Question
The diagram shows one of Thomas Hunt Morgan’s crosses of Drosophila in the early 20th century
Total offspring = 2300
a. State the type of inheritance shown [1]
b. Identify the recombinants [1]
The chi-squared value was calculated as shown Deduce, with reasons, whether the observed ratio differed significantly from the expected Mendelian ratio. [2]
c2 = ∑ 
= 1002.6
▶️Answer/Explanation
Ans:
a «gene/autosomal» linkage
b grey vestigial and black normal
c a
yes/observed ratio did differ significantly «from the expected Mendelian ratio»
OR
expected ratio is 1:1:1:1 / 575 of each type / 25 % of each type ✔
c b 3 degrees of freedom
c c critical value is 7.815 «at the 5% level / 11.345 «at the 1% level»
c d chi-squared value «of 1002.6» exceeds the critical value
Question
The diagram below shows the structure of lactase
A study of 600 adolescents in Sweden showed that milk consumption has a positive effect on height which shows continuous variation. However, milk contains lactose which some people can digest but some cannot.
State the pattern of inheritance that contributes to continuous variation.
Explain the production of lactose-free milk.
Identify the protein structures indicated by I and II.
I: ………………………………………………………
II: ………………………………………………………
Describe how structure I is held together.
This protein is described as a globular protein. Distinguish between globular and fibrous proteins.
▶️Answer/Explanation
Markscheme
polygenic / more than one gene
Accept polygenetic. Mark only first answer if more than one answer given.
lactase added to milk / lactase immobilised;
lactose hydrolysed/broken down into glucose and galactose;
for people who are lactose intolerant/lack lactase;
increases sweetness/solubility/smooth texture (in processed foods);
I is alpha helix and II is beta pleated sheet
Reject (α) double helix but accept α/A/a and β/B/b instead of alpha and beta.
hydrogen bonds;
Reject hydrogen and covalent bonds unqualified and hydrogen bonds between bases.
(hydrogen bonds) between N–H and C=O (on different amino acids);
Reject between amine and carboxyl groups.
(hydrogen bonds) between adjacent turns of the helix/every fourth amino
acid;
Accept above points in an annotated diagram.
A table is not required but for each feature the difference between globular and fibrous proteins must be made clear.
Question
In the pea plant (Pisum sativum), the allele for tall plants is A and the allele for short plants is a. The allele for green plants is B and the allele for yellow plants is b.
Determine the phenotype of Aabb.
Compare the information that could be deduced when the genotypes are presented as AaBb or
Deduce one possible recombinant offspring of individual 
after a test cross.
▶️Answer/Explanation
Markscheme
tall and yellow
Question
The image shows the karyotype of a person who developed as a female.
In a strain of soybeans, high oil content (H) in seeds is dominant to low oil content (h) and four seeds in a pod (F) is dominant to two seeds in a pod (f). A farmer crosses two soybean plants, both with high oil content and four seeds in a pod. The offspring have a phenotypic ratio of 9 : 3 : 3 :
Identify the genotypes of the soybean plants with high oil content and four seeds in a pod that were used in the cross.
In a strain of soybeans, high oil content (H) in seeds is dominant to low oil content (h) and four seeds in a pod (F) is dominant to two seeds in a pod (f). A farmer crosses two soybean plants, both with high oil content and four seeds in a pod. The offspring have a phenotypic ratio of 9 : 3 : 3 :
Determine the genotypes of the gametes and offspring using a Punnett grid.
In a strain of soybeans, high oil content (H) in seeds is dominant to low oil content (h) and four seeds in a pod (F) is dominant to two seeds in a pod (f). A farmer crosses two soybean plants, both with high oil content and four seeds in a pod. The offspring have a phenotypic ratio of 9 : 3 : 3 :
Identify the phenotypes of each part of the phenotypic ratio.
Deduce the reason for the person developing as a female.
Determine, with a reason, whether this karyotype shows that non-disjunction has occurred.
▶️Answer/Explanation
Markscheme
HhFf HhFf / (both) HhFf;
all gametes shown correctly on Punnett grid;
all offspring genotypes correct;
Award [1] for any two correct phenotypes.
no Y chromosome.
yes as there is only one X chromosome/chromosome missing/only 45 chromosomes