Chromosomes & Inheritance

Question 1

What are chromosomes?

Answer 1

Thread-like structures, made up of DNA

• located within nucleus of a cell

Question 2

Autosomal chromosomes v/s Sex chromosomes

Answer 2

Autosomal: 1 - 22 pair

Sex: last one pair

Question 3

What is human karyotype?

Answer 3

Visual representation of all 46 chromosomes of one cell arranged in pairs

Question 4

What is an acrocentric chromosome?

Answer 4

A chromosome with its centromere closer near one end

• hence, has a short p arm & longer q arm

Question 5

Types of chromosomal abnormalities

Answer 5

1. Numerical
   e.g. aneuploidy
2. Structural
   e.g. deletions, duplications

Question 6

What is nondisjunction?

Answer 6

Failure of homologous chromosomes or sister chromatids to separate properly during mitosis / meiosis

Question 7

What is aneuploidy?

Answer 7

Having an abnormal number of chromosomes

normal → 1 pair

abnormal → monosomy, trisomy

Question 8

Nondisjunction during Meiosis I is more serious compared to that during Meiosis II.

Why?

Answer 8

If occurs during meiosis I,
→ All gametes abnormal

If occurs during meiosis II,
→ half abnormal

Question 9

How chromosomal abnormalities arise?

Answer 9

due to errors in mitosis or in meiosis

e.g. numerical abnormalities - due to
nondisjunction
structural abnormalities - due to
deletions

Question 10

What is trisomy?

Answer 10

Presence of an extra chromosome
- 3 instead of 2

Examples:
- Down syndrome (21)
- Patau syndrome (13)
- Edward syndrome (18)

Question 11

What is monosomy?

Answer 11

One chromosome missing
- 1 instead of 2

Example: Turner syndrome
(45, X)
affecting females only

Question 12

What is Klinefelter syndrome?

Answer 12

Extra X chromosome in males

(47, XXY)

Question 13

How chromosomal structural abnormalities occur?

Answer 13

1. Deletions
2. Duplications
3. Translocations
4. Inversions

Question 14

2 main types of translocations

Answer 14

1. Reciprocal
2. Robertsonian

Question 15

What is reciprocal translocation?

Answer 15

Exchange of segments between 2 non-homologous chromosomes

Question 16

What is Robertsonian translocation?

Answer 16

Fusion of 2 acrocentric chromosomes at the centromere

Question 17

Balanced Robertsonian translocation

Answer 17

All genetic material present, but rearranged

• usually no phenotype expressed

Question 18

Unbalanced Robertsonian translocation

Answer 18

Loss or gain of genetic material

• often causes disorders

Question 19

Techniques used to detect chromosomal abnormalities

Answer 19

• Karyotyping
• FISH
• array CGH
• PCR

Question 20

What is FISH?

Answer 20

Fluorescent In Situ Hybridization

Uses fluorescent probes to detect DNA sequences

Question 21

What are monogenic defects?

Answer 21

Disorders caused by mutations in a single gene

Question 22

True / False

Recessive, dominant, and X-linked inheritance patterns are all examples of monogenic defects.

Answer 22

True.

involves a single gene defect

Question 23

Common cause of monogenic defects

Answer 23

MUTATIONS

Question 24

Examples of mutations

Answer 24

• Missense
• Nonsense
• Frameshift

Question 25

Mechanism of **recessive inheritance**

Answer 25

both alleles must be mutated for disease expression → aa - each parent of affected individual must carry one copy of the mutated gene

Question 26

Examples of autosomal **recessive** diseases

Answer 26

1. Cystic fibrosis 2. Thalassemia 3. Phenylketonuria 4. Hartnup disease

Question 27

Mechanism of autosomal dominant inheritance

Answer 27

A single mutated allele is enough for the genetic condition to manifest - if one parent has altered gene, child has a 50% chance of inheriting the condition

Question 28

Examples of autosomal **dominant** diseases

Answer 28

1. Huntington 2. Marfan 3. Neurofibromatosis 4. Achondroplasia

Question 29

Autosomal **dominant** inheritance v/s Autosomal **recessive** inheritance

Answer 29

**Dominant:** may be present in every generation **Recessive:** conditions can skip generations

Question 30

What is **X-linked inheritance**?

Answer 30

defective gene located on the **X chromosome**