Errors in Meiosis

Question 1

what is meiotic non-disjunction

Answer 1

the failure of chromosomes to separate (disjoin) properly during meiosis (or mitosis)

Question 2

non-disjunction in meiosis I

Answer 2

homologous chromosomes do not disjoin

Question 3

non-disjunction in meiosis II

Answer 3

sister chromatids do non disjoin

Question 4

can non disjunction occur in mitosis

Answer 4

yes - not as serious as during meiosis as cell mostly likely just dies where in meiosis the error can be passed down generations

Question 5

what is aneuploidy

Answer 5

condition where gametes with abnormal number of a particular chromosome fuse with a normal gamete, the resulting zygote will also have an abnormal number of a particular chromosomes

Question 6

what happens if a zygote is monosomic

Answer 6

when fertilization involves a gamete with no copy of a particular chromosome which results in zygote missing a chromosome
2n-1

Question 7

what happens if a zygote is trisomic

Answer 7

when fertilization involves a gamete with an extra copy of a particular chromosome (triplicate chromosome) which results in gamete having an extra chromosome
2n+1

Question 8

what is down syndrome

Answer 8

an autosomal aneuploid condition where there are 3 copies of chromosome 21 (trisomy 21) resulting in karyotype having 47 chromosomes

Question 9

what is Klinefelter syndrome

Answer 9

an aneuploid condition of a sex chromosome where individuals have an extra copy of chromosome X resulting in karyotype having 47 chromosomes

Question 10

what is turner syndrome

Answer 10

an aneuploid condition of sex chromosomes where individuals only have one X chromosome resulting in karyotype having 45 chromosomes
condition can vary depending if X chromosome is from mother or father

Question 11

what is polyploidy

Answer 11

the possession of more than 2 complete chromosome sets which may have arise due to disjunction of all chromosomes in one gamete or the failure of a diploid zygote to divide after replicating its chromosomes during interphase

Question 12

breakage in a chromosome structure can result in changes to chromosomes in 4 ways

Answer 12

1. deletion
2. duplication
3. inversion
4. translocation

Question 13

explain deletion

Answer 13

deletion is the missing piece when a chromosome breaks in one or more places and a portion is lost
- can result in a loss of genes but do not change the order of the remaining genes

Question 14

explain duplication

Answer 14

duplication is a result of when part of a chromosome is present more than once in the genome
- this may happen when a broken fragment of one chromosome reattaches as an extra segment to a sister or non sister chromatid
-can results in change of number of some genes on a chromosome but will not change the order of the remaining genes

Question 15

explain inversions

Answer 15

inversion is when part of a chromosome is inverted (turned 180) within a chromosome
- requires breaks at 2 points along the length of the chromosome and subsequent insertion of the inverted segment
- does not change the number of genes on a chromosome but will change the order of the inverted segment

Question 16

explain translocations

Answer 16

translocation is where a segment of chromosome attaches to a non homologous chromosome
- doesnt change the overall number of genes but they can sometimes change gene expression

Question 17

what is familial down syndrome

Answer 17

In Familial down syndrome, one parent is a carrier of a 14/21 translocation which could have arise when following a breakage, the majority of chromosome 21 attaches to chromosome 14
- the carrier parent is phenotypically normal even though they only have 45 chromosomes
- during synapsis the 14/21 translocation chromosome may result in a gamete that has 2 copies of chromosome 21 (one normal and one 14/21)
- when fertilized the resulting zygote will have 46 chromosomes but it contains 3 copies of chromosome 21
- it is heritable