10.2 Inheritance

1.In a plant, dark leaves are dominant to pale leaves and yellow seeds are dominant to white seeds. A heterozygous dark-leaved plant with yellow seeds was crossed with a pale-leaved plant with white seeds. A large number of offspring were produced. They were either dark-leaved with yellow seeds or pale-leaved with white seeds in equal number. What is the most likely cause of this pattern?

2. Which structure found in eukaryotes has a single membrane?

3. The genetic determination of dogs’ coats can be quite complex, with many different genes acting at the same time.

• The dominant allele E gives brown tones. The recessive allele e results in red tones. • The colour intensity is due to another gene. The dominant allele B gives a dark colour, whereas the recessive allele b results in a light colour.

What would be the genotype of a light brown dog produced from a cross between a dark brown dog and a light red dog?

4. The diagram shows a pedigree chart. What does it reveal about the inheritance of the blood disorder beta-thalassaemia?

5. Some of the ratios that Morgan investigated in genetic crosses did not correspond with expected Mendelian ratios. What was the cause?

6. The statement is about the genetic control of cat coat colour. In a cross between two double heterozygous tabby cats, what would the expected proportion of black offspring be?

7. This is the cross that led to the discovery of non-Mendelian ratios in Morgan’s experiments with Drosophila. Which is a recombinant genotype?

8. In a fruit fly experiment, grey body, normal winged (homozygous dominant) fruit flies were mated with black body, short winged (homozygous recessive) fruit flies. The F1 dihybrid females were then used in a test cross. If the genes are always linked and no crossing over occurs, what would be the predicted ratio in the F2 generation?  

9. Skin colour is a trait controlled by polygenic inheritance. Which statement is correct?

10. The curly hair of the coat of Selkirk Rex cats is due to the presence of the allele SC. These cats can either have tight curls or be moderately curly, whereas the coat of other cats is usually made of straight hair with no curls because of the allele SS. Circles indicate female cats and squares indicate males. What are the phenotypes of cats with these genotypes?

11. Which is a statement of Mendel’s law of independent assortment?

12. In a variety of tulips, V is the allele for variegated colour and C is the allele for compound flower. Which cross will give a 1:1:1:1 ratio of phenotypes in the offspring?  

13. In fruit flies (Drosophila melanogaster) grey body is dominant to black body and long wings are dominant to vestigial wings. Two flies heterozygous for both genes were crossed. What proportion of the offspring would be expected to have black bodies and long wings?  

14. Human skin colour shows continuous variation. What does this indicate about the pattern of inheritance of human skin colour?  

15. A test cross of linked genes was performed with fruit flies (Drosophila melanogaster). What is the most likely explanation for these results not fitting the expected ratio?

16. Why do humans inherit continuous variation with regard to height?

17. In humans, wavy hair is dominant to straight hair and free ear lobes are dominant to fixed ear lobes. A man and a woman are heterozygous for both characteristics. What is the probability that their first child will have straight hair and fixed ear lobes?

18. What causes variation in both sexually and asexually reproducing organisms?

19. What causes genetic variety in the formation of gametes during meiosis?

20. What is a suspected heterozygous individual crossed with in a test cross?

21. A test cross resulted in these recombinants: Which of the following was the parental test cross?

22. Which are the possible recombinants in a dihybrid test cross involving the linked genes JQ/jq?

23. What is polygenic inheritance?

24. Which of the following processes result in the production of recombinants? I.   Crossing over between linked genes II.  Reassortment of non-linked genes III.  Mutation

25. If a heterozygous grey fruit fly is mated with a black-bodied fruit fly, what proportion of the offspring would be black?  

26. Male flies, heterozygous for both grey body and normal wings, were mated with black-bodied, vestigial-winged females. 2000 offspring were counted. The resulting percentage of each type of offspring is shown in the table below. What conclusion can be drawn from the information given above?