25 Questions
What is the primary difference between polyploid cells and diploid cells?
Polyploid cells have a longer G1 phase and grow to a larger size
Which type of polyploidy involves genetic doubling of AB to produce AABB gametes?
Allopolyploidy
What is a common consequence of structural changes in chromosomes due to breaks and rearrangements?
Loss of chromosomal information
In the context of variations in chromosome composition, what process involves the total amount of genetic information changing?
Duplications
What is characteristic of allopolyploids when they are known species and result in AABB gametes?
They are considered amphidiploids
What is the primary cause of death in older individuals with Down syndrome?
Alzheimer's disease
What is the term for variations in chromosome number where an organism gains or loses one or more chromosomes and does not have an exact multiple of the haploid set?
Aneuploidy
Which stage of meiosis is primarily responsible for the majority of cases of Down syndrome?
Meiosis I in females
Which process disrupts the normal distribution of chromosomes into gametes during meiosis I or II, potentially leading to trisomy or monosomy?
Nondisjunction
What is the term for the condition where more than two sets of chromosomes are present in an organism?
Polyploidy
How does an extra copy of the DSCR1 gene affect cancer risk in individuals with Down syndrome?
Decreases cancer risk
What type of chromosomal variation can result in zygotes with three members (trisomy) or only one member (monosomy) of a particular chromosome?
Nondisjunction
Why is genetic counseling recommended for women who become pregnant late in their reproductive years?
To assess potential risks and outcomes for the fetus
What is the term for the loss of one chromosome (2n – 1) that may have severe phenotypic effects?
Monosomy
What is the effect of increased maternal age on the incidence of Down syndrome?
Increases incidence
Which term describes the phenomenon when a chromosome breaks in one or more places and a portion of it is lost?
Deletion
How can deletions occur on a chromosome?
By terminal or intercalary deletion
What happens when a chromosome undergoes duplication?
Unequal crossing over during meiosis
Why are the ends produced by chromosomal breakages referred to as 'sticky'?
To facilitate rejoining with other broken ends
In the context of chromosomal alterations, what is a notable feature of deletions that affect gametes?
They are heritable
What is the main difference between a paracentric inversion and a pericentric inversion?
Paracentric inversion involves the centromere, while pericentric inversion does not.
How does an inversion differ from a loss of genetic information?
An inversion involves rearrangement of gene sequence, while loss of genetic information results in gene deletion.
What is a common feature of organisms known as inversion heterozygotes?
They have one inverted and one noninverted chromosome.
How is an inversion different from gene duplication?
Inversions rearrange a segment of a chromosome, while gene duplication creates additional copies of a gene.
What process may lead to the formation of an inversion?
Chromosomal looping
Study Notes
Chromosome Mutations: Variations in Chromosome Number and Arrangement
- Chromosomal mutations or aberrations can result in variations in chromosome number or arrangement, leading to phenotypic changes or even lethality.
Changes in Chromosome Number
- Aneuploidy occurs when an organism gains or loses one or more chromosomes, resulting in an abnormal number of chromosomes.
- Euploidy occurs when an organism has complete sets of chromosomes.
- Polyploidy occurs when an organism has more than two sets of chromosomes.
Chromosomal Disjunction
- Nondisjunction occurs when chromosomes or chromatids fail to separate during meiosis I or II, leading to abnormal gametes.
- Fertilization of abnormal gametes with normal gametes can result in zygotes with an abnormal number of chromosomes (e.g. trisomy or monosomy).
Monosomy
- Monosomy occurs when one chromosome is lost, resulting in severe phenotypic effects.
- Breakages can occur spontaneously or as a result of exposure to chemicals or radiation.
Deletion
- A deletion occurs when a portion of a chromosome is lost, resulting in a missing piece of genetic material.
- Deletions can occur near the end (terminal deletion) or within the interior (intercalary deletion) of a chromosome.
Duplication
- Duplications arise from unequal crossing over or replication errors, resulting in gene redundancy and potential phenotypic variation.
- Duplications have been linked to an increased incidence of leukemia and Alzheimer's disease.
Trisomy 21 (Down Syndrome)
- Trisomy 21 occurs when an individual has an extra copy of chromosome 21, resulting in Down syndrome.
- The Down syndrome critical region (DSCR) on chromosome 21 is responsible for many of the phenotypes associated with the condition.
- Trisomy 21 most frequently occurs due to nondisjunction of chromosome 21 during anaphase I or II, with 95% of cases occurring in the egg.
Allopolyploidy
- Allopolyploidy arises from the hybridization of two closely related species, resulting in homeologous (partly homologous) chromosome sets.
- Genetic doubling can result in fertile allotetraploids (AABB) with AB gametes.
Variations in Chromosome Structure
- Chromosomal structure can be altered through deletions, duplications, inversions, and translocations.
- Breaks along the chromosomal axis can result in loss or rearrangement of genetic material.
Inversions
- Inversions involve a rearrangement of the linear gene sequence, resulting in a changed order of genes.
- Inversions can arise from chromosomal looping and require two breaks in the chromosome with subsequent reinsertion of the inverted segment.
- Inversions can be paracentric (not including the centromere) or pericentric (including the centromere).
- Organisms with one inverted chromosome and one noninverted chromosome are called inversion heterozygotes.
Explore the variations in chromosome number and arrangement, as well as the concept of chromosomal mutations such as changes in total number of chromosomes, gene deletions or duplications, and rearrangements of genetic material. Test your knowledge on this topic.
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