IB Biology Topic D2.1.10 Down Syndrome and Non-disjunction Revision Notes (SL/HL)

IB Biology Topic D2.1.10 Down Syndrome and Non-disjunction Revision Notes (SL/HL) | RevisionDojo

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Non-Disjunction: When Chromosomes Fail to Separate in Meiosis

Definition

Non-Disjunction

The failure of homologous chromosomes or sister chromatids to separate properly during meiosis.

Where Non-Disjunction Happens

Meiosis normally separates chromosomes so each gamete receives one copy of each chromosome.
Non-disjunction is the failure of chromosomes to separate properly during meiosis.
It produces gametes with one too many or one too few chromosomes.
This can happen at either of two separation steps in meiosis.
1. Anaphase I: a pair of homologous chromosomes fails to separate.
2. Anaphase II: a pair of sister chromatids fails to separate.

Trisomy 21: Non-Disjunction of Chromosome 21 Causes Down Syndrome

Down syndrome is a genetic condition caused by trisomy 21, having three copies of chromosome 21 instead of the usual two.
The extra chromosome comes from non-disjunction during meiosis in one parent's gamete.
At fertilisation, a gamete carrying two copies of chromosome 21 fuses with a normal gamete carrying one copy.
The resulting zygote has 47 chromosomes instead of the typical diploid number of 46.

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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.

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Non-Disjunction: When Chromosomes Fail to Separate in Meiosis

Definition

Non-Disjunction

The failure of homologous chromosomes or sister chromatids to separate properly during meiosis.

Where Non-Disjunction Happens

Meiosis normally separates chromosomes so each gamete receives one copy of each chromosome.
Non-disjunction is the failure of chromosomes to separate properly during meiosis.
It produces gametes with one too many or one too few chromosomes.
This can happen at either of two separation steps in meiosis.
1. Anaphase I: a pair of homologous chromosomes fails to separate.
2. Anaphase II: a pair of sister chromatids fails to separate.

Trisomy 21: Non-Disjunction of Chromosome 21 Causes Down Syndrome

Down syndrome is a genetic condition caused by trisomy 21, having three copies of chromosome 21 instead of the usual two.
The extra chromosome comes from non-disjunction during meiosis in one parent's gamete.
At fertilisation, a gamete carrying two copies of chromosome 21 fuses with a normal gamete carrying one copy.
The resulting zygote has 47 chromosomes instead of the typical diploid number of 46.

Definition

Paywall

(on a website) an arrangement whereby access is restricted to users who have paid to subscribe to the site.

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

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 D2.1.10: Down Syndrome and Non-disjunction Notes

A - Unity and Diversity9 subtopics

B - Form and Function10 subtopics

C - Interaction and Interdependence9 subtopics

D - Continuity and Change12 subtopics

Non-Disjunction: When Chromosomes Fail to Separate in Meiosis

Where Non-Disjunction Happens

Trisomy 21: Non-Disjunction of Chromosome 21 Causes Down Syndrome

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

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Non-Disjunction: When Chromosomes Fail to Separate in Meiosis

Where Non-Disjunction Happens

Trisomy 21: Non-Disjunction of Chromosome 21 Causes Down Syndrome

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