



Study with the several resources on Docsity
Earn points by helping other students or get them with a premium plan
Prepare for your exams
Study with the several resources on Docsity
Earn points to download
Earn points by helping other students or get them with a premium plan
Community
Ask the community for help and clear up your study doubts
Discover the best universities in your country according to Docsity users
Free resources
Download our free guides on studying techniques, anxiety management strategies, and thesis advice from Docsity tutors
An in-depth exploration of meiosis, a type of cell division used by eukaryotic cells to produce haploid cells. It covers the stages of meiosis, the processes of independent assortment and crossing over, and the importance of meiosis in transmitting genetic information during eukaryotic life cycles.
Typology: Summaries
1 / 6
This page cannot be seen from the preview
Don't miss anything!
1
Meiosis and Sexual Life Cycles In this topic we will examine a second type of cell division used by eukaryotic cells: meiosis. In addition, we will see how the 2 types of eukaryotic cell division, mitosis and meiosis, are involved in transmitting genetic information from one generation to the next during eukaryotic life cycles. (^2)
Objective # 1
3
Objective 1
Only diploid cells can divide by meiosis.
We will examine the stages of meiosis in a diploid cell where 2N = 6
Meiosis involves 2 consecutive cell divisions. Since the DNA is duplicated only prior to the first division, the final result is 4 haploid cells:
4
Objective 1
DNA duplication during interphase
Meiosis I
Meiosis II
Overview of meiosis in a cell where 2N = 6
After meiosis I the cells are haploid.
Objective 1, Stages of Meiosis Prophase I: ¾ Chromosomes condense. Because of replication during interphase, each chromosome consists of 2 sister chromatids joined by a centromere. ¾ Synapsis – the 2 members of each homologous pair of chromosomes line up side-by-side to form a tetrad consisting of 4 chromatids: (^6)
Objective 1, Stages of Meiosis
7
Objective 1, Stages of Meiosis Prophase I: ¾ During synapsis, sometimes there is an exchange of homologous parts between non-sister chromatids. This exchange is called crossing over.
8
Objective 1, Stages of Meiosis
9
Objective 1, Stages of Meiosis Prophase I: ¾ the spindle apparatus begins to form. ¾ the nuclear membrane breaks down:
10
Objective 1, Stages of Meiosis (2N=6)
Prophase I
11
Objective 1, Stages of Meiosis
Metaphase I:
¾ chromosomes line up along the equatorial plate in pairs, i.e. homologous chromosomes remain paired.
¾ spindle microtubules attach to the kinetochores on each centromere
¾ orientation of each pair of chromosomes is random and independent of the other pairs (independent assortment): 12
Objective 1, 4 Possible Metaphase I Arrangements:
Metaphase I
*We will follow this arrangement
19
Objective 1, Stages of Meiosis
Metaphase II:
¾ chromosomes line up along the equatorial plate
¾ spindle microtubules attach to the kinetochores on each centromere:
20
Objective 1, Stages of Meiosis (2N=6)
Metaphase II
21
Objective 1 Stages of Meiosis
Anaphase II:
¾ centromeres split and each former chromosome becomes 2 separate chromosomes
¾ spindle microtubules contract pulling the 2 members of each pair of chromosomes (that were formerly sister chromatids) to opposite poles of the cell: (^22)
Objective 1, Stages of Meiosis (2N=6)
Anaphase II
23
Objective 1, Stages of Meiosis
Telophase II:
¾ nuclear envelope reforms around the 4 sets of daughter chromosomes
¾ chromosomes uncoil
¾ cytokinesis divides the 2 daughter cells into 4, genetically unique, haploid cells:
24
Objective 1, Stages of Meiosis (2N=6)
Telophase II
25
Objective # 2
26
Objective 2 Independent assortment and crossing over increase genetic variability among the daughter cells produced during meiosis. If there are n pairs of chromosomes in the original cell, independent assortment produces 2n^ possible chromosome combinations in the daughter cells:
27
Objective 2
28
Objective 2 In addition, because of crossing over, each chromosome involved in meiosis winds up with a different combination of genes. Therefore, an almost limitless number of gene combinations are possible in the daughter cells produced during meiosis:
Objective 2
With just 1 crossover, the number of possible gene combinations increases from 8 to 16!
Objective # 3
Compare mitosis with meiosis and explain the importance of each.