1. MEIOSIS A1. B A2. C A3. A A4. C A5. A A6. crossing over / chiasmata;
shuffles alleles;
random orientation of chromosomes;
at metaphase I:
at metaphase II; 2 max
A7. non disjunction
J WERBA – IB BIOLOGY 1

2. INHERITANCE
A1.
a cross with a homozygous recessive genotype to allow the genotype of unknowns to be inferred
- the genes did not move independently of one another; - only crossing over & recombination will allow you to get the other 2 phenotypes in smaller numbers
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3. INHERITANCE
A1.
parental-type offspring? (normal & normal and purple & black)
recombinant offspring? (purple & normal and normal & black) P B p b
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4. INHERITANCE
A1.
6%  6 map units apart
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5. INHERITANCE A2. D A3. 20 map units apart
 20% recombination fraction (θ= 0.2)
Parents: x
Gametes: AB, ab x ab
F1 genotype ratio:
parental-type offspring – ;
recombinant offspring – ;
 must add up to 80% (ie. 40% each)
 add up to 20% (ie. 10% each)
J WERBA – IB BIOLOGY 5

6. INHERITANCE
A4. C
A5.
unenclosed seeds, starchy and tunica present, sugary and (both needed)
crossing over; between non-sister chromatids (in prophase I); results in exchange of alleles / change in linkage groups; so some gametes are T e or t E; test cross expect ratio of two phenotypes / correct Punnett Square showing test cross; but instead get four phenotypes with smaller percentage of recombinants; Above points can be shown in diagrams.
J WERBA – IB BIOLOGY 6

7. INHERITANCE
A6. A
A7.
Character affected / influenced /defined / determined / controlled by two or more genes [1]
human skin colour can vary from pale to very dark / amount of melanin varies; skin colour/melanin controlled by (alleles from) at least 3 / several genes; alleles are co-dominant / incomplete dominance; many different possible combinations of alleles; skin colour controlled by cumulative effect/combination of genes/alleles; 2 Award the above marking points for any other valid example.
J WERBA – IB BIOLOGY 7

8. GENE POOLS and SPECIATION
populations 1 and 2 (both needed) [1]
population 11 or population 7 [1]
PanIA 0.75 and PanIB 0.25 / 3 PanIA to 1 PanIB [1] Both must be correct for the mark to be awarded, accept frequencies in form of ratio.
any population from and any population from [1]
Cooler water temp favours PanIB; interbreeding with icelanic / more northern populations [2]
J WERBA – IB BIOLOGY 8

9. GENE POOLS and SPECIATION
A2. process by which one / more species arise from previously existing species; populations become genetically isolated; natural selection acts independently on each population; results in changes in allele / genotype frequencies; inability of organisms / gametes to meet leads to reproductive isolation; ecological isolation occurs when two species inhabit similar ranges but have different habitat preferences (eg two species of plants grow on different types of soil) / courtship / feeding differences; geographical barriers (such as mountain ranges, seas, rivers) produce barrier to gene flow due to spatial separation; after prolonged separation / genetic isolation over long period of time no longer able to interbreed and speciation has occurred; [5]
J WERBA – IB BIOLOGY 9

10. GENE POOLS and SPECIATION
A3. gradualism; slow, continuous change over a long period of time; gradual accumulation of (neutral) mutations / variations; punctuated equilibrium; long periods of stability followed by sudden changes; fossil record supports this; natural selection can be intense and can cause rapid change / evolution; rapid evolution due to major environmental changes / volcanic eruptions / meteor impact / other example; only advantageous alleles ultimately survive; some mutations had no morphological effects so not visible in the fossil record; rate of evolution could have fluctuated over time; [6 max] Award [4 max] if only one idea is discussed.
J WERBA – IB BIOLOGY 10