CHROMOSOMAL STRUCTURE & MUTATION Flashcards
The human genome consists of ______________________ of DNA organized into ________
2.9 billion nucleotide bp
23 chromosomes
As ______ organisms, humans inherit a ______ set of genes (23 chromosomes) from each parent, so humans have two copies of every gene (except for some on the _______ chromosomes).
diploid
haploid
X and Y
Each chromosome is a double helix of DNA:
*Chromosome 1 –
*Chromosome 2 –
the largest (246 million nucleotide bp)
the smallest (48 million nucleotide bp)
is carried on the chromosomes in the form of the order or sequence of nucleotides in the DNA helix.
Genetic information
is a trait or group of traits resulting from the transcription and translation of these genes.
phenotype
is the DNA nucleotide sequence responsible for a phenotype.
genotype
A DNA sequence change that is present in a relatively small proportion of a population is a
mutation
The more general term ______ may be used, particularly to describe inherited or somatic sequence alterations, reserving the term mutation for rarer, usually somatic changes, for example, changes found only in tumor tissue.
variant
A variant that is present in at least 1% to 2% of a population is considered a
polymorphism
Polymorphisms are casually considered _______ that do not severely affect phenotype.
mutations
1) ABO blood groups
2) Major Histocompatibility Complex 3) Polymorphisms for human identification and paternity testing
Examples of Benign Polymorphisms:
3 Categories of DNA Mutation:
Gene Mutations
Chromosome Mutations
Genome Mutations
DNA Mutation:
– affect single genes and are often, but not always, small changes in the DNA sequence.
Gene Mutations
DNA Mutation:
– affect the structures of entire chromosomes; the movement of large chromosomal regions either within the same chromosome or to another chromosome.
Chromosome Mutations
DNA Mutation:
– changes in the number of chromosomes.
Genome Mutations
3 CHROMOSOMAL ABNORMALITIES
Position effect
Aneuploid
Euploid
CHROMOSOMAL ABNORMALITy
– a cell or cell population with a normal complement of chromosomes.
Euploid
CHROMOSOMAL ABNORMALITy
– mostly observed as increased numbers of chromosomes or when there are more than two copies of one or more chromosomes.
Aneuploid
a disease resulting from aneuploidy, where there are three copies or trisomy of chromosome 21
Down syndrome
CHROMOSOMAL ABNORMALITy
– a phenomenon that a gene inserted or moved into a different chromosomal location may be expressed differently than it was in its original position.
Position effect
A eukaryotic chromosome is a .
double helix of DNA
➢An extended DNA double helix undergoes __________ compaction to make a metaphase chromosome.
8,000-fold
Approx. 160 to 180 bp of DNA are wrapped around a set of eight histone proteins (two each of ________________) to form a nucleosome.
H2a, H2b, H3, and H4
Nucleosomes are visible by electron microscopy as 100-Å beadlike structures that are separated by short (70–90 bp) strands of a free double helix or linker DNA. This _______________ arrangement comprises the 10-nm.
“bead-on-a-string”
The structure of metaphase chromosomes is maintained by more than just histones. Metaphase chromatin is
1/3 of DNA,
1/3 of histones,
and 1/3 of nonhistone proteins.
complexes termed condensin I and condensin II, maintain mitotic chromosome structure.
Nonhistone protein
Chromosomal Compaction and Histones
Interphase nucleus:
➢The 10-micron fiber is further coiled around histone H1 (or H5 in certain cells) into a thicker and shorter 30-nm or 30-micron fiber. The 30-nm interphase fibers represent the _______________ of DNA.
“resting state”
When the DNA is relaxed into 10-micron fibers for ______________, the placement of nucleosomes along the double helix can be detected using nucleases.
transcription or replication
The 30-nm interphase fibers are looped onto protein scaffolds to form 300-nm fibers before entry into the _________________________, and the looped fibers are wound into 700-nm solenoid coils.
M phase of the cell cycle (mitosis)
The 700-nm coils are compacted into the 1,400-nm fibers that can be seen microscopically in metaphase nuclei and as _____________ in laboratory testing.
karyotypes
In the 30-nm interphase chromatin fiber, the internucleosomal DNA is wound into a solenoid coil. Loss of this level of organization is the first classic indicator of
apoptosis, or programmed cell death.
– is the state of compaction of the DNA double helix that affectsgene activity
Chromosome topology
