15-chromosomal mutations

Question 1

euploid vs aneuploid

Answer 1

Euploidy: Gain or loss of entire sets of chromosomes (e.g., haploid n, diploid 2n, triploid 3n).
Aneuploidy: Gain or loss of individual chromosomes, not entire sets (e.g., 2n+1 for trisomy or 2n-1 for monosomy).
Key Difference: Euploidy involves complete sets, while aneuploidy disrupts chromosome balance.

“eu dippers”= euploidy eg. diploid
“an=abnormal”=an in aneuploidy is for abnormal number in one set

Question 2

What is colchicine and how does it induce autopolyploidy? what is its use?

Answer 2

Colchicine: A chemical that inhibits microtubule polymerization, preventing spindle fiber formation during cell division.
Effect: Stops cell division at metaphase, preventing chromosome segregation in anaphase.
Outcome: Failure of cytokinesis leads to chromosome doubling (e.g., 2n → 4n), inducing polyploidy.

to create bigger cells to end up with larger fruit.

Question 3

polyploidy includes? what are the diff types and their differences?

Answer 3

Polyploidy (General Term):
=euploidy
Refers to any condition where an organism has more than two complete sets of chromosomes (e.g., 3n, 4n, etc.).
It includes both autopolyploidy and allopolyploidy.

Autopolyploidy (Specific Type):

Involves the duplication of chromosome sets within the same species.
cause=colchicine
All chromosome sets are identical (e.g., 4n in a species originally 2n).
Example: Seedless watermelons.

Allopolyploidy (Another Type):

Involves combining chromosome sets from different species through hybridization and chromosome doubling.These hybrids are often sterile because they have an unbalanced chromosome number.
Chromosome sets are not identical.
Example: Bread wheat (Triticum aestivum).

Question 4

diploid parents produce a diploid hybrid which is sterile. how can it become fertile?

Answer 4

by doubling via colchicine treatment, natural chromosome doubling (spontaneously) like errors in cytokineis or nondisjunction during mitosis or meiosis. or backcrossing; hypridxparent to get more chroms similar to the parent it crossed with. so this would be a tetraploid (4n=4copies of each unique chrom), thus diploid gametes.

Question 5

What is allopolyploidy?

Answer 5

Allopolyploidy is a type of polyploidy where chromosome sets come from two different species through hybridization and chromosome doubling, allowing the hybrid to become fertile.

Question 6

Why are hybrids sterile after crossing two species?

Answer 6

because chromosomes from different species are not homologous and cannot pair properly during meiosis.

Question 7

What happens to the chromosome numbers during allopolyploidy?

Answer 7

Each parent contributes n chromosomes (haploid number).
The hybrid has n (from parent A) + n (from parent B) chromosomes.
After doubling: The hybrid becomes 2n (from parent A) + 2n (from parent B).

Question 8

How does bread wheat (Triticum aestivum) illustrate allopolyploidy?

Answer 8

Bread wheat is an allopolyploid (6n).
It combines chromosome sets from three species, with spontaneous chromosome doubling allowing homologous pairing and fertility.

Question 9

cause of triploidy. is it sterile?

Answer 9

1. make a tetraploid (4n) using colchicine and cross it with a diploid (2n)
2. sterile because they have an uneven number of chromosomes, making it difficult for their chromosomes to pair up properly during meiosis, leading to problems in producing viable gametes.

Question 10

what are triploids used for

Answer 10

making seedless fruits like bananas and watermelons. due to triploids not making seeds/gametes

Question 11

rank these in order of most to least likely to survive 3n, 2n+1, 2n-1

Answer 11

*same order
gene balance (euploidy has balance) so 3n can survive normally it just is sterile (triploid), 2n+1 is where one pair has an extra chrom. monosmy is worse than trisomy cuz mono tends to unmask recessive alleles. trisomy can still be lethal but less than mono

Question 12

when can monosomy be viable? and what is the condition called

Answer 12

not viable with autosomes
viable with sex chrom

eg) turners syndrome-where a female has only one X chromosome

Question 13

What are some examples of trisomy and their associated conditions?

Answer 13

Trisomy 21 – Down Syndrome
Trisomy 13 – Patau Syndrome
Trisomy 18 – Edwards Syndrome

Trisomy can occur in sex chromosomes or autosomes, leading to developmental and health issues, but some individuals with trisomy can survive, depending on the chromosome involved.

*notice the smaller chroms are the ones that have viable trisomies bc they have fewer genes

Question 14

What causes aneuploidies and how do they occur?

Answer 14

Aneuploids are caused by nondisjunction, where homologous chromosomes (meiosis I) or sister chromatids (meiosis II) fail to separate properly during meiosis. This results in gametes with an abnormal number of chromosomes. When these gametes fuse during fertilization, the zygote ends up with an incorrect number of chromosomes, leading to conditions like Down syndrome (trisomy 21) or Turner syndrome (monosomy X).

Question 15

types of deletions?

Answer 15

Terminal Deletion: Loss of a portion at the end of the chromosome. (small peice from end it lost)
Intercalary Deletion: Loss of a portion within the chromosome (not at the ends). (middle peice lost and chrom shortens, still 1 chrom)
Remember: “Terminal” = end, “Intercalary” = in between!

Question 16

deletion example

Answer 16

cri du chat
-terminal deletion on chrom 5
-size of deletion potentialy affects extent of disorder
-chaeacteristic high pitched cry in infants

Question 17

What are the effects of chromosomal deletions?

Answer 17

Recessive alleles can become unmasked.
Reduced protein production due to loss of genes.
Altered gene regulation from mixing new promoters or regulatory regions.

Question 18

How can deletions alter gene regulation?

Answer 18

Deletions can disrupt gene regulation by removing regulatory regions like strong promoters or enhancers. This can:

Reduce or eliminate the expression of the deleted gene.
Cause neighboring genes (not the same gene’s allele) to come under the influence of a strong promoter or enhancer, leading to overexpression.
If only one allele is deleted, the remaining allele may not compensate, especially if it has a weaker promoter.

Question 19

How do duplications occur, and how are they related to deletions?

Answer 19

Duplications occur during unequal crossing over in meiosis when homologous chromosomes don’t align properly. This results in:

Duplication: One chromosome gains an extra copy of a segment.
Deletion: The other chromosome loses that segment (usually the smaller part).
Duplications and deletions are linked because they arise from the same misalignment event.

Question 20

How does unequal crossing over lead to duplications and deletions in chromosomes?

Answer 20

Unequal crossing over occurs when homologous chromosomes don’t align properly during meiosis, causing:

Duplication: One chromosome ends up with 3 copies of a gene (due to a segment being copied over).
Deletion: The other chromosome loses a segment, becoming shorter and missing a different gene (the part that was deleted).
This leads to an imbalance in gene copies and affects gene expression.

Question 21

What are the results of crossing over between a paracentric inverted chromosome and a normal chromosome?

Answer 21

Crossing over between a paracentric inverted chromosome and a normal chromosome can produce 4 gametes:

2 viable gametes:
One with a normal chromosome (no inversion).
One with an inverted chromosome (with the inversion sequence).
2 non-viable gametes:
Dicentric chromosome: A chromosome with two centromeres, which causes issues during segregation.
Acentric fragment: A chromosome fragment without a centromere, which is typically lost during cell division.
This results from the paracentric inversion forming a loop during synapsis and crossing over.

Question 22

What is a pericentric inversion and what are the results of crossing over between a pericentric inverted chromosome and a normal chromosome?

Answer 22

A pericentric inversion involves a chromosome segment that includes the centromere and is reversed in orientation.

Results of crossing over between a pericentric inverted chromosome and a normal chromosome:

Viable gametes:
One gamete with a normal chromosome.
One gamete with a chromosome having the inverted sequence.
Non-viable gametes:
Chromosomes with duplications and deletions resulting from the misalignment and crossing over in the inverted region.
These outcomes occur because the inversion involves the centromere, which leads to chromosome rearrangements that can create structural changes (duplications and deletions) in the gametes.

Question 23

What is Robertsonian translocation and how does it lead to Down syndrome?

Answer 23

Robertsonian translocation involves a fusion between the long arms of two chromosomes, usually chromosome 21 and chromosome 14, with the short arms lost and degraded.
A carrier of this translocation has a balanced chromosomal arrangement, meaning they have the correct amount of genetic material (just rearranged), so they typically do not show symptoms of Down syndrome.

During meiosis, the carrier produces 4 gametes:
2 gametes with normal chromosomes (one chromosome 14 and one chromosome 21).
2 gametes with the translocated chromosome (chromosome 14 with part of chromosome 21 and chromosome 21 missing the short arm).

If a normal gamete (with a full chromosome 21) fuses with a translocated gamete (containing part of chromosome 21 on chromosome 14), the result is trisomy 21, leading to Down syndrome. and monosomy if the other gamete with only chrom 14, the unaffected long one)