Download The Transmission of Hereditary Characteristics

The Transmission
of Hereditary Characteristics
BLG–5065-2
Learning Guide
THE
TRANSMISSION
OF HEREDITARY
CHARACTERISTICS
BLG-5065-2
Learning Guide
The Secondary V biology learning guides
are published by SOFAD
The Human Respiratory System
The Human Reproductive System and the Perinatal Period
The Transmission of Hereditary Characteristics
The learning guides in this collection have been adapted from the online courses of the same name
which were produced first. The decision to produce both an online and a printed version of the same
course was made to meet the requirements of those who do not have access to the Internet or who
prefer to work with “paper,” in accordance with the need to diversify the tools and venues for distance
learning.
The Transmission of Hereditary Characteristics
This learning guide was produced by the Société de formation à distance des commissions scolaires
du Québec (SOFAD).
Project coordinator:
Jean-François Bojanowski (SOFAD)
Pedagogical design:
Jean-François Bojanowski (SOFAD)
Jean-Simon Labrecque (SOFAD)
Author:
Jean-Marc Robitaille (Didactica)
Illustrations:
Sylvie Leduc
Pedagogical revision: Jean-François Bojanowski (SOFAD)
Diane Ménard
Translation:
Claudia de Fulviis
Linguistic Revision:
Barbara Chunn
Proofreading:
Valérie Champoux
Claudia de Fulviis
Graphics and Layout:
Daniel Rémy
First Edition:
February 2010
January 2016
© Société de formation à distance des commissions scolaires du Québec
All rights for translation and adaptation, in whole or in part, reserved for all countries. Any reproduction
by mechanical or electronic means, including micro-reproduction, is forbidden without the written
permission of a duly authorized representative of the Société de formation à distance des commissions
scolaires du Québec (SOFAD).
Legal Deposit - 2010
Bibliothèque et Archives nationales du Québec
Library and Archives Canada
ISBN 978-2-89493-380-0
Table of Contents
of
This is a preview
:
General Introduction ....................................................................................................
VII
The Biology Program ............................................................................................
troduction; and
VII
- the in
e.
Using the Learning Guide .....................................................................................
- the first modul
Evaluation
VII
........................................................................................................
IX
Succeeding at Distance Learning ..........................................................................
IX
The Transmission of Hereditary Characteristics ....................................................
X
Reader’s Comments .............................................................................................
XI
Section 1 – The Mechanisms of Heredity ......................................................................
1.0
Module 1 – Cell Basics ..........................................................................................
1.1
◆
The Cell .................................................................................................
1.4
◆
Genes ....................................................................................................
1.16
Module 2 – Cell Division .......................................................................................
2.1
◆
Mitosis ...................................................................................................
2.4
◆
Meiosis ..................................................................................................
2.13
Section 2 – The Laws of Heredity ..................................................................................
3.0
Module 3 – Mendel’s Experiments ........................................................................
3.1
◆
Basic Concepts .......................................................................................
3.4
◆
Mendel’s Laws ........................................................................................
3.17
Module 4 – Crossbreeding ....................................................................................
4.1
◆
Monohybrid Crosses
............................................................................
4.4
◆
Dihybrid Crosses ....................................................................................
4.19
Section 3 – Health Problems Related to Heredity .........................................................
5.0
Module 5 – The Heredity of Blood Types
.............................................................
5.1
◆
The Antigens and Antibodies Specific to Blood Types .............................
5.4
◆
The Transmission of Alleles Responsible for Blood Types .......................
5.19
Module 6 – Sex Chromosomes, Mutations and Hereditary Diseases .......................
6.1
© SOFAD
◆
The Transmission of Sex-linked Genes ...................................................
6.4
◆
Mutations and Hereditary Diseases in Humans .......................................
6.17
V
Unit Summaries
...........................................................................................................
7.1
Module 1 – The Cell .............................................................................................
7.3
Genes ................................................................................................
7.4
Module 2 – Mitosis ..............................................................................................
7.5
Meiosis ..............................................................................................
7.6
Module 3 – Basic Concepts ..................................................................................
7.8
Mendel’s Laws ...................................................................................
7.9
Module 4 – Monohybrid Crosses .........................................................................
7.11
Dihybrid Crosses ...............................................................................
7.12
Module 5 – The Antigens and Antibodies Specific to Blood Types .......................
7.13
The Transmission of Alleles Responsible for Blood Types ..................
7.15
Module 6 – The Transmission of Sex-linked Genes ...............................................
7.16
Mutations and Hereditary Diseases in Humans ..................................
7.17
General Conclusion ............................................................................................................
8.1
Self-evaluation Activity ......................................................................................................
9.1
Answer Key ........................................................................................................................
10.1
Glossary .............................................................................................................................
11.1
VI
© SOFAD
Introduction
TABLE OF
CONTENTS
ANSWER
KEY
General Introduction
◆
The Biology Program
The Société de formation à distance des commissions scolaires du Québec (SOFAD) welcomes you to
the course entitled The Transmission of Hereditary Characteristics. This course is part of the Secondary
V Biology Program for basic adult general education, which is composed of the following nine courses:
BLG-5061-1
The Human Respiratory System
BLG-5062-2
The Human Reproductive System and the Perinatal Period
BLG-5063-2
The Human Digestive System
BLG-5064-2
The Anatomy and Physiology of Cells
BLG-5065-2
The Transmission of Hereditary Characteristics
BLG-5066-1
The Human Skeletal and Muscular System
BLG-5067-1
The Human Endocrine System
BLG-5068-2
The Human Nervous System
BLG-5069-1
Ecology
Students who complete this 50-hour course can earn two Secondary V credits provided they pass
a supervised examination administered by a Québec school board. There are no prerequisites for
the courses in this program, and there is no equivalent program in the youth sector. The course’s
general objective is as follows: “By learning concepts of anatomy and physiology, adults will gain a
better understanding of the transmission of human hereditary characteristics, and the health problems
associated with it.”
◆
Using the Learning Guide
This learning guide is the main work tool for this course and has been designed to meet the
specific needs of adult students enrolled in an individualized learning or a distance learning
program. Furthermore, a webography can be viewed at the following internet address:
http://cours1.sofad.qc.ca/ressources/fichiers/BLG_5065_webography.html
The contents of this guide are divided into three main sections, which in turn are subdivided into
modules, which are again subdivided into units. In each unit, the subject matter is presented in a
number of ways (e.g. text, tables, illustrations, exercises) in order to facilitate mastery of the program
objectives. In addition, at the end of each unit, just before the conclusion, you will be required to do
a review activity in which all the main illustrations are shown in colour. By doing these exercises, you
will be building an excellent summary of the entire course. Lastly, at the end of this guide you will
find a conclusion, a self-evaluation activity and the corresponding answer key as well as an answer
key for the exercises in the modules and a glossary.
© SOFAD
VII
Introduction
TABLE OF
CONTENTS
ANSWER
KEY
Learning Activities
This guide includes theoretical sections as well as practical activities in the form of exercises. These
exercises come with an answer key. Start by skimming through each part of this guide to familiarize
yourself with the content and the main headings. Then read the theory carefully:
◆
Highlight the important points.
◆
Make notes in the margins.
◆
Look up new words in the dictionary.
◆
Study the diagrams carefully.
◆
Write down questions relating to ideas you don’t understand.
Exercises
The exercises come with an answer key found at the end of this guide.
◆
Do all the exercises and, at the end of each modules, quizzes.
◆
Read the instructions and questions carefully before writing your answer.
◆
Do all the exercises to the best of your ability without looking at the answer key. Reread the
questions and your answers and revise your answers, if necessary. Then, check your answers
against the answer key and try to understand any mistakes you made.
◆
Complete a module before doing the corresponding review exercises. Doing these exercises
without referring to the lesson you have just completed is a better way to prepare for the final
examination.
Self-evaluation Activity
The purpose of the self-evaluation activity is to help you prepare for the final examination. Before
you tackle the self-evaluation activity, reread your notes to ensure you have covered all the material
pertaining to the learning objectives cited at the beginning of each module. Make sure you understand
the learning objectives. Then do the self-evaluation activity without referring to the main body of the
guide or the summaries. Compare your answers with those in the answer key and review any areas
you had difficulty with.
Materials
Have all the materials you need close at hand.
◆
Learning materials: this guide and a notebook in which you will summarize important concepts
relating to the learning objectives for each module.
◆
Reference materials: a dictionary.
◆
Miscellaneous materials: a calculator, a pencil for writing your answers and your notes in this
guide, a coloured pen for correcting your answers, a highlighter (or a pale-coloured felt marker)
to highlight important ideas, a ruler, an eraser, etc.
VIII
© SOFAD
Introduction
TABLE OF
CONTENTS
◆
ANSWER
KEY
Evaluation
In order to earn the two credits for this course and towards your Secondary School Diploma, you must
score at least 60% on a supervised examination dealing with the learning objectives outlined in this
guide and administered in an adult education centre. The two-hour written examination counts for
100% of the final course mark. The examination will consist of multiple-choice questions and shortanswer questions.
◆
Succeeding at Distance Learning
Work Pace
A few tips for organizing your time are given below:
◆
Set up a study schedule that takes into account your availability, your needs and your family and
work obligations.
◆
Try to devote a few hours a week to the course, preferably in blocks of two hours.
◆
As much as possible, stick to the schedule you have established.
Your Tutor
Your instructor is the person who will give you any help you need throughout this course. He or she is
available to answer your questions and correct and comment on your assignments. Don’t hesitate to contact
your instructor if you are having difficulty with the theory or the exercises, or if you need some words of
encouragement to help you get through this course. Information about how to contact your instructor
that is not already contained in this guide will be made available to you. Write out your questions and
get in touch with your instructor during his or her available hours. If necessary, write to him or her. Your
instructor will guide you in your work and provide you with the advice, constructive criticism and support
that will help you succeed in this course.
Homework Assignments
This guide is sold with three homework assignments designed solely for distance learning students.
The homework assignments are to be completed at the end of each of the three sections that make up
this guide. These assignments will show your tutor whether you understand the subject matter and are
ready to go on to the next part of the course. If your tutor feels you are not ready to move on, he or she
will indicate this on your homework assignments, providing comments and suggestions to help you get
back on track. It is important that you read these corrections and comments carefully. Do your homework
assignments without referring to the learning guide and take note of your tutor’s corrections so that you
can make any necessary adjustments. This is also an excellent way to prepare for the final examination.
Remember not to send in the next assignment until you have received the corrections for the previous
one.
© SOFAD
IX
Introduction
TABLE OF
CONTENTS
◆
ANSWER
KEY
The Transmission of Hereditary Characteristics
What do blond, black or brown hair, curly hair, eye colour, and the shape of the nose and ears have in
common? They are all characteristics, or traits, that are transmitted from one generation to the next.
While leafing through family photo albums, people often comment on the resemblances they see—or
don’t see—between parents and their children: “Sylvia has blond hair, yet both her mom and dad have
jet black hair!”
Although resemblances among family members have been noticed since the beginning of time, it was
the work of Gregor Mendel (1822-1884) that provided the first real insight into heredity, that is, the
transmission of biological information, or family traits, from parents to offspring. While all children
resemble their parents, in no way are they a carbon copy.
Over time, the study of heredity and the expression of hereditary characteristics in individuals gave
rise to the science of genetics.
Biology Course BLG 5065-2, The Transmission of Hereditary Characteristics, will enable you to expand
your knowledge of such topics as the mechanisms of heredity, cross-breeding, the genetics of blood
types, sex chromosomes, hereditary diseases, and the causes and effects of certain mutations.
Course Outline
General Introduction
Section 1 – The Mechanisms of Heredity
Module 1
Module 2
Cell Basics
Cell Division
Assignment 1
Section 2 – The Laws of Heredity
Module 3
Module 4
Mendel’s Experiments
Crossbreeding
Assignment 2
Section 3 – Health Problems Related to Heredity
Module 5
Module 6
The Heredity of Blood Types
Sex Chromosomes, Mutations
and Hereditary Diseases
✁
Assignment 3
General Conclusion
Self-evaluation Activity
X
© SOFAD
TABLE OF
CONTENTS
◆
ANSWER
KEY
Reader’s Comments
The Transmission of Hereditary Characteristics (February 2010)
SOFAD is committed to providing course materials adapted to your needs, and we value your opinion.
Please write your comments, questions or suggestions on this sheet, or contact us by phone, fax or
email. If you find any errors, ambiguities, typographical errors, etc., we would appreciate hearing
from you.
Thank you for giving us your feedback.
Alain Pednault
Project Coordinator, Sciences and Technology
Tel.: (514) 529-2193
2200, rue Sainte-Catherine Est
Fax: (514) 529-2190
Montréal (Québec) H2K 2J1
Email: [email protected]
Comments:
From: _________________________________________________________________________________________________________________
✁
School Board: ______________________________________________________________________________________________________
Student:
Other:
❑
❑
Tutor:
❑
Specify: ______________________________________________________________________________________________
ANSWER
KEY
TABLE OF
CONTENTS
Section 1
The Mechanisms of Heredity
At the end of the 19th century, Mendel conducted
conclusiv experiments on the transmission of
conclusive
hered
hereditary characteristics. It was not until the
20t
20th century, however, that understanding
of the mechanisms of heredity was
p
possible thanks to knowledge acquired
about cells, chromosomes and genes.
By the end of this section, you will be
able to explain the mechanisms of
heredity.
T
This
section is divided into two modules.
The first, entitled Cell Basics, deals with the
cell, the nucleus, chromosomes, genes and
the stru
structure of cellular proteins.
The second, entitled Cell Division, explains how genetic
material is transmitted from one cell to another during the formation and growth of sex
cells, which are essential for reproduction.
© SOFAD
© SOFAD
TABLE OF
CONTENTS
Module 1
u
ANSWER
KEY
Food for Thought
Can we select specific traits for our offspring through genetic
CELL
manipulation? Can genes be transferred from one species to
another species? If your parents could have chosen specific
BASICS
traits for you, do you think your life would be any different?
What is the basis of heredity for living beings?
Start pondering these questions now, as you will be asked
to state your views at the end of this section.
The Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4
Genes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.16
© SOFAD
1.1
Module 1 – Cell Basics
TABLE OF
CONTENTS
u
ANSWER
KEY
What I Already Know
In the 21st century, basic knowledge about the transmission of hereditary characteristics is part
of general culture in industrialized countries. This knowledge allows us to understand critical
discoveries that influence our beliefs, our social values and our health.
The purpose of this exercise is to help you determine what you already know, and identify topics
with which you are less familiar. You will come back to it at the end of the module. This will allow
you to assess your progress. Answer the following questions in your own words, using one or two
sentences. Write what you know.
1. What is responsible for the transmission of hereditary characteristics?
2. Is it heredity or the environment that shapes how an organism will develop?
3. Can you give an example of one type of human cell?
4. Why has it become so important to collect DNA samples at crime scenes?
1.2
© SOFAD
Lead-in
TABLE OF
CONTENTS
u
ANSWER
KEY
Objectives of the Module
After completing this module, you will be familiar with the biological basis for heredity, thanks to
the activities you will be working through in the following two units: The Cell and Genes.
More specifically, you will be able to:
u associate the cell nucleus, chromosomes and DNA with the transmission of hereditary
characteristics;
u describe the structure of a chromosome and a gene.
© SOFAD
1.3
Module 1 – Cell Basics
TABLE OF
CONTENTS
ANSWER
KEY
The Cell
uIntroduction
All living beings are composed of cells. Each type of cell plays a specific role. For example, the human
body uses muscle cells for movement, white blood cells to fight off microbes, and nerve cells to control
its vital functions.
There are approximately 200 types of cells in the human body. Cells behave in the same manner as the
body as a whole; they need food to survive, they transform food into cellular structures, they develop
and communicate with one another, and they also reproduce and die. The muscle fibre, white blood
cell and brain neuron shown below are three types of cells found in the human body.
All of these activities are carried out according to a blueprint that is passed on from one generation
to the next.
In this unit, we will examine the overall structure of a cell and cell nucleus. We will also describe what
role the nucleus plays in the transmission of hereditary characteristics.
You will learn about the components of a cell, about chromosomes and about the structure of DNA.
1.4
© SOFAD
The Cell
TABLE OF
CONTENTS
u
ANSWER
KEY
The Organization of Living Organisms
Living organisms vary in their complexity. The most complex organisms have systems of organs made
of different types of tissue adapted to their specific functions. Identify the various tissues found in
different parts of the human body.
E
B
C
Epidermis
A-Cartilage
B-Epidermis
C- Muscle tissue
D
D-Blood
E- Nervous tissue
A
A- Cartilage is a flexible tissue and less rigid than bone. Like bone, cartilage contains very few cells.
The ear and the nose are good examples of cartilage. Cartilage forms the “disks” between the
vertebrae and plays a protective role in joints such as the knee.
B- The epidermis is the outermost layer of the skin. Epidermal cells are under constant “assault”
from the environment, but rapid renewal of the epidermis compensates for the loss of cells on
the skin’s surface.
C- Muscle tissue is composed of elongated cells called fibers. Their elongated shape makes it easier
for them to contract in response to a nerve impulse.
D- Blood is about 55% liquid (plasma) and 45% blood cells. The majority of cells are red blood cells
(containing hemoglobin), which carry oxygen. Blood also contains white blood cells, which
provide protection against microbes.
E- Nervous tissue is composed mainly of neurons, or nerve cells. The long, slender projections of
nerve cells are called axons. Many axons make up a nerve.
© SOFAD
1.5
Module 1 – Cell Basics
ANSWER
KEY
TABLE OF
CONTENTS
Quick Check
1.1 Which of the following is a tissue.
qblood
q the knee
q
q
the brain
the liver
1.2 Which of the following is an organ?
q
q
q
a red blood cell
a muscle fiber
a stomach
Validate with the answer key.
Recap
In the beginning, there is only one cell. This cell divides and the thousands of cells that are produced
specialize and form different types of tissue. Organs are made of different types of tissue adapted to
their specific functions. Organs are grouped into systems that allow the organism to adapt efficiently
to its environment.
u
The Components of a Cell
Every living organism is composed of cells. Each cell has several components that perform different
functions and ensure the cell’s survival. Identify the essential components of a cell and discover their
functions.
D
B
C
E
A- Cell membrane
B-Cytoplasm
G
C-Nucleus
D- Mitochondria
F
E-Ribosomes
F- Endoplasmic reticulum
G- Golgi complex
D
H-Centrosome
A
E
H
A- The semi-permeable cell membrane (also called the plasma membrane) controls the concentration
of nutrients and waste in the cytoplasm.
1.6
© SOFAD
The Cell
ANSWER
KEY
TABLE OF
CONTENTS
B- The cytoplasm is essentially a thick liquid substance. It contains specialized structures, called
organelles*,
that perform different functions enabling the cell to carry out vital life processes.
C- The nucleus contains most of the cell’s
genome.
The nucleus is referred to as the control centre
of the cell because it controls all of its activities.
D- The number of these organelles in a cell depends on what the cell needs to do. They are the
powerhouses of the cell in that they use the oxygen provided by blood circulation to create cell
energy.
E- These cellular structures are the protein builders of the cell. Proteins are the cell’s tools and are
synthesized using information contained in the genetic code.
F- A network of canals that runs through the entire cytoplasm. Proteins synthesized by ribosomes
enter the endoplasmic reticulum.
G- Proteins synthesized by the cell reach the Golgi complex through the endoplasmic reticulum.
There, they are processed, stored or sent to the required destination in order to play a specific
role.
H- Centrosomes are regions of the cell that produce the microtubules enabling chromosomes to
move to opposite ends of the nucleus during cell division.
Quick Check
1.3 To which person in a large company would you compare the cell nucleus?
q
q
the lawyer the accountant q
q
the big boss
the maintenance manager
1.4 Which of the following cell structures is involved in cell division?
q
q
centrosome q
cell membrane
cytoplasm
Validate with the answer key.
Recap
The cell nucleus contains the genetic material responsible for the synthesis and operation of all
cell structures.
The human body has several million cells, each containing within its nucleus all the genetic
information needed to build and support the functions of the entire organism.
A single cell is all that is needed to make a completely new you!
*
© SOFAD
Words appearing in small caps are defined in the glossary at the end of this guide.
1.7
Module 1 – Cell Basics
TABLE OF
CONTENTS
u
ANSWER
KEY
The Cell Nucleus
The nucleus houses the cell’s genetic material. Let us examine what form this genetic material takes
in the nucleus.
DNA
Cell membrane
Nucleosome
(bead)
Chromatin
(in the nucleus)
Nuclear envelope
The genetic material consists of molecules of DNA packaged as chromatin or chromosomes,
depending on whether the cell is growing or in the process of dividing.
Chromatin has a “beads on a string” appearance. The beads (nucleosomes) consisting of deoxyribonucleic
acid (DNA) and
proteins
(histones) form a core around which the DNA molecule coils.
Early in the process of cell division, the chromatin coils, supercoils and becomes more and more
compact. This material undergoes a process of segmentation giving rise to chromosomes. Once the
cell has divided, the chromosomes decondense to become chromatin strands again.
1.8
© SOFAD
The Cell
TABLE OF
CONTENTS
ANSWER
KEY
uChromosomes
Genetic material is generally described as being carried on chromosomes. We will now examine the
structure of chromosomes.
Chromosomes become visible in the nucleus during cell division. In the illustration below, the
chromosome is composed of two strands, called
DNA and are joined in the
chromatids.
Chromatids are composed of identical
centromere .
When the mother cell divides, each of the two daughter cells that are produced receives one of the
two identical chromatids making up each chromosome.
© SOFAD
1.9
Module 1 – Cell Basics
ANSWER
KEY
TABLE OF
CONTENTS
u
DNA Structure
The DNA molecule has a specific structure that allows it to store and transmit genetic information. It
resembles a ladder whose rungs are joined like a zipper. Identify the components of DNA.
B
Chemical bonds
C
G
A- Analog model
A
T
B- Schematic model
G
C
T
A
C- Simplified model
A
C
G
A
T
A
T
C
G
T
A
A
T
G
C
C
A- DNA has a spiral staircase-like structure. The sides of the ladder are composed of hundreds of
small blocks called nucleotides. The two sides are joined together like the teeth of a zipper, with
the teeth representing the four nitrogenous bases. Each nucleotide is composed of one of the
following nitrogenous bases:
adenine
(A),
thymine
(T),
guanine
(G),
cytosine
(C).
B- This model of the same molecule shows two chains of nucleotides, composed of a nitrogenous base
(A, T, G, C), a sugar (in red) and a phosphate (in green). The illustration shows how nucleotides
containing nitrogenous bases join the two open chains. The shapes of the nitrogenous bases are
complementary. Adenine can bind only with thymine (A-T) and guanine can bind only with cytosine
(G-C).
C- The simplified model shows a ladder whose rungs are formed of either an A-T pair or a G-C pair.
The sides represent the two nucleotide chains.
1.10
© SOFAD
The Cell
ANSWER
KEY
TABLE OF
CONTENTS
Quick Check
1.5 In a DNA molecule, what joins the two sides of the ladder?
q
q
nitrogenous bases
nucleotides q genes
qproteins
1.6 What encodes genetic information?
q
q
the A-T and G-C pairs q
the nucleotides facing each other
the order in which the nitrogenous bases are arranged on a chain
Validate with the answer key.
Recap
The DNA molecule consists of two chains of nucleotides. Genetic information is determined by
the properties of one of the three components of a
nucleotide:
the
nitrogenous base.
There are
four nitrogenous bases: adenine, thymine, guanine, cytosine.
The order in which the nitrogenous bases are arranged encodes genetic information.
u
Did You Know?
Human cells contain 46 chromosomes (23 pairs). If the
DNA from all 46 chromosomes that make up the human
genome were laid out end to end, it would stretch about
two metres, or more than six feet!
The number of chromosomes varies between species.
Fruit flies have only 4 pairs of chromosomes, horses
have 32 pairs, and dogs, 39 pairs!
2 meters
© SOFAD
1.11
Module 1 – Cell Basics
TABLE OF
CONTENTS
u
ANSWER
KEY
Complementary Bases
Nitrogenous bases follow base-pairing rules. Correctly match the four nitrogenous bases below.
A
C
C
G
C
A
A
G
T
C
G
T
C
Validate with
the answer key.
A
A
G
A- Adenine forms a complementary base pair with thymine.
G- Guanine forms a complementary base pair with cytosine.
C- Cytosine forms a complementary base pair with guanine.
T- Thymine forms a complementary base pair with adenine.
Recap
On complementary DNA strands, adenine is always paired with thymine and guanine is always
paired with cytosine.
Adenine also pairs with another nitrogenous base called uracil. In RNA, or ribonucleic acid, uracil
(instead of thymine) pairs with adenine.
1.12
© SOFAD
The Cell
TABLE OF
CONTENTS
u
ANSWER
KEY
Did You Know?
The human genome is composed of 3.2 billion base pairs. The sequence of nitrogenous bases (adenine,
thymine, guanine and cytosine) that make up the long nucleotide chains of our DNA allows for all the
variations contained in tens of thousands of genes.
Imagine the genome is a book. The information it contains would be equivalent to that in about 1000
telephone books.
As impressive as it is, the human genome is small compared with that of an organism called Amoeba
dubia. This unicellular organism has a genome containing a record 670 billion base pairs!
That is at least 200 times larger than the human genome.
© SOFAD
1.13
Module 1 – Cell Basics
TABLE OF
CONTENTS
u
ANSWER
KEY
The Cell and Its Nucleus
The cell, the nucleus and the chromosomes are the basic building blocks of life. Review some related
terminology by completing the following crossword puzzle.
1
C
H
2
C
R
O
M
3
4
C
A
T
I
5
E
N
Validate with
the answer key.
1- Segments of condensed, tightly folded and coiled chromatin.
2- The constricted region joining the two sister chromatids that make up an X-shaped, or double,
chromosome.
3- It is part of a DNA nucleotide and pairs with thymine.
4- Each chromosome contains two, identical ones. During DNA replication, one of them serves as a
model for the other.
5- It surrounds the nucleus and controls the exchange of substances between the nucleus and the
cytoplasm.
Recap
At the beginning of the 20th century, research on the cell and the nucleus advanced by leaps and
bounds. During the 1950s, the discovery of DNA in the cell nucleus paved the way for achieving
understanding of where genetic information is stored and how this information is passed from
one cell to its progeny during the growth of an organism.
1.14
© SOFAD
The Cell
TABLE OF
CONTENTS
ANSWER
KEY
uConclusion
The column headings in the following table are related to topics covered in this unit. Fill in the blank
spaces with the appropriate terms from the list to the right of the table.
CHROMOSOME
CELL
DNA
Centromere
Chromatid
Ribosomes
Nucleus
Validate with the answer key.
Nucleotides
AT and GC
Recap
The cell is the basic unit of life. The human body has 200 different types of specialized cells
that make up the tissues of the various organs. The DNA in the nucleus of each cell makes up
the genome of the organism. The human genome consists of 23 pairs of chromosomes: each
chromosome consists of a DNA molecule composed of roughly 200 million pairs of nucleotides.
This genetic information ensures that hereditary characteristics are preserved and passed on.
End of unit
Before you continue, go to the “Unit Summaries” section
and complete the corresponding review activity.
© SOFAD
1.15
Module 1 – Cell Basics
TABLE OF
CONTENTS
ANSWER
KEY
Genes
uIntroduction
Gene for
iris colour
A
T
C
G
T
A
A
T
G
C
The DNA in the cell nucleus makes up the genetic material (i.e., genome) of all living organisms.
Hereditary characteristics, or traits, are encoded in nucleotide sequences hundreds of base pairs long.
These DNA sequences are
genes.
Cells of various types carry out different functions. The cell carries out two vital tasks: it copies its
genes so that a set can be passed on to each daughter cell during cell division and it uses its genes
to synthesize proteins that are involved in the expression of hereditary traits.
In this unit, we will examine the mechanism of DNA replication in the nucleus and the mechanisms
by which the information carried by a gene is expressed.
1.16
© SOFAD
Genes
ANSWER
KEY
TABLE OF
CONTENTS
uGenes
A chromosome carries thousands of genes, each of which contains a specific sequence of nucleotide
base pairs. Now we will look at the differences and similarities between genes.
A
T
C
G
C
G
G
C
C
G
A
T
A
T
G
C
C
G
A
T
T
A
G
C
2
1
4
3
G
C
G
C
A
T
G
C
A
T
A
T
A
T
G
C
C
G
C
G
T
A
T
A
A portion of gene 1 = A-C-C-G-C-A-A-G-C-A-T-G
A portion of gene 2 = A-C-C-G-C-A-A-G-C-A-T-G
A portion of gene 3 = G-G-A-G-A-A-A-G-C-C-T-T
A portion of gene 4 = G-G-A-G-A-A-A-G-C-C-T-T
© SOFAD
1.17
Module 1 – Cell Basics
TABLE OF
CONTENTS
ANSWER
KEY
Quick Check
1.7 Why are genes 1 and 2 and genes 3 and 4 identical?
q
q
q
the sister chromatids from the same chromosome come from a single parent the cell copied one of the chromatids from the other
both parents passed on the same genes
1.8 Would replacing one nitrogenous base by a different base on a gene have an effect?
q
q
q
such a subtle change would have no effect
changing a single base modifies the information and so has an effect
changing three nitrogenous bases would have an effect
1.9 Which of the following three statements do you agree with?
q
q
each sister chromatid from the same chromosome carries its own genes
each sister chromatid from the same chromosome carries half the genes contained in
a chromosome
q
each sister chromatid from the same chromosome carries the same genes in the same order
Validate with the answer key.
Recap
The specific order in which nucleotide base pairs are arranged encodes genetic information. A
gene is an ordered sequence of nucleotides that encodes the information needed to synthesize
a specific protein and express a particular hereditary trait. Some genes do not carry hereditary
information; they act as switches by turning gene expression on or off.
uAlleles
Humans have 23 pairs of chromosomes. One chromosome in each pair is contributed by the father
and one by the mother. For any given trait, there are two sources of information: the gene passed
on by the mother and the gene passed on by the father. These genes are the two alleles that control
specific traits, for example, eye or hair colour.
For each hereditary trait, one
1.18
allele
is paternally derived and the other is maternally derived.
© SOFAD
Genes
ANSWER
KEY
TABLE OF
CONTENTS
u
Copying a Gene
With a few exceptions, every cell in your body contains a
complete copy of your genome, or roughly 30 000 genes.
A cell generally uses only the genes it needs to function
and deactivates the rest.
In the next 60 seconds, your body will produce enough
new DNA that, if linked together, it would stretch 100 000
km, or the average distance a car travels in five years.
The cell must have the ability to keep genetic information
intact, for its own benefit and for that of its progeny. The
genes in a cell must be copied in order to preserve and
transmit information from one cell to another.
u
DNA Replication
Before a cell can divide it must first make a copy of its DNA. In each box below, write the uppercase
letter representing the base that pairs with the nitrogenous base indicated.
A
C
C
G
C
A
A
G
C
A
T
G
A
C
C
G
C
A
A
G
C
A
T
G
Validate with the answer key.
In DNA replication, new strands of DNA are copied through complementary base pairing. This dynamic
process requires the action of proteins called enzymes. These are the cell’s tools.
© SOFAD
1.19
Module 1 – Cell Basics
ANSWER
KEY
TABLE OF
CONTENTS
u
Find Out More - DNA Replication
This material is not covered in the course.
A
T
DNA replication by complementary pairing of
C
G
a new DNA strand is constructed from one of
G
C
T
nitrogenous bases is the mechanism whereby
the two chains of the original DNA sequence.
This process requires the help of proteins
A
called enzymes. Click on the following link
C
http://cours1.sofad.qc.ca/ressources/fichiers/
to watch an animation of DNA replication:
BLG_5065_webography.html
G
u
From Genes to Hereditary Characteristics
In general, it is easy to distinguish individuals by their facial features, or physiognomy. Physiognomy is the
outward expression of each person’s
specific genome, which is found in
the cell nucleus. A photograph of an
individual’s genome is equivalent to
Hair
the main component of
hair fibre is keratin
a photograph of his or her face.
A hereditary characteristic can be
observed only at the level of tissues
or organs, but genes express
themselves only at the cellular level.
Kidneys
renin controls blood
pressure
How is a gene expressed at the
cellular level?
Salivary glands
amylase in the saliva breaks
down sugar like starch in
bread
Red blood cells
hemoglobin carries
oxygen
Muscles
myosin is responsible for
contraction
Gene expression occurs through
the synthesis of different proteins.
Each protein within the body has a
specific function. Some proteins
serve as construction materials
(structural proteins), while others
act as catalysts (enzymes). Hormones
and antibodies are also proteins.
The human body needs 20 amino
acids to synthesize the thousands of proteins it uses.
1.20
© SOFAD
Genes
ANSWER
KEY
TABLE OF
CONTENTS
u
Find Out More - Protein Construction
This material is not covered in the course.
DNA molecule
Genons
A
C
C
C
G
A
A
G
C
A
T
G
DNA strand
Transcription
mRNA
U
G
G
G
C
U
U
C
G
U
A
C
Codons
Translation
Amino acids
Tryptophan
Arginine
Serine
Tyrosine
Protein
How do cells go about building proteins?
Proteins are synthesized on the ribosomes found in the cell cytoplasm.
1. DNA carries genetic information on segments called genes and is enclosed in the cell nucleus.
2. The cell transcribes, or transfers, the genetic information to a strand of messenger RNA (mRNA).
This process is called transcription. The mRNA carries the genetic information out of the nucleus
to the ribosomes.
3. The amino acids encoded in the mRNA are transported to the ribosomes. Transfer RNA, or tRNA
(not shown), are molecules that bind to and carry specific amino acids, of which there are 20, to
the ribosomes and places them opposite a mRNA codon.
4. The amino acids must be assembled in the order determined by the mRNA. Each tRNA molecule
carries an anticodon that is complentary to a specific codon of mRNA on the ribosome. When a
given codon and anticodon pair up, the ribosome removes the amino acid from the tRNA. This
process is called translation.
A protein can consist of between 100 and 300 amino acids.
Visit http://cours1.sofad.qc.ca/ressources/fichiers/BLG_5065_webography.html to see an animation
of cell protein construction.
© SOFAD
1.21
Module 1 – Cell Basics
TABLE OF
CONTENTS
u
ANSWER
KEY
DNA, Genes, Alleles and Chromosomes
The four terms in the table below are related. Match each description in the right-hand column with
the corresponding term in the left-hand column by drawing a line between them.
DNA
Made up of DNA and histone
proteins, it carries several
genes.
GENE
A giant molecule composed
of two chains of nucleotides.
There are four different
nucleotides, each of which has
a different nitrogenous base.
CHROMOSOME
One of two alternative forms
of a gene (one from the father
and one from the mother)
specifying an inherited
characteristic.
ALLELE
A sequence of DNA
nucleotides that occupies a
specific site on a chromosome.
This sequence serves as a
template for the synthesis of a
specific protein.
Validate with the answer key.
Recap
Each chromosome is composed of DNA, specific segments of which serve to synthesize cell proteins.
These segments of DNA are genes. Genes can either carry or control inherited characteristics. In
living organisms that reproduce sexually, like humans, chromosomes exist in pairs. Each inherited
characteristic, such as eye colour, is determined by two variants of a specific gene, one from the
father’s chromosome and the other from the mother’s chromosome. Thus, a pair of chromosomes
contains a paternal allele and a maternal allele, the two versions of the gene that controls a given
hereditary trait.
1.22
© SOFAD
Genes
ANSWER
KEY
TABLE OF
CONTENTS
u
Did You Know?
We have more in common with other
living beings than we could ever imagine!
In their genome, individuals have traces of
ancient genes stemming from the beginning
of time that they share with every living organism.
What
do
you
have
in
common
with
a
MONKEY or a MOUSE? Find out more at:
http://cours1.sofad.qc.ca/ressources/fichiers/
BLG_5065_webography.html
u
Example: Chromosome 7
Several genes located on human chromosomes have been mapped. Identify some of the genes on
chromosome 7.
Osteoporosis
1
1- NUMBER OF GENES
1443 genes
2
Colon cancer
2- GENES AND DISEASES
3- GENE FOR COLOUR BLINDNESS
Colour blindness
3
1- Genes occupy specific spots, or loci, on a chromosome. To date, 1443 genes have been identified
on chromosome 7.
2- Although genes work together in complex ways to keep our bodies functioning properly, some
alleles have defects that can result in disease. Several genes on chromosome 7 predispose to
disease. Osteoporosis and colon cancer are two examples.
3- Many colour blind people have a defective perception of red and green. This deficiency is caused
by an abnormality in the structure of the retina. The gene that codes for blue pigment is located
on chromosome 7. The other two genes involved in colour blindness, those coding for red and
green pigments, are located on the X chromosome.
© SOFAD
1.23
Module 1 – Cell Basics
TABLE OF
CONTENTS
u
ANSWER
KEY
A Silk Goat!
What is a GMO? A genetically modified organism (GMO) is a
plant, animal or microorganism whose genetic code has been
altered in order to give it characteristics that it does not have
naturally.
Scientists can now transfer genes between species
that otherwise would be incapable of mating, for
example, a goat and a spider. Find out more at:
http://cours1.sofad.qc.ca/ressources/fichiers/BLG_5065_
webography.html
u
DNA and Genes
Genes are located on chromosomes. What concepts are used to define a gene and its role in the
transmission of inherited characteristics? Review these concepts by completing the following crossword
puzzle.
1
C
H
2
P
R
O
M
O
3
A
S
O
M
4
5
G
G
Validate with
the answer key.
E
S
1- A function of genes that are not carriers of hereditary characteristics.
2- Each carrier gene expresses itself by synthesizing these.
3- A pair of genes that determine the same characteristic and that are provided by each parent.
4- Each chromosome contains hundreds of these.
5- Small segments of a DNA molecule that express hereditary characteristics.
1.24
© SOFAD
Genes
TABLE OF
CONTENTS
ANSWER
KEY
Recap
Cell activities are regulated by the expression of the genes located on the chromosomes, i.e., the
alleles received from both parents. Genes express themselves by synthesizing proteins on the
cell’s ribosomes. Not all genes are carriers of inherited characteristics; some control cell activities.
Depending on its needs, the cell can switch genes on or off.
uConclusion
The column headings in the following table are related to topics covered in this unit. Fill in the blank
spaces with the appropriate terms from the list to the right of the table.
GENE
CHROMOSOME
PROTEINS
Chromatids
Insulin
Sequence of
nucleotides
Amino acid
Validate with the answer key.
Alleles
Centromere
Recap
Cells carry out two vital tasks related to genes. First, they accurately copy the genes prior to cell
division. Second, they translate the information encoded in the genes by making thousands of
proteins.
End of unit
Before you continue, go to the “Unit Summaries” section
and complete the corresponding review activity.
© SOFAD
1.25
Module 1 – Cell Basics
TABLE OF
CONTENTS
u
ANSWER
KEY
What I Know Now
At the beginning of this module, you answered four questions about the learning content of each
of the two units to the best of your knowledge. Here are the same questions. Answer them again,
then compare your answers to your previous ones.
1. What is responsible for the transmission of hereditary characteristics?
2. Is it heredity or the environment that determines how an organism will develop?
3. Can you give an example of one type of human cell?
4. Why has it become so important to collect DNA samples at crime scenes?
1.26
© SOFAD
Wrap-up
TABLE OF
CONTENTS
u
ANSWER
KEY
Share Your Opinion
Given what you have learned about the cell and genes, you should now be able to understand the
social issues related to genetically modified organisms.
If it were possible to alter the human genome, would you want to select hereditary characteristics
that could be passed on to your children?
q
Yes qNo
q
I don’t know
Recap
More and more people are turning to plastic surgery (e.g., facelifts), a wide range of medications,
hormones and nutritional supplements to enhance their appearance or their performance, or to
simply improve their quality of life. Now that researchers have identified the location of certain
defective genes on human chromosomes, work is under way on approaches for inserting new,
functional genes or for repairing defective ones. This is called gene therapy. Although the
technology is still in its infancy, it holds considerable promise.
uQuiz
1. Living organisms vary in their complexity. The most complex are composed of systems of
organs consisting of different types of tissue adapted to the function of each organ. Which of
the following is a type of tissue?
A.cartilage
B. the liver
C. the knee
D. the brain
2. What am I? In the cell, I contain specialized structures called organelles, which carry out the
various tasks that ensure proper functioning of the cell.
A. the nucleus
B. mitochondria
C. cytoplasm
D. a ribosome
3. What am I? In the cell, I serve as the assembly site for cellular proteins, which are synthesized
from the information in the genome.
A. the endoplasmic reticulum
B. the Golgi complex
C. a ribosome
D. the centrosome
© SOFAD
1.27
Module 1 – Cell Basics
TABLE OF
CONTENTS
ANSWER
KEY
4. The genome is contained in the cell nucleus. The form in which the genome exists in the cell
can be described in different ways. Which of the following statements is true?
A. Chromatin is composed of chromatids.
B. A chromosome is composed of one chromatid and two centromeres.
C. A chromatid is composed of 46 strands of chromatin.
D. A chromosome consists of a DNA molecule and proteins called histones.
5. DNA and the cell. Which of the following statements is false?
A. DNA is contained in the nucleus and cannot leave it.
B. Only chromosomes (not chromatin), once formed, are made up of DNA.
C. There are 46 DNA molecules in a cell.
D. DNA consists of two chains of nucleotides.
6. How is a gene represented in a cell?
A. by each DNA base pair
B. by a nitrogenous base pair, A-T or G-C
C. by a sequence of DNA base pairs
D. by a group of three base pairs out of four
7. How is a gene expressed in a cell?
A. by protein synthesis
B. by the synthesis of alleles
C. by DNA replication
D. by the transformation of chromatin into a chromosome
8. What roles do genes play?
A. They transform chromatin into chromosomes.
B. They carry genetic information or control the activity of other genes.
C. They form the ribosomes.
D. They join the chromatids together.
9. Which of the following statements is true?
A. A chromosome contains hundreds of different genes.
B. A hereditary characteristic is determined by an allele from one parent.
C. The cell nucleus contains only the DNA necessary for the activities of a single cell.
D. It is impossible to add genes to or to alter the genome of a living being.
1.28
© SOFAD
Wrap-up
TABLE OF
CONTENTS
ANSWER
KEY
10.All living organisms are composed of cells. How many types of cells are there in the human
body?
A. The human body has only one type of cells: human cells.
B. There are 200 types of cells grouped into tissues.
C. There are 2000 types of cells grouped into different organs.
D. Each organ in the human body has its own type of cells.
Validate with the answer key.
© SOFAD
1.29