sickle cell

Question 1

what is sickle cell disease?

Answer 1

inherited disease which happens in ppl who produced malformed (sickle-shaped) red blood cells (normally disc-shaped)

Question 2

how does sickle cell disease occur?

Answer 2

it happens when there’s a mutation in the Hb gene which encodes hemoglobin molecules
this causes normal hemoglobin alleles (HbA) to become sickle cell alleles (HbS)
ppl who inherit homozygous/two HbS alleles will develop sickle cell disease

Question 3

what are hemoglobin molecules?

Answer 3

iron rich protein complexes which carry oxygen from lungs to rest of body

Question 4

what is the effect of sickle cell disease?

Answer 4

it causes rigid and closed blood flow in veins

this can cause intense pain, strokes, infections, organ damage and usually kills ppl b4 reproductive maturity

Question 5

where is sickle cell disease most common and why?

Answer 5

its most common in sub-Saharan Africa most likely because HbS allele protects ppl from malaria which kills 600 000+ ppl each yr 90% of which occurs in africa

Question 6

how do HbS alleles protect against malaria?

Answer 6

red blood cells from ppl w/ HbA/HbS will sickle when they become infected w/ malaria parasites and be discarded by the immune system

Question 7

how does climate correlate w/ HbS allele frequency?

Answer 7

In wetter parts of Africa there are more mosquitos and more malaria and more HbS alleles

Question 8

what is fixation and when does it usually occur?

Answer 8

fixation is when there is only one allele for a gene and so the frequency for the allele will always be one
it happens in small populations where there is no genetic selection (which means neither allele has an advantage) and so genetic drift take control

Question 9

how is pop allele frequency calculated?

Answer 9

since there are 2 alleles at every locus, allele frequency in n population is calculated by allele/2n

Question 10

what first does sickle cell disease represent?

Answer 10

first time specific mutation was identified as the cause of a genetic disease

Question 11

how do mutations and dna interact?

Answer 11

random mutations in dna causes new alleles

Question 12

what’s the correlation b/w number of offsprings and alleles

Answer 12

more offsprings = higher change to pass down certain alleles
chance of passing down certain combos of alleles is raised to the number of offsprings which are had
ex. 25% of HbA/HbA if 1 offsrping, 6% if 2 offspring etc.

Question 13

how does genotype fitness affects correlate w/ results of harvey weinberg equilibrium and why?

Answer 13

genotypes w/ higher fitness will have higher frequency than predicted by hard-weinberg equation due to strong natural selection
of there isn’t a genotype w/ higher fitness then genotype frequency will be similar w/ predictions due to lack of natural selection

Question 14

what is a null model?

Answer 14

a null model is simplified version of a system where nothing interesting happens
ex. hardy weinberg model

Question 15

what are null models used for?

Answer 15

they’re useful for generating hypotheses abt whether interesting things ex. evolution are happening

Question 16

what is a null hypothesis and what does it tell us?

Answer 16

it predicts that there will be no diff b/w what null model predicts and what will be observed in reality and if its rejected it means alternate hypothesis is true
ex. that results/predictions hardy weinberg model will be observed/met in real life

Question 17

what is an alternative hypthesis?

Answer 17

it predicts the opp of a null hypothesis, that there’ll be differences b/w null model and what’s actually observed supporting that something interesting is happening
ex. when nul hypothesis from hardy-weinberg model is rejected it means one or more conditions have been rejected (ex. no natural selection, not random mating) and interesting things are happening

Question 18

how cld successful treatment of sickle cell disease be negative?

Answer 18

it cld increase disease frequency as it wld increase HbS/HbS genotype fitness to same level as HbA/HbA and natural selection will favour HbS alleles even more causing an increase in frequency

Question 19

in what environment are alleles able to persist longest

Answer 19

rare alleles even non-adaptive ones will persist longer in larger pops that smaller ones

Question 20

what are the benefit of rare alleles w/ no selective advantage persisting?

Answer 20

if the enviroment changes so that the allele becomes advantageous
ex. if climate change causes mosquitos to be more common in na, rare sickle cell allele cld rescue pop from all dying from malaria

Question 21

what do conservation biologists do?

Answer 21

try to maintain genetic diversity in endangered species and species w/ rapidly changing enviros

Question 22

what do agriculture biologists do?

Answer 22

they deal w/ crop genetics and diversity loss caused by artificial selection?

Question 23

how has aritificial selection affected domesticated crops?

Answer 23

it has caused lower genetic diversity which means higher susceptibility to disease
ex. cacao crisis which is potential future chocolate shortage due to large-scale artifically selected cacao monoculture that has resulted in loss of genetic diversity and increase in disease outbreaks