WEEK 1 Flashcards
What are the categories of medical genetic disease?
- Chromosome disorders
- Single-gene defects
- Multifactorial disease with complex inheritance
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
Chromosome disorders
An extra copy of one chromosome on chromosome 21 underlies which disorder?
Down syndrome
What causes single-gene defects in individual genes?
Pathogenic mutations
List examples of single-gene defects
Cystic fibrosis
Sickle cell anaemia
Marfan syndrome
___________________ 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
Multifactorial disease
List examples of multifactorial disease
Hirschsprung disease
Cleft lip and palate
Congenital heart defects
Define ‘Gene’
A gene is the functional unit of heredity and contains a sequence of nucleotides that code for the synthesis of proteins
What sugar are genes made out of?
Deoxyribose Nucleic Acid (DNA)
What do you call the genes that do not code for proteins?
Exons
Define ‘Chromosome’
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
What is a chromatin?
A substance within a chromosome consisting of DNA and protein (histones)
Define ‘Chromatid’
One copy of a newly copied chromosome which is still joined to the original chromosome by a single centromere
What are the differences between Chromosomes and Chromatids?
- 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
What are Mendel’s first three postulates?
- Unit factors in pairs
- Dominance/Recessiveness
- Segregation
What does the first postulate “Unit factors in pairs” mean?
Genetic characters are controlled by unit factors existing in pairs in individual organisms therefore a specific unit factor exists for each trait
Describe the second postulate “Dominance/Recessiveness”
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
Describe the third postulate “Segregation”
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
Define ‘Mutation’
Any heritable change in the DNA sequence and is the source of all genetic variation
What is an allele?
Alternative forms of a gene
What is the difference between genotype and phenotype?
GENOTYPE is the set of alleles for a given trait carried by an organism and PHENOTYPE is the observable features
Geneticists can map out the location of genes on chromosomes using what?
By using mutant genes as markers
When a __________ alters a gene, it may modify or even eliminate the encoded protein’s usual function and cause an altered phenotype
mutation
What are the consequences of the mutation that forms Sickle-cell anaemia?
Sickle-cell anaemia is caused by a mutant form of haemoglobin which is made up of two different proteins alpha-globin and beta-globin
- A mutation in the gene encoding alpha-globin causes an amino acid substitution in 1 of the 146 amino acids
- The change in one DNA nucleotide causes a change in codon 6 in mRNA from GAG to GUG
- Amino acid number 6 in beta-globin changes from glutamic acid to valine
- 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
