Meiosis And Chromosomal Aberrations

Question 1

What is meiosis

Answer 1

Special type of cell division resulting in formation of gametes whose chromosome number has been reduced from diploid to haploid

Question 2

What are the 2 crucial results of meiosis

Answer 2

▪️Reduction in number of chromosomes from diploid to haploid (for dna and chromosomes)
▪️Recombination of genes ensuring genetic variability and diversity of gene pool

Question 3

Describe meiosis 1

Answer 3

Reduction division
Homologous pairs of chromosomes line up and members of each pair separate and go to opposite poles and the cell divides
So each cell has half the number of chromosomes

Question 4

Describe meiosis two

Answer 4

▪️Equilateral division
▪️the 2 chromatids of each chromosome are separated as in mitosis followed by migration of the chromatids to opposite poles and the formation of two daughter cells
▪️four cells are produced each with the haploid number of chromosomes and haploid DNA content

Question 5

What happens in S phase

Answer 5

The amount of DNA is doubled to 4n but the chromosome number remains at 2n

Question 6

Describe prophase one

Answer 6

▪️homologous pairs of chromosomes approximate each other and condense ▪️chiasmata formation

Question 7

Describe metaphase one

Answer 7

Homologous pairs of chromosomes line up at the equilateral plate of the meiotic spindle

Question 8

Describe anaphase one

Answer 8

Homologous chromosomes migrate away from each other going to opposite poles

Question 9

Describe telophase one

Answer 9

▪️Cytokinesis occurs
▪️Two daughter cells are produced
▪️DNA content is still diploid but chromosome number is haploid

Question 10

Why is DNA number still diploid after telophase one

Answer 10

Because each chromosome possesses two chromatids

Question 11

What is the outcome of meiosis two

Answer 11

▪️Four daughter cells
▪️Haploid DNA and chromosome number
▪️Cells are genetically distinct due to the reshuffling and crossing over

Question 12

What is euploidy

Answer 12

The normal number of chromosomes for a species

Question 13

What are the types of numerical chromosomal abnormalities

Answer 13

Polyploidy 
a)triploidy  b)tetraploidy 
Aneuploidy
a)non disjunction b)anaphase lag
Trisomy 
Monosomy 
Mixoploidy

Question 14

Define polyploidy

Answer 14

A condition in which the chromosome number is a simple multiple of a haploid chromosome set

Question 15

What are the two types of polyploidy and define them

Answer 15

Triploidy :69 chromosomes with XXX or XXY or XYY
there are three copies for each chromosome
caused by the failure of reduction division in meiosis or fertilization of an ovum by 2 sperms known as dispermy

Tetraploidy: 92 chromosomes with XXXX or XXYY (4n)
occurs due to failure of the first cleavage zygotic division resulting in doubling of the chromosome number immediately after fertilization

Question 16

Define aneuploidy 

Answer 16

▪️Abnormal chromosome number due to an extra or missing chromosome but does not involve the whole chromosome set
▪️Autosome is more severe than sex chromosomes

Question 17

What can aneuploidy be caused by

Answer 17

Nondisjunction:failure of homologous chromosome segregation during meiosis 1 or failure of segregation of sister chromatids during meiosis 2 or mitosis

Anaphase lag: failure of chromosome or chromatid to be incorporated into one of the daughter nuclei following cell division

Question 18

What are the two types of aneuploidy and describe them

Answer 18

Trisomy: presence of 3 copies instead of 2 for an autosome or sex chromosome
47 chromosomes

Monosomy: absence of a single chromosome
Only surviving condition is turner syndrome

Question 19

Define mixoploidy

Answer 19

▪️Having two or more genetically different cells lineages
▪️ Could arise from the same zygote resulting in mosaicism or may result from the fusion of two different twin zygotes resulting in chimerism

Question 20

Structural aberrations can be..

Answer 20

Balanced: no gain or loss of genetic material
Unbalanced: incorrect amount of chromosomal material

Question 21

What are the types of structures chromosomal abnormalities

Answer 21

Deletion 
inversion 
insertion 
duplication 
translocation 
Isochromosomes
ring chromosomes

Question 22

Describe deletion

Answer 22

Involves loss of a part of a chromosome

Question 23

Define inversion

Answer 23

Two break rearrangement involving a single chromosome in which a segment is reversed in position
Balanced

Question 24

Describe insertion

Answer 24

Segment of one chromosome becomes inserted into another chromosome

Can be balanced or unbalanced

Question 25

Describe duplication

Answer 25

Gain of chromosomal material through production of one or more copies of a gene or region of a chromosome

Question 26

Describe translocation

Answer 26

Reverse the transfer of genetic material from one chromosome to another
1- Reciprocal translocation 
Formed when a break occurs in each of the two chromosomes of metacentric and sub metacentric types with the segments being exchanged to form two new derivative chromosomes
Usually remains 46
2-robertsonian translocation
Results from the breakage of two acrocentric chromosomes (13.14.15.21.22)
Fusion of their long arms
Reduced to 45
UnBalanced 

Question 27

What are Isochromosomes

Answer 27

Results from the abnormal Central Mirrick division that is at a right angle to the normal separation

Question 28

What are ring chromosomes

Answer 28

A ring chromosome is formed when a break occurs on each arm of a chromosome leaving two sticky ends on the central portion that reunites as a ring