Inheritance
Chromosomes and inheritance.
Unit 1
Sub-topic 6
Cell Function and Inheritance
Chromosomes and DNA replication
Inheritance is the passing of genetic information from one generation to the next. The
vehicles for the transfer of this information are chromosomes present in the nucleus of
cells.
1 a) Distinguish between the terms “gene” and “chromosome”.
b) Explain fully what a gene is composed of and what its function is.
c) Identify and label the following structures on
the simplified diagram of gene structure:
nucleus
DNA helix
chromosome
bases
gene locus
centromere
2a) (i) What term is used to refer to the characteristic
number of chromosomes possessed by a species?
b) Karyotype is term is used to refer to the appearance of this set of chromosomes as
shown below.
(i) What are a homologous pair of chromosomes?
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(ii) Into how many homologous pairs can a full set of human chromosomes be arranged?
c) Circle and label the sex chromosomes on the previous karyotype diagrams and identify
which is the male and which is the female karyotype.
3a) Distinguish clearly between the following pairs of terms: (i) autosome and sex chromosome
(ii) haploid and diploid
(iii) mitosis and meiosis
4 a) Within the human life cycle, a cell preparing to undergo division must double its
quantity of genetic material. By what means is this brought about?
b) This picture represents the human life cycle.
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Key
= process
= type of cell
(i) Complete the diagram using the following labels:
meiosis
mitosis
fertilisation
sperm
egg mother cell
(ii) Identify which cells are haploid (n) and which are diploid (2n)?
c) In terms of chromosome complement, why is fertilisation important?
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Replication of DNA
Both types of cell division (mitosis and meiosis) are dependent on DNAs ability to make
exact copies of itself in a unique process called DNA replication.
The picture below illustrates DNA replication.
5 Annotate the diagram with brief descriptions of what is happening at each stage.
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6 a) Name FOUR substances that must be present in a nucleus for DNA replication to
occur.
b) Draw a simple diagram to explain why DNA replication is said to be semiconservative.
c)(i) With the aid of the diagrams, describe the difference between a chromosome before
and after DNA replication.
before
after
(ii) When does DNA replication occur?
7a) Explain fully the importance of DNA replication and the consequences of a failure to
replicate.
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Mitosis
Use class resources to label the diagram of the process of mitosis.
(ii) What is the function of mitosis?
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Meiosis
1 a) Define the term meiosis.
b) Identify the sites where meiosis occurs in men and women.
2 a) As a result of DNA replication, prior to meiosis each chromosome is made up of two
identical structures called chromatids.
(i) What name is given to points of direct contact between adjacent chromatids during
the first meiotic division? Label the diagram below to show this point.
pair of homologous
chromosomes
(ii) At these points a process called crossing over occurs. Explain fully what crossing
over involves and what effect this has on the gametes produced.
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3 a) Explain clearly why meiosis is termed a “reduction division”
b) Why is this difference in chromosome number important?
Use class resources to note what is happening at each stage in diagram of the process of
meiosis below.
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4. Different forms of the same gene are called alleles. The combination of alleles that an
organism inherits determines what it is like and makes it vary from other individuals.
a)(i) Identify the TWO ways in which new combinations of existing alleles may arise
during meiosis, so increasing variety.
(ii) Explain fully what independent assortment of chromosomes is. Use diagrams if
you wish.
b)(i) What are linked genes, and how could they potentially be affected by crossing over?
(ii) Why does sexual reproduction result in genetically unique individuals?
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(ii) Explain why the variation that exists amongst the members of the human species is
of survival value.
5 Complete the summary table of comparisons of the processes of mitosis and meiosis.
mitosis
site of division
occurs all over body of
growing animal
function
production of new body cells
for growth or repair
exchange of genetic
material
does not happen
number of divisions
double division of nucleus
number of cells produced
2
type of cells produced
daughter cells identical to
mother cell
effect on chromosome
number
effect on variation
meiosis
chromosome number halved
= haploid (n)
does not increase variation
within a population.
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Genetic Fingerprinting
6 a) Note the meaning of the terms genome and genetic fingerprinting?
genome =
genetic fingerprinting =
b) Give a practical use to which genetic fingerprinting can be put and describe how it
works.
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