16.17 End of Chapter Questions
Question 1 – 3
1. A cell in the process of meiosis was seen to have a spindle with sister chromatids being drawn towards opposite poles of the cell. In what stage of meiosis was the cell? [1]
A anaphase I
B anaphase II
C metaphase I
D metaphase II
B;
2. All the offspring of a cross between pure-bred red-flowered and pure-bred white-flowered snapdragons were pink.
Two of these pink-flowered plants were interbred. What proportion of the offspring were pink? [1]
A 25%
B 33%
C 50%
D 100%
C;
3. A man has haemophilia. Which statement correctly describes the inheritance of the gene causing his condition? [1]
A He inherited the recessive allele from his mother.
B He inherited the dominant allele from his father.
C He can pass the recessive allele to a son.
D He can pass the dominant allele to a daughter.
A;
Question 4
The diploid (2n) chromosome number of Drosophila is 8. Copy and complete the table to show the different outcomes of mitotic and meiotic division of a Drosophila cell. [3]
| number of division cycles | Mitosis | Meiosis |
| number of daughter cells | ||
| number of chromosomes per nucleus in daughter cells |
| Mitosis | Meiosis | |
| number of division cycles | 1 | 2 |
| number of daughter cells | 2 | 4 |
| number of chromosomes per nucleus in daughter cells | 8 | 4 |
Question 5
Copy and complete the table to compare meiosis with mitosis. [3]
| Mitosis | Meiosis |
| maintains the chromosome number | |
| does not involve crossing over or independent assortment | |
| gives daughter nuclei that are genetically identical (apart from mutation) to one another and to the parent nucleus |
| Mitosis | Meiosis |
| maintains the chromosome number | halves the chromosome number |
| does not involve crossing over or independent assortment | involves both crossing over and independent assortment |
| gives daughter nuclei that are genetically identical (apart from mutation) to one another and to the parent nucleus | gives daughter cells that are genetically different from each other and from the parent nucleus |
[3]
Question 6
a. Describe the essential difference between meiosis I and meiosis II. [2]
meiosis I: separates homologous
chromosomes;
meiosis II: separates sister chromatids;
b. State the similarity between meiosis II and mitosis. [1]
both separate sister chromatids;
Question 7
Diagram 1 shows chromosomes in the nucleus of a diploid cell.
a. Draw the nucleus of a gamete produced from this cell. [1]
one long, one short and one hooked chromosome present inside a circle (nucleus);
b. What type of nuclear division would be used in the production of the gamete? [1]
meiosis;
c. Draw a diagram to show what the nucleus would look like in anaphase of mitosis. [3]
six chromatids about half-way between equator and each pole (12 chromatids in all);
two long, two short, two hooked in each direction;
centromere leading for each chromatid;
Diagrams 2 and 3 below show the same diploid nucleus as in diagram 1. However, the chromosomes have been shaded.
d. State what the diff erent types of shading represent in each nucleus. [2]
- in diagram 2, shading represent sets of chromosomes / one type of shading represents set of chromosomes from mother, other type of shading represents set of chromosomes from father; AW
- in diagram 3, shading represent homologous pairs of chromosomes / differently numbered chromosomes; AW
e. Draw a karyogram based on the diploid nucleus shown in all three diagrams. [3]
only chromosomes drawn (no nuclear envelope);
three separate homologous pairs drawn side by side;
pairs arranged in order of size, starting with largest;
Question 8
There is no crossing over during meiosis in male Drosophila. Assuming that no mutation occurs, the only source of genetic variation is independent assortment. Given that the diploid (2n) chromosome number is 8, calculate the number of genetically different spermatozoa that can be produced. [1]
(2n, where n = 4) 2 × 2 × 2 × 2 = 16;
Question 9
Distinguish between the following pairs of terms.
a. genotype and phenotype [2]
genotype: the genetic constitution of an organism with respect to a gene or genes;
phenotype: the physical, detectable expression of the particular alleles of a gene or genes present in an individual;
b. homozygous and heterozygous [2]
homozygous: describes a diploid organism that has the same allele of a gene at the gene’s locus on both copies of the homologous chromosomes;
heterozygous: describes a diploid organism that has different alleles of a gene at the gene’s locus on the homologous chromosomes;
Question 10
In sweet-pea plants, the gene A/a controls flower colour. The dominant allele gives purple flowers and the recessive allele red flowers.
A second gene, B/b, controls the shape of the pollen grains. The dominant allele gives elongated grains and the recessive allele spherical grains.
A plant with the genotype AaBb was test-crossed by interbreeding it with a plant with red flowers and spherical pollen grains.
Copy and complete the table to show the expected ratio of phenotypes of the off spring of this cross.
The gametes from one parent are already in the table. [5]
| Gametes | ab |
| AB | genotype: AaBb phenotype: purple flowers and elongated pollen |
| Ab | genotype: Aabb phenotype: purple flowers and spherical pollen |
| aB | genotype: aaBb phenotype: red flowers and elongated pollen |
| ab | genotype: aabb phenotype: red flowers and spherical pollen |
Question 11
a. The fruit fly, Drosophila melanogaster, feeds on sugars found in damaged fruits. A fly with normal features is called a wild type. It has a grey striped body and its wings are longer than its abdomen. There are mutant variations such as an ebony-coloured body or vestigial wings. These three types of fly are shown in the diagrams.
Wild-type features are coded for by dominant alleles: A for wild-type body and B for wild-type wings.
Explain what is meant by the terms allele and dominant. [2]
allele: variant form of a gene;
dominant: allele that always expresses itself in the phenotype when present;
Two wild-type fruit flies were crossed. Each had alleles A and B and carried alleles for ebony body and vestigial wings.
Draw a genetic diagram to show the possible off spring of this cross. [6]
parental phenotypes: wild type × wild type;
parental genotypes: AaBb × AaBb;
gametes: AB, Ab, aB, ab × AB, Ab, aB, ab;
offspring genotypes;;
offspring phenotypes;
| Gametes | AB | Ab | aB | ab |
| AB | AABB wild type | AABb wild type | AaBB wild type | AaBb wild type |
| Ab | AABb wild type | AAbb grey body vestigial wings | AaBb wild type | Aabb grey body vestigial wings |
| aB | AABB wild type | AaBb wild type | aaBB ebony body long wings | aaBb ebony body long wings |
| ab | AaBb wild type | Aabb grey body vestigial wings | aaBb ebony body long wings | aabb ebony body vestigial, wings |
When the two heterozygous flies in b were crossed, 384 eggs hatched and developed into adult flies.
A chi-squared (χ2) test was carried out to test the significance of the differences between observed and expected results:
where:
∑ = sum of
O = observed value
E = expected value
i. Copy and complete the table. [3]
ii. Calculate the value for χ2. [1]
The table below relates χ2 values to probability values.
As four classes of data were counted, the number of degrees of freedom was 4 − 1 = 3. The table gives values of χ2 where there are three degrees of freedom.
| Probability greater than | 0.50 | 0.20 | 0.10 | 0.05 | 0.01 | 0.001 |
| Values for χ2 | 2.37 | 4.64 | 6.25 | 7.82 | 11.34 | 16.27 |
2.78;
iii. Using your value for χ2 and the table above, explain whether or not the observed results were significantly different from the expected results. [2]
χ2 value represents probability of > 0.05;
difference in observed and expected results is not significant and is due to chance;