Genetics Notes

In case you were wondering -

YES !You need to copy

down all pictures /

diagrams (with labels)

from these notes.

Genetics

- The science that studies heredity.

Heredity is the process by which offspring resemble their parents. It is the passing of traits from one generation to the next.

Trait: A characteristic of an organism.

Examples of traits – hair color, eye color, height, intelligence, blood type, etc…

Forms of a trait (such as brown vs. blond hair) are called alleles.

Traits are controlled by our genes.

We inherit at least 2 genes for every trait – one from mom and one from dad.

Trait

A characteristic of an organism

(for example hair color, seed shape)

Inherit - To pass traits from parent to offspring

Genes

Tiny sections of chromosomes which carry information

about the traits of an organism. Organisms inherit 2

genes for each trait– one from each parent

How do we inherit our genes?

• 23 chromosomes are in the sperm from the father

• 23 chromosomes are in an egg from the mother

• 23 + 23 = 46 chromosomes in each of our cells

Recall from cells

and organelles:

All our genes

together make up

our chromosomes

that are found in the

nuclei of our cells.

DNA is in

DNA is the chemical that

makes up our genes – it is

in the shape of a double

helix.

DNA

• Genetic material within the

nucleus. (Deoxyribonucleic

Acid) This contains the

instructions for the cell

Why do we have some traits instead of others?

This is a result of dominant and recessive genes.

Dominant gene: one that prevents the

appearance of another (it masks or hides the

other one).

Represented by a capital letter.

Recessive gene: one that does not appear when it

is hidden by a dominant gene.

Represented by a lower-case letter.

Alleles

• The different forms of

a gene (ex. Black,

brown, or white fur in

rabbits)

An individual can only be homozygous

(pure/purebred is another term for

homozygous) for a trait if they have 2

dominant or 2 recessive alleles. (for example BB or tt)

An individual is heterozygous (hybrid is

another term for heterozygous)

for a trait when they have 1 dominant

and 1 recessive alleles.(for example Bb or Tt)

Note!

You will only express a

recessive gene if you inherit

2 recessive alleles!

• Genotype = the genetic make-up of the individual (the actual genes in the cells)

– BB, Tt, Ww, EE, cc (Example = Tt = one dominant and one recessive allele)

• Phenotype = the physical appearance of the individual – (Example = red hair)

• We can use Punnett squares to predict the possible outcomes/types for a cross (or mating).

Types ?

Sexual Reproduction

• Both male and female are present;

offspring is a combination of both parents.

(diverse)

Asexual reproduction • Reproduction resulting in offspring

identical to the parent. One parent is

involved (either male OR female)

• Your environment or circumstances may affect certain traits.

– Example: A person may be overweight due to genetics or they may be overweight because their family eats too much junk food.

• An organism may have an adaptation in which a trait changes based on the environment.

– Example: An artic fox that has brown fur in summer and white fur in winter.

What about the environment’s

affect on traits ?

Time to study!