GED L15 Notes Flashcards
What is aneuploidy?
• Aneuploidy: Chromosome abnormality -> abnormal number of chromosomes -> no loss / gain of complete chromosome set. Types: - Monosomy (Monosomic): Loss of single chromosome (2n – 1) - Trisomy (Trisomic): One extra chromosome (2n + 1) - Tetrasomy (Tetrasomic): Extra pair of chromosomes (2n + 2)
Name the types of aneuploidy?
- Monosomy (Monosomic):
- Trisomy (Trisomic):
- Tetrasomy (Tetrasomic):
Name the process in which there is abnormal chromosome segregation in meiosis?
Non-disjunction
What is Non-disjunction?
Non-disjunction:
Mistake -> chromosome segregation during meiosis
»_space; Produce aneuploid gametes
Describe Aneuploidy in Autosomes
• Aneuploidy -> Autosomes:
20-50% human conceptions -> aneuploid
- < 0.5% live births
All autosomal monosomies (2n -1) -> Inviable
Trisomy 13 (Patau Syndrome) & Trisomy 18 (Edwards Syndrome)
Death -> children within few months.
Down’s Syndrome: Charcteristics: - Characteristic facial features - Short stature - Learning disabilities - Higher risk -> Heart defects - Alzheimers & some cancers -> 1/1000
Causes: Trisomy (2n +1): - Trisomy 21 Robertsian Translocation: - Chromosome 21 & 14 Genetic mosaicism: - Mix of normal & trisomy 21 cells >>Non-disjunction -> early embryonic mitotic divisions
What is a characteristic of autosomal monosomies in autosomes?
All autosomal monosomies (2n -1) -> Inviable
Give examples of aneuploidy in autosomes
Trisomy 13 (Patau Syndrome) & Trisomy 18 (Edwards Syndrome)
Down’s Syndrome:
Name the type of aneuploidy in autosomes which causes death of children within months.
Trisomy 13 (Patau Syndrome) & Trisomy 18 (Edwards Syndrome)
Death -> children within few months.
Describe Down’s Syndrome
Down’s Syndrome: Charcteristics: - Characteristic facial features - Short stature - Learning disabilities - Higher risk -> Heart defects - Alzheimers & some cancers -> 1/1000
Causes: Trisomy (2n +1): - Trisomy 21 Robertsian Translocation: - Chromosome 21 & 14 Genetic mosaicism: - Mix of normal & trisomy 21 cells >>Non-disjunction -> early embryonic mitotic divisions
What are the characteristics of Down’s Syndrome?
Charcteristics:
- Characteristic facial features
- Short stature
- Learning disabilities
- Higher risk -> Heart defects
- Alzheimers & some cancers -> 1/1000
What are the causes of Downs Syndrome?
Causes: Trisomy (2n +1): - Trisomy 21 Robertsian Translocation: - Chromosome 21 & 14 Genetic mosaicism: - Mix of normal & trisomy 21 cells >>Non-disjunction -> early embryonic mitotic divisions
Describe genetic mosaicism
Genetic mosaicism:
- Mix of normal & trisomy 21 cells
»Non-disjunction -> early embryonic mitotic divisions
What chromosomes does Robertsian Translocation occur on & what disease is this present in?
Robertsian Translocation:
- Chromosome 21 & 14 –> Down’s Syndrome
Describe Trisomy & the chromosome on which it is located
Trisomy (2n +1):
- Trisomy 21
Describe Aneuploidy in sex chromosomes
• Aneuploidy -> Sex Chromosomes: Normal human karyotype - 46 XY -> Males ; 46 XX -> Females Monosomy (2n -1) Turner Syndrome (XO) -> (45, X) - Sterile females - Short stature - Some -> learning difficulties - 1/2500 female births - At least 1 X required -> embryonic development Trisomy (2n + 1) Klinefelter Syndrome (47, XXY) Triplo-X (47, XXX) XYY Syndrome (47, XYY) Some individuals -> more than 47 chromosomes -> (48, XXXY / 48, XXYY)
What are the characteristics of the normal human karyotype?
Normal human karyotype
- 46 XY -> Males ; 46 XX -> Females
Name the types of aneuploidy in sex chromosomes
Monosomy (2n -1) Trisomy (2n + 1)
What disease is monosomy found in (Aneuploidy -> sex chromosomes) ?
Turner Syndrome (XO) -> (45, X)
What is the chromosomal no. in monosomy?
Monosomy (2n -1)
Describe the characteristics of Turner Syndrome
Turner Syndrome (XO) -> (45, X)
- Sterile females
- Short stature
- Some -> learning difficulties
- 1/2500 female births
- At least 1 X required -> embryonic development
Name the diseases in which Trisomy is found (Aneuploidy -> sex chromosomes)?
Klinefelter Syndrome (47, XXY)
Triplo-X (47, XXX)
XYY Syndrome (47, XYY)
Some individuals -> more than 47 chromosomes -> (48, XXXY / 48, XXYY)
What is the chromosome number & conformation in normal human karyotype?
Normal human karyotype
- 46 XY -> Males ; 46 XX -> Females
What is the chromosome number & conformation in Turner Syndrome?
Turner Syndrome (XO) -> (45, X)
What is the chromosome number & conformation in Klinefelter Syndrome?
Klinefelter Syndrome (47, XXY)
What is the chromosome number & conformation in Triplo-X?
Triplo-X (47, XXX)
What is the chromosome number & conformation in XYY Syndrome?
XYY Syndrome (47, XYY)
What is the chromosome number & conformation in individuals with more than 47 chromosomes?
Some individuals -> more than 47 chromosomes -> (48, XXXY / 48, XXYY)
What does X chromosome inactivation cause?
• X chromosome inactivation switches off all but one X chromosome
Describe maternal age & trisomy
• Maternal Age & Trisomy
Incr. trisomy
Responsible for incr. miscarriage -> older women.
95% -> trisomy 21
Maternal non-disjunction -> meiosis 1
Human oocytes
Paused -> late meiotic prophase I (diplotene)
»_space; Alongside paired, replicated chromosomes
Begins before birth
»_space; Maintained -> decades
-> Until egg matures -> menstrual cycle
Loss of cohesion -> Prophase I
Aneuploidy -> older women
» Premature loss -> cohesion
-» 2 univalents -> segregate independently
> Aneuploid (n +1) gametes
What is a result of incr. trisomy?
Incr. trisomy
Responsible for incr. miscarriage -> older women
What process is trisomy 21 responsible for & what percentage does it occur?
95% -> trisomy 21
Maternal non-disjunction -> meiosis 1
Describe maternal age & trisomy in terms of human oocytes
Human oocytes
Paused -> late meiotic prophase I (diplotene)
»_space; Alongside paired, replicated chromosomes
Begins before birth
»_space; Maintained -> decades
-> Until egg matures -> menstrual cycle
Describe the pause of human oocytes in meiosis
Human oocytes
Paused -> late meiotic prophase I (diplotene)
»_space; Alongside paired, replicated chromosomes
Begins before birth
»_space; Maintained -> decades
-> Until egg matures -> menstrual cycle
Describe loss of cohesion in prophase I
Loss of cohesion -> Prophase I Aneuploidy -> older women >> Premature loss -> cohesion ->> 2 univalents -> segregate independently > Aneuploid (n +1) gametes
Describe extranuclear genomes of mitochondria & chloroplasts
• Extranuclear genomes -> mitochondria & chloroplasts:
- Circular dsDNA genomes
- Ribosomes -> mitochondria & chloroplasts
» Different -> cytoplasmic ribosomes
» Sensitive -> Bacterial antibiotics
Mitochondrial Genomes / DNA:
- Components -> Translation
Eg. tRNAs & rRNAs
- Structural genes -> proteins involved -> oxidative phosphorylation
Eg. Cytochrome oxidase, NADH-dehydrogenase, ATPase
Chloroplast Genomes / DNA:
- Genes encoding tRNAs & rRNAs involved -> translation
- Structural genes -> proteins involved -> photosynthesis
Eg. Biphosphate decarboxylase
• Transmission -> Extranuclear Genomes:
Describe ribosomes of mitochondria & chloroplasts & the type of genomes they contain
• Extranuclear genomes -> mitochondria & chloroplasts:
- Circular dsDNA genomes
- Ribosomes -> mitochondria & chloroplasts
» Different -> cytoplasmic ribosomes
» Sensitive -> Bacterial antibiotics
Describe mitochondrial Genomes / DNA
Mitochondrial Genomes / DNA:
- Components -> Translation
Eg. tRNAs & rRNAs
- Structural genes -> proteins involved -> oxidative phosphorylation
Eg. Cytochrome oxidase, NADH-dehydrogenase, ATPase
Describe chloroplast genomes / DNA
Chloroplast Genomes / DNA:
- Genes encoding tRNAs & rRNAs involved -> translation
- Structural genes -> proteins involved -> photosynthesis
Eg. Biphosphate decarboxylase
Describe transmission of extranuclear genomes
• Transmission -> Extranuclear Genomes: Egg Diameter -> ~100um > 100,000 copies mitochondrial DNA Sperm Diameter -> ~5um < 1000 copies mitochondrial DNA Transmission -> mitochondrial & chloroplast genomes Uniparental pattern >> Usually maternal inheritance ->> Females transmit -> All children ->> Males never transmit Paternal mammalian mitochondria & sperm components (excl. nucleus) destroyed after fertilisation. Plants: Maternal inheritance common Paternal & Biparental inheritance also found
Describe characteristics of the egg in terms of mitochondrial DNA
Egg
Diameter -> ~100um
> 100,000 copies mitochondrial DNA
Describe the characteristics of the sperm in terms of mitochondrial DNA
Sperm
Diameter -> ~5um
< 1000 copies mitochondrial DNA
Describe transmission of mitochondrial & chloroplast genomes
Transmission -> mitochondrial & chloroplast genomes Uniparental pattern >> Usually maternal inheritance ->> Females transmit -> All children ->> Males never transmit
Describe what happens to paternal mammalian mitochondria & sperm components after fertilisation
Paternal mammalian mitochondria & sperm components (excl. nucleus) destroyed after fertilisation.
What is destroyed after fertilisation?
Paternal mammalian mitochondria & sperm components (excl. nucleus) destroyed after fertilisation.
Name the types of inheritance found in plants -> Extranuclear genome transmission
Plants:
Maternal inheritance common
Paternal & Biparental inheritance also found
Describe mitochondrial DNA disease
• Mitochondrial DNA Disease:
- ~1/200 healthy individuals -> pathological mtDNA mutation
- ~ 1/10,000 adults -> mtDNA disease
- > 1000 mitochondrial proteins encoded -> nuclear genome
Mutations here can cause mitochondrial disease
- Signs & symptoms
Highly variable -> Even within family
- Same mtDNA mutation
Different signs & symptoms -> diff individuals
Describe characteristics of mitochondrial DNA disease
• Mitochondrial DNA Disease:
- ~1/200 healthy individuals -> pathological mtDNA mutation
- ~ 1/10,000 adults -> mtDNA disease
- > 1000 mitochondrial proteins encoded -> nuclear genome
Mutations here can cause mitochondrial disease
What are the signs & symptoms of mitochondrial DNA disease
Highly variable -> Even within family
- Same mtDNA mutation
Different signs & symptoms -> diff individuals
Describe heteroplasmy
• Heteroplasmy:
Mutation -> mitochondrial genome
Mixture -> normal & mutant mitochondria
»_space; Passive segregation -> mitochondria -> cell division
Proportion -> mutant mitochondria -> affects severity
» Varies between
-» Individuals
-» Tissues -> single individual
What affects the severity of heteroplasmy?
Proportion -> mutant mitochondria -> affects severity
What does the severity of heteroplasmy vary in?
Proportion -> mutant mitochondria -> affects severity
» Varies between
-» Individuals
-» Tissues -> single individual
What is heteroplasmy and how is it caused?
• Heteroplasmy:
Mutation -> mitochondrial genome
Mixture -> normal & mutant mitochondria
»_space; Passive segregation -> mitochondria -> cell division
Describe mitochondrial Replacement therapy
• Mitochondrial Replacement Therapy:
Maternal Spindle Transfer:
Repair -> egg -> before fertilisation
Metaphase II spindle & associated chromosomes -> mother’s egg
»_space; Transplanted -> donor egg
-» Nucleus removed
Some unhealthy mitochondria possibly transferred alongside mother’s nucleus.
Name the process in which mitochondrial replacement therapy occurs
Maternal Spindle Transfer:
Describe the process of mitotic spindle transfer
Maternal Spindle Transfer:
Repair -> egg -> before fertilisation
Metaphase II spindle & associated chromosomes -> mother’s egg
»_space; Transplanted -> donor egg
-» Nucleus removed
Some unhealthy mitochondria possibly transferred alongside mother’s nucleus.
Describe monosomy
- Monosomy (Monosomic):
Loss of single chromosome (2n – 1)
What is monosomy?
- Monosomy (Monosomic):
Loss of single chromosome (2n – 1)
Describe Trisonomy?
- Trisomy (Trisomic):
One extra chromosome (2n + 1)
What is Trisonomy?
- Trisomy (Trisomic):
One extra chromosome (2n + 1)
Describe Tetrasomy?
- Tetrasomy (Tetrasomic):
Extra pair of chromosomes (2n + 2)
What is Tetrasomy?
- Tetrasomy (Tetrasomic):
Extra pair of chromosomes (2n + 2)