What if human gametes were diploid

Possible Answers: Four times as many 4n. Correct answer: Twice as many 2n. Explanation : Diploid cells contain two copies of each chromosome, therefore containing twice as many 2n chromosomes as a haploid cell n , which contain only one copy of each chromosome. Example Question 36 : Understanding Meiosis. What is the cell division error that causes trisomy 21, or Down syndrome?

Possible Answers: Nondisjunction. Correct answer: Nondisjunction. Explanation : Trisomy 21, or Down syndrome results when a human individual inherits three copies of chromosome 21, instead of the normal two copies one maternal and one paternal. Example Question 37 : Understanding Meiosis. Which molecular mechanism is not a possible cause of nondisjunction? Possible Answers: Maternal gametes have a higher chance of exhibiting nondisjunction. Older age of an individual leads to weaker cohesin complexes at the centromere.

Failure to pass the spindle assembly checkpoint. Correct answer: Error in cytoplasmic partitioning. Explanation : Nondisjunction is the improper segregation of chromosomes during meiosis or mitosis. Example Question 38 : Understanding Meiosis. Which of the following organisms do not perform meiosis? Possible Answers: Mammals. Correct answer: Bacteria. Explanation : Meiosis is a process that produces gametes in sexual reproduction. Example Question 39 : Understanding Meiosis.

What enzyme aids in chromosomal crossing over during prophase I of meiosis? Possible Answers: Recombinase. Correct answer: Recombinase. Explanation : During crossing over in prophase I of meiosis, there is a physical exchange of genetic material between homologous chromosomes.

Example Question 40 : Understanding Meiosis. Possible Answers: Holliday junction. Correct answer: Holliday junction. Explanation : During prophase I of meiosis, homologous chromosomes exchange genetic material in a process called crossing over. Copyright Notice. The continuity of life from one cell to another has its foundation in the reproduction of cells by way of the cell cycle. The cell cycle is an orderly sequence of events in the life of a cell from the division of a single parent cell to produce two new daughter cells, to the subsequent division of those daughter cells.

The mechanisms involved in the cell cycle are highly conserved across eukaryotes. Organisms as diverse as protists, plants, and animals employ similar steps. In prokaryotes , the genome is composed of a single, double-stranded DNA molecule in the form of a loop or circle. The region in the cell containing this genetic material is called a nucleoid. Some prokaryotes also have smaller loops of DNA called plasmids that are not essential for normal growth.

In eukaryotes , the genome comprises several double-stranded, linear DNA molecules Figure 6. Nature Methods 4, All rights reserved. Aberrations That Alter Chromosome Number. Figure 3: Nondisjunction results in daughter cells with unusual chromosome numbers. Nondisjunction, in which chromosomes fail to separate equally, can occur in meiosis I first row , meiosis II second row , and mitosis third row.

These unequal separations can produce daughter cells with unexpected chromosome numbers, called aneuploids. When a haploid gamete does not receive a chromosome during meiosis as a result of nondisjunction, it combines with another gamete to form a monosomic zygote.

When a gamete receives a complete homologous chromosome pair as a result of nondisjunction, it combines with another gamete to form a trisomic zygote. Genetics: A Conceptual Approach , 2nd ed. Figure 4: Jimsonweed seed pod shapes. Trisomy in any of Jimsonweed's 12 chromosomes will cause seed pods to deviate from a wild-type, spherical shape.

References and Recommended Reading Belling, J. Genetics: A Conceptual Approach W. Freeman, New York, Article History Close. Share Cancel. Revoke Cancel. Keywords Keywords for this Article. Save Cancel. Flag Inappropriate The Content is: Objectionable. Flag Content Cancel. Email your Friend. Submit Cancel. This content is currently under construction.

Explore This Subject. Gene Linkage. The Foundation of Inheritance Studies. Methods for Studying Inheritance Patterns. Variation in Gene Expression. Topic rooms within Gene Inheritance and Transmission Close. No topic rooms are there. Or Browse Visually. Other Topic Rooms Genetics. Student Voices. Creature Cast. Simply Science. Green Screen. Green Science. Bio 2. The Success Code. Why Science Matters. The Beyond. It separates the chromatids so that there are now four haploid daughter cells having one copy of each of the 23 human chromosomes.

These are gametes eggs and sperm. The reduction division accompished by meiosis is necessary for sexual reproduction. Most cells, and animal cells in particular, are very sensitive to having extra copies or extra sets of chromosomes.

For example, having 3 of Chromosome 21 a very small one with relatively few genes instead of the normal 2 leads to Down's syndrome. Having an extra Chromosome 1 or 8 or a whole extra set of chromsomes triploid or lacking one or more chromosomes is nearly always deleterious to cells, especially animal cells.

During sexual reproduction, two cells from two different individuals fuse to produce a new, genetically unique individual.

If these two cells were diploid, the resulting zygote would not survive on a consistent basis because it would have four sets of chromosomes.