Heredity, genes and alleles

1. LESSON #7 Heredity

2. HEREDITY Traits and genes

3. SPECIES
A specie is a group of organisms that can
reproduce amongst themselves and have fertile
descendants.
Name of a species: Genus specie (Homo sapiens)
Closely related species may belong to the same
genus, but be different species. Quercus rober and
Quercus ilex
Exercise
 Dog: Canis lupus familiaris
 Wolf: Canis lupus
 Do you think a wolf and a dog can interbreed to have fertile
descendants?

4. EXERCISE 1
1. Find the scientific name of the following species:
a) Domestic Cat Sand cat
b) Bengal Tiger Lion
c) Leopard
d) Homing Pigeon
e) Maple tree (Falso plátano)
f) Poppy
2. Choose a species from above and find another
organism that belongs to the same genus (very closely
related), but is a different species.
You
need
your
compute
rs
Inquiry

5. Within members of a species
there is variability.
How is diversity an
advantage?

6. VARIABILITY WITHIN A
SPECIES
Specific characteristics: the same to all members of
the specie.
Individual variations: make each individual unique.
 Continuous variations: variations that go from low to
high quantities. (Height, Weight…)
 Discontinuous variations: if you can divide the specie
in groups according to this variation. (Individuals with
attached ear lobes; individuals with separated ear
lobes)
The characteristics that let us distinguish among
individuals are called traits.
Think of
more
examples

7. TRAITS
Inherited traits: they are passed down to the following
generations, although they may not be present in all
generations. (Skin color, hair color, shape of the face,
blood type…)
Acquired traits: they do not pass on to the descendants.
They appear during the lifetime due to different life
conditions, accidents, diseases, etc. (Darkened skin,
freckels, muscle development, hair loss…)

8. EXERCISE 2: CLASSIFY
TRAITS
Inherited
Acquired
DiscontinuousContinuous
Work in
groups of
4.
Take
turns

9. Familia Santos da Silva, Brasil
Foto: Andressa Anholete, Metro Brasilia
WHY ARE SOME GENETIC
TRAITS INHERITED AND
OTHERS AREN’T?

10. WHAT IS A GENE?
o Unit of heredity.
o Segment of DNA on a specific locus (site of a
chromosome) which is responsible for a specific
phenotype.
o A section of DNA that codifies for a specific protein is a
gene.
o Each chromosome has hundreds of genes, some parts
of a chromosome do not codify for proteins, therefore
they are not considered genes.
o The complete human genome has around 30,000 genes
spread through out the 46 chromosomes/ DNA
molecules

11. HOMOLOGOUS
CHROMOSOMES
• 2 chromosomes that have the same genes in the same
loci
• They are pairs.
• Humans have 23 pairs of homologous chromosomes.
• One inherited from the mother and the other inherited
from the father.

12. GENES AND ALLELES
For each gene there can be many different alleles.
Each individual only carries 2 alleles for each gene. The
individual’s traits will depend on the combination of
alleles that individual carries for each gene.

13. HOW ARE TRAITS STUDIED?
Phenotype
The observable
characteristics or traits
that an individual shows.
This is a result of the
alleles that an individual
carries for a gene.
Genotype
The combination of alleles
for a gene.
Each individual carries two
alleles for each gene.

14. HOMOZYGOUS AND
HETEROZYGOUS
Homozygous
An individual is
homozygous for a gene
when both alleles it carries
for that gene are the same.
Heterozygous.
An individual is
heterozygous for a gene
when it carries 2 different
alleles for that gene.
Image Source: BBC GCSE Bitesize
Gene for eye
color.
Locus: 3p21
4 alleles
possible:
• Blue
• Brown
• Green
• Black

16. EXERCISE
Refers to phenotype or genotype?
1. The cat has brown fur.
2. It’s a boy.
3. Has genes for blue eyes
and for brown eyes.
4. Jack is heterozygous for
haemophilia.
5. That man is bald.
6. Homozygous for white
color flowers.
7. This man is
haemophilic.
8. I have curly hair
9. The hen is
heterozygous for black
feathers.
10. The pea plant has tall
stems.
11. The boy has two alleles
that codify for a
defective Haemoglobin.