How many fragile sites have been identified on human chromosomes?
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More than 100.
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How many fragile sites have been identified on human chromosomes?
More than 100.
What does unbalanced gene dosage lead to?
Developmental abnormalities.
What happens during a reciprocal translocation?
Parts of chromosomes move to other nonhomologous chromosomes or to other regions of the same chromosome.
How can an inversion affect the expression of a wild-type allele in Drosophila?
It can move the allele to a region with inactive chromatin, preventing its expression and resulting in red and white spotted eyes.
How can large deletions be detected?
Because the chromosome is noticeably shortened.
What happens to recombinant gametes in the presence of a pericentric inversion?
The resulting recombinant gametes are not viable, so no recombinant progeny are observed.
What is the outcome of a Robertsonian translocation?
One large metacentric chromosome and one very small chromosome with two very short arms.
What forms in an individual heterozygous for a reciprocal translocation during homologous pairing?
Crosslike structures.
What role may inversions have played in human evolution?
Inversions may have contributed to differences between human and chimpanzee chromosomes.
What type of double crossover results in functional recombinant chromosomes?
Two-strand double crossovers.
What are copy-number variations?
Variations in the number of copies of particular DNA sequences in the human genome.
What is a chromosome deletion?
The loss of a chromosome segment.
What occurs in meiosis when an individual is heterozygous for an inversion?
The homologous sequences can align and pair only if the chromosomes form an inversion loop.
What is the color of the top chromosome in pair 1 of the described translocation?
Red.
What is a pericentric inversion?
A type of inversion that involves the centromere and alters the DNA sequence without losing or gaining genetic material.
Which genes are duplicated in the chromosome with duplication?
Big E and big F.
What is created when the short arm of one acrocentric chromosome is exchanged with the long arm of another?
A large metacentric chromosome and a fragment that often fails to segregate and is lost.
What syndrome is caused by a deletion on the short arm of chromosome 5?
Cri-du-chat syndrome.
What are fragile sites on human chromosomes?
Chromosomal regions susceptible to breakage under certain conditions.
What process produces duplications and deletions in chromosomes?
Unequal crossing over.
What must happen during the pairing of homologs in prophase I of meiosis for individuals heterozygous for deletions?
The normal chromosome must loop out to allow homologous regions to align.
What are chromosome rearrangements?
Chromosome mutations that change the structure of individual chromosomes.
How do the chromosomes appear during the formation of the inversion loop?
One chromosome forms a bump while the other rises upwards, turns down, and lies parallel.
What are the three different ways chromosomes can separate during anaphase 1?
What frequently accompanies translocations?
Deletions.
What is a translocation?
The movement of genetic material between nonhomologous chromosomes or within the same chromosome.
What are the main characteristics of Hirschhorn syndrome?
Cleft lip and palate, severe intellectual disability, deletion on chromosome 4 (long arm).
What does it mean for an individual to be heterozygous for a duplication?
The individual has one normal chromosome and one chromosome with the duplication.
Which chromosome is shown to have a fragile site in the provided information?
The human X chromosome.
How can translocations affect phenotype?
By causing genes to move to new locations or by breaking genes and disrupting their function.
What genes are involved in the paracentric inversion described?
Genes big C, big D, and big E.
What do Figures 8.14 and 8.15 illustrate?
The results of single crossovers within inversions.
What is a characteristic of individuals heterozygous for inversions regarding recombination?
They exhibit reduced recombination among genes located in the inverted region.
What does it mean if a gene is haploinsufficient?
A single copy of the gene is not sufficient to produce a wild-type phenotype.
What are the characteristics of the two gametes that contain non-recombinant chromosomes?
One is wild type (normal) and the other has an inversion.
How were chromosome rearrangements traditionally detected?
By examining chromosomes with a microscope.
What is the significance of the looped out region during chromosome alignment?
It allows the homologous sequences of the chromosomes to align.
What happens to a gene during an inversion?
An inversion may break a gene into two parts, potentially destroying its function.
What changes can be observed through visual examination of chromosomes?
Changes in overall size, alteration of banding patterns, and behavior in meiosis.
What genes are present in the non-recombinant gamete with the paracentric inversion?
Big C, big D, and big E.
What is formed during prophase 1 in a heterozygote with a paracentric inversion?
An inversion loop.
What chromosomes are involved in the translocation described?
T₂ (blue) and N₂ (blue) with genes M, N, O, P, Q, R, S, T.
What is the effect of the Bar mutation in fruit flies?
It results in a reduced number of facets in the eye, making the eye smaller and bar-shaped instead of oval.
What occurs during prophase I in individuals heterozygous for a paracentric inversion?
The chromosomes form an inversion loop.
What happens during meiosis when an individual is homozygous for an inversion?
No special problems arise, and the homologous chromosomes can pair and separate normally.
What does unbalanced gene dosage refer to?
The unequal number of gene copies resulting from duplications and deletions.
Which genes are present on the top chromosome named N1 in pair 1?
A, B, C, D, E, F, and G.
What are interchromosomal duplications?
Duplications where the two copies are found on different chromosomes.
What is the visual difference between normal wing venation and that produced by a Notch mutation?
Normal wing venation has a round outer edge, while Notch mutation shows notches at the edges and tips.
What happens if the broken ends of DNA are rejoined correctly?
The original chromosome is restored, and no rearrangement occurs.
What is depicted in the diagram regarding homologous chromosomes?
Two homologous chromosomes with genes A, B, C, D, E, F, and G on the top chromosome, and A, B, C, D, and G on the bottom chromosome.
Why can't gametes with recombinant chromosomes produce viable progeny?
Because they have too many copies of some genes and no copies of others.
What phenotype results from an X-linked duplication in Drosophila melanogaster?
The Bar phenotype.
What syndrome is associated with deletion on chromosome 7 (long arm) and includes distinctive facial features?
Williams–Beuren syndrome.
What problems arise in heterozygotes during prophase I of meiosis?
Problems in chromosome pairing due to non-homologous chromosomes.
What occurs in prophase I of meiosis in individuals heterozygous for a chromosome inversion?
The homologous chromosomes form an inversion loop.
What is the result of a Robertsonian translocation?
An overall reduction in chromosome number.
What is a chromosome inversion?
A rearrangement where a chromosome segment is inverted—turned 180 degrees.
What genetic condition results from a male inheriting a chromosome missing one of the opsin genes?
Red–green color blindness.
What happens to a chromosome with segments AB•CDEFG that undergoes a deletion of segment EF?
It generates the mutated chromosome AB•CDG.
What is the result of the inversion loop formation during meiosis?
Homologous sequences align.
What is the consequence of altered gene order due to inversions?
Phenotypic effects may arise even when breaks lie between genes.
What genes are present on the normal chromosome in the described scenario?
Big A, big B, big C, big D, big E, big F, and big G.
What genes are involved in the pericentric inversion described?
Genes big C, big D, and big E.
What are Notch mutations in Drosophila?
A series of X-linked wing mutations often resulting from chromosome deletions.
Why are gametes from adjacent-1 and adjacent-2 segregation considered non-viable?
Because some genes are present in two copies.
What type of translocation occurs when acrocentric chromosomes exchange arms?
Robertsonian translocation.
What happens during prophase I of meiosis in individuals heterozygous for a deletion?
The normal chromosome loops out.
What happens to chromosome segregation in meiosis for an individual heterozygous for a reciprocal translocation?
It depends on the nature of the translocation.
What is a chromosome duplication?
A mutation that doubles part of a chromosome.
What happens in a reciprocal translocation?
There is a two-way exchange of segments between nonhomologous chromosomes.
What are copy-number variations (CNVs)?
Variations that include duplications and deletions of DNA sequences.
What do the translocated chromosomes contain segments homologous to?
Segments of two other chromosomes.
What is formed between the fused arms of chromosomes during anaphase 1?
A dicentric bridge.
What is the phenotype of homozygous female and hemizygous male fruit flies with the Bar mutation?
They have greatly reduced numbers of facets in their eyes.
What is a common feature of deletions on chromosome 18 (long arm)?
Distinctive mouth shape, small hands, small head, and intellectual disability.
What occurs in chromosome deletion?
A segment of the chromosome is deleted, leaving fewer genes.
What is the effect of the double Bar mutation on the number of facets in fruit flies?
The number of facets is extremely reduced.
What is a position effect in genetics?
It refers to the alteration in gene expression due to changes in gene position caused by inversions.
What happens during unequal crossing over?
Chromosomes do not align properly, leading to duplications and deletions.
What is pseudodominance?
Expression of a normally recessive mutation indicating a deletion on one of the homologous chromosomes.
What is the configuration of chromosomes during prophase 1 of meiosis in the presence of a translocation?
A cross-like configuration forms due to homologous sections of chromosomes.
What is a consequence of recombination within a pericentric inversion?
Recombination is reduced, leading to recombinant chromosomes with too many copies of some genes and no copies of others.
How common are submicroscopic chromosome duplications and deletions?
They are quite common, with each person possibly having as many as a thousand copy-number variations.
What is the outcome of alternate segregation?
It results in 4 viable gametes: N₁, N₂; N₁, N₂; T₁, T₂; and T₁, T₂.
What occurs in a heterozygous individual with a paracentric inversion during meiosis?
A single crossover within the inversion leads to abnormal gametes.
What is the origin of the genes encoding globins?
They arose from an original primordial globin gene that underwent a series of duplications.
Do inversions result in the loss or gain of genetic material?
No, inversions do not result in the loss or gain of genetic material; they only alter the DNA sequence.
What are the outcomes of anaphase 1 in this scenario?
The chromosomes separate, resulting in gametes with different gene combinations.
What is the effect of inversions on phenotypes?
Inversions can have pronounced phenotypic effects despite not changing the amount of genetic material.
What are the symptoms of Prader–Willi syndrome?
Feeding difficulty at early age, obesity after one year, mild to moderate intellectual disability, deletion on chromosome 18 (short arm).
What are the designations for the normal chromosomes in the example provided?
N and N for normal chromosomes 1 and 2.
What is the eye appearance of homozygous Bar flies?
They have relatively thinner bar eyes.
What happens to the acentric fragment during meiosis?
It is usually lost when the nucleus re-forms because spindle microtubules do not attach to it.
What are the four basic types of chromosome rearrangements?
Duplications, deletions, inversions, and translocations.
What is the outcome of crossing over within a paracentric inversion?
No recombinant progeny result because the gametes are missing some genes.
What recent techniques have improved the detection of chromosome rearrangements?
Rapid genome sequencing techniques.
What type of mutation causes fragile-X syndrome?
Expanding nucleotide repeats, specifically an increase in CGG trinucleotide repeats.
What often results if the amount of one gene product increases while others remain the same?
Developmental problems.
What is the expected outcome for most gametes from an individual heterozygous for a reciprocal translocation?
Approximately half of the gametes are produced by alternate or adjacent-1 segregation.
How long are many fragile sites in terms of base pairs?
More than 100,000 bp in length.
What happens at fragile sites during DNA replication?
Enzymes may stall while unwinding the DNA, leading to unwound stretches that are vulnerable to breakage.
What happens if a single crossover occurs in the inverted region during meiosis?
An unusual structure results with abnormal chromatids.
What are fragile sites on chromosomes?
Sites that develop constrictions or gaps when cells are grown in culture and are prone to breakage under certain conditions.
What happens to the duplicated region in a heterozygous individual during prophase I?
The duplicated region loops out during pairing.
What structure is generated when the normal chromosome loops out during chromosome pairing in prophase I?
A structure similar to that seen in individuals heterozygous for duplications.
What are the four basic types of chromosome rearrangements?
Duplications, deletions, inversions, and translocations.
What genetic disorder is associated with the identification of a specific gene?
Neurofibromatosis.
What additional part does the bottom chromosome T1 in pair 1 have?
A blue part with genes Q, R, S, and T.
What are the functions of different globin chains?
Some function during adult stages, while others function during embryonic and fetal development.
What is a Robertsonian translocation?
A type of translocation where the long arms of two acrocentric chromosomes join at a common centromere, forming a metacentric chromosome.
What diseases and disorders have been associated with copy-number variations?
Osteoporosis, autism, schizophrenia, and others.
What are the eye characteristics of wild-type fruit flies?
They have normal-sized eyes.
What is the role of the Notch gene?
It encodes a receptor that transmits signals from outside the cell to its interior, important for fly development.
What happens to the eyes of heterozygous Bar flies?
They have smaller, bar-shaped eyes.
What is fragile-X syndrome associated with?
A fragile site on the human X chromosome.
What occurs if a deletion includes the centromere?
The chromosome will not segregate in meiosis or mitosis and will usually be lost.
What condition is caused by a deletion of a tiny segment of chromosome 7?
Williams–Beuren syndrome.
How do chromosome duplications contribute to gene evolution?
They provide extra copies of genes that can mutate while the original copy maintains essential functions.
What is a potential consequence of extra copies of genes within a duplicated region?
They do not pair in meiosis.
What is the appearance of the mutant fish compared to the wild-type fish?
It has spots rather than stripes.
What type of gametes does alternate segregation produce?
Gametes that possess one complete set of chromosome segments, which are functional and can produce viable progeny.
What is a reciprocal translocation?
A process where segments of two chromosomes are exchanged, such as between chromosomes AB•CDEFG and MN•OPQRS.
What is the DNA sequence similarity between red and green opsin genes?
They are 98% identical.
What genes remain after a chromosome deletion?
Big A, big B, big C, big D, and big G.
What is the outcome of crossing over in the presence of a paracentric inversion?
Abnormal gametes that do not give rise to viable offspring.
What is the result of unequal crossing over in the described scenario?
One chromosome has 1 red opsin gene and 2 green opsin genes (duplication), while the other chromosome is missing the green opsin gene (deletion).
What occurs in a heterozygous individual with a pericentric inversion during meiosis?
A single crossover leads to abnormal gametes.
What phenotype is produced by a chromosome deletion that includes the Notch gene?
The Notch phenotype.
How do G-banding patterns help in studying chromosome differences?
They reveal that several human chromosomes differ from those of chimpanzees by pericentric inversions.
What forms during prophase 1 in a heterozygote with a pericentric inversion?
An inversion loop.
Why are the two normal recombinant gametes considered nonviable?
They are shorter and do not contain all the genes present in the original.
How do Notch deletions behave in Drosophila?
They behave in a dominant manner, causing notched wings when heterozygous.
What is a chromosome deletion?
A mutation in which a part of a chromosome is lost.
How does translocation differ from crossing over?
Translocation involves movement between nonhomologous chromosomes, while crossing over involves exchange between homologous chromosomes.
What are some characteristics of a child with cri-du-chat syndrome?
Small head, widely spaced eyes, round face, and intellectual disability.
What are the three different ways chromosomes may segregate with a reciprocal translocation?
Alternate segregation, adjacent-1 segregation, and adjacent-2 segregation.
What is pseudodominance?
The expression of recessive genes on the homologous chromosome due to a deletion.
What happens during alternate segregation?
N and N move toward one pole, and T and T move toward the opposite pole.
What are the symptoms of Wolf–Hirschhorn syndrome?
Seizures, severe intellectual disability, and delayed growth.
Why does the Notch deletion act as a recessive lethal?
The loss of all copies of the Notch gene prevents normal development.
What are paracentric inversions?
Inversions that do not include the centromere.
In a Robertsonian translocation, what is exchanged between acrocentric chromosomes?
The short arm of one chromosome is exchanged with the long arm of another.
What happens during chromosome duplication?
A segment of the chromosome is duplicated, resulting in an additional set of genes.
What is the term for flies that carry three copies of the Bar duplication?
Double Bar.
What can happen if the amount of one protein increases while others remain constant?
It can lead to problems in developmental processes that depend on the interaction of many proteins.
Where are the red and green opsin genes located?
On the X chromosome.
What syndrome is associated with deletion on chromosome 5, short arm?
Cri-du-chat syndrome.
What type of duplications are most segmental duplications?
Intrachromosomal duplications, where the two copies are found on the same chromosome.
What forms during prophase I of meiosis in an individual heterozygous for an inversion?
An inversion loop.
What is the effect of inversions on the overall rate of recombination?
It is reduced within an inversion.
What type of chromosome rearrangement produces a dicentric chromosome when crossing over occurs?
c. Paracentric inversion.
What types of fragments are produced during recombination in a pericentric inversion?
No dicentric bridges or acentric fragments are produced.
What does it mean for an individual to be homozygous for a duplication?
The individual carries the duplication on both homologous chromosomes.
What percentage of children with unexplained intellectual disability had copy-number variations in the study by Janine Wagenstaller?
16% (11 out of 67 children).
What happens if crossing over occurs within the inverted region?
Two resulting chromatids have too many copies of some genes and no copies of others.
What is the role of homologous centromeres during anaphase I of meiosis?
They separate and move toward opposite poles.
What is the minimum size of chromosome rearrangements that microscopy can detect?
At least 5 million base pairs.
What is a nonreciprocal translocation?
A translocation where genetic material moves from one chromosome to another without reciprocal exchange.
What happens to the chromosomes during crossing over within the inverted region?
They form an unusual structure and can result in fused chromosomes.
What structure is formed when a dicentric chromatid is stretched across the nucleus?
A dicentric bridge.
What happens to the duplicated region of a chromosome in heterozygous individuals during meiosis?
It loops out when homologous chromosomes pair in prophase I.
What are the resulting chromosomes after a nonreciprocal translocation of segment EF?
AB•CDG and MN•OPEFQRS.
What is the range in length for copy-number variations?
From thousands of base pairs to several million base pairs.
What happens when duplications and other chromosome mutations occur?
They produce extra copies of some genes, altering the relative amounts of interacting products.
Why is adjacent-2 segregation considered rare?
Because the two homologous chromosomes usually separate in meiosis.
What genes are involved in the inversion and crossing over process described?
Genes big C, big D, and big E.
What is a displaced duplication?
A duplication where the duplicated segment is located some distance from the original segment, either on the same chromosome or a different one.
What is a position effect in the context of translocations?
It refers to changes in gene expression due to a gene being moved to a new location under different regulatory control.
What genetic disease is associated with a translocation affecting chromosome 17?
Neurofibromatosis.
What are the characteristics of the two inner chromatids after crossing over in a paracentric inversion?
They have two copies of some genes and no copies of others.
What often causes chromosome rearrangements?
Double-stranded breaks in the DNA molecule.
How do inversions contribute to evolution?
By suppressing recombination among a set of genes.
What happens when crossing over occurs within an inversion in a heterozygous individual?
It leads to unbalanced gametes and no recombinant progeny.
What can lead to chromosome rearrangements besides double-stranded breaks?
Errors in crossing over or crossing over between repeated DNA sequences.
What happens to females that are homozygous for a Notch deletion?
They die early in embryonic development.
What happens to the smaller chromosome in a Robertsonian translocation?
It is often lost due to insufficient mass to segregate properly during mitosis and meiosis.
Do most copy-number variations have observable phenotypic effects?
Many probably have no observable phenotypic effects.
What types of gametes are produced after anaphase 2?
One normal non-recombinant gamete, two non-viable recombinant gametes, and one non-recombinant gamete with pericentric inversion.
What is the result of crossing over within the inverted region of a chromosome?
Nonviable gametes are usually produced.
What is the significance of duplications in evolution?
Duplications allow for the evolution of new genes by providing extra copies that can mutate and assume new functions.
What type of inheritance does fragile-X syndrome exhibit?
X-linked inheritance.
What forms during prophase I of meiosis when homologous segments pair in an individual heterozygous for a reciprocal translocation?
Crosslike configurations consisting of all four chromosomes.
What happens to the chromatid without a centromere during anaphase 1?
It is lost.
What must happen for a chromosome inversion to take place?
The chromosome must break in two places.
What is a characteristic of deletions on chromosome 4?
Small head and mild to moderate intellectual disability.
What is a reverse duplication?
A duplication where the duplicated segment is inverted compared to the original sequence.
How can chromosome breaks from translocations disrupt gene function?
If a break occurs within a gene, it can lead to the disruption of that gene's function.
What was the outcome of sequencing DNA around the breaks in translocations?
It helped identify the precise location of the gene associated with neurofibromatosis.
What occurs during alignment in prophase I of meiosis for the chromosome with duplication?
The duplicated region (big E and big F) must loop out.
What happens during prophase 1 when homologous chromosomes pair?
The normal chromosome must loop out to align homologous sequences, causing genes E and F to loop out from the top chromosome.
What happens during anaphase I of meiosis regarding homologous chromosomes?
The centromeres are pulled toward opposite poles, separating the homologous chromosomes.
What disorder results from a deletion of part of the short arm of chromosome 4?
Wolf–Hirschhorn syndrome.
What is the significance of the red portions of chromosomes T₁ and T₂?
They align with the red chromosome N₁ to form a bookend shape during meiosis.
How is the Bar mutation inherited?
As an incompletely dominant, X-linked trait.
Why are the recombinant gametes considered nonviable?
Because genes are either missing or present in too many copies.
How does chromosome duplication affect phenotype?
It leads to imbalances in the amounts of gene products due to abnormal gene dosage.
What is the eye characteristic of flies with double Bar?
They have the thinnest and shortest bar eyes.
What are pericentric inversions?
Inversions that include the centromere.
What defects may individuals heterozygous for a deletion experience?
Imbalances in gene product amounts, expression of normally recessive mutations, and loss of wild-type allele masking.
What are structural variants?
Chromosome rearrangements and copy-number variations collectively.
In which organisms are inversion heterozygotes common?
Many plants, some species of Drosophila, and mosquitoes.
What role does FMRP play in the body?
It regulates the translation of other proteins and plays a role in the development of neural synapses.
What are segmental duplications?
Duplicated sequences in the human genome that are greater than a thousand base pairs in length.
What genes switch places during translocation?
Genes big E, big F, and big G switch with big Q, big R, and big S.
What is an acentric chromatid?
A chromatid that lacks a centromere.
What is the structural change that occurs in a chromosome during an inversion?
A segment of a chromosome is turned 180 degrees.
What percentage of the human genome consists of segmental duplications?
About 4%.
What is required for developmental processes according to the diagram?
The interaction of many genes.
What significant project provided detailed information about DNA sequences on human chromosomes?
The Human Genome Project.
What is required for the pairing and synapsis of homologous regions in heterozygotes?
One or both chromosomes must loop and twist to line up homologous regions.
What is a consequence of crossing over in a paracentric inversion?
One chromatid may have two centromeres, while another may lack a centromere.
What chromosome disorder can be caused by Robertsonian translocations?
Some cases of Down syndrome.
Why do duplications often result in abnormal phenotypes?
Because developmental processes depend on the relative amounts of proteins encoded by different genes.
What remains unchanged in gene sequences after duplication?
The gene sequences themselves are not altered, and no genetic information is missing.
What causes duplications and deletions in chromosomes?
Unequal crossing over.
What is a possible effect of the chromosome looping during meiosis?
The chromosome is more likely to break.
What is a tandem duplication?
A duplication where the duplicated segment is immediately adjacent to the original segment.
What are the potential consequences of duplications in gene products?
Duplications can have severe consequences when the precise balance of gene products is critical to cell function.
In chromosome duplication, which genes are duplicated?
Genes big E and big F.
Which genes are flipped during chromosome inversion?
Genes big D, big E, and big F.
What are the characteristics of the two outer chromatids after crossing over in a paracentric inversion?
They contain original, nonrecombinant gene sequences.
What are the phenotypic consequences of a deletion dependent on?
The specific genes located in the deleted region.
How can developmental processes be affected?
By the relative amounts of gene products.
What occurs during adjacent-1 segregation?
N and T move toward one pole, and T and N move toward the other pole.
What does a wild-type fish exhibit in terms of appearance?
Stripes running horizontally over the body.
Why are gametes produced by adjacent-1 and adjacent-2 segregation not viable?
Because some chromosome segments are present in two copies, while others are missing.
What are the characteristics of Williams–Beuren syndrome?
Distinctive facial features, heart defects, high blood pressure, and cognitive impairments.
How does the number of gene copies relate to protein synthesis?
The amount of a particular protein synthesized is often directly related to the number of copies of its corresponding gene.
What genetic condition can arise from unequal crossing over in humans?
Red–green color blindness.
What gene is disrupted in fragile-X syndrome?
The gene that encodes fragile X mental retardation protein (FMRP).
What is translocation in chromosomes?
A segment of a chromosome moves to a non-homologous chromosome or another place on the same chromosome.
What are the symptoms of duplication on chromosome 7, long arm?
Delayed development, asymmetry of the head, fuzzy scalp, small nose, low-set ears.
What type of mutation causes neurofibromatosis?
An autosomal dominant mutation.
How can duplications be detected during meiosis?
By the appearance of a characteristic loop structure.
What happens to heterozygous female fruit flies with the Bar mutation?
They have somewhat smaller eyes with a reduced number of facets.
Why are many deletions lethal in the homozygous state?
Because all copies of any essential genes located in the deleted region are missing.
What is the frequency of fragile-X syndrome in male births?
About 1 in 5000 male births.
What is a chromosome duplication?
A mutation in which part of the chromosome has been doubled.
What is the role of existing gene copies after a chromosome duplication?
The original copy maintains essential functions while the extra copy is free to undergo mutations.
Describe chromosome inversion.
A segment of the chromosome is turned 180 degrees, reversing the order of genes.
How can translocations affect gene expression?
By physically linking genes that were formerly on different chromosomes, potentially altering their regulatory sequences.
When are fragile sites typically replicated?
Late in S phase.
How did geneticists narrow down the location of the neurofibromatosis gene?
By identifying patients with a translocation affecting chromosome 17.
What are some symptoms of duplication on chromosome 4, short arm?
Small head, short neck, low hairline, reduced growth, intellectual disability.
What occurs during prophase I that can lead to unequal crossing over?
Two paired X chromosomes do not align properly.
Is the nature of fragile sites completely understood?
No, it is not completely understood despite recent advances.
What is a dicentric chromatid?
A chromatid that has two centromeres.
