Inherited gene

INHERITED
GENE

9th

grade

Before we
start

Read the Science in context feature
entitled Breeding chinchillas at the start
of the chapter (Chromosomes, Gene and Protein) in your Coursebook.

DISCUSSION QUESTION

Open Ended

What do ou think determines the coat colour of a chinchilla?

Open Ended

Do you think that all the features of a chinchilla are determined in this way?

LEARNING OBJECTIVES:

●Describe inheritance as the transmission of genetic information from generation
to generation

●Describe genotype as the genetic make-up of an organism and in terms of the
alleles present

●Describe phenotype as the observable features of an organism

●Describe homozygous as having two identical alleles of a particular gene

●State that two identical homozygous individuals that breed together will be
pure-breeding

●Describe heterozygous as having two different alleles of a particular gene

●State that a heterozygous individual will not be pure-breeding

●Describe a dominant allele as an allele that is expressed if it is present in the
genotype

●Describe a recessive allele as an allele that is only expressed when there is no
dominant allele of the gene present in the genotype

DO YOU STILL REMEMBER?

●Each chromosome contain many genes.

●In human, 23 pairs of chromosomes contain about 20.000
genes.

GENE AND ALLELE

GENE AND ALLELE

In Chinchillas, gene determine the colour of the fur.

There aredifferent form of the fur
colours gene, called alleles

As we have two copies of each chromosome,
we have two copies of each gene and
therefore two alleles for each gene

One of the alleles is inherited from the mother and
the other from the father

GENE AND ALLELE

We can use letter as symbols of alleles.
For Example :
●

G for grey fur

●

g for charcoal fur

Possible combination of
alleles:
●

GG (homozygous)

●

Gg (heterozygous)

●

gg (?)

Alleles can be dominant (written in capital letters) or recessive (written in smallcase)

GENOTYPE

PHENOTYPE

The combination of

alleles that control each

characteristic

The observable

characteristics of an

organism

QUESTIONS

CODOMINANCE

​Codominance occurs when both alleles in heterozygous organisms contribute to the phenotype

CODOMINANCE

​Inheritance of blood group another

example of codominance.

Alleles I^A and I^B are codominant, but both are dominant to I^O

​I represents the gene and the superscript A, B and O represent the alleles

• I^A results in the production of antigen A in the blood

• I^B results in the production of antigen B in the blood

• I^O results in no antigens being produced in the blood

These three possible alleles can give us the following genotypes and phenotypes:

 

These three possible alleles can give us the following genotypes and phenotypes: