LESSON #7 Heredity

HEREDITY Traits and genes

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, butbe different species. Quercus rober and Quercus ilex

Excercise Dog: Canis lupus familiaris

Genus: Canis lupus Do you think a wolf and a dog can interbreed to have fertile descendants?

Within members of a species

there is variability.

How is diversity an advantage?

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 seperated ear lobes)

The characteristics that let us distinguish among individual are

called traits.

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…)

Familia Santos da Silva, Brasil

Foto: Andressa Anholete, Metro Brasilia

WHY ARE SOME GENETIC TRAITS INHERITED AND OTHERS AREN’T?

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

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.

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.

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.

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

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.