L18: Genetics Flashcards
What is a chromosome
Made of a single molecule of DNA
What is a gene
A specific stretch of DNA where the sequence contains the genetic instruction to make a protein.
How many genes does one chromosome have
Hundreds of genes
What are the 2 types of cell division
Mitosis
Meiosis
What does mitosis procure
Identical daughter cells
What does meiosis produce
Haploid gametes
Describe the process of meiosis
1) replicate DNA
2) meiosis 1 division with crossing over and recombination
3) meiosis 2 division
4) this results in 4 haploid gametes
What are the 2 purposes of meiosis
Reduce chromosome number
Promote genetic diversity through re-assortment of genes where chromosomes cross over
What are the 2 stages where error in meiosis can appear
DNA replication
Meiotic cells division
What type of error would dna replication give rise to
New mutations (copying errors)
What type of errors would meiotic cell division five rise to
Anomalies in chromosome number
Anomalies in chromosome structure due to unequal crossing over
What are the classes of genetic disorder
Single gene disorders
Multifactorial disorders
Chromosomal disorders
Mitochondrial
What are single gene disorders
Mutation in the single gene that affects the function of the gene so it produces a faulty protein
What are multifactorial disorders
Variants within multiple genes that have minor effects but come together with the environment to cross the threshold to cause disease
What is chromosomal disorders
Genes themselves are normal but there is a dosage problem e.g trisomy
What type of mutations can occur in single gene disorders
Missense Nonsense Frameshift Duplication Deletion Insertion
What is missence mutation
Where you have a substitution of a single base e.g swap b to c, it can either change the protein are does not because the code is degenerative
What is frameshift mutation
Insertion or deletion less than 3 base so whole reading frame is altered
What are the 2 subtypes that we can classify chromosomal anomalies into
Numerical
Structural
What are the numberical chromosomal disorders
Aneuploidy
Polyploidy
What does aneuploidy chromosomal disorders give rise to
Monosomy
Trisomy
What does polyploidy chromosomal disorders give rise to
Triploidy
What are the structural chromosomal disorder types
Translocation
Deletion
Duplication
Inversion- turned by 180 degrees
What are the 2 types of translocation that can occur
Reciprocal
Robertsonian
What are the 3 most common trisomy chromosomal disorders that occur in the new born
Trisomy 21= Down’s syndrome
Trisomy 18= edwards syndrome
Trisomy 13= patau syndrome
What are the common numerical chromosome disorders that occur in sex chromosome
Turners syndrome 45 X
Klinefelters syndrome 47 XXY
If an individual is affected by a condition what type of symbol are they on a pedigree
Shaded
What is the symbol that represent a male on a pedigree
Box
What is the symbol that represents a female on the pedigree
Circle
What symbol represents marriage on a prefigure
Horizontal line connecting the box and circle
What symbol represents consanguineous couples
Double horizontal line
What does consanguinity mean
Couples that are related other than marriage e.g causing that are married
What are the factors that increase the risk of pregnancy genetic disorder
Family history of the genetic disorder Parental consanguinity Population ancestry of parents Increased maternal age Increased paternal age Environmental exposure to DNA
What type of condition is cystic fibrosis
Autosomal recessive
If 2 couples are both carriers for CFTR gene what are the possible outcomes in the offspring
Unaffected
2 carrier
1 affected
Therefore What is the chance of CF affecting the pregnancy
1/4
If a couple does not have a family history of CF what is there chance for being a carrier
Same as the rest of the population i.e 1 in 23 (1/23)
If there is a recessive condition in the family what does consanguinity increase the risk of
Carrier
What are the 2 types of translocations
Robertosnian
Reciprocal
What is robertsonian translocation
When you get a fusion of the centromeres of the short and long arm between specific chromosomes of (13,14,15,21,22)
What is reciprocal translocation
When you have a break in 2 chromosome which exchange fragments
What is balanced reciprocal translocation
When the chromosome breaks and joins to another, it is balanced because the fragments switch places and all the genetic material is still there
What can balanced recipricol translocation result in
Balanced carrier
What zygote does balanced recipriocla translocation carrier form with normal gametes at fertilisation
1 Normal
1 balanced carrier
2 partial trisomy and partial monosomy
What does partial monosomy and partial trisomy have a risk of
Miscarriage
Congenital malformation
Developmental delay
Intellectual disability
Why is it important to know the ancestral population of a person
Because some genetic condition are more common in certain ancestors
Why does the risk of genetic disorders increase with increased maternal age
When an egg ovulates it is in meiosis 1 block until fertilisation occurs so meiosis 2 happens. The length interval for meiosis increases the risk of spindle formation so you can get non-disjunction effect
What does non disjunction result In
An egg having 2 chromosome instead and of 1 so when it joins with the sperm that has 1 chromosome this results in trisomy.
Why does the risk of genetic disorders increase with increased paternal age
1) When sperm is produced one spermatogonium remains behind to maintain the division and divide
2) older the sperm is the more cell division it has gone through
3) it has replicated DNA more often so you increase the risk of mutation i.e single gene disorders
On a pedigree how does a gene disorder look like if the cause is due to increased paternal age
Only one child is affected
Name a condition that is due to elevated paternal age
Achondroplasia
What are the option available for couples with increased genetic disorder
Adoption Postpone pregnancy Accept the risk Prenatal diagnosis Artificial insemination by donor egg/sperm
What does prenatal diagnosis involve
Ultrasound scanning
Chorionic villus sampling
Amniocentesis
Non invasive blood testing
What does ultrasound scanning look at
Structural anomalies at 20 weeks
What does chorionic villus sampling involve
You collect a chorionic villus sample and look at the chromosome of the baby
What is amniocentesis
You take a sample of the amniocentesis and look at babies chromosome of dna
What is non invasive genetic testing
A blood test as fetal blood circulates in maternal blood
What are the 2 methods of non invasive genetic testing for x linked conditions
Fetal sexing
What is the method of non invasive genetic testing for trisomy 21/18/13
NIPT (screening not definite diagnosis)
