Genetic Variation In Human Health

Question 1

DNA structure

Answer 1

Deoxyribonucleic acid uses 4 nucleotides adenine (A), thymine (T), guanine (G) and cytosine (C) to code for all proteins, peptides and RNA’s needed by the body.

Question 2

Types of mutation

Answer 2

• Aneuploidy
• Chromosomal
rearrangements
• Dynamic mutations
• SNPs and indels

Question 3

Aneuploidy

Answer 3

-is an abnormal number of chromosomes
-Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate properly during cell division.
-The deleterious phenotypes associated with aneuploidy are likely a result of the imbalance in the levels of gene products produced by the abnormal number of chromosomes.

Question 4

Down syndrome (trisomy 21)

Answer 4

• 1/800 live births
• abnormal features
• Malformation: atresia of esophagus,
duodenum or anus, structural heart defects, hearing loss, hypothyroidism, eye abnormalities
• respiratory infection, leukemia
• mental retardation
• sterile

Question 5

Human mosaic

Answer 5

Mosaicism can be:
• somatic (ie in most body cells) or
• gonadal (confined solely to the gonads).

Question 6

Types of chromosomal rearrangement

Answer 6

Deletion
Duplication
Inversion
Insertion
Translocation

Question 7

Philadelphia chromosome

Answer 7

Research

Question 8

Partial trisomy 21

Answer 8

-Very rarely a person may have three copies of only part of 21. One way this can happen is an unbalanced translocation.
-Unbalanced translocations can result in offspring with gene copy number variation.

Question 9

Acrocentric chromosome

Answer 9

A chromosome in which the centromere is located quite near one end of the chromosome

Question 10

Tandem repeats

Answer 10

Microsatellites (Short Tandem Repeats; STR): repeated sequences of around 2-5bp, such as CA, CAG or ATTC
Minisatellites: repeated sequences of between 14 and 100 base.
Variable number tandem repeats (VNTR): Linear arrangement of multiple copies of short repeated DNA sequences that vary in length.

Question 11

Huntingtons disease

Answer 11

12/100000 in uk
• progressive degeneration of neurons
• Average age of onset is 35 to 44 but can occur in juveniles.
• symptoms can include uncontrolled movements, loss of intellectual abilities, and emotional and psychiatric problems.
• Death usually occurs with 15 to 20 years of onset.

• Autosomal dominant
• CAG repeat in exon 1 of the huntingtin (HTT) gene • Progressive neurological disorder

Question 12

disease causing mutations

Answer 12

Loss of function mutations involve a reduction or complete loss of function of the gene product.
Gain of function mutations can be beneficial but can also result in a non- beneficial gene product, excess production of the gene product or a functionally altered gene product.

Question 13

Slippage misparing mechanism

Answer 13

-starting template strand of genomic DNA
Replicating strand detaches inappropriately from template during replication
-replicating strand slips from its proper alignment with the template strand,by one repeat(R) length.Mismacthed R2 repeat loops out
-newly synthesised strand contains an extra repeat

• Repeat length can change from one generation to the next.
• A larger number of repeats is usually associated with an earlier onset of signs and
symptoms. This phenomenon is called anticipation.
• People with the adult-onset form of Huntington disease typically have 40 to 50 CAG repeats in the HTT gene, while people with the juvenile form of the disorder tend to have more than 60 CAG repeats.
• Individuals with 27 to 35 CAG repeats in the HTT gene are at risk of having children who will develop the disorder.

Question 14

Fragile X syndrome