BI111 Lecture Notes - Lecture 1: Genetic Drift, Mendelian Inheritance, Mitosis

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4 May 2017
BI111-Lecture 1 January 4th, 2017
DNA are long sequences of nucleotides:
Each nucleotide made of a deoxyribose sugar, phosphate and nitrogenous base (Long chains with
sugar phosphate backbone which expose the bases, bases form complimentary bonds which form
in opposite directions)
Cytosine and Guanine have a triple bond
Adenine and thymine has a double bond
Double helix and can be very long which contains a huge amount of genetic information
(each cell has over 3billion genes)-Ladder
Semi-Conservative replication process (DNA Helix is unzipped and a complimentary
strand is synthesized which then creates a new DNA molecule using an old RNA strand)
Proofreaders which ensures that DNA replication is quite accurate because they repair
mismatch that occurs during synthesis
Typos are always made but that’s what creates evolution (creates mutations that are
added into the gene pool- gives us new, novel traits and species which leads to the
evolution of life)
Mutation Rates
Vary within and between taxa
Vary with environmental conditions
Higher in RNA viruses than in DNA viruses (Because RNA is single stranded so it
doesn’t have a template that will catch mistakes thus resulting in higher mutations)
Higher in mitochondrial DNA than in genomic DNA
Higher in asexual species than sexual species
In humans- 1.1x10-8mutations, per site per generation (1 or 2 novel mutations per
Humans contain huge genetic variations (missense mutations- From the slide 15 “there
are lots of mutations out there”)
On the road to the Phenotype…
Introns are removed from Pre-mRNA before translation
Alternate mRNA transcripts created by selective slicing/arrangement of exons
All mRNA strands are turned into amino acid sequences which are determined by codons
Lots of redundancy in amino acid codons but the genetic code also has specificity
mRNA has the sequence which creates the polypeptide
Start codon: AUG, Stop Codon: UAA, UAG, UGA
Mutations in mRNA (Affect the relationship between genotype and phenotype- Change the
word, placement, letters)
Missense Mutation-Typo where there is a single nucleotide change which results in a
codon that codes for a different amino acid
Nonsense Mutation- A mutation in which a sense codon that corresponds to an amino
acid specified by the genetic code is changed to a chain- terminating codon
Silent Mutation- A mutation in DNA that do not significantly alter the phenotype, which
can occur in non-coding regions (introns), or exons (AAA, AAG)
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Frameshift Mutation- Genetic Mutation caused by indels (insertions or deletions) of
several nucleotides in a DNA sequence that is not divisible by three
Mutations can Affect Phenotype
Can cause sickle cell anemia which is a malformed hemoglobin
Due to a change in the polypeptide from Glu to Val
Create genetic variation
Many Alleles, Varying effects on Phenotype
Inherited alleles, one from mother and one form father
Homozygous- Same alleles (A-A or a-a)
Heterozygous- Different alleles (A-a)
BI110- Lecture 2 January 6th, 2017
Dominant- One allele overrides the allele of another (Big A) and will always be
o We are a diploid organism; we can have genes that are homozygous (both
recessive alleles will be the only possibility for the recessive allele to be shown as
a phenotype) or heterozygous (Will display the phenotype of the dominant allele)
Manx Cat
Interferes with the production of the spinal cord (a genetic mutation)
They have one copy of this dominant allele that causes this mutation and results in a lack
of a tail (Aa)
Tailless mutation is dominant and homozygous is lethal (AA)
“All white” fur controlled by “White masking” gene
They carry one allele for white hair which lacks melanin which gives rise to pigment-
Dominant (Melanocytes form the inner part of the ear of cats which allows sound to
travel through the ear)
Epistatic- A gene that determines whether or not a trait will be expressed
Pleiotropic- Producing or having multiple effects from a single gene
Mutations usually makes things much worse (deleterious)- which is less efficient in
Cat Examples
Dense Pigment-Recessive homozygous (Black vs. Grey)
Piebald Spotting Gene- Dominant gene (Ginger, ginger spotted, Little ginger spots but
mostly white)- Modifier genes can produce wider array of phenotypes
So far we have been talking about auto-chromosomes…
Sex chromosomes- Genes on these chromosomes complicate matters because they
determine which pathway biological sex is determined
Turtles are sensitive temperature to develop their biological sex
X and Y(few genes and degenerative) chromosomes determine sex
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o Same gamete (Homogametic XX)
o Different gamete (Heterogametic XY)
o In birds, the male is Homogametic sex (ZZ) and the female is heterogametic (WZ)
The male can give off one X and one Y while the female can give off two X’s but the
offspring receives one chromosome from each parent
Consequences of Sex Chromosomes
Two copies of X has twice as many genes to transcribe
Dosage compensation
o Inactive one of the X chromosomes are deactivated by curling itself up into an
inert cell, it gets copied but it is never expressed (X-inactivation)
o A cell can express different phenotypes of a gene
Is this the only way to compensate for differences between the sexes in the number of sex
o Fruit flies increase rate of transcription and translation of X chromosomes in
How is Genetic Diversity possible?
Principle of Independent Assortment
Two stages of meiosis
Different possibility of chromosomal arrangement produced by two gametes
2^23 for unique combinations of gametes (excluding mutations)
Genetic Recombination
One of the pairs of the sister chromatids from the homologous pairs intertwines and
exchanges a section of its genetic coding, its cut at an exact point
Unique combinations of different sets of loci (genetic variation creating diversity)
Some genes such as Tyrosine will less likely be broken apart which causes different
frequencies than what would occur by chance
Qualitative traits (Phenotype)
Gregory Mendel (Purple or white flowers, peas were yellow or green, wrinkled or soft)
Most traits are quantitative (lots of variation) and polygenic
o Traits that involve colour, texture are monogenic (Under synthetic control)
o Traits that involve length/width or speed are polygenic (Multiple genetic control)
Chromosomal Alterations (Consequence for genetic change)
Deletion: Broken segment lost from chromosome
Duplication: Broken segment inserted into homologous chromosome
Translocation: Broken segment attached to non-homologous chromosome
Inversion: Broken segment reattached in reversed orientation
Non- disjunction
Failure of homologous separation during Meiosis I
Failure of chromatid separation during Meiosis II
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