Lecture 3 and 4- Chromosome structure and meiosis Flashcards Preview

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What is a chromosome?

The chromosome is a compontnet of the the cell that carry genetic information in the form of DNA


What does an eukaryotic chromosome contain?

An eukaryotic chromosome contains one single strand of DNA before replication and two identical strands of DNA after replication


What is a centromere?

The centromere is the region where the two sister chromatids are joined together


What are the two functions of the centromere?

The function of the centromere are: to holds the two sister chromatids together and they are the site of kinetochore formation


How can a chromosome be classified according to the position of its centromere?

1- Metacentric 2- Acrocentric 3- Telocentric


Describe metacentric chromosome:

A metacentric chromosome has the centromere located near the centre


Describe acrocentric chromosome:

An acrocentric chromosome has the centromere located toward one of the ends


Describe telocentric chromosome:

A telocentric chromosome has the centromere located right at one end of the chromosome


Describe the telomere:

The telomere is the region at the end of the chromosome and it contains the free ends of the chromosome


What are the two problems caused by the presence of free ends in the telomere?

1- The normal mechanism of DNA replication cannot extend all the way to the end of a linear chromosome. 2- The free ends of a chromosome looks like a broken DNA part.


What does telomerase do?

To avoid the shortening of the telomere, telomerase add simple DNA repeats to mantain its length.


Describe chromatin:

Chromatin is a specifica association of DNA and proteins that constitute a functional eukaryotic chromosome.


What are the three roles of chromatin?

1- packaging and protecting DNA 2- Dna replication 3- Facilitation of gene expression


What is a nucleosome:

A nucleosome is the basic subunit of chromatin and it's made up of 145 bp od DNA wrapped around a disc shaped octamer of histones.


What is chromatin condensation?

Chromatin condensation is a series of higher structures of chromatin that include topoisomerase.


What's topoisomerase:

Topoisomerase is an enzyme that participate in the condensation of the chromatin removing tension.


What's chromosome scaffold?

Chromosome scaffold is a seris of protein associated with the higher structure of chromatin.


What are the two states in which interphase chromatin can be found?

1-Euchromatin 2-Heterochromatin


Describe euchromatin:

Euchromatin is largely decondensed chromatin and potentially active in gene expression.


Describe heterochromatin:

Heterochromatin is highly condensed chromatin and it's inactive for gene expression. It's made of highly repetitive DNA sequences.


Describe sexual lifecycles:

Sexual lifecycle is a lifecycle that allows recombination by alternating an haploid phase to a diploid phase.


What's meiosis?

Meiosis is the division process that halves the number of chromosomes.


What are the two successive steps of meiosis?

Meiosis 1 and Meiosis 2


Describe meiosis 1:

Meiosis 1 is a reduction of the number of chromosome number (diploid to haploid)


Describe meiosis 2:

Meiosis 2 is an equational division that halves the number of chromatids per chromosomes (it's really similar to mitosis).


Describe early prophase 1:

-Chromatin condense -Chromosomes pair up with their homologues and are zipped together by the synaptonemal complex.


Describe mid prophase 1:

-Once pairing is completed, crossing over occurs. -Chromatids breaks and rejoin across the synaptonemal comples.


Describe late prophase:

-Synaptonemal comples breaks down -Homologues remain attached at points of crossover called chiasmata.


Describe metaphase 1:

The spinde microtubules align the homologus pairs at the central plate of the cell randomly with respect to one another.


What's independent assortment?

Indipendent assortment is the result of random allignment in metaphase 1. It's consequence is that it's a matter of chance which homolog goes to which daughter cell during anaphase 1.