W12

Question 1

what are the type of distribution of phenotypes possible

Answer 1

A. discontinuous distribution of phenotypes

1. one gene, eg. blood groups
2. several genes + environment; therefore multifactorial

B: continuous distribution of phenotypes
- several genes and influenced by environment; quantitative traits

Question 2

what are multifactorial traits

Answer 2

• discontinuous distribution of phenotype where the trait is either present or not
• if these multifactorial traits are influenced by the environment, identifying the environmental component and reducing it may reduce incidence

Question 3

what is a threshold model and to what type of trait/distribution does it occur in

Answer 3

• multifactorial traits which come from discontinuous distribution
• where we can have different thresholds for makes and females so more common in the sex with the lower threshold

what happens?
- accumulate genetic predisposition from many genes until enough environmental factors present

Question 4

what is a continuous distribution of phenotypes and what are the properties of its trait

Answer 4

quantitiative

1. continuous distribution
2. controlled by many genes- polygenic
3. affected by environmental factors

Question 5

what is polygenic inheritance, what are its assumptions

Answer 5

assumptions:
- many gene loci contributing to the phenotype of the quantitative trait
- each locus has two alleles, A1 and A2
- there is no dominant phenotype
- alleles are inherited in a similar way to any other trait
- assume Allele A1 adds to trait contributor
- assume Allele A2 does not add to trait, therefore, non contributor
- the effect of the alleles is cumulative

HOW DO WE TELL POLYGENIC INHERITANCE IS OCCURING?
- F1 can be explained by other gene interactions, but looking at F2, we see a difference ie. 2 genes, but 5 phenotypes

Question 6

what is the effect of increasing number of loci influencing a quantitative trait

Answer 6

as the number of genes controlling a phenotypic character increases, the differences between phenotypic classes becomes less distinct

Question 7

what is heritability and its application

Answer 7

a statistical measure of how strongly the phenotype of the offspring will resemble the phenotype fo the parents

breeding for improvement, leading to a new mean in the next population.

Question 8

how can heritability be measured in humans

Answer 8

twin studies using MZ/DZ twins

• concordance: both twins with trait
• non concordance: one twin with and one without

if the difference in concordance between MZ and DZ twins is high, it suggests there is a large genetic component

there are many bewares for using this method tho, lets say for infectious disease; everyone will be affected, shciz; depends on paper definition of schiz,

we make the assumption there is a similar environment so the variable is in the genes

Question 9

how do we work out how many polygenes there are and how much they contribute

Answer 9

1. find number of offspring for one trait same as parent and divide this by total number of offpsring
2. which ratio match (¼)^n, n=number of polygenes
3. range of trait: max-min=base of trait
4. how many contributing allies max=number of polygenes times 2
5. base of trait/max contrib. of alleles
6. what genotype? = how many contributors

Question 10

what is epigenetic

Answer 10

changes in gene expression that do not involve the change in DNA sequence
for example:
- methylation can influence gene expression
- modifications of chromatin structure can influence gene expression without changing the dna
+dna methylation/demthylation
+histone acetylation/deacetylation
+rna interference

Question 11

what is genomic imprinting

Answer 11

the sex of transmitting parent produces observable differences in phenotype
- this is due to specific genes being differentially marked during parental gametogenesis

Question 12

what is the evidence of genomic imprinting

Answer 12

1. triploids (3N) with 2N pat + 1N mat are different from 2N mat and 1N pat
   - 2N pat + 1N mat: teratoma with teeth/hair evidence of embryo
   - 2N mat and 1N pat: hydatidiform mole; mass of membrane, no evidence in embryo
2. 15q11-q13 mutation selection leads to different syndromes: mono allelic expression
   - del of mat 15q11-q13: Angelmann syndrome: electrophoresis will show no A from mother
   - del of pat 15q11-q13: Prader Willi syndrome where electrophoresis will show no A from father

Question 13

how can electrophoresis be sued to differentiate prayer willi syndrome and angelmann syndrome

Answer 13

choose a region of dna with polymorphism, then PCR region and run on a gel

• no A from mat, angelmann

- no A from pat, prayer willi

Question 14

what other causes are there for PWS/AS

Answer 14

uniparental disomy where both chromosomes of a pair come from same parent
A. PWS, UPD- mat 15
B. AS/UPD - pat 15

Question 15

describe types of UPD

Answer 15

heterodisomy: non disjunction of meiosis 1
- electrophoresis will show 2 bands
isodisomy: non disjunction of meiosis 2
- electrophoresis will show 1 band (thick-ish)

Question 16

what is process of inheritance of imprint

Answer 16

• due to methylation, if a male inherits a maternal imprint but passes to his daughter, the imprint changes to the paternal imprint
• this is because: early spermatogenesis or early oogenesis wipes imprints in primordial germ cells, but this is reestablished according to the sex of the parent
• new methylation patterns according to the sex of the parent (which may be different from what the parent had)

Question 17

what are some facts about imprinting

Answer 17

approximately 60 human loci
has to be reversible
reverse in gametogenesis
methylation of cytosines

Question 18

in population genetics how can variation be detected

Answer 18

• look for visible differences in phenotype
• chromosome differences eg. length of long arm of y
• immunological markers like blood groups
• protein gel electrophoresis, eg. drosophila enzymes (will have different weights)
• minisatellites
• microsatelites
  singel nucleotide polymorphisms

Question 19

what are variable regions often in non coding regions and describe them

Answer 19

minisatellitles of 15-100b, total length is 1-5kb
- tandem repeats of 18 bases

microsatellitles- STR - 2-9 bases
- can have several alleles according to how many repeats

single nucleotide polymorphism (SNP)
- 1 base can onus have two alleles at a locus

Question 20

what is variable number of of tandem repeats

Answer 20

• minisaatellitles or micrositellites
• in non coding regions of genome
• repeat sequence between 15bp-100bp
• but varies between person to person
• THIS REPEAT IS INHERITED FROM PARENTS

Question 21

what analyses can be done on variable regions in non-coding regions

Answer 21

1. multilocus probe- found in more than one location
   - use primers that locate several regions
   - mini satellites
2. single locus probe- use primers that find one locus
   - minisatellites
   - micro satellites

Question 22

what is the original source of variation?

Answer 22

mutation- original source of all variation

Question 23

how is variation maintained?

Answer 23

1. mutation- original source of all variation
2. recombination at prophase 1 of meiosis
3. segregation of alleles at anaphase 1 of meiosis
4. independent assortment of chromosomes at anaphase 1 of meiosis
5. fertilisation between genetically different gametes

Question 24

how are SNIPS detected?

Answer 24

• dna sequencing

- restriction cutting sites where the change results in the loss or gain of a restriction enzyme recognition sequence

Question 25

what are the applications of SNIPS

Answer 25

• identification
• parentage testing
• forensic analysis- crime
• victim identification in a mass disaster
• animal identification eg. racehorses
• conservation biology in evolutionary studies

Question 26

how are SNIPS used? the process

Answer 26

extract dna sample

• make multiple copies via PCR
• run samples on gel

Question 27

what is mendelian population

Answer 27

a community of interbreeding organisms

the set of genetic information carried by the population is called the gene pool ie. all the alleles carried by all members of the population

gene flow occurs when members of the population move

Question 28

what is meant by polymorphism and monomorphism

Answer 28

poly: two or more forms of a trait exist in a mendelian population of an organism
- the frequency of the rarest form cannot be explained by recurrent mutation alone

mono: only one form is found in a mendelian population

Question 29

what is HW equilibrium

Answer 29

• untrue: alleles for dominant traits always increased and recessive alleles decreased
• HW: genotypes in proportion of p=f(A) and q=f(a)
  p^2+2pq+q^2=1
  p^2=f(AA)

if heterozygote cannot be distinguished, allele frequency of recessive allele can be assumed as following HW equilibrium

this remains constant across generations

note: HBS can have constancy of allele freq. does not mean HW equilibrium

Question 30

what are the assumptions of random mating?

Answer 30

1. random mating
2. no migration, no gene flow
3. no selection acting
4. no mutation
5. infinite population size- large enough to prevent sampling errors and random effects

Question 31

in what cases will HW equilibrium

Answer 31

if a population is not in HW equilibrium, one generation fo random mating will esrtabluhs HW equilibrium if HW assumptions apply and locus is autosomal

Question 32

if a population is not in HW equilibrium for an x linked trait, one generation of (…) will (…)

Answer 32

if a population is not in HW equilibrium for an x linked trait, one generation of random mating will NOT restore equilibrium