WEEK 1

Question 1

What are the categories of medical genetic disease?

Answer 1

• Chromosome disorders
• Single-gene defects
• Multifactorial disease with complex inheritance

Question 2

In _____________________ the defect is due not to a single mistake in the genetic blueprint but to an excess or a deficiency of the genes located on entire chromosomes or chromosome segments

Answer 2

Chromosome disorders

Question 3

An extra copy of one chromosome on chromosome 21 underlies which disorder?

Answer 3

Down syndrome

Question 4

What causes single-gene defects in individual genes?

Answer 4

Pathogenic mutations

Question 5

List examples of single-gene defects

Answer 5

Cystic fibrosis
Sickle cell anaemia
Marfan syndrome

Question 6

___________________ with complex inheritance is when there is genetic contribution yet the family history does not fit the inheritance patterns seen typically in single-gene defects

Answer 6

Multifactorial disease

Question 7

List examples of multifactorial disease

Answer 7

Hirschsprung disease
Cleft lip and palate
Congenital heart defects

Question 8

Define ‘Gene’

Answer 8

A gene is the functional unit of heredity and contains a sequence of nucleotides that code for the synthesis of proteins

Question 9

What sugar are genes made out of?

Answer 9

Deoxyribose Nucleic Acid (DNA)

Question 10

What do you call the genes that do not code for proteins?

Answer 10

Exons

Question 11

Define ‘Chromosome’

Answer 11

A long DNA molecule that contains part or all of the genetic material of the an organism which is bound to packaging proteins (histones) that condense the molecule

Question 12

What is a chromatin?

Answer 12

A substance within a chromosome consisting of DNA and protein (histones)

Question 13

Define ‘Chromatid’

Answer 13

One copy of a newly copied chromosome which is still joined to the original chromosome by a single centromere

Question 14

What are the differences between Chromosomes and Chromatids?

Answer 14

• Chromosome main function is to carry genetic information whereas chromatid main function is for cell to duplicate
• Chromosome is present throughout the whole cell cycle, Chromatid is only present during mitosis or meiosis
• Chromosomes are not exact copies of each other (one from each parent), Sister chromatids are identical copies of each other

Question 15

What are Mendel’s first three postulates?

Answer 15

1. Unit factors in pairs
2. Dominance/Recessiveness
3. Segregation

Question 16

What does the first postulate “Unit factors in pairs” mean?

Answer 16

Genetic characters are controlled by unit factors existing in pairs in individual organisms therefore a specific unit factor exists for each trait

Question 17

Describe the second postulate “Dominance/Recessiveness”

Answer 17

When two unit factors are responsible for a single character trait in an individual, one unit factor is dominant to the other which is recessive.

In a monohybrid cross, the trait expressed in the F1 generation is controlled by the dominant unit factor

Question 18

Describe the third postulate “Segregation”

Answer 18

During the formation of gametes in meiosis, the paired unit factors separate randomly so that each gamete receives one or the other with equal likelihood

Question 19

Define ‘Mutation’

Answer 19

Any heritable change in the DNA sequence and is the source of all genetic variation

Question 20

What is an allele?

Answer 20

Alternative forms of a gene

Question 21

What is the difference between genotype and phenotype?

Answer 21

GENOTYPE is the set of alleles for a given trait carried by an organism and PHENOTYPE is the observable features

Question 22

Geneticists can map out the location of genes on chromosomes using what?

Answer 22

By using mutant genes as markers

Question 23

When a __________ alters a gene, it may modify or even eliminate the encoded protein’s usual function and cause an altered phenotype

Answer 23

mutation

Question 24

What are the consequences of the mutation that forms Sickle-cell anaemia?

Answer 24

Sickle-cell anaemia is caused by a mutant form of haemoglobin which is made up of two different proteins alpha-globin and beta-globin

1. A mutation in the gene encoding alpha-globin causes an amino acid substitution in 1 of the 146 amino acids
2. The change in one DNA nucleotide causes a change in codon 6 in mRNA from GAG to GUG
3. Amino acid number 6 in beta-globin changes from glutamic acid to valine
4. Individuals with two mutant copies of the beta-globin have sickle cell anaemia; the mutant B-globin proteins cause haemoglobin molecules in red blood cells to polymerise when the blood’s oxygen concentration is low, forming long chains of haemoglobin which distorts the shape of red blood cells.

• Deformed cells break easily reducing the number of red blood cells in circulation
• Sickle-shaped blood cells block blood flow in capillaries and small blood vessels causing severe pain and damage to the heart, brain, muscles and kidneys