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Propfase One

Prophase I is the first stage of meiosis I, and is characterized by the pairing of homologous chromosomes

and the exchange of genetic material between them

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Prophase I has five stages: 

leptotene:

where chromosomes begin to condense and become visible as thread-like structures. 

chromosomes can converge to one side of the nucleus, often near the centrosome

During this stage, individual chromosomes, each consisting of two sister chromatids, become visible as distinct strands

These bead-like structures along the chromosomes become apparent

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zygotene:

where homologous chromosomes pair up

where one chromosome is inherited from each parent. They have the same genes in the same order, but may have different versions of those genes (alleles)

alleles are:

An allele is a variant form of a gene. It represents one of the different versions of a gene at a specific location (locus) on a chromosome

locus is:

A locus is a precise location on the chromosome where a particular gene resides

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a process called synapsis

While the synaptonemal complex is present, crossing over (recombination)

recombination:

shuffling genes and creating new combinations, it introduces variation that can be acted upon by natural selection

between non-sister chromatids can occur at specific sites (chiasmata)

chiasmata:

These are the physical manifestations of crossing over, visualized as X-shaped structures where the homologous chromosomes are connected

the pachytene stage

characterized by fully synapsed homologous chromosomes

forming a tetrad:

a pair of homologous chromosomes that have replicated, resulting in four sister chromatids

Tetrads are then separated during anaphase I of meiosis, with one chromosome from each pair going to each daughter cell

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pachytene:

the two replicated chromosomes (sister chromatids)

of each homolog

pair up with their corresponding homolog

genes, proteins, or structures that share a common evolutionary origin, meaning they are descended from a feature present in a common ancestor

forming a bivalent structure called a tetrad

When the paired homologous chromosomes (bivalent) undergo further coiling and sister chromatids become distinct, they appear as a tetrad, which consists of four chromatids

 This pairing is facilitated by a protein structure called the synaptonemal complex

The SC helps regulate the number and distribution of crossovers between homologous chromosomes

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diplotene:

It's characterized by the separation of homologous chromosomes, except where crossing over has occurred

forming structures called chiasmata

Chiasmata are involved in signaling the bivalent (paired homologs) has attached to the spindle in a bipolar orientation, which is essential for proper segregation

During diplotene, the synaptonemal complex, which held the homologous chromosomes together, dissolves

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diakinesis:

Chromosomes reach their maximum coiling and shorten, making the four chromatids visible

The meiotic spindle begins to assemble

composed of microtubules, which are long, cylindrical structures

the spindle forms at opposite poles of the cell, and microtubules attach to the chromosomes

The chiasmata, which hold homologous chromosomes together, move towards the ends of the chromatids which are one half of a duplicated chromosome

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Homologous recombination: Homologous chromosomes exchange DNA through homologous recombination

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Crossing over: 

Non-sister chromatids of homologous chromosomes cross over at chiasmata

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Genetic variation: 

Prophase I increases genetic variation

Cell division: 

Prophase I leads to the formation of four daughter cells with half the number of chromosomes of the parent cell

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