Variation from Meiosis

0.0(0)
studied byStudied by 0 people
GameKnowt Play
learnLearn
examPractice Test
spaced repetitionSpaced Repetition
heart puzzleMatch
flashcardsFlashcards
Card Sorting

1/7

encourage image

There's no tags or description

Looks like no tags are added yet.

Study Analytics
Name
Mastery
Learn
Test
Matching
Spaced

No study sessions yet.

8 Terms

1
New cards

Variation

Produced during meiosis, it is important for the daughter cells (and potentially offspring) to differ genetically.

2
New cards

Variation causes

  • Crossing over

  • Independent assortment

  • Non-disjunction

3
New cards

Crossing over

  • Occurs = During prophase 1.

  • Homologous chromosomes form tetrads consisting of 4 chromatids.

  • Can occur between non-sister chromatids.

  • Part of the chromatid breaks off and reattaches to the non-sister chromatid.

  • Chromosomes passed onto offspring are not identical to the parents.

4
New cards

Chiasma

The point where two chromatids cross during crossing over.

<p>The point where two chromatids cross during crossing over.</p>
5
New cards

Recombination

After crossing over - occurs as there is a new combination of alleles on the chromosomes.

<p>After crossing over - occurs as there is a new combination of alleles on the chromosomes.</p>
6
New cards

Independent assortment

  • Occurs = During metaphase 1.

  • Tetrads can align at the equator of the cell in a number of different combinations. The maternal and paternal homologous chromosomes can be on the left or the right of each other.

  • Number of possible combinations can be calculated by 2n (where n = haploid number of chromosomes) → 223 = 8.4 million.

  • Process is random and the way one chromosome pair separates is independent of how all the other pairs of chromosomes separate.

  • The zygote produced from fertilisation contains a set of genes arranged in an order that has never occurred before and will probably never occur again.

<ul><li><p>Occurs = During metaphase 1.</p></li><li><p>Tetrads can align at the equator of the cell in a number of different combinations. The maternal and paternal homologous chromosomes can be on the left or the right of each other.</p></li><li><p>Number of possible combinations can be calculated by 2<sup>n</sup> (where n = haploid number of chromosomes) → 2<sup>23</sup> = 8.4 million.</p></li><li><p>Process is random and the way one chromosome pair separates is independent of how all the other pairs of chromosomes separate.</p></li><li><p>The zygote produced from fertilisation contains a set of genes arranged in an order that has never occurred before and will probably never occur again. </p></li></ul><p></p>
7
New cards

Non-Disjunction

  • Occurs = During anaphase 1 and anaphase 2

  • Sometimes homologous chromosomes do not pull apart during anaphase 1. Both homologous chromosomes are pulled to the same pole of the cell.

  • Alternatively, sister chromatids may not pull apart in anaphase 2. Both sister chromatids are pulled to the same pole of the cell.

  • Non-disjunction results in gametes that have an abnormal number of chromosomes.

    • one has an extra chromosome (24 in humans)

    • The other is missing one (22 in humans)

8
New cards

Non-disjunction results

  • After fertilisation with a normal gamete of the opposite sex, the zygote will have either 45 or 47 chromosomes.

  • Often causes miscarriage or birth defects.

  • Trisomy = occurs when an individual inherits an extra copy of a chromosome:

    • Trisomy-21 occurs quite frequently (Down Syndrome)

    • Trisomy-13 (Patau syndrome)

    • Trisomy-18 (Edwards Syndrome)

  • Monosomy = occurs when an individual is missing a chromosome.

  • Partial monosomy/trisomy = chromosome is missing a part/has an extra part.

Explore top notes

Explore top flashcards