Lecture 15 Chromosome abnormalities

Question 1

Define Anueploidy

Answer 1

This is the loss of gain of a single chromosome.

- Examples include monosomy, trisomy,

Question 2

What is meant by aneuploidy

Answer 2

Type of chromosomal abnormality where the number of chromosomes is abnormal but not loss or gain of a complete set of chromosomes.

Question 3

Explain the two main causes of Aneuploidy in humans (be specific)

Answer 3

1) Non disjunction of homologous chromosomes in Meiosis I

2) Non disjunction of sister chromatids in meiosis II.

Question 4

Downs syndrome is which type of aneuploidy

Answer 4

Trisomy 21. Involves an extra copy of chromosome 21. 2n +1.

Question 5

State the cause of 95 percent of downs syndrome cases

Answer 5

Non disjunction of homologous chromosomes in meiosis I or non disjunction of sister chromatids in meiosis II.

Question 6

State the cause of 5 percent of down syndrom cases. Explain what it is.

Answer 6

• Robertsonian translocation accounts for 5% of all DS cases.
• ## Robertsonian translocation involves both chromosome 21 and 14.

Question 7

State the type of Aneuploidy involded in turners syndrome

Answer 7

Monosomy ( 2n-1).

Turners syndrome results due to the loss of an X chromosome

Question 8

State the karyotype for Turners syndrome

Answer 8

45 XO

Question 9

Turners syndrome only affects which sex

Answer 9

Females

Question 10

How many barr bodies will be visible in those affected by turners syndrome

Answer 10

No barr bodies visible because only one X chromosome undergoes inactivation!

Question 11

State the karyotype of those affected by Klinefelters syndrome

Answer 11

47 XXY

Question 12

Klinefelters syndrome affects which sex only

Answer 12

Males

Question 13

How many barr bodies will be visible in klinefelters syndrome patients ( per cell)

Answer 13

1

Question 14

Define and explain the pseudoautosomal region

Answer 14

• pseudoautosomal region is a conserved, homologous DNA sequences that exist on the X and Y chromosome.
• Genes in the PAR region are inherited just like any autosomal genes.

Question 15

What is the function of the pseudoautosomal region

Answer 15

Crossing over between the X and Y chromosomes is restricted to the PAR regions.
The function of the PAR regions is that they allow X and Y chromosomes to pair and properly segregate during meiosis in males.

Question 16

Explain the process of X chromosome inactivation

Answer 16

Females have 2 X chromsomes.
Thus, as a form of dosage compensation, ONE of the X chromsomes is inactivated. This inactivated chromosome is cytologically visible as a barr body.

Question 17

How many X chromosmes undergo inactivation per cell in a female?

Answer 17

Per cell, just one X chromosome is inactivated, showing up as one X chromosome per barr body.

Question 18

What happens to the pseudoautosomal genes during X inactivation

Answer 18

The PAR regions escape X inactivation.

Question 19

What happens to human oocytes?

Answer 19

Human oocytes are paused in meiosis I for decades.

Question 20

When are human oocytes produced?

Answer 20

Before birth in a female

Question 21

What is a major cause of aneuploidy in older women

Answer 21

Premature loss of cohesion protein complex which holds the two homologues together up until anaphase causes formation of 2 univalents.

Question 22

How many protein encoding genes are found in the mitochondrial genome. Are the genes within the mitochondrial genome smaller or larger than normal mitochondrial regions?

Answer 22

• Theres 13 protein encoding genes in the mitochondrial genome.
• Genes of the mt genome are usually smaller.
• Many of the genes code for proteins involved in oxidative phosphorylation.

Question 23

Explain how the mitochondrial genome is inherited?

Answer 23

Maternal inheritance of extra nuclear mitochondria

Question 24

Describe the transmission of extranuclear genomes (mitochondria and chloroplast)

Answer 24

Often transmitted from one generation to the next in a uniparental pattern - maternal inheritance

Question 25

State the most common mode of transmission of extranuclear genomes in plants and algae

Answer 25

Uniparental maternal inheritance.

Question 26

Explain mitochondrial DNA disease/s

Answer 26

Genetic disorder that occurs when the mitochondria of the cell fail to produce enough energy for the cell or organ to function.

• Many forms of mitochondrial disease, and can arise from defe

Question 27

Defects which cause mitochondrial disease can be from which type of DNA

Answer 27

Mutations in either the mitochondrial dna iteslf or the cells nuclear DNA.

Question 28

How many barr bodies does a patient with Turners syndrome typically have?

Answer 28

No barr bodies because at least one X chromosome is required for embryonic development, so you cannot have both X chromosomes being inactivated or you wouldn’t exist/survive.

Question 29

State the mode of inheritance in pseudoautosomal genes

Answer 29

Pseudoautosomal genes exhibit autosomal patterns of inheritance, rather than a sex linked pattern of inheritance.

Question 30

An XX female has how may barr bodies per cell

Answer 30

One barr body

Question 31

An XXX female has how many barr bodies per cell

Answer 31

2 barr bodies per cell

Question 32

An XXY klineflter male has how many barr bodies per cell

Answer 32

1 barr body per cell. as one is needed/

Question 33

Which phase are primary oocytes paused in before birth

Answer 33

Before birth primary oocytes are arrested in prophase I, with paired replicated chromosomes.

Question 34

Explain why premature loss of cohesion gives rise to aneuploid (n+1) gametes eg instead of n=23, n=24.

Answer 34

dont knowwwww

Question 35

Name some examples of molecules endoded for by the mitochondrial genome

Answer 35

cytochrome oxidase, NADH dehydrogenase, and ATPase.