Genes, Molecules and Cells Exam

What are features of autosomal dominant inheritance?

Vertical pattern of inheritance.

can be male to male inheritance.

Condition affects both males and females.

What are some examples of autosomal dominant genetic diseases?

Achondroplasia.

Familial cancer.

What are features of autosomal recessive inheritance?

Individuals must have both genes affected to present.

Children's parents must both carry the mutation.

Horizontal pattern.

Affects both males and females.

What is an example of a autosomal recessive genetic disease?

Cystic fibrosis.

What are features of X-linked inheritance?

No male-male transmissions.

Mostly present in males.

Fathers pass on mutation to female carriers.

What is an example of an X-linked genetic disease?

Duchenne muscular dystrophy.

What are some basic model organisms?

E.coli.

Drosophila melanogaster.

Mice.

C. elegans.

Arabidopsis thaliana.

Saccharomyces cerevisiae.

What are model organisms used for?

Used as tools to allow for the study of specific areas of biology.

What are mice models used for?

Physiology and neurobiology.

What are fly and worm models used for?

Multicellular development.

What are yeast models used for?

Cell biology.

What is known as a 'sugar loving fungus'?

Saccharomyces cerevisiae.

What do Saccharomyces cerevisiae metabolise?

Sugar - forms CO2 and ethanol.

Products used in bread and alcohol.

What are the three cell types of yeast cells?

Two are haploid and the other one is diploid.

What is the reproduction methodology of yeast cells?

diploid (a/alpha) = haploid (a), haploid (alpha).

These haploids can reproduce to make another diploid.

How do yeast cells proliferate?

Via budding.

What will starvation of yeast cells result in?

Meiosis = meiotic body (ascus).

When conditions are good the ascus releases haploid cells.

What are yeast cell types determined by?

The mating locus (MAT).

MATa or MATalpha.

How are mutations inherited in yeast cells?

Recessive: diploid - mut/WT = WT phenotype, haploid - WT = WT phenotype or mut = mutated phenotype.

Dominant: diploid - mut/WT = mutated phenotype, haploid - WT = WT phenotype or mut = mutated phenotype.

What are prototrophs?

Wild type yeast cells which can grow on minimal medium.

What are auxotrophs?

Yeast cells which can only grow on His/Ade and minimal medium.

What conditions are required for a successful complementation test?

Only works if both mutations are recessive.

What are the three steps required in carrying out a complementation test?

1. Determine if mutations are recessive.

2. Cross the homozygous mutants.

3. Phenotype F1 progeny - look at children.

If the parents are both mutant in the same genes what phenotype will their children have?

Children will also show the mutant phenotype.

What happens when parents are mutant in different genes?

Children behave the same as each other but will express a wild type phenotype.

Different mutations on parent complement each other.

What are the four oculocutaneous albinism genes?

OCA1.

OCA2.

OCA3.

OCA4.

What is OCA1?

Worst albinism.

Mutation of tyrosinase enzyme.

What is OCA2?

Weak albinism.

Mutation of tyrosinase helper (P protein).

What is OCA3?

Weak albinism.

Mutation of the tyrosine gene.

What is OCA4?

Mild albinism.

Mutation of tyrosine helper (SLC45A2).

What results from crossing two homozygous mutants of the same gene?

All their offspring will be mutants - F1 and F".

What results from crossing two homozygous mutants of different genes?

aaBB x AAbb = AaBb (dominance in F1).

AaBb x AaBb = at least one presents different genes in F2 (means parents have mutations on different genes).

What are the two laws of Mendelian inheritance?

1. Law of segregation.

2. Law of independent assortment.

What are monohybrid ratios?

Self cross: genotypic - 1:2:1, phenotypic - 3:1.

Test cross: genotypic - 1:1, phenotypic - 1:1.

What is the inheritance pattern in Mendelian diseases?

Single gene inheritance - autosomal dominant/recessive, and X-linked.

What are monogenetic disorders?

Conditions which are produced by a single variant gene.

What gene determines earwax?

ABCC11 - wet (homo/heterozygous dominant G), dry (homozygous dominant AA).

What changes the genes for earwax?

SNPs changing glycine to arginine.

What are symptoms of myotonic dystrophy?

Myotonia, muscle weakness, heart problems, chest and breathing problems, digestive problems, eye problems, thinking and planning.

What causes myotonic dystrophy?

CTG repeats in DM protein kinase gene.

Size of repeats correlates with severity.

What is the inheritance pattern of myotonic dystrophy?

Autosomal dominant - translated into mRNA not protein.

What is RNA induced toxicity?

Occurs as a result of sequence repeats = hairpin fold.

What are hairpin folds?

Abnormal folding of sequences due to extreme repeats - sequence folds and binds to itself resulting in an accumulation in the nuclei.

Accumulation = disturbing of biological functions.

What is a test cross?

A test cross is the crossing of two homozygous genes - TT x TT, TT x tt, tt x tt.

F1 ratio - all dominant, 1/2 and 1/2, all recessive.

What happens to musclebind-like splice regulators in a hairpin fold?

They are seqyestered = depletion and loss of function.

What happens to CUG triple repeat RNA binding protein in a hairpin fold?

Increased levels = mis-regulation of splicing events.

What is anticipation?

Earlier and more severe expression of disease in subsequent generations.

What is somatic mosaicism?

Genetic defect in tissues in an individual which can change over time.

What is penetrance?

Proportion of people with repeat expansion for DM who will develop the condition.

What is the cause of Sickle cell anaemia?

A single change in amino acid - haemoglobin muitation.

What are the two amino acids on the outside of the haemoglobin molecule?

Glutamic acid - hydrophilic.

Caline 0 hydrophobic.

What is the difference between HbS/HbS homozygous carriers and HbS/HbA heterozygous carriers?

Heterozygous carriers develop a less severe form of anaemia.

What is pleiotropy?

The ability of a single gene having multiple phenotypic effects.

e.g. Sickle cell anaemia.

What are some examples of X-linked diseases?

Recessive - haemophilia, Duchenne muscular dystrophy.

Dominant - Vitamin D resistant rickets, Rett syndrome.

What is X-linked inheritance?

A gene passed only through the X chromosomes - fathers can't pass to sons.

What is Rett syndrome?

Progressive neurological disorder - mainly affecting girls with unaffected parents.

X-linked dominant inheritance.

What is a dihybrid cross?

A cross involving two traits.

What is the phenotypic ratio of a dihybrid cross?

Self cross - 9:3:3:1.

Test cross - 1:1:1:1.

What is epistasis?

The modification of gene expression by the influence of one gene over another.

What three events can lead to epistasis?

1. When two or more loci interact to create new phenotypes.

2. Whenever an allele at one locus masks the effects of alleles at one or more loci.

3. Whenever an allele at one locus modifies the effects of alleles at one or more loci.

What happens in recessive epistasis?

A recessive mutation in one gene masks the phenotypic effects of another.

e.g. ee is epistatic to the pigment gene BB (BBee = golden coat).

What happens in dominant epistasis?

A dominant mutation in one gene masks the phenotypic trait of another.

e.g. I (white) is dominant to E (dark) - IIEE = white coat.

What is redundancy?

When two or more genes perform the same function so one is inactivated - no effect is caused on phenotype.

What is the modifier effect?

Modifier genes produce a secondary effect to alter the phenotypes produced by primary genes.

What is polygenic inheritance?

Characteristics that are influenced by more than one gene in an additive effect.

e.g. skin colour, Alzheimer's, Diabetes, Cancer, Eczema.

What are copy number variations?

when the number of copies of a particular gene varies from one individual to the next - duplication or deletion event.

How much of the human genome is copy number variants?

5%.

What copy number variants can have obvious impacts?

Those which affect critical developmental genes - Parkinson's and Alzheimer's disease.

What can impact the AMY1 gene copy number variation?

Diets.

Low starch = low AMY1 copy number.

High starch = high AMY1 copy number.

What are multifactorial traits?

Traits influenced by multiple genes and environmental factors.

What type conditions are caused by multifactorial traits?

Congenital malformations - cleft lip (epilepsy drugs consumed by parent - environmental factor).

Adult onset disorders.

What is population genetics?

The study of the distributions and changes of allele frequency in a population.

What are the four main evolutionary processes?

Mutations.

Selection.

Gene flow.

Genetic drift.

What is the Hardy-Weinberg Equilibrium?

Populations in equilibrium maintain stable allele frequencies from one to the next generation.

Assuming - large populations, random and fertile mating, closed population.

What cause the majority of mutations?

Single nucleotide polymorphisms.

What are some selection methods of mutations within a population?

Negative selection - mutation is not kept.

Positive selection - the mutation takes over.

Genetic drift - neutral levels between mutated individuals and wild-type.

What are some examples of selection pressures?

Resource competition - food, habitats, mates...

Predation.

death or illness due to parasites or infectious diseases.

What is an example of natural positive selection?

Sickle cell and malaria.

What can increase the fitness of an individual?

A greater contribution of phenotypes to the next generation.

What is a selection sweep?

When an allele becomes more common in a population as a result of positive selection.

Mutation increases the fitness of the carrier.

What is an example of a selection sweep?

Lactase (LCT) locus - gene variants allow humans to digest milk in adulthood (rise of dairy farming increased mutated individuals fitness).

What is artificial selection?

The selective breeding of plants and animals to promote the occurrence of desirable traits in offspring.

e.g. high oil content in maize.

What are problems with artificial selection?

Development of monoculture (aka all individuals have same advantages and disadvantages) results in no genetic variation.

e.g. Irish potato famine - all wiped out by a single blight.

What is gene flow?

Movement of alleles frequencies between populations.

What can impact gene flow?

Migrations.

Immigration - bringing alleles into a population.

Emigration - loss of alleles out of a population.

What is genetic drift?

A change in allele frequencies caused by random events.

NOT SELECTION.

What are some examples of genetic drift methods?

Bottle neck effect.

The founder effect.

What is the bottleneck effect?

A change in allele frequency following a dramatic reduction in the size of a population (due to natural disaster meaning no trait is favoured).

What is an example of the bottleneck effect in action?

Cheetahs:

Spread across globe but all European population wiped out after Ice Age leaving only African populations.

All pretty inbred now and can succumb to infectious diseases easily and have trouble reproducing.

What is the founder effect?

A reduction in genetic diversity that results when a population is descended from a small number of colonizing ancestors.

What is an example of the founder effect in action?

The Amish - extra digits and heart defects.

What are some examples of population biased diseases?

Cystic fibrosis - most common in Europe, 1:20 individuals are carriers.

HIV - most prevalent in South Africa.

What is GWAS?

Genome wide association studies - examine common variations which could be linked to disorders.

What are the three different GWAS studies?

Clinical.

Molecular.

Cellular.

What is clinical GWAS?

Study associations between genetic differences and human disease traits.

What is molecular GWAS?

Study associations between SNP's and molecular phenotypes.

What is cellular GWAS?

Study associations between SNPs and cellular processes.

What mutations are required for the formation of a cancer?

Two hits are required to form a mutant phenotype as most mutations are recessive.

What are known as the breast cancer genes?

BRCA1 and 2 - expressed in breast tissue cells to help repair damaged DNA or destroy unrepairable cells.

What happens if a BRCA gene is mutated?

No repair of damaged DNA which increases the risk of developing breast cancer.

1:20 people with breast cancer have an inherited BRCA mutation.