ch 9 g

What is aneuploidy?

Gain or loss of one or more chromosomes, resulting in a number that is not an exact multiple of the haploid set.

What is euploidy?

Presence of complete haploid sets of chromosomes. 1n, 2n, 3n…

What is polyploidy?

Presence of more than two complete sets of chromosomes. 3n+

What is monosomy?

Loss of one chromosome (2n−1). type of aneuploidy

What is trisomy?

Gain of one chromosome (2n+1).

What is haploinsufficiency?

One functional copy of a gene is insufficient to provide normal function.

What is autopolyploidy?

Multiple chromosome sets originating from the same species.

What is allopolyploidy or amphidiploidy?

Multiple chromosome sets derived from closely related species through hybridization and chromosome doubling.

What does n represent?

One complete haploid set of chromosomes.

What does 2n represent?

Diploid; two complete sets of chromosomes.

What does 2n−1 represent?

Monosomy; one chromosome missing.

What does 2n+1 represent?

Trisomy; one extra chromosome.

What does 2n−2 represent?

Nullisomy; both chromosomes of one homologous pair are missing.

What does 2n+2 represent?

Tetrasomy; two extra copies of one chromosome.

What do 3n and 4n represent?

3n = Triploidy (three sets); 4n = Tetraploidy (four sets).

What is nondisjunction?

Failure of chromosomes or chromatids to separate properly during meiosis.

How does nondisjunction in meiosis I differ from meiosis II?

Meiosis I = homologous chromosomes fail to separate; Meiosis II = sister chromatids fail to separate.

How does nondisjunction cause monosomy or trisomy?

Abnormal gametes with n−1 or n+1 chromosomes fuse with normal gametes, producing 2n−1 or 2n+1 zygotes.

Which is generally more viable, monosomy or trisomy?

Trisomy is generally more viable than monosomy.

What is Down syndrome and its chromosome notation?

Trisomy 21; 47, 21+ (an extra chromosome 21).

What is the most common cause of Down syndrome?

Nondisjunction of chromosome 21 during meiosis.

How is Down syndrome related to maternal age?

The incidence increases with maternal age.

Is Down syndrome usually inherited?

No, it usually results from random nondisjunction.

How can Down syndrome be inherited?

Through a familial translocation involving chromosome 21, commonly chromosomes 14 and 21.

How common is polyploidy in animals versus plants?

Relatively infrequent in animals but common in plants; found in lizards, amphibians, and fish.

How does polyploidy affect cell and organism size?

Polyploid cells are often larger, and plants may have larger flowers and fruits.

What are triploidy, tetraploidy, and pentaploidy?

Triploidy = 3n; Tetraploidy = 4n; Pentaploidy = 5n.

What is the difference between autopolyploidy and allopolyploidy?

Autopolyploidy involves chromosome sets from the same species; allopolyploidy involves sets from different species.

How can autopolyploidy occur?

Chromosomes replicate, but the cell fails to divide, doubling the chromosome number.

What does colchicine do?

Disrupts microtubules and prevents normal chromosome separation during cell division. causes polyploidy

How does colchicine change the ploidy level?

It prevents spindle function and cell division, allowing chromosome doubling from 2n to 4n.

What is an allopolyploid or amphidiploid?

An organism containing chromosome sets derived from two closely related species.

How does allopolyploidy occur?

Hybridization between two closely related species followed by chromosome doubling.

Why are initial interspecies hybrids often sterile?

Their chromosomes lack matching homologous partners for proper pairing during meiosis.

How can fertility be restored in an allopolyploid?

Chromosome doubling creates homologous pairs, allowing normal meiosis and balanced gametes.

What are the five major types of chromosome structural changes?

Deletions, insertions, duplications, inversions, and translocations.

What is a chromosomal deletion?

Loss of a chromosome segment.

What is a chromosomal insertion?

Addition of a DNA segment into a chromosome.

What is a chromosomal duplication?

An extra copy of a chromosome segment.

What is a chromosomal inversion?

A chromosome segment breaks, reverses orientation, and rejoins.

What is a chromosomal translocation?

Movement of a chromosome segment to a new location in the genome.

How does an inversion occur?

A chromosome breaks at two points, the segment rotates 180°, and the ends rejoin.

What is cri du chat syndrome and its genetic cause?

Cat cry syndrome caused by deletion of part of the short arm of chromosome 5 (46, 5p−).

How can structural changes affect chromosome alignment during meiosis?

Deletions and inversions can form loops; reciprocal translocations can form cross-shaped pairing structures.

How can inversions affect chromosome segregation?

Crossing over within an inversion can produce chromosomes with duplications, deletions, or abnormal centromere numbers.

How can translocations affect chromosome segregation?

Alternate segregation produces balanced gametes; adjacent segregation produces gametes with duplications and deficiencies.

What are fragile loci?

Chromosome regions especially susceptible to breakage, sometimes associated with loosely coiled chromatin.

What is unequal crossing over?

Recombination between misaligned homologous chromosomes, producing duplication in one chromosome and deletion in another.

What is the rDNA locus?

A chromosome region containing multiple copies of genes encoding ribosomal RNA.

What is the nucleolar organizer region (NOR)?

A chromosome region containing clustered rDNA genes involved in ribosome production.

Why are multiple copies of rDNA important?

They allow production of large amounts of ribosomal RNA needed for ribosome formation and protein synthesis.

How does gene duplication contribute to evolution?

Extra gene copies accumulate mutations and may evolve new functions while the original gene maintains its function.

What happens during nondisjunction in meiosis I?

Homologous chromosomes fail to separate, producing two n+1 gametes and two n−1 gametes.

What happens during nondisjunction in meiosis II?

Sister chromatids fail to separate, producing two normal gametes, one n+1 gamete, and one n−1 gamete.

Why does maternal age increase the risk of Down syndrome?

Older eggs have a greater risk of chromosome segregation errors during meiosis.

What is the difference between triploid and tetraploid fertility?

Triploids are usually sterile because chromosomes cannot pair evenly; tetraploids are more likely to produce balanced gametes.

What happens to chromosomes when colchicine is added?

Microtubules are disrupted, preventing chromosome separation and allowing chromosome doubling.

What is the difference between reciprocal and nonreciprocal translocations?

Reciprocal = exchange of segments between nonhomologous chromosomes; nonreciprocal = one-way transfer.

What is the difference between alternate and adjacent segregation?

Alternate produces balanced gametes; adjacent produces gametes with duplications and deficiencies.

How can unequal crossing over affect gene dosage?

It produces duplicated genes on one chromosome and deleted genes on the other, changing gene expression.

The most important things to understand rather than just memorize are how nondisjunction produces monosomy/trisomy, how colchicine doubles chromosome sets, how chromosome doubling restores fertility in allopolyploids, and how inversions or translocations affect chromosome pairing and segregation. These are the process-based questions explicitly emphasized in your study guide.