Coding Life: Patterns of Inheritence Flashcards
patterns of inheritance
how genes are passed down from one generation to the next.
molecular level of genetics
for instance genes that control certain traits
transmission level
how a gene is passed from one generation to the next
population level
advantages of traits in different environments
trait
characteristic of an organism eg. Seed colour
phenotype
appearance of an organism eg. Yellow seed
genotype
genetic composition of an individual eg. YY, Yy or yy
gene
unit of heredity (region of DNA) that influences a trait eg. Gene for seed colour
allele
alternate version of the same gene eg. Y or y
locus
specific place on a chromosome occupied by a gene
homozygote
an organism with two of the same alleles at a locus
heterozygote
an organism with two different alleles at a locus.
modern transmission genetics - Mendel and his discoveries
Mendel observed how traits passed down in peas
Chose traits he was interested in - seed colour, shape (round or wrinkled)
All happened to be controlled by single genes (fortunate)
Had two true breeding strains (always give yellow or always give green) and crossed them to produce F1 generation and observe the phenotype
Found that all were yellow!
Yellow is dominant and green is recessive (do not blend)
reciprocal cross
involve swapping the phenotypes of male and female parents
Same result in F1 offspring
Gender of parent does not matter in this case
F2 generation
Cross F1 together and look at phenotypes
Found that 3:1 yellow to green
7 different traits that all end up about 3:1 (Law of Segregation)
law of segregation
Cross AA and aa
F1 are all Aa
Half gametes are A and the other half are a
From a punnet square, AA, Aa, Aa and aa form
3 out of 4 are yellow
3:1 ratio for all 7 traits
segregation and test crosses
Test cross: a cross with a homozygous recessive individual that reveals the genotype of the other parent.
Can work out if AA or Aa
segregation of alleles in meiosis
One chromosome for AA and the other for aa (cell is heterozygous) in meiosis 1
Segregate to get 2 A gametes and 2 a gametes (haploid)
product rule
probability of independent events occurring together is the product of the probabilities of the individual events (can be multiplied).
sum rule
probability of either of two mutually exclusive events occurring is the su, of their individual probabilities.
incomplete dominance
intermediate phenotype in the heterozygote forms. eg. Red and white flower produce pink.
Pea seeds are complete
codominance
both phenotypes are seen in the heterozygote.
A and B are co-dominant so some people have blood group AB in the genotype and phenotype
pleiotropy
Pleiotropy: one gene can affect multiple traits
Eg. Cross two Manx cats together and progeny = 2 Manx : 1 normal
MM results in death
Gene that affects trail development and viability
independent assortment
inheritance of one gene does not influence the inheritance of another. Located on different chromosomes.
mendel and the law of independent assortment
True breeding strain of yellow wrinkled and green round crossed
Get 9 yellow round, 3 green round, 3 yellow wrinkled and 1 green wrinkled
9:3:3:1
Gametes can be AB, Ab, aB or ab
These genes are acting independent to each other so we can predict this ratio
independent assortment in meiosis
Diploid cell is Aa and Bb
Can get AB x2 and ab x2 or Ab x2 and aB x2
Completely random, two traits controlled by two genes that behave independently
epistasis
Two breeds of chooks
One is white because of an inhibitor that inhibits pigment
One does not produce pigment
In F2 generation, most are white but some are brown (lack inhibitor and have one dominant allele for colour)
Inhibitor masks what is happening at colour locus so the ratio is 13:3 instead
Not independent assortment
pedigree and conventions
Horizontal line is mating Vertical line is progeny Squares are males Circles are females Diamond is when gender is unknown Identical twins have a big triangle joining them Fraternal twins have a small triangle Double line horizontally means mating between relatives The shaded symbol is affected by a trait
dominant alleles in pedigrees- penetrance and expressivity
Affected individuals in each generation
Vertical transmission from generation to generation
About half of progeny are affected
Equally likely to be males or females
Penetrance: has the trait or does not have it
Reduced penetrance: has the alleles but does not show it and looks like the trait skips a generation
Expressivity: can have it to different degrees
recessive alleles in pedigrees
Skips generations
Equally likely to be males or females
Often results from incest (consanguineous)
inheritance of mitochondrial DNA in pedigrees
Small circular DNA in mitochondria Mutations in it can lead to disease Passed from mother to children Affected female passes it onto all her children An affected male will not pass it on All that are affected show the trait
human sex chromosomes
Only share a few genes (at the tips which helps them to pair up)
50% males and 50% females
x-linked genes
Red eyes female crossed with white eyes male
F1 all have red eyes
F2 have females with red eyes and males are 1:1 red or white
X-linked recessive (females are heterozygous or homozygous without the trait) and males have it and are affected or do not have it
x-linked recessive mutations in humans
Usually affected individuals are male (one X)
Heterozygous female may be unaffected but can pass it onto sons
Sisters of affected males might have affected sons
If a male is affected, sons are not affected (receive the Y)
x linked dominant have different frequencies (more 50/50)
genetic linkage
Two genes are located on the same chromosome and do not segregate independently - always red eyes and weird wings (parental combinations)
But crossing over and recombination can mean that white eyes have weird wings (recombinant)
recombinant and non-recombinant chromosomes
Cross over in prophase 1 and physical exchange of chromosome occurs
Frequency is a measure of the physical distance between the two genes - can form genetic maps
The further apart, the more likely recombination will occur between them.
More likely to stay together if closer
Non-recombinant are parental
complex traits
multiple genes and environmental factors influence traits
Height in humans
Milk production in cows
Skin colour
Get a distribution curve
Twin studies can look at how much genes are involved
what are exceptions to Mendel?
Genetic linage and x linkage are exceptions to Mendel
what is hemizygous?
Males are hemizygous (only a single copy of a chromosome, resulting in expression of the phenotype)
proband
the person seeking genetic counselling
wildtyle
most abundant trait in a population (anything else is a mutation)
mendelian genetics of Wilson’s disease
Copper builds up in the body Autosomal recessive Pre-natal screening Discuss treatment options Better disease surveillance - keep in touch with family to see what’s going on
how much DNA do we share with other humans? fingerprinting?
Humans share 99.9% of their DNA
0.01% is large and can be used to build a unique profile like a fingerprint
Used in forensics, paternity testing etc.
STR
Short Tandem Repeats (STR) is used - consider them like alleles. All are equal but have different numbers of repeat 15/11 heterozygous or 15/15 homozygous
No dominant or recessive
Inherited from parents
Can see what repeat come from each parent
We will use STR to determine what baby belongs to what mother
We will have 3 loci
Less repeats = shorter PCR
PCR
Amplifies specific sections of DNA
Increases exponentially
Requires primers that bind to the chromosome at specific regions
Bind outside the STR region
Replication forks form and move towards each other
Use temperature (94) to seperate strands, decrease to 64 for annealing and raise again for extension
agarose gel electrophoresis
DNA is negative when dissolved in water
Oxygens lose a hydrogen and become negative
Apply electric current and it moves away from the cathode (negative electrode) to positive electrode
Smaller molecules will move further
Longer ones have more resistance
Wear gloves to prevent cancer (chemical binds to DNA permanently)
Use pipette to load ladder (DNA strands)
Load into well
Use a new tip for each sample
Thicker, brighter band (doublet) means they are homozygous for the same locus
50% DNA will be shared with the mother so we can work out whose baby is whose
gene regulation
Turning genes off and on
Looking at prokaryotic gene structure
Organised in operons (grouped genes that have same function)
No introns
Promoter - located upstream of genes. RNA polymerase binds here to transcribe
Operator may inhibit RNA polymerase by putting proteins on the operator
araC binds to operator and bends DNA so that the RNA polymerase is blocked
Insulin is produced by using recombinant plasmids - needs to be controlled otherwise cells die
gene regulation in our experiment
Using reporter genes (gfp) behind op and prom and this allows us to determine the amount of therapeutic generated
Strength of promoter determined by the amount of GFP produced
Tight = how stringent it is = specificity of regulation
Only want it expressed when it is turned on
Be given different op and prom mutants and work out when best GFP production occurs
GFP will glow green under UV light
In silico analysis we will look at sequences of DNA
Compare each mutant to the wild type
Lack of asterixes mean there is disparity and might be the cause of change in results
