IB Biology Topic A3.1.13 Chromosome Number as a Shared Trait Within a Species Revision Notes (HL)

IB Biology Topic A3.1.13 Chromosome Number as a Shared Trait Within a Species Revision Notes (HL) | RevisionDojo

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Different Chromosome Numbers Prevent Meiosis and Create Hybrid Sterility

Chromosomes are the carriers of genetic information, organized in pairs in sexually reproducing organisms.
During reproduction:
1. Gametes (sperm and egg cells) are formed via meiosis, which reduces the chromosome number by half.
2. For meiosis to succeed, homologous chromosomes (matching pairs inherited from each parent) must align and segregate properly.
When two species with different chromosome numbers interbreed, their hybrid offspring may inherit an uneven chromosome set.

Example

A classic example is the mule, a hybrid between:
- Horses: 64 chromosomes.
- Donkeys: 62 chromosomes.
Mules inherit 63 chromosomes, which cannot form homologous pairs.
As a result:
- Meiosis fails.
- Functional gametes cannot form, rendering mules sterile.

Common Mistake

It’s a common misconception that all hybrids are sterile.
While this is often true, there are exceptions.
For example, some female ligers (lion × tiger hybrids) can produce offspring.

Plants Can Overcome Chromosome Mismatch Problems Through Polyploidy

Unlike animals, many plants can bypass these issues through polyploidy.

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Different Chromosome Numbers Prevent Meiosis and Create Hybrid Sterility

Chromosomes are the carriers of genetic information, organized in pairs in sexually reproducing organisms.
During reproduction:
1. Gametes (sperm and egg cells) are formed via meiosis, which reduces the chromosome number by half.
2. For meiosis to succeed, homologous chromosomes (matching pairs inherited from each parent) must align and segregate properly.
When two species with different chromosome numbers interbreed, their hybrid offspring may inherit an uneven chromosome set.

Example

A classic example is the mule, a hybrid between:
- Horses: 64 chromosomes.
- Donkeys: 62 chromosomes.
Mules inherit 63 chromosomes, which cannot form homologous pairs.
As a result:
- Meiosis fails.
- Functional gametes cannot form, rendering mules sterile.

Common Mistake

It’s a common misconception that all hybrids are sterile.
While this is often true, there are exceptions.
For example, some female ligers (lion × tiger hybrids) can produce offspring.

Plants Can Overcome Chromosome Mismatch Problems Through Polyploidy

Unlike animals, many plants can bypass these issues through polyploidy.

Definition

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Note

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam quis nostrud exercitation.

Excepteur sint occaecat cupidatat non proident

Tip

Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris.
Duis aute irure dolor in reprehenderit in voluptate velit esse cillum.

A - Unity and Diversity9 subtopics

B - Form and Function10 subtopics

C - Interaction and Interdependence9 subtopics

D - Continuity and Change12 subtopics

IB Biology Topic A3.1.13: Chromosome Number as a Shared Trait Within a Species Notes

A - Unity and Diversity9 subtopics

B - Form and Function10 subtopics

C - Interaction and Interdependence9 subtopics

D - Continuity and Change12 subtopics

Different Chromosome Numbers Prevent Meiosis and Create Hybrid Sterility

Plants Can Overcome Chromosome Mismatch Problems Through Polyploidy

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Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

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Different Chromosome Numbers Prevent Meiosis and Create Hybrid Sterility

Plants Can Overcome Chromosome Mismatch Problems Through Polyploidy

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account