Intro to neurogenetics Flashcards
What is the building blocks of the genetic code
Nucleotide or bases
What are the four bases in DNA
adenine (A), cytosine (C), guanine (G) and thymine (T)
What are the building blocks of proteins
Amino acids
What constitutes the genetic code for a particular amino acid?
A specific sequence of three bases, called codon
What is the structure of a DNA helix
Double-stranded
What is about the two strands in a DNA helix
Each base has a partner on the other strand Cytosine pairs with Guanine (C–G) Adenine pairs with Thymine (A–T)
Where is DNA bundled in
Chromosomes
How many chromosomes the human karyotype comprises
46 chromosomes 22 pairs of autosomal chromosomes (1–22) Two sex chromosomes (XX or XY)
What determines the function of a protein
its structure
What determines the structure of a protein
its sequence of amino acids
Can a change to just a single base of a codon change the amino acid?
can but not necessary as each amino acid has multiple possible codons; for example, the codons GCT, GCC, GCA and GCG all represent Alanine
What is a SNP
Single-nucleotide polymorphism
A position on the genome at which the base (nucleotide) differs between individuals
e.g., some of us have a T (the major, most common) while some have G (the minor, less common)
What determines an individual’s genotype at a SNP
the two alleles on the two copies of the chromosome
What are the types of genetic varients?
Single-nucleotide variants
Structural variants:
- Insertion–deletion variant - Bases added or missing
- Block-substitution variant - Multiple bases substituted
- Inversion variant - Bases replaced with reversed sequence from other strand
- Copy-number variant - Sequence of bases repeated one or more times
What is the random X-chromosome inactivation
To avoid excess dosage of X-chromosome proteins in females, one copy of the X chromosome in each cell is silenced or inactivated. In many mammals (including humans), this process is random in each cell, and occurs earlier in the development
What will happen where there are two X-chromosome in one cell
The XIST gene produces an RNA transcript that coats one chromosome, which is inactivated as a Barr body The TSIX gene on the other chromosome produces an RNA transcript that suppresses transcription of XIST TSIX is the antisense partner of XIST, both are encoded by the same stretch of DNA, but are transcribed in opposite directions
What is RNA transcript in X-chromosome inactivation
An RNA transcript is an intermediate step in the process of converting a gene encoded in DNA to a protein
What is the formula for classical genetics heritability
- P (phenotypic variance) = G (variance from genes) + E (variance from environment)
- P = G + E + G*E (variance from gene-environment interactions)
- P = G + E + G*E + 2covGE (covariance between genes and environment)
H(heritability)2 = G/P:
- It is a local measurement, valid for a specific population at a specific time
- It depends on the amount of genetic and environmental variation present in the population
How can we measure heritability?
Before the advent of molecular genetics, we used genetic epidemiology
Study designs in genetic epidemiology all exploit the fact that related individuals share a predictable amount of genetic material
For example, in twin studies, we look at concordance rates
Dominant vs recessive
Dominant traits require mutation on one copy of the chromosome for expression of the phenotype Recessive traits require mutation on both copies (or only copy) of the chromosome
Autosomal vs X-linked
Autosomal traits are carried on the autosomal chromosomes (1–22) X-linked traits are carried on the X chromosome
In a pedigree chart, what represents female and male
female is circle male is square
Which mode of inheritance says equally common in both sexes
autosomal dominant autosomal recessive
Which mode of inheritance says cannot transfer father to son
X-linked dominant X-linked recessive
Which mode of inheritance says cannot skip generations
autosomal dominant X-linked dominant
Which mode of inheritance says two unaffected parents cannot have affected offspring
autosomal dominant X-linked dominant
Which mode of inheritance says two affected parents cannot have unaffected offspring
autosomal recessive X-linked recessive
Which mode of inheritance says daughter of affected father must be affected
X-linked dominant
Which mode of inheritance says father of affected daughter must be affected
X-linked recessive
Which mode of inheritance is more common in males
X-linked recessive
Which mode of inheritance
recessive
Trait cannot be dominant as unaffected parents have affected offspring
Which mode of inheritance?
autosomal recessive
Trait cannot be X-linked recessive as an unaffected father has an affected daughter
Which mode of inheritance?
dominant
Trait cannot be recessive as affected parents have unaffected offspring
Which mode of inheritance?
autosomal dominant
Trait cannot be X-linked dominant because affected father has an unaffected daughter
Which mode of inheritance?
Probable X-linked dominant inheritance
Sex linkage cannot be confirmed (only disconfirmed) from pedigree charts
Autosomal traits could generate the same pedigrees
Unaffected father with affected daughter rules out X-linked recessive inheritance
Which mode of inheritance?
Probable X-linked dominant inheritance
Affected father with all daughters and no sons affected suggests X-linked dominance
Which mode of inheritance?
Probable X-linked recessive inheritance
Unaffected father with affected offspring rules out dominant inheritance
Which mode of inheritance?
Probable X-linked recessive inheritance
Unaffected parents with all sons and no daughters affected suggests X-linked recessive inheritance
Which mode of inheritance best explains this pedigree?
Autosomal: Father-to-son transmission
Dominant (most likely)*: No skipping over five generations
Which mode of inheritance best explains this pedigree?
Recessive: Unaffected parents with affected offspring
X-linked (most likely): Only males affected in large pedigree
