids together?
A. Condensin
B. Cohesin
C. Telomerase
D. Histone H1

Cohesin

What enzyme cleaves cohesin to allow chromatid separation?
A. DNAse
B. Primase
C. Separase
D. Ligase

Separase

Why do sister chromatids remain connected at centromeres during anaphase I of meiosis?
A. Cohesin is permanently bound
B. Histones block separase
C. Shugoshin protects centromeric cohesin
D. Telomerase prevents cleavage

Shugoshin protects centromeric cohesin

What happens to shugoshin during metaphase II?
A. It is transcribed
B. It is degraded
C. It binds nucleosomes
D. It is reactivated

It is degraded

What best describes the role of condensins?
A. Protect centromeric DNA
B. Initiate transcription
C. Organize higher-order chromatin loops
D. Replicate telomeres

Organize higher-order chromatin loops

What component of telomerase serves as a template for DNA extension?
A. DNA polymerase
B. Protein subunit
C. Guide RNA
D. Topoisomerase

Guide RNA