Genetics Flashcards
Define genotype.
The genetic constitution of an individual.
Define phenotype.
The appearance of an individual due to the environment and genetics.
Define allele.
An alternative form of a gene at a specific locus.
Summarise autosomal dominant inheritance:
Manifests in the heterozygous state (2 different gene alleles on a gene locus)
Both males and females are affected equally.
The disease is present in several generations.
There is a 50% chance of offspring having the disease.
Give an example of an autosomal dominant condition.
Huntingtons disease
Summarise autosomal recessive inheritance:
Manifests in the homozygous state.
The disease is often not seen in every generation.
25% chance of offspring having the disease.
50% chance of offspring being carriers.
Healthy siblings have a 2/3 chance of being carriers.
Give an example of an autosomal recessive condition.
Cystic fibrosis
What is x linked inheritance?
A mutated gene on the X chromosome causes the phenotype to always be expressed in males.
Females with the mutated gene on the X chromosome are carriers.
Give an example of an X linked recessive condition.
Duchenne muscular dystrophy
What is a mis-sense mutation?
A single nucleotide change results in a codon coding for a different amino acid. This can result in a non functional protein or can have no effect (degenerative nature of the genetic code).
What is a non-sense mutation?
A single nucleotide change that produces a premature stop codon. This results in an incomplete/non-functional protein.
What is mitosis used for?
Growth and repair.
What are the 4 phases of the cell cycle?
G1, S, G2 and M
What phases of the cell cycle make up interphase?
G1, S and G2
What happens in prophase?
Chromatin condenses into chromosomes. Nuclear membrane begins to break down.
What happens in prometaphase?
Spindles form. Nuclear membrane completely breaks down.
What happens in metaphase?
The chromosomes line up along the midline of the cell. The spindles attach to the centromeres.
What happens in anaphase?
The chromosomes are pulled apart and the sister chromatids are pulled towards the nuclear poles.
What happens in telophase?
he nuclear membrane reforms and the chromosomes unravel to form chromatin. The spindle fibres disappear.
What happens in cytokinesis?
The cytoplasm divides producing 2 genetically identical daughter cells.
How is genetic diversity introduced in meiosis?
Metaphase 1 = random assortment.
What is splicing?
The removal of introns from pre-mRNA
List 3 features of the genetic code.
- Non-overlapping
- Universal
- Degenerate
Define lyonisation.
One of the female X chromosomes becomes inactivated early in embryogenesis.
Name 3 molecules that make a nucleotide.
- Pentose sugar.
- Phosphate.
- Nitrogenous base.
Name 2 places DNA can be found.
Cell nucleus DNA
Mitrochondrial DNA
What are removed in splicing of pre-mRNA?
Introns
What is gametogenesis?
Precursor cells undergo cell division and differentiation to form haploid gametes.
Gametogenesis: when do meiotic divisions occur in a male?
At puberty.
Gametogenesis: when is meiosis 1 complete in a female?
At ovulation.
Gametogenesis: when is meiosis 2 complete in a female?
If fertilisation occurs.
Would an x linked dominant condition be more common in males or females?
X linked dominant conditions occur twice as frequently in females as they do in males.
Would an X linked recessive condition be more common in males or females?
More common in males.
Would an affected male of an x-linked recessive condition and an unaffected female have any affected children?
No affected children but all the daughters would be carriers.
What is multifactorial disease?
A disease due to genetic and environmental factors e.g. diabetes or schizophrenia.
Define karyotype.
The number and appearance of chromosomes in the nucleus of a eukaryotic cell.
Define penetrance.
The proportion of people with a gene who show the expected phenotype.
Define sex limitation.
Both sexes have a gene but its expression is limited to only one of the sexes and it is turned off in the other.
Define variable expression.
Variation in clinical features of a genetic disorder between individuals with the same gene alteration.
What is Mendel’s second law?
The law of independent assortment. The alleles of one gene sort into gametes independently of the alleles of another gene.
A gene sequence is coded in…
Single strand DNA.
A promoter sequence is coded in …
Single strand DNA.
What is a promoter sequence?
The promoter region controls when and where the RNA polymerase will attach to DNA so transcription can commence.
What is a transcriptome?
All the messenger RNA molecules in a cell.
How many genes are there in the human genome?
20,000
What is it called when a child shows a phenotype for a disease younger than their father/mother does? e.g. in huntington’s disease.
Anticipation
What are Mendel’s 3 laws?
- Law of dominance.
- Law of independent assortment.
- Law of segregation.
How many hydrogen bonds form between adenine and thymine?
2
How many hydrogen bonds form between cytosine and guanine?
3
What type of inheritance pattern is seen with sickle cell disease?
Autosomal recessive
What is a single nucleotide polymorphism?
A single nucleotide substitution in DNA resulting in variation amongst a population.
Which phase of mitosis is this: The chromosomes are moving towards opposite poles of the cell and there are no nuclear membranes.
Anaphase
What is non-disjunction?
The failure of chromatids to separate.
What are the 4 bases in RNA?
Adenine, Cytosine, Guanine, Uracil.
Briefly describe translation.
A tRNA with a complementary anticodon to the codon on mRNA binds. Peptide bonds from between amino acids = polypeptide chain.
Where does translation occur?
Ribosome
What is the product of transcription?
mRNA
In what direction does DNA polymerase read?
3’ to 5’ (but replication occurs in the 5’ to 3’ direction).
What is the function of topoisomerase?
It unwinds the DNA double helix by relieving the supercoils.
What is gonadal mosaicism?
When there are 2 different populations of cells in the gonads. One population is normal and the other is mutated. All gametes from the mutated line are effected
What condition is trisomy 21?
Down’s syndrome
What causes trisomy 21?
Failure of the chromatids to separate; non-dysjunction.
