Meiosis And Chromosomal Aberrations Flashcards
What is meiosis
Special type of cell division resulting in formation of gametes whose chromosome number has been reduced from diploid to haploid
What are the 2 crucial results of meiosis
▪️Reduction in number of chromosomes from diploid to haploid (for dna and chromosomes)
▪️Recombination of genes ensuring genetic variability and diversity of gene pool
Describe meiosis 1
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
Describe meiosis two
▪️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
What happens in S phase
The amount of DNA is doubled to 4n but the chromosome number remains at 2n
Describe prophase one
▪️homologous pairs of chromosomes approximate each other and condense ▪️chiasmata formation
Describe metaphase one
Homologous pairs of chromosomes line up at the equilateral plate of the meiotic spindle
Describe anaphase one
Homologous chromosomes migrate away from each other going to opposite poles
Describe telophase one
▪️Cytokinesis occurs
▪️Two daughter cells are produced
▪️DNA content is still diploid but chromosome number is haploid
Why is DNA number still diploid after telophase one
Because each chromosome possesses two chromatids
What is the outcome of meiosis two
▪️Four daughter cells
▪️Haploid DNA and chromosome number
▪️Cells are genetically distinct due to the reshuffling and crossing over
What is euploidy
The normal number of chromosomes for a species
What are the types of numerical chromosomal abnormalities
Polyploidy a)triploidy b)tetraploidy Aneuploidy a)non disjunction b)anaphase lag Trisomy Monosomy Mixoploidy
Define polyploidy
A condition in which the chromosome number is a simple multiple of a haploid chromosome set
What are the two types of polyploidy and define them
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
Define aneuploidy 
▪️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
What can aneuploidy be caused by
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
What are the two types of aneuploidy and describe them
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
Define mixoploidy
▪️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
Structural aberrations can be..
Balanced: no gain or loss of genetic material
Unbalanced: incorrect amount of chromosomal material
What are the types of structures chromosomal abnormalities
Deletion inversion insertion duplication translocation Isochromosomes ring chromosomes
Describe deletion
Involves loss of a part of a chromosome
Define inversion
Two break rearrangement involving a single chromosome in which a segment is reversed in position
Balanced
Describe insertion
Segment of one chromosome becomes inserted into another chromosome
Can be balanced or unbalanced
Describe duplication
Gain of chromosomal material through production of one or more copies of a gene or region of a chromosome
Describe translocation
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 
What are Isochromosomes
Results from the abnormal Central Mirrick division that is at a right angle to the normal separation
What are ring chromosomes
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
