Lecture 3 and 4- Chromosome structure and meiosis

Question 1

What is a chromosome?

Answer 1

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

Question 2

What does an eukaryotic chromosome contain?

Answer 2

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

Question 3

What is a centromere?

Answer 3

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

Question 4

What are the two functions of the centromere?

Answer 4

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

Question 5

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

Answer 5

1- Metacentric 2- Acrocentric 3- Telocentric

Question 6

Describe metacentric chromosome:

Answer 6

A metacentric chromosome has the centromere located near the centre

Question 7

Describe acrocentric chromosome:

Answer 7

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

Question 8

Describe telocentric chromosome:

Answer 8

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

Question 9

Describe the telomere:

Answer 9

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

Question 10

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

Answer 10

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.

Question 11

What does telomerase do?

Answer 11

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

Question 12

Describe chromatin:

Answer 12

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

Question 13

What are the three roles of chromatin?

Answer 13

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

Question 14

What is a nucleosome:

Answer 14

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.

Question 15

What is chromatin condensation?

Answer 15

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

Question 16

What’s topoisomerase:

Answer 16

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

Question 17

What’s chromosome scaffold?

Answer 17

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

Question 18

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

Answer 18

1-Euchromatin 2-Heterochromatin

Question 19

Describe euchromatin:

Answer 19

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

Question 20

Describe heterochromatin:

Answer 20

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

Question 21

Describe sexual lifecycles:

Answer 21

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

Question 22

What’s meiosis?

Answer 22

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

Question 23

What are the two successive steps of meiosis?

Answer 23

Meiosis 1 and Meiosis 2

Question 24

Describe meiosis 1:

Answer 24

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

Question 25

Describe meiosis 2:

Answer 25

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

Question 26

Describe early prophase 1:

Answer 26

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

Question 27

Describe mid prophase 1:

Answer 27

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

Question 28

Describe late prophase:

Answer 28

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

Question 29

Describe metaphase 1:

Answer 29

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

Question 30

What’s independent assortment?

Answer 30

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.

Question 31

Describe anaphase 1:

Answer 31

-The spinde microtubules pull the homologues pairs apart. -Chiasmata resolve towards the end of the chromosomes. -The result of crossing over is reciprocal exchange between homologues.

Question 32

Describe telophase 1:

Answer 32

At the end of the first meiotic round the original diploid nucleus produced two haploid nuclei (two cells are formed)

Question 33

Describe metaphase 2:

Answer 33

The spindle microtubules align all the chromosome at the central plate of the cell.

Question 34

Describe anaphase 2:

Answer 34

The sister chromatids are segregated and if crossing over has occured they’re not identical to each other.

Question 35

Describe telophase 2:

Answer 35

-The final result of meiosis are 4 haploid cell that are genetically different. -The nuclear envelope reform around the nuclei and chromosome decondense.