Origins of Individual Differences

1. Pairs of chromosomes we have?

2. Autoosmes: what are they, how many do we have?

1. 23

2. Chrom we all share - 22 pairs

What are alleles? How many do we get from each parent?

Variants of genes, get one from each parent in each cell

Genotype vs phenotype difference?

Geno = unqiue combo of all alleles (diff for everyone) vs pheno = measurable characteristics, e.g. weight (combo of genoa nd environment)

What are the 4 bases of DNA? Which strands are complimentary to each other?

1. Adenine

2. Guanine

3. Cytosine

4. Thymine

A on one strand pairs witrh T on other, C with G (same amount of each pair on each mol)

What are 4 stages of DNA replication?

1. Parent DNA strands separate via helicase enzyme

2. Polymerase enzyme makes parent strands create new complementary strands

3. Complementary bases on parent and new strands bond together (A with T, C with G) -- now have 2 mols of DNA, each with 1 parent and 1 new strand

4. DNA coils back into double helix struc

What does transcription of DNA create? After replication, describe the 2 steps of DNA transcription.

DNA transcrip creates RNA

1. DNA replicates

2. 1 of DNA’s strands is copied (called template strand)

3. Complementary bases bond between template (i.e. copied) and non-template (i.e. original) DNA strand — eventually new RNA strand peels away from original DNA strand

Differnce in strutcure and bases between RNA (ribonucleic acid) and DNA?

1. DNA = 2 strands, RNA = 1

2. RNA replaces base T with base U (A will pair with U on RNA)

1. What is a codon? How does it relate to RNA?

2. Codons code for what?

1. RNA = amde of codons: 3-base sequence, e.g. ACA

2. Code for amino acids —> build proteins

1. What is mRNA transcribed from and where is it made in the cell?

2. What is tRNA? Include where translation occurs in body.

1. Transcribed from DNA, made in nucleus

2. tRNA translates mRNA’s codon sequence into amino acids and transfers them to ribosomes for DNA translation

3 steps of DNA translation (using mRNA and tRNA)?

1. mRNA triplet code (e.g. GUA) attracts a tRNA with a complimentary code (e.g. VAU)

2. tRNA transfers its associated amino acid

3. Amino acid bonds to growing chain of amino acid and tRNA mol Is released —> Process repeats

What is a stop codon?

Stop producing extra amino acids, completing chain

Why is the structure of a protein/ amino acids important to its function? What’s the potential effect of DNA changes on protein structure?

Amino acids = unqiue 3D struc which folds into ptotein and lets it perform specific func —> change in DNA can change shape of amino acid —> affects protein struc —> may affect behaviour as proteins create body’s physical systems, e.g. nervous system

Purpose of non-coding DNA (don’t code for proteins) in relation to genes?

Switching them on/ off - regulates gene expression

Exons vs Introns?

1. Exons = protein-coding DNA

2. Introns = non-coding DNA

1. What’s a regulatory sequence?

2. What’s a transcription factor?

1. Non-coding part of intron that regs expression of nearby protein-coding exon

2. Regulates if gene is trasncribed or not - if bind to reg sequence, causes transcrip and protein formation

What is epigenetics?

Environmental factors affecting if genes are turned on/ off (if are expressed) — affect transcription and translation

1. How many base pairs and protein-coding genes do we have?

2. How do individual differnces arrive?

1. 3 billion base pairs, code for 25k protein-coding genes

2. Ind diff in 1 in 1000 base pairs — can change genetic coding of portiens —> ind diff in behaviour and cog

Briefly describe meiosis of gametes

1. Egg and sperm cells = diploids — they split into haploid cells (1 chrom in each cell)

2. Sperm fertilises egg — combines genetic info from haploid cells (one from mum, one from dad) to create diploid cell w/ 23 chrom pairs

What are 3 causes of genetic variation?

1. Segregation - one of each chrom pair from mum and dad separately = transmitted

2. Rnadom transmission of which chrom (creates diff chrom combos between siblings)

3. Crossing over - in a cell, sections of chrom 1 break up and swap with chrom 2

Somatic vs polymorphic mutation?

1. Somatic = changes in DNA of somatic cells (non-gametes) — not inherited by kids

2. Mutations in gametes —> create new alleles —> kids can inherit

What are SNPs (Single-Nucelotide Polymorphisms)? How many gene variants do they have?

Only 1 nucleotide in DNA sequence has changed, e.g. replacing base of a nucleotide — SNPs = only 1 gene variant

1. Synonymous vs nonsynonymous SNPs?

2. What is each one also called>

1. Synonymous (or nonsense) = despite change, still code for sae amino acid

2. Nonsynonymous (or missense) = changes amino acid sequence (so can make new protein as change 3D struc (not always!))

What are triplet repeat mutations? Give example in Huntington’s Disease.

Triplet mut = 3 nucleotides repeat more than normal (if have too many, can cause disease) —> e/g/ H.D.: 40-100 repeats of CAG

How does a triplet repeat of CAG cause Huntington’s Disase?

HD gene = active in nerve cells —> if protein becomes mutated, creates longer glutamine chain —> causes neurodegeneration of nerve cells —> causes HD

What is fragile X syndrome and what kind of impairment can it cause and when (i.e. what needs to happen?)

Triplet repeat of CGG on X chromosome makes longer amino acid sequence —> if have over 200 repeats, can get intellectual disability

In fragile X syndrome, how can a mutation affect genes and cause the intellectual impairment?

Mutation blocks FMR1 gene in brain being transcribed —> FMR1 gene codes for FMR1 protein - protein establishes brain cell connections

1. Why are females less likely to be affected by fragile X syndrome?

2. Why are females’ symptoms with it more varied?

1. we have 2 X chroms — so mutation only makes 1 inactive (which prevents inactive chrom’s genes being transcribed into mRNA)

2. Mutation will only be active in some cells, causing varied symptoms if have FXS (or no symptoms)

What are insertions/ deletions in genetic mutations?

Inserting/ deleting bases — affects amino acid chain length

What is a copy number variation mutation?

Large amount of genome (DNA bases) is deleted or duplicated (could give you more copies of a gene) — more/ less proteins being made — affects Sz and biploar

What are de novo mutations? What families are they more common in: simplex or multiplex?

Mutation during egg/ sperm formation that is only inherited — more common in simplex fams with1 affected person (multiplex = many affected)

What is nondisjunction of chromosomes?

Incorrect meiosis divison — gametes get diff num of chrom copies (e.g. one with 2 and otehr with 0 copies)

What is trisomony? It’s related to what condition?

Having 3 copies of a chromosome — having 3 copies of chrom 21 = can cuase Down syndrome

Why are older mums more likely to have kids with Down Syndrome?

If egg is made clsoer to menopause, higehr chance of nondisjunction occurring —> chrom 21 trisomy may cause Downs

What are these 2 types of chromosome abnormalities:

1. Inversion

2. Translocation

1. Part of chromosome breaks up and joins back in wrong place on SAME chromosome

2. Broken chrom piece joins onto wrong chromosome