Question
The dolichos bean (Lablab purpureus) is cultivated as a food crop in tropical countries. Leaf
cells in L. purpureus have 24 chromosomes.
(a) State how many chromosomes there would be in male or female gametes of L. purpureus.
L. purpureus can have purple or white flowers. Two pure-breeding varieties were crossed: HA 4 with white flowers and GL 424 with purple flowers. All of the \(F_1\) plants had purple flowers. The \(F_1\) plants were self-pollinated to produce an \(F_2\) generation. There were 97 plants with
purple flowers and 38 plants with white flowers in the \(F_2\) generation.
(b) Using a Punnett grid, explain the results of this cross.
(c) Suggest a reason for the \(F_2\) generation not corresponding exactly to the expected ratio of purple-flowered and white-flowered plants.
Answer/Explanation
Answer:
(a) 12;
(b)
a. male and female gamete genotypes/alleles shown as P and p (or others following convention with a suitable key) in a punnet grid;
b. \(F_2\) genotypes shown as PP, Pp, pP and pp;
c. \(F_2\) phenotypes indicated for each genotype on the Punnett grid / 3 purple to 1
white ratio indicated;
(c)
chance / OWWTE;
Question
The spider Dolomedes plantarius usually has white bands down the left and right sides of its body, but some individuals lack these bands. The photograph shows the banded form of D. plantarius with a ball of spiderlings.
Crosses were performed to investigate the inheritance of this trait, by allowing specific males and females to mate. Numbers of banded and unbanded spiderlings that hatched out from all the eggs laid by the female were recorded. Results are shown in the table.
(a) Explain the conclusion that can be drawn from Cross 1.
(b) Deduce reasons for the difference between the results of Cross 2 and Cross 3.
(c) There were 79 progeny in Cross 4. Predict the expected results by completing the table.
(d) The proportion of banded and unbanded individuals in a population of D. plantarius can change. Suggest how such a change could occur.
Answer/Explanation
Answer:
(a)
a. allele/trait/gene for banded is dominant/allele for unbanded is recessive;
b. because two banded spiders produced some unbanded offspring
OR
because there is a ratio of 3 banded:1 unbanded;
c. both parents are heterozygous;
(b)
a. (1:1 ratio) in cross 2 banded parent is heterozygous/has one copy of each allele;
b. (no unbanded offspring) in cross 3 as banded parent is homozygous/has two
alleles for banded;
c. (In crosses 2 and 3) banded parental phenotypes are the same, but their
genotypes are different;
(c) 
(d)
a. natural selection could favour one type over the other;
b. greater survival of one type
OR
one type better camouflaged than the other type;
c. one type more attractive during courtship/mate selection;
Question
Mutations are the ultimate source of genetic variation and are essential to evolution.
Lice are wingless insects that belong to the phylum arthropoda.
a.i. State one type of environmental factor that may increase the mutation rate of a gene.[1]
a.ii.ldentify one type of gene mutation.[1]
b. State two characteristics that identify lice as members of the arthropoda.[2]
1.
2.
b.ii.Some lice live in human hair and feed on blood. Shampoos that kill lice have been available for many years but some lice are now resistant to
[3] those shampoos. Two possible hypotheses are:
Discuss which hypothesis is a better explanation of the theory of evolution by natural selection.
▶️Answer/Explanation
Ans:
a.i.a. radiation
b. chemical mutagens/carcinogens/papilloma virus/cigarette smoke
a.iibase substitution/insertion/deletion/frameshift
b. a. jointed appendages
b. «chitinous» exoskeleton
C. segmented body
OR
bilateral symmetry
OR
mouth \(A N D\) anus
OR
paired appendages
b.ii.a. «scientists would accept» hypothesis \(A\) as the better one as mutations are random
b. scientists would reject hypothesis B because characteristics acquired during the lifetime of the individual being inherited is Lamarckian/not part of the evolution by natural selection theory/not all mutations are heritable
c. «the resistance» mutation would be present in the population initially and not caused by the shampoo «as hypothesis B states»
d. both hypotheses include variation in the population of lice «resistant and non-resistant»
e. variation is necessary for natural selection to occur
f. frequency of the best adapted increases and these individuals reproduce/pass on resistance to their offspring, so the resistant population increases «so hypothesis \(\mathrm{A}\) is better»
OWTTE can be used for any of the answers in this part.
Question
a.The images show parts of plants belonging to two different phyla.
State the phylum of plant \(\mathrm{X}\) and of plant \(\mathrm{Y}\).
\(\mathrm{X}\) :
\(Y:\)
b. Explain one cause of mutation.[2]
c. Outline the types of evidence that can be used to place a species in a particular clade.[3]
d. The cladogram includes four marsupial (non-placental mammal) families.[1]
Deduce the family that is most closely related to the Diprotodontoidea.
▶️Answer/Explanation
Ans:
X: Filicinophyta ✔
Not chromosomal.
Y: Coniferophyta/Conifera/Gymnosperms ✔
c. a. a clade is a group of organisms that have evolved from a common ancestor \(\checkmark\)
b. identify the base sequences of a gene \(\checkmark\)
c. identify amino acid sequence of a protein \(\checkmark\)
d. comparing homologous structures \(\checkmark\)
e. the fewer the differences, the closer they diverged in time from a common ancestor \(\checkmark\) Accept vice versa.
d. Vombatidae/wombats \(\checkmark\)