Lecture 10: The consequence and application of chromosome number/structure variations

Question 1

Diagnose human diseases if there is a chromosome structure variation: BANDING
- What are the special staining techniques (4)
- Why Band them?

Answer 1

Human chromosomes can
be banded by special staining techniques.
a. G banding
b. Q banding
c. C banding
d. R banding

The examination of the banding patterns can identify chromosome mutations such as rearrangements, aneuploid and polyploid

Question 2

Explain Down Syndrome - trisomic 21.

Answer 2

Karyotypes of G-banded chromosomes reveal
Left – trisomic 21

example: familial down syndrome =monosomic 21 & translocation of 21 to 14.

Question 3

What is Fluorescence In Situ Hybridization (FISH):

Answer 3

FISH is a molecular cytogenetic technique that uses fluorescent probes to detect specific DNA sequences on chromosomes.

it can be used to identify structural changes, such as deletions, duplications, and translocations, by visualizing the location and arrangement of the probes on the chromosomes.

Question 4

Explain Polyploid Crops

• Allopolyploids are common in crops
• Polyploids exhibit GIGA effects
• Increased adaptability
• Significance in evolution

Answer 4

• Allopolyploids are commonly found in crop plants.
• Polyploidy leads to “GIGA effects” - increased vigor, larger size, and enhanced traits.
• Polyploid crops are more adaptable to harsh environments and demonstrate improved stress tolerance.
• Polyploidy plays a crucial role in the evolution and diversification of crop species.
• In the production of allopolyploids, two or more species contribute their genetic material to form a new polyploid organism.
• Bread wheat is an example of an allopolyploid crop.
• In bread wheat, the chromosome number is not a multiple of a single haploid set (n), but rather 6 times the haploid set (2n = 6x = 42).
• This means bread wheat is not 3n, 4n, or 6n, but rather a hexaploid (6x) with 42 chromosomes.

Question 5

ExplainMeiosis of Triploid Polyploids

• Triploid polyploids have three sets of chromosomes instead of the usual two.
• During meiosis in triploids, the pairing and segregation of chromosomes can be more complex.

Answer 5

Meiosis of Triploid Polyploids
MIEOSIS 1:
1. TWO Homologous chromosomes attempt to pair during prophase, WHILE the other segregates randomly.

2. In metaphase I, the unpaired chromosome will not align properly on the metaphase plate.
3. In anaphase I, unequal chromosome segregation occurs, leading to an unequal distribution of chromosomes into the daughter cells.
   - all 3 chromosomes pair and segregate randomly.
   - NONE OF THE CHROMOSOMES PAIR AND ALL 3 MOVE TO THE SAME CELL.
4. In metaphase II, the chromosomes may not align properly again, leading to further unequal chromosome segregation during anaphase II.
   - SOME OF THE RESULTING GAMETES HAVE EXTRA CHROMOSOMES AND SOME HAVE NONE
5. The final outcome is the production of gametes with different chromosomal compositions, including aneuploid gametes.
6. Aneuploid gametes have an abnormal number of chromosomes, which can have significant consequences for fertility and offspring viability in polyploid organisms.

DIFFERENT GAMETES FORMED - SEEDLESSNESS

Question 6

Applications of haploids in plants (3)

Answer 6

1. Rapid generation of pure lines without the need for 6+ generations of inbreeding - DH
   - Anther/microspore culture or wide crossing
   followed by colchicine treatment
2. Allows easy determination of recessive traits
3. Amphihaploids can be used to determine ancestrally related chromosomes (HOMEOLOGUES will pair at meiosis)

Question 7

Flow cytometry and flow karyotypes - what are their main characteristics? (3)

Answer 7

they are

1. Technology that measures properties of single cells or subcellular organelles such as chromosomes
2. Measures fluorescence, light scatter, and other properties of cells and particles
3. The whole wheat genome sequence is based on sorted chromosomes or chromosome arms

Question 8

How to make CHROMOSOME SOUP? (5)

Answer 8

1 * Grow the right plants

2 * Synchronise mitosis in root tips by chemical treatment

3 * Collect root tips and homogenise

4 * Filter and centrifuge to remove the rubbish.

5 * A pure chromosome soup

Question 9

What is a FLOW CYTOMETER?

Answer 9

A flow cytometer is a machine that can detect cells and sub-cellular organelles based on their size, shape and light emission intensity, etc. and subsequently sort them into different fractions

Question 10

How to Flow Karyotyping – wheat chromosomes

Answer 10

Specific chromosome is identified based on flow karyotype and sorted into a test tube
at a speed of about 1,000 per second.

Question 11

Karyotyping

• Definition: A technique for examining an individual’s chromosomes
• Purpose: To analyze the number, size, and structure of chromosomes
• Used in: Genetic diagnosis, prenatal screening, research studies

Answer 11

Karyotyping

• Involves: Staining and visualization of chromosomes from a cell sample
• Procedure: Cells are cultured, arrested in metaphase, and stained
• Analysis: Chromosomes are arranged in pairs according to size, banding patterns, and centromere position
• Abnormalities: Detects numerical or structural chromosomal abnormalities
• Applications: Genetic disorders, chromosomal syndromes, cancer genetics, reproductive issues

Question 12

Explain QTL Mapping:

Answer 12

• Used to study relationships of genes/traits
• Early linkage maps were based on morphological markers
• These are few in number in any given cross-making map construction tortuous

Question 13

Explain Linkage mapping: How hard can it be = HOW WAS IT USED PREVIOUSLY?

Answer 13

• The first ever genetic map was of fruit flies in 1913
• First maps of plant species were not produced until 1935 (maize and tomato) and were syntheses of dozens of experiments
• The first human genetic map was in 1980 with the advent of molecular markers

Question 14

Explain Molecular mapping – based on meiosis
How used? Specific Characteristics? = 5

Answer 14

• Molecular markers can be treated the same way as morphological markers
• DNA variations are much more plentiful
• They are also neutral in evolution
• They are often used together with morphological markers/traits – e.g. QTL mapping
• Now it is relatively easy to produce dense genetic maps

Question 15

Genetic Significance of Mitosis

• Definition: Cell division process in which one cell gives rise to two genetically identical daughter cells
• Key Functions: Growth, tissue repair, asexual reproduction

Answer 15

Genetic Significance of Mitosis

• Preservation of Genetic Information: Ensures each daughter cell receives an identical set of chromosomes as the parent cell
• Maintenance of Chromosome Number: Prevents changes in the chromosome number (ploidy) across generations
• Consistency of Genetic Material: Ensures stability and integrity of the genome throughout development and life
• Somatic Cell Production: Generates new somatic cells that contribute to the growth and maintenance of multicellular organisms
• Genetic Diversity: Provides the foundation for genetic diversity in populations through DNA replication and distribution to daughter cells

Question 16

How many different kinds of gametes can be produced in wheat (2n=6x=42) when no crossover happens through meiosis (21 pairs of chromosomes) and how many in reality (c10,000 genes)?

Answer 16

Gamete Production in Wheat (2n=6x=42)

No Crossover Occurs

• Theoretical Number of Gametes: 2^21 (2 to the power of 21) = 2,097,152 possible combinations
• Reality: Considering the vast number of genes in wheat (approximately 10,000 genes), the actual number of unique gametes would be significantly higher due to genetic recombination during crossover.