Unit 2: Genetic Processes
Lesson 1: The Nature of Heredity
Genetics: the scientific study of heredity and variation or inherited characteristics
Heredity: the passing of traits from parent to offspring
Chromosomes carry information for traits that are passed on from parent to offspring through cell
division and reproduction. Multicellular organisms use cell division for growth and repair whereas
unicellular organisms use it as a means of reproduction. Living things inherit traits from their parents –
but what causes traits to be passed on from parent to offspring?
Genetic Material:
Genetic material is a term used to describe all the material in an organism that stores genetic
information. In a chromosome, genetic information is contained in a molecule of DNA (deoxyribonucleic
acid). Each DNA molecule is composed of hundreds of thousands of chemical subunits that act as a set
of chemical instructions for the cell. These instructions occur as distinct sequences of information along
the DNA molecule. Each of these distinct sequences of genetic information is called a gene.
Gene: a portion or segment of a DNA molecule that carries the information that helps to produce
a particular trait of an organism. Each gene occupies a specific location, or locus (plural – loci) on
a chromosome.
Chromosomes:
A typical chromosome carries information for hundreds or
thousands of different genes. When we ‘inherit’ traits from our
parents, what we actually inherit is genetic information. This
genetic information is contained in segments of DNA called genes,
and these genes are located at specific positions along
chromosomes. Chromosomes , and all the genetic information they
contain, are duplicated during cell division.
Chromosomes are found in the nucleus of all eukaryotic
cells, but vary widely between organisms of different species in
their number, shape and size. In most multicellular organisms have
less than 100 chromosomes in the nucleus of each body cell
(somatic cell).
In most multicellular organisms, chromosomes occur in sets.
Diploid: cells have two sets of chromosomes. Diploid (2n). Humans
are diploids. We have 46 chromosomes in each somatic cells of
which 23 came from our mom and 23 came from our dad.
Haploid: cells have half the normal number of chromosomes.
Haploid (n). Human sex cells (gametes) have 23 chromosomes
each.
Polyploid: cells that contain three or more sets of chromosomes.
(3n, 4n etc). Some plants species demonstrate polyploidy.
Reproduction – copy or combine?
Organisms inherit genetic information from their parents. Some organisms have only a single parent
(asexual reproduction) while others have two parents (sexual reproduction). How do these different
forms of reproduction influence heredity? What are the advantages and disadvantages of one form of
reproduction over the other?
Asexual Reproduction
Sexual Reproduction
The production of offspring from a single parent;
The production of offspring from the fusion of two
the genetic makeup of the offspring is identical to sex cells (usually from two different parents); the
that of the parent
genetic makeup of the offspring is different from
that of the either parent.
Advantages:
Disadvantages: (reasons why sex is biologically
 Parent organism does not have to seek out a ‘costly’)
mate
 Must have specialized organs to produce sex
 Does not have to perform specialized
cells
behaviours or possess specialized anatomy
 In animals, producing mating calls or being
 Results in heredity that is direct and
brightly coloured can help attract a mate –
invariable
but can also attract predators
 Quick and ‘easy’
 In plants, producing flowers attracts
pollinators like bees, but also requires the
Disadvantage:
production of nectar which is biologically
Since asexual reproduction has so many biological
‘costly’
Advantages:
‘benefits’, why don’t all organisms use this
reproductive strategy?
Why bother going through sexual reproduction if it
 Lack variability in the population –
is so ‘costly’?
vulnerable to changes in the environment
 Variability! – allows an organism to adapt and
survive if the environment changed; leads to
evolution
Homework Questions:
1. In your own words, describe the relationship between each of the following pairs of terms
a) Reproduction and heredity
b) DNA and chromosomes
c) genetic information and gene
d) diploid and haploid
2. Use the internet to research and compare the diploid numbers of the following pairs of species:
i)
Lion and tiger
ii) Elephant and wooly mammoth
iii)
Chimpanzee and gorilla
iv) Dog and wolf
What do you notice about chromosome number and the similarity of these species? Choose any
two other pairs of animals and compare their chromosome numbers.
3. List several biological advantages of asexual reproduction
4. Describe the added ‘costs’ of sexual reproduction for an organism.
5. When is the production of genetically identical offspring a disadvantage? Explain.
6. Moose antlers and peacock tails are classic examples of features related to sexual reproduction.
Explain what advantage and disadvantages might be associated with each of the following:
a) Mating calls of birds
b) Release of chemical scents into the air by female moths
c) The very large size of male elephant seals compared to females
d) The production of nectar by many flowers.
Teaching Notes:
1. Do a word wall brainstorm with genetics in the centre – just to get a sense of what topics they
already know
2. Show family pictures – me and the family; me, aji and pranav. Who looks like whom? Why? How
does that happen?
Thought Question – how do we get the traits we get? Why do I have black eyes, you have brown,
blue, green eyes etc. Why do we all look so different?
3. Do the Mini investigation on pg. 137 – coin toss first
4. Brainstorm – what is heredity? How do we get the traits that we do? (tease out what they know
and what conceptions and misconceptions they have about DNA/Chromosomes/Genes/Inheritance
Unit 2: Genetic Processes
Lesson 1: The Nature of Heredity
Genetics: the scientific study of ______________ and ____________ or inherited characteristics
Heredity: the passing of traits from _____________ to __________________
Chromosomes carry information for traits that are passed on from parent to offspring through cell
division and reproduction. Multicellular organisms use cell division for growth and repair whereas
unicellular organisms use it as a means of reproduction. Living things inherit traits from their parents –
but what causes traits to be passed on from parent to offspring?
Genetic Material:
Genetic material is a term used to describe ____________________________________________.
In a chromosome, genetic information is contained in a molecule of ___ _______________
___________. Each DNA molecule is composed of hundreds of thousands of chemical subunits that
act as a set of chemical instructions for the cell. These instructions occur as distinct sequences of
information along the DNA molecule. Each of these distinct sequences of genetic information is called a
________.
Gene: a portion or segment of a DNA molecule that carries the information that helps to produce
a particular trait of an organism. Each gene occupies a specific location, or locus (plural – loci) on
a chromosome.
Chromosomes:
A typical chromosome carries information for hundreds or
thousands of different genes. When we ‘inherit’ traits from our
parents, what we actually inherit is genetic information. This
genetic information is contained in segments of DNA called genes,
and these genes are located at specific positions along
chromosomes. Chromosomes, and all the genetic information they
contain, are ________________ during cell division.
Chromosomes are found in the ___________ of all
eukaryotic cells, but vary widely between organisms of different
species in their number, shape and size. In most multicellular
organisms have less than 100 chromosomes in the nucleus of each
________ cell (somatic cell).
In most multicellular organisms, chromosomes occur in sets.
Diploid: cells have _____ sets of chromosomes. Diploid (2n). Humans
are diploids. We have 46 chromosomes in each somatic cells of which
____ came from our _____ and ____ came from our _____.
Haploid: cells have _____ the normal number of chromosomes.
Haploid (n). Human sex cells (gametes) have 23 chromosomes each.
Polyploid: cells that contain three or more sets of chromosomes. (3n,
4n etc). Some plants species demonstrate polyploidy.
Reproduction – copy or combine?
Organisms inherit genetic information from their parents. Some organisms have only a single parent
(asexual reproduction) while others have two parents (sexual reproduction). How do these different
forms of reproduction influence heredity? What are the advantages and disadvantages of one form of
reproduction over the other?
Asexual Reproduction
Sexual Reproduction
The production of offspring from a single parent;
The production of offspring from the fusion of two
the genetic makeup of the offspring is identical to sex cells (usually from two different parents); the
that of the parent
genetic makeup of the offspring is different from
Advantages:
that of the either parent.
Disadvantages: (reasons why sex is biologically
‘costly’)
Disadvantage:
Since asexual reproduction has so many biological
‘benefits’, why don’t all organisms use this
reproductive strategy?
Advantages:
Why bother going through sexual reproduction if it
is so ‘costly’?
Homework Questions:
1. In your own words, describe the relationship between each of the following pairs of terms
a) Reproduction and heredity
b) DNA and chromosomes
c) genetic information and gene
d) diploid and haploid
2. Use the internet to research and compare the diploid numbers of the following pairs of species:
ii)
Lion and tiger
ii) Elephant and wooly mammoth
iv)
Chimpanzee and gorilla
iv) Dog and wolf
What do you notice about chromosome number and the similarity of these species? Choose any
two other pairs of animals and compare their chromosome numbers.
3. List several biological advantages of asexual reproduction
4. Describe the added ‘costs’ of sexual reproduction for an organism.
5. When is the production of genetically identical offspring a disadvantage? Explain.
6. Moose antlers and peacock tails are classic examples of features related to sexual reproduction.
Explain what advantage and disadvantages might be associated with each of the following:
a) Mating calls of birds
b) Release of chemical scents into the air by female moths
c) The very large size of male elephant seals compared to females
d) The production of nectar by many flowers.
Solutions:
1.
2.
3.
4.
5.
6.