Genes Lecture 7-Chromosome Abnormalities & Cytoplasmic Inheritance

Question 1

aneuploidy

Answer 1

abnormal number of chromosomes

Question 2

euploid

Answer 2

normal human karyotype

Question 3

monosomy

Answer 3

2n-1
one chromosome missing

Question 4

Trisomy

Answer 4

2n+1
extra chromosome

Question 5

tetrasomy

Answer 5

2n+2
entire pair duplicated

Question 6

meiotic non-dysjunction

Answer 6

mistakes in chromosome segregation during meiosis

Question 8

meiosis 1 non dysjunction

Answer 8

pair of homologous chromosomes will fail to segregate resulting in aneuploid gametes ( Two have an extra chromosome 21 and two are lacking chromosome 21)

Question 9

meiosis 2 non disjunction

Answer 9

one of the sister chromosomes fail to segregate: two normal gametes and two aneuploid. One trisomy and the other monosomy

Question 10

why are autosomal monosomies (2n-1) inviable

Answer 10

essential genes are present in all autosomal chromosomes

Question 11

trisomy examples

Answer 11

Down syndrome (trisomy 21)
Children with trisomy 13 (Patau syndrome) and trisomy 18 (Edwards syndrome) die within a few months after birth

Question 12

prenatal screening for downs syndrome

Answer 12

Chorionic villus sampling (CVS) and amniocentesis is used to sample cells from the foetus

he karyotype of the foetal cells is determined

Question 13

Robertsonian translocation in downs syndrome

Answer 13

illegitimate recombination between rDNA repeats on the short arms of chromosome 14 and 21 fuses the long arms of the chromosomes

Question 14

genetic mosaicism in downs syndrome

Answer 14

individuals have a mix of normal and trisomy 21 cells
arises from embryo with trisomy 21 followed by loss of the extra chromosome 21 by mitotic non-disjunction in early cleavage divisions OR by from a euploid embryo with mitotic non-disjunction

Question 15

monosomy examples

Answer 15

Turner syndrome
not diagnosed as babies
at least one x required for embryonic development

Question 16

Examples of trisomy in human sex chromosomes

Answer 16

Klinefelter syndrome (47,XXY)
Triplo-X (47,XXX)
XYY syndrome (47,XYY)

not as lethal as aneuploidy in autosomal chromosomes

Question 17

maternal non-dysjunction

Answer 17

most maternal non-disjunction occurs in meiosis 1 where there is a loss of cohesion in prophase 1 giving two univalents that segregate independently giving aneuploid (n+1) gametes

Question 18

What types of genes are found in mitochondrial genomes?

Answer 18

mtDNA
-components for translation
-structural genes for proteins involved in oxidative phosphorylation

Question 19

What types of genes are found in chloroplast genomes?

Answer 19

cpDNA
-genes encoding for non-coding RNAs involved in chloroplast translation
-structural genes for proteins involved in photosynthesis

Question 20

how is mtDNA inherited in mammals

Answer 20

maternally inherited
-in mammals paternal mitochondria and other components are destroyed during fertilisation

Question 21

transmission of mitochondria and chloroplast genomes

Answer 21

uniparental pattern
females transmit the trait to all of their children
males never transmit the trait
-can see this through mitochondrial disease pedigrees

Question 22

Mitochondrial DNA disease

Answer 22

-signs and symptoms are highly variable within one family
-the same mtDNA mutation may cause different signs and symptoms in different individuals
-may arise from mutations in mitochondrial proteins

Question 23

heteroplasmy

Answer 23

passive segregation of mitochondria during cell division (creates differences in phenotypes of offspring; one cell may have more mutant mtdna)

Question 24

Mitochondrial replacement therapy – “three-person” baby

Answer 24

repair done to unhealthy mitochondria in the egg before fertilisation using donor mitochondria