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Flashcards in Week 3 Genetic Basis of Evolution Deck (40)
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1

Define a Gene

a DNA segment that contributes to phenotype/function 

2

Define a Locus (pl. Loci)

‚Äì  The position on a chromosome of a gene or other chromosome marker

‚Äì  Can also refer to the DNA at that position
‚Äì  The use of locus is sometimes restricted to mean regions of DNA that are expressed

3

What procedure can be used to find specific DNA sequences in the genome?

FISH = flourescence in situ hybridisation

MYCN is an oncogene in Neuroblastoma, the FISH procedure can find the locus of this oncogene

4

Define an Allele

Variant of a gene
Different alleles can lead to different phenotype 

5

How many copies of each gene does a diploid carry?

2 copies of each gene

6

Alleles present in a homozygote and heterozygote?

homozygote: possesses two copies of the same allele 
heterozygote: possesses two different alleles 

7

What is the allele frequency (proportion) calculation?

(2xHomozygote + Heterozygote) / (total)

8

Define a Genotype

The genetic makeup of an individual (one or more loci) 

9

Genotype Frequency Calculation

10

When alleles are rare, are they more commonly found in homozygote or heterozygote genotypes?

Heterozygote genotypes




11

Define a Phenotype

The physical/behavioural (etc.) characteristics of an individual

Interaction of genes and environment. Genetic component of the phenotype is heritable, environmentally acquired component of phenotype is not. 

12

Define a Gamete

Germline cell that is able to unite with another of the opposite sex during sexual reproduction

– Produced by meiosis
‚Äì Contains half the chromosomes of the parents 

13

Define a Zygote

The earliest developmental stage of the embryo

‚Äì Produced by the fusion of two gametes 

14

Does the terms ‚Äòdominant‚Äô and ‚Äòrecessive‚Äô apply to genes or alleles? 

Alleles

15

What is the Hardy-Weinberg Equilibrium? 

Developed as a null model, in order to understand how changes in gene frequencies occur. That is, we need to understand the conditions under which NO evolution will occur

In 1908, GH Hardy and W Weinberg independently published a theorem showing how allele frequencies behave given a particular set of assumptions. 

16

Assumptions of Hardy-Weinberg Equilibrium:

‚Ä¢  The organism is diploid
‚Ä¢  Reproduction is sexual
‚Ä¢  Generations are non-overlapping
‚Ä¢  Mating is random
‚Ä¢  Populations are infinite
‚Ä¢  There is no mutation
‚Ä¢  There is no migration
‚Ä¢  There is no natural selection/drift 

17

HWE: Given the adult population, what is the value of f(p) and f(q)?


f(p) = 137/200 = 0.685 
f(q) = 63/200 = 0.315 

18

HWE: Gene and genotype frequencies must sum up to what? 

What are the equations for the theorem?
p + q = 1 
p2 + 2pq + q2 = 1 

1

19

HWE: If the assumptions of HWE are met, frequecies change or do not change?

do not change

20

HWE: When observed genotype frequencies are equal to the expected genotype frequencies under the HWT, we say that the population is in .... 

HWE

21

HWE: A population will go to HWE in only .... generation of random mating 

in only one generation of random mating 

22

Define Evolution

A change in allele frequencies over time 

23

What are the two factors which are major contributors to genetic differentiation? 

Genetic drift & Selection

24

Define Genetic Drift 

(what is it a consequence of & where does it take place)

process by which allele frequencies change over time due to the effects of random sampling 

- Takes place as a consequence of finite population size
- Genetic drift takes place in all populations, and any selection must occur against this background of drift

25

How does genetic drift work?

- the change is due to "sampling error" in selecting the alleles for the next generation from the gene pool of the current generation. 

- By pure chance we might sample a particular allele more or less often than expected, causing the allele frequencies to change from one generation to the next

26

Graph of a particular allele frequency as it changes over time:

what happens?


- allele frequency eventually gets to p=1

27

Graph of a particular allele frequency as it changes over time: why does the allele frequncy get stuck at p=1?

Fixation - stuck at p=1 because there is only 1 allele left to sample

The allele has become fixed in the population

The other possibility is that the allele gets lost, in which case the other allele must have become fixed (assuming two alleles) 

28

Graph of genetic drift with the process of evolution:

what happens?


- Equal chance of drifting up or down
- Overtime it is certain that one or the other allele will become fixed and the other will become lost. 
- The likelyhood of these events depends on the starting allele frequency
- No selection in this model

29

Is genetic drift stronger in a smaller or larger population?

Genetic drift is stronger in a small population
The effect of random sampling is greater 

30

Genetic Drift: what is the bottleneck effect?

an extreme example of genetic drift that happens when the size of a population is severely reduced

Events like natural disasters can decimate a population, killing most indviduals and leaving behind a small, random assortment of survivors