Plant Genetics and Chromosomal Abnormalities

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Questions and Answers

What is the haploid chromosome number in the case presented?

Two

Five

Three (correct)

Four

What is the primary method through which gametes are produced in monoploids?

Meiosis

Fission

Mitosis (correct)

Fusion

Which statement about triploids is correct?

They are usually fertile.

They have paired homologs at meiosis.

They possess four sets of chromosomes.

They are typically sterile or highly infertile. (correct)

What effect does colchicine have on plants?

It induces polyploidy. Signup and view all the answers

How does polyploidy generally affect plant sizes?

It can increase their sizes. Signup and view all the answers

What is a key characteristic of aneuploid gametes formed during meiosis?

They are nonfunctional. Signup and view all the answers

Which of the following statements about allopolyploids is correct?

They result from hybridization between species. Signup and view all the answers

Which group of organisms is less likely to display polyploidy?

Animals Signup and view all the answers

What reproductive method do some polyploid species of flatworms, leeches, and brine shrimps primarily use?

Parthenogenesis Signup and view all the answers

Which family of fish is believed to have originated through ancestral polyploidy?

Salmonidae Signup and view all the answers

Triploid oysters are developed for which primary reason?

To have a commercial advantage Signup and view all the answers

What type of chromosomal abnormality is characterized by having one less chromosome than normal?

Monosomic Signup and view all the answers

Klinefelter syndrome individuals are characterized by which chromosomal composition?

XXY Signup and view all the answers

What is the primary cause of Down syndrome?

Extra copy of chromosome 21 due to nondisjunction Signup and view all the answers

Which type of chromosome has the centromere located at the center?

Metacentric Signup and view all the answers

The average life expectancy of individuals with Down syndrome is approximately how many years?

60 years Signup and view all the answers

What characteristic is NOT associated with Edwards syndrome?

Increased athletic ability Signup and view all the answers

Which condition has an extra chromosome 13 associated with it?

Patau syndrome Signup and view all the answers

How do telocentric chromosomes differ from other types of chromosomes?

They have the centromere at the very end. Signup and view all the answers

What is one effect of maternal age on chromosome abnormalities?

Older mothers have an elevated risk of having a child with Down syndrome. Signup and view all the answers

Which type of chromosome number change is typically more tolerated in plants compared to animals?

Aneuploidy Signup and view all the answers

What describes the concept of gene balance in aneuploidy?

Aneuploidy disrupts the normal gene dosage equilibrium. Signup and view all the answers

What is a common characteristic of individuals with trisomy 18?

Delayed development and mental retardation Signup and view all the answers

Which cellular event is primarily related to the risk of chromosomal abnormalities in older mothers?

Anaphase I nondisjunction Signup and view all the answers

What is the primary reason aneuploidy is considered deleterious?

It causes gene imbalance. Signup and view all the answers

What occurs to phenotypes of deleterious recessive alleles on a monosomic autosome?

They are automatically expressed. Signup and view all the answers

What type of chromosomal rearrangement results from unequal crossing over?

Production of duplications and deletions. Signup and view all the answers

What is a characteristic of unbalanced chromosomal rearrangements?

They can lead to the unmasking of recessive alleles. Signup and view all the answers

What is required for double-stranded breaks in DNA to be lethal?

They must remain unrepaired. Signup and view all the answers

Which type of chromosomal rearrangement does NOT affect gene dosage?

Inversions Signup and view all the answers

How do repair systems in the cell function in relation to double-stranded breaks?

They always restore the original DNA order. Signup and view all the answers

What is the gene-dosage effect?

The relationship between gene copy number and the amount of its product. Signup and view all the answers

What characterizes balanced rearrangements in chromosomes?

They alter chromosomal gene order without DNA loss. Signup and view all the answers

What type of inversion occurs when the centromere is within the inverted segment?

Pericentric inversion Signup and view all the answers

What is a potential outcome of a paracentric inversion during meiosis?

Inviable meiotic products Signup and view all the answers

How do segmental duplications influence genetic variation in humans and apes?

They act as substrates for nonallelic homologous recombination (NAHR). Signup and view all the answers

What defines an inversion in chromosome structure?

A segment is twisted, removed, and replaced in reverse order. Signup and view all the answers

Which rearrangement is likely to cause gene imbalance in the resulting zygote?

Pericentric inversion Signup and view all the answers

What effect may inversions have on genes within the affected chromosome segment?

They can disrupt genes or fuse parts of two genes. Signup and view all the answers

During meiosis, what mechanism occurs for chromosomes with paracentric inversions?

Creation of inviable gametes due to a dicentric bridge Signup and view all the answers

What is a key outcome of a reciprocal translocation in a heterozygote?

It leads to a cross-shaped pairing configuration. Signup and view all the answers

How do chromosome inversions potentially affect evolutionary traits like butterfly mimicry?

By altering phenotypic traits associated with coloration. Signup and view all the answers

What genetic condition is associated with Robertsonian translocations involving chromosomes 14 and 21?

Down syndrome Signup and view all the answers

What typically happens to recombinant offspring produced by a translocation heterozygote?

Many do not survive due to unbalanced genomes. Signup and view all the answers

Which type of chromosomal rearrangement involves two homologous chromosomes exchanging segments?

Reciprocal translocation Signup and view all the answers

What is a common result of chromosomal fusion events in closely related species?

Variation in chromosome number Signup and view all the answers

What percent reduction in viable gametes or zygotes is likely due to the presence of a reciprocal translocation?

50% Signup and view all the answers

Which of the following accurately describes inversions in chromosomes?

They involve the flipping of a chromosome segment. Signup and view all the answers

Study Notes

Introduction to Genetic Analysis

The text is about genetic analysis, specifically focusing on Chapter Seventeen, which discusses changes in chromosome numbers.
It outlines key questions related to polyploids (3n, 4n, etc.), aneuploids (2n-1, 2n+1, etc.), duplications, deletions, inversions, and translocations, along with their relevance to humans.
The chapter objective is to differentiate major types of chromosomal mutations and predict their organismal phenotypic effects. This study material contains some figure and table data that details the key concepts related to chromosome and gene mutations.
The study also covers concepts such as Down syndrome and chromosome mutations in general.

Changes in Chromosome Numbers

Polyploids/Euploids: Organisms with more than two sets of chromosomes (e.g., 3n, 4n). Common in plants and rare in animals.
Aneuploids: Organisms with an abnormal number of chromosomes. Includes trisomy (2n+1) and monosomy (2n-1), where one chromosome is present in a number other than two. Occurs due to chromosomal non-disjunction during meiosis.

Chromosome Constitutions

A table presents different euploid and aneuploid constitutions (n, 2n, 3n, 4n etc.) in a hypothetical diploid organism with three chromosomes (A, B, C). It specifically details the number of chromosomes for each constitution.

Polyploids and Monoploids

Monoploids (N): Contain only one set of chromosomes. Seen in certain insects (e.g., male bees, wasps, ants). Parthenogenesis (asexual reproduction) is the way they reproduce via mitosis.
Polyploidy: Triploid (3n), tetraploid (4n), pentaploid (5n), hexaploid (6n), etc., are various forms of polyploidy where the organism has three or more sets of chromosomes. Polyploids frequently exhibit larger sizes and component parts compared to diploids.

Meiotic Pairing in Triploids

Polyploids having odd numbers of chromosome sets (e.g., triploids) are generally sterile or highly infertile.
During meiosis, unpaired chromosomes result in aneuploid gametes.
Paired homologs comprise a bivalent, and unpaired homologs are univalents. The combination of bivalents and univalents create trivalents.

Colchicine-Induced Polyploidy

Colchicine induces polyploidy by inhibiting spindle fiber formation. This results in doubling the alleles in the genotype.
Plants are generally more tolerant of polyploidy than animals; natural and induced autotetraploid plants are, for example, notably larger and increase in size.

Origin of Polyploid Species

Example data points describing the development of different types of wheat through hybridization and natural allopolyploidy mechanisms. Triploid and octoploid individuals are likely to be sterile or less functional. Examples of plants formed through the hybridization and doubling of parental chromosome sets.

Meiotic Nondisjunction

Nondisjunction at meiosis can create aneuploid products. Nondisjunction at the first division may yield products that have one more or less than the usual haploid chromosome set, whereas nondisjunction at the second division results in having one more or one fewer than usual chromosomes in some cells.

Monosomics (2n-1)

Turner syndrome (XO): Females with only one X chromosome. The incidence is approximately one in every 5000 female births.

Trisomics (2n+1)

Klinefelter syndrome (XXY): Males exhibiting a lanky appearance, moderate intellectual impairment, and sterility. Common characteristic is having an XXY chromosomal constitution.
Down syndrome (Trisomy 21): An added copy of chromosome 21; affects various organ systems (e.g., mental retardation, delayed development, high muscle tone). Common characteristic is having an extra chromosome 21.
Edwards syndrome (Trisomy 18): An extra copy of chromosome 18. Frequently associated with physical malformations and high muscle tone.
Patau syndrome (Trisomy 13): An extra copy of chromosome 13. Often linked to a variety of physical malformations.

Changes in Chromosome Structure

Duplications: Region of a chromosome is present twice.
Deletions: Segment of a chromosome is lost.
Inversions: Chromosome region is flipped, affecting gene order.
Translocations: Chromosome segment is moved to a non-homologous chromosome.

Meiotic Nondisjunction and Aneuploidy

Causes of aneuploidy include nondisjunction of chromosomes during meiosis, which can have variable degrees of lethality. Aneuploidy also relates to chromosome structure and gene balance and is linked to several types of genetic disorders.

Chromosome Structure and Rearrangements

DNA breakage (or crossing over between repetitive DNA segments) can produce chromosomal rearrangements (deletions, duplications, inversions, translocations).
Unbalanced rearrangements alter gene dosage, which can cause phenotypic changes.
Balanced rearrangements influence gene order, potentially disrupting gene function, while not necessarily affecting gene dosage.

Specific Chromosome Rearrangements

Cri-du-chat syndrome: A deletion of the short arm of chromosome 5; characterized by a cat-like cry and other physical and mental disabilities.
Williams Syndrome: A translocation or deletion on chromosome 7 that results in a spectrum of developmental and physical abnormalities.
Prader-Willi Syndrome: A deletion on chromosome 15; affects growth, development, and metabolism.
Robertsonian Translocations: Involvement of acrocentric chromosomes and chromosome fusions resulting in large and small chromosomes; associated with genetic disorders.

Chromosome Rearrangements and Evolution

Chromosome number can differ significantly between closely related species because of chromosomal fusion events.
Inversions can play a role in speciation and adaptation.

Reciprocal Translocations

Reciprocal translocations occur when segments of two different chromosomes exchange positions with each other.
In reciprocal translocation heterozygotes, a portion of a chromosome is duplicated or deleted; in other words, there is an imbalance in gene location and dosage.
50% reduction in viable gametes or zygotes occurs in a translocation heterozygote, depending on the type of segregation. This is due to imbalanced chromosomal material.

Robertsonian Translocations

A type of translocation involving the fusion of two acrocentric chromosomes.
The fusion leads to a substantial reduction in the number of chromosomes.
Down syndrome is frequently associated with a Robertsonian translocation involving chromosomes 14 and 21.

Phenotypic Consequences

Chromosome number variations, gene dosage, and the number of copies of a gene can result in a variety of observable phenotypic traits. This is often due to gene imbalance.
Inversions can have no apparent phenotypic effect.
Several rearrangements result in abnormal development or conditions; for example, changes in gene expression or imbalanced chromosomal material can result in developmental disabilities and physical manifestations.

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Description

This quiz focuses on key concepts in plant genetics, particularly the characteristics and effects of polyploidy, aneuploidy, and various chromosomal compositions. Explore the implications of these genetic phenomena and their impact on plant and animal species. Test your knowledge on gamete formation and the various chromosomal conditions presented in the quiz.