Biology – Genetics
Questions Sheet B
Question 1
In humans, the failure to develop a normal enamel coating on teeth is due to sex link dominant allele (gene variant). If a
woman is a heterozygous (genotype has varying alleles) for this trait with a man who does not show this trait, what is the
percentage of offspring you would expect to show this trait?
Question 2
In humans a male parent can never pass on their x chromosomes to their sons and daughters always receive the x from the
father. Draw a pedigree chart or Punnett Square to help you with the following.
a) Will the granddaughter get the x chromosome?
b) Will the grand sons get the x chromosomes?
c) Will the daughter always pass their fathers chromosomes to their sons
Question 3
Figure 10 represents a piece of DNA from a gene. The template strand for a section of the gene is shown.
a. In the space provided in Figure 10 write in
the complementary bases for the other
strand of DNA.
b. What does the A represent in this DNA
sequence?
c. The first step in the process of gene
expression is transcription. What is produced
during the process?
d. The molecule produced during transcription attaches to organelle in the cell.
i. What is the name of this organelle?
ii. What is the name of the step in gene expression which follows transcription and occurs at this organelle?
iii. What is produced during this process mentioned in part ii.?
In the section of the gene sequence shown in Figure 10 a base substitution mutation occurred. The 9th base from the left,
Guanine, was replaced by Thymine (at arrow). The genetic code is provided below (Figure 11).
e. What effect will this mutation have on the sequence of amino acids? 1 mark
QUESTION 4
The domestic cat, Felis catus, has a diploid number of 38.
a. How many chromosomes would a gamete of a cat contain? 1 mark
Genetic ‘accidents’ can occur in chromosomes. One type of accident is when one chromosome becomes permanently
attached to another. This kind of arrangement is called a translocation. A scientist observed a translocation involving
chromosomes 9 and 18 in somatic (body) cells of a male cat. Figure 8 shows chromosomes 9 and 18 in a normal male cat and
their arrangement in the cat carrying the translocation. Note that the centromere of the translocated number 18
chromosome has been lost.
In some cases translocations lead to abnormalities, but that was not the case here. The cat had a normal phenotype.
What is meant by the phenotype of an organism? Explain in relation to Genotype.
In specialized cells in the ovary and testis, cells divide by the process of meiosis to produce gametes. A cell with a diploid
number of 4 underwent meiosis. The following images illustrate different stages throughout the total process of meiosis in
this cell.
a. Using the letters under each cell (A–F), put the cells in order commencing with the earliest stage of meiosis shown.
b. In this species a male locust has a diploid number of 16.
What is the chromosome number of each of the two daughter cells produced during a mitotic division in a male? 1 mark
The difference in chromosome number between the sexes is the result of a difference in the number of sex chromosomes (X
chromosomes in this case). Female locusts have two X chromosomes (XX) and male locusts have only one X chromosome
and Y sex chromosome (XY).
c. At the end of a meiotic division, how many chromosomes would you expect in the gametes of
i. a female?
ii. a male?
The colour of the locust is determined by a gene on the X chromosome with two alleles
.
XG = grey Xg = green
d. Show the genotypes and corresponding phenotypes, including the sex, of the parents and offspring of a cross of a grey male
to a green female. 3 marks
Question 5
Bay scallops (Argopecten irradians) have three shell colours: orange, yellow and black. It is known that the colour is under
the control of one gene locus with three alleles.
a. What is a gene locus? 1 mark
b. If you compared the alleles of this locus at the molecular level, what would be different? 1 mark
c. What is the name given to the process which gives rise to new alleles? 1 mark
The pedigree below (Figure 9) shows the inheritance of coat colour in a group of cocker spaniels.
a. Consider location II-2. What is the sex and genotype of that particular cocker spaniel
b. I–1 and I–2 are heterozygous at both the R and B locus. What evidence from the pedigree supports this conclusion?
c. i. What is the specific genotype of II–4?
d. Explain how many different phenotypes could be expected in the offspring of a mating between individuals II–4 and III–4.
Show all working. 2 marks
e. What is meant by sex linked genes?
Question 6