Chromosome Abnormalities/ Cytoplasmic Inheritance

Question 1

What is aneuploidy?

Answer 1

Aneuploidy is a type of chromosome abnormality where the number of chromosomes is abnormal (but NOT loss or gain of a complete chromosome set).

Question 2

What is the normal human karyotype for males and females?

Answer 2

46, XY for males and 46, XX for females.

Question 3

What process can give rise to aneuploid gametes?

Answer 3

Abnormal chromosome segregation during meiosis, specifically non-disjunction.

Question 4

What percentage of human conceptions are aneuploid?

Answer 4

20-50% of human conceptions are aneuploid, but <0.5% of live births are aneuploid.

Question 5

What is Down syndrome associated with?

Answer 5

Trisomy 21, characterized by facial features, short stature, learning disabilities, and higher risk of heart defects.

Question 6

What is the risk of Down syndrome at birth?

Answer 6

Approximately 1/1000 births.

Question 7

What prenatal tests are offered to pregnant women in the UK to identify risk of aneuploidy?

Answer 7

The combined test (ultrasound + blood test) and the quadruple test (blood test).

Question 8

What is chorionic villus sampling (CVS)?

Answer 8

A procedure used to sample cells from the fetus to determine the karyotype.

Question 9

What is the most common cause of Down syndrome?

Answer 9

Maternal non-disjunction, accounting for 95% of cases.

Question 10

What is Turner syndrome?

Answer 10

A condition characterized by monosomy (2n - 1) where individuals have 45 chromosomes (XO), leading to sterile females and short stature.

Question 11

What is Klinefelter syndrome?

Answer 11

A condition involving trisomy (2n + 1) where males have an extra X chromosome (47, XXY), leading to sterility and slower muscle growth.

Question 12

What is the significance of maternal age in relation to trisomy?

Answer 12

The incidence of trisomy increases with maternal age, largely due to non-disjunction during meiosis.

Question 13

What are mitochondrial and chloroplast genomes characterized by?

Answer 13

They have circular double-stranded DNA genomes and many prokaryotic features.

Question 14

What types of genes are found in mitochondrial genomes?

Answer 14

• Components required for translation (e.g., tRNAs and rRNAs)
• Structural genes for proteins involved in oxidative phosphorylation.

Question 15

How is mitochondrial DNA inherited in mammals?

Answer 15

Maternal inheritance; paternal mitochondria are destroyed after fertilization.

Question 16

What is heteroplasmy?

Answer 16

The presence of more than one type of mitochondrial DNA within a cell.

Question 17

What is mitochondrial replacement therapy?

Answer 17

A technique where the mother’s egg is repaired before fertilization by transplanting the metaphase II spindle and associated chromosomes to a donor egg.

Question 18

What are the learning outcomes of the lecture?

Answer 18

• Explain how aneuploidy arises by non-disjunction in meiosis
• Give examples of aneuploidy in humans
• Explain extranuclear inheritance of mitochondrial and chloroplast genes.

Question 19

Fill in the blank: The normal human karyotype for females is _______.

Answer 19

46, XX

Question 20

True or False: Most individuals with Klinefelter syndrome are diagnosed at birth.

Answer 20

False

Question 21

What is the typical size difference between human eggs and sperm?

Answer 21

Egg diameter ~100 mm, sperm head ~5 mm.