Genetics: Polyploidy and Ploidy Levels

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Questions and Answers

What type of cells are referred to as haploid in humans?

Liver cells

Skin cells

Sperm and eggs (correct)

Body cells

Which of the following best describes euploidy?

An individual with mixed sets of chromosomes

An individual with one or more whole sets of chromosomes (correct)

An individual with no complete sets of chromosomes

An individual with more than two sets of chromosomes

Which statement correctly distinguishes haploid from diploid cells?

Diploid cells have pairs of chromosomes, while haploid has a single set. (correct)

Haploid cells have pairs of chromosomes, while diploid has a single set.

Diploid cells have one copy of each chromosome, while haploid has two.

Haploid cells contain more chromosomes than diploid cells.

What term describes an organism with more than two complete sets of chromosomes?

Polyploid Signup and view all the answers

Which scenario exemplifies allopolyploidy?

A hybrid plant arises from two different species. Signup and view all the answers

How many chromosomes do diploid cells have in humans?

46 pairs of chromosomes Signup and view all the answers

What does the term 'autopolyploidy' refer to?

Doubling of the same chromosome set within a species Signup and view all the answers

Why is an organism created through the hybridization of a diploid and haploid genome typically sterile?

It lacks the required number of chromosomes to reproduce. Signup and view all the answers

What term is used to describe an allopolyploid that results from chromosome doubling in a sterile hybrid derived from hybridization between two unrelated diploid species?

Amphidiploid Signup and view all the answers

How does autopolyploidy differ from allopolyploidy in terms of chromosome sets?

Autopolyploids contain homologous chromosome sets. Signup and view all the answers

What is primarily responsible for the formation of autopolyploids?

Nondisjunction of chromosomes. Signup and view all the answers

Which of the following crops is an example of an allopolyploid?

Wheat Signup and view all the answers

In which type of polyploidy are the chromosome complements derived from two different species?

Allopolyploidy Signup and view all the answers

Which statement about the meiosis of autopolyploids is true?

Autopolyploids do not undergo meiosis. Signup and view all the answers

What type of polyploidy results from the fusion of gametes from different species?

Allopolyploidy Signup and view all the answers

Which of the following examples is primarily seen in organisms with allopolyploidy?

Mule Signup and view all the answers

What is a characteristic feature of allopolyploids?

Recessive characters may appear less frequent Signup and view all the answers

How can allopolyploids facilitate gene transfer?

Facilitating the transfer of genes from related species Signup and view all the answers

What is the chromosomal structure of a Raphanobrassica plant?

2n + 2n = 18 + 18 = 4n = 36 Signup and view all the answers

What role does colchicine play in polyploidy induction?

Prevents spindle migration of daughter chromosomes Signup and view all the answers

What benefit does allopolyploidy provide in crop improvement?

Creation of new crop species Signup and view all the answers

What is the result of the natural induction process of polyploidy?

Unreduced gametes Signup and view all the answers

What describes a bridging cross in allopolyploidy?

Using amphidiploids to enable crosses between sterile species Signup and view all the answers

What is a distinguishing feature of autopolyploids compared to allopolyploids?

Autopolyploids arise from a single species Signup and view all the answers

What is the primary effect of colchicine on chromosomal division?

It dissolves spindle fibers. Signup and view all the answers

Which type of aneuploidy involves having one missing chromosome?

Monosomy Signup and view all the answers

What distinguishes polyploidy from aneuploidy?

Aneuploidy involves the addition or loss of individual chromosomes. Signup and view all the answers

Which type of polyploidy is defined as the multiplication of the same genome?

Autopolyploidy Signup and view all the answers

Which of the following is a common outcome of increased polyploidy in plants?

Increased seed size Signup and view all the answers

Which term refers to two copies each of two distinct genomes?

Allotetraploidy Signup and view all the answers

Which aneuploid condition results in two extra chromosomes?

Tetrasomy Signup and view all the answers

How does the presence of an odd ploidy level affect fertility?

It generally reduces fertility. Signup and view all the answers

Study Notes

Polyploidy

Polyploidy is a condition where an organism possesses more than two complete sets of chromosomes.
Polyploidy can be classified as autopolyploidy or allopolyploidy.
Autopolyploidy occurs within the same species where the genome is duplicated.
Allopolyploidy arises from hybridization between two different species, combining their genomes.

Ploidy Levels

Haploid (1N): Cells with one set of chromosomes. For example, human sex cells (sperm and eggs) are haploid with 23 chromosomes.
Diploid (2N): Cells with two sets of chromosomes. For example, human body cells are diploid with 46 chromosomes.

Differences Between Diploid and Haploid

Diploid cells: possess two copies of each chromosome, one from each parent, forming homologous pairs.
Haploid cells: possess only one copy of each chromosome.

Visual Representation of Ploidy

A haploid cell contains one pair of chromosomes.
A diploid cell contains two pairs of chromosomes.
A polyploid cell contains more than two pairs of chromosomes.

Types of Polyploids

Euploidy: Organisms with one or more complete sets of chromosomes, where each chromosome is represented once within each set.
- Haploidy: Organisms with half the number of chromosomes in somatic cells.
- Diploidy: Organisms with two complete sets of chromosomes.
- Polyploidy: Organisms with more than two complete sets of chromosomes.
Autopolyploidy: Derived from a single species through genome duplication, often resulting in larger varieties.
Allopolyploidy: Arises from hybridization between different species, often resulting in larger varieties.
- Amphiploidy: A fertile allopolyploid resulting from chromosome doubling in a sterile hybrid.
- Amphipolyploidy: Derived from hybridization between two polyploid species.

Autopolyploidy

Involves multiple copies of the same genome's chromosomes.
Can occur due to meiotic errors or self-fertilization, leading to viable but polyploid offspring.

Allopolyploidy

Combines genomes from different species.
Can arise when one species experiences meiotic errors, producing a gamete with the full diploid number (2n) instead of the haploid number (n), while the other species produces a normal gamete.

Autopolyploidy vs Allopolyploidy

Origin: Autopolyploidy originates within a single species, while allopolyploidy arises from hybridization between different species.
Chromosome sets: Autopolyploidy involves multiple copies of homologous chromosomes, while allopolyploidy contains chromosome sets from different species, which are not homologous.
Examples: Autopolyploidy is observed in crops like wheat, oats, sugarcane, potato, peanuts, bananas, and coffee. Allopolyploidy is found in crops like wheat and animals like mules.

Characteristics of Allopolyploids

Larger cells.
Vigorous growth.
Simpler genetic structure compared to autopolyploids.
Recessive traits may be less frequent.

Allopolyploids in Plant Breeding

Used to identify the genetic origin of plant species.
Facilitate the creation of new plant genotypes and species.
Enable the transfer of genes from related species.
Allow the transfer of individual chromosomes or pairs of chromosomes.

Example of Allopolyploid Hybridization: Rabbage

Parents: Raphanus (2n=18) and Brassica (2n=18).
Sterile F1 hybrid: Combines chromosomes from both parents, but sterility arises due to mismatched chromosomes (2n=18).
Raphanobrassica (Rabbage): A fertile amphidiploid resulting from chromosome doubling in the sterile F1 hybrid, forming a tetraploid (4n=36).

Formation of Fertile Tetraploid Rabbage

Steps: Chromosome doubling occurs in the sterile F1 hybrid, resulting in two sets of each parent's chromosomes, leading to chromosome pairing and fertility.

Application of Allopolyploidy in Crop Improvement

Bridging Crosses: Amphidiploids serve as bridges for gene transfer between species that are otherwise incompatible due to sterility.
Creation of New Crop Species: Examples include Triticale, Raphanobrassica, triploid (AAC), and tetraploids.
Interspecific Gene Transfer: Introduces desirable traits from related species into a specific crop.
Tracing Crop Origins: Alloploidy analysis helps determine the origin of natural polyploid crop species.

Induction of Ploidy

Natural Induction: Arise through: -Unreduced gametes: Meiosis fails to reduce chromosome number, resulting in gametes with a diploid number of chromosomes. -Natural wide crossing followed by chromosome doubling: Hybridization between different species followed by genome duplication.
Artificial Induction:
- Environmental shock: Exposure to extreme temperatures or chemical treatments.
- Chemicals:
  - Colchicine: A drug extracted from the Colchicum autumnale plant.
  - Mechanism: Disrupts the spindle apparatus, preventing chromosome segregation during cell division, leading to chromosome doubling.
  - Application: Applied to meristematic tissues (budding, seed germination, or root).

Effect of Polyploidy

Increased fruit weight, fruit size, seed size, crop load, flower size.
Reduced fertility in organisms with odd ploidy levels.
Alterations in growth patterns.
Provides opportunities for creating higher diversity in crops and organisms.

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Description

Explore the fascinating concepts of polyploidy and ploidy levels in genetics. This quiz covers topics such as autopolyploidy, allopolyploidy, and the distinctions between haploid and diploid cells. Test your understanding of these fundamental biological principles.