Genes & Alleles Genotype & Phenotype Homozygous & Heterozygous

Created by

Sima Mathew

and

Jennifer Dietz

Gregor Mendel known as::THE FATHER OF GENETICS.

- laid the foundations for the SCIENCE OF GENETICS through his study of inheritance patterns of traits in pea plants.

What is heredity or inheritance? Passing of traits from parent to offspring

or from one generation to the next.

Genes are the coded instructions that define our traits.

How are genes inherited? Humans have 2 sets of chromosomes for a total of

46 chromosomes. Each parent contributes only 1 set of chromosomes to their child.

When a sperm cell (23 chromosomes) and an egg cell (23 chromosomes) join during fertilization, it results in a zygote (46 chromosomes).

What is a trait? Notable feature or quality in a person.

What are the two types of traits? Physical traits are traits that can be

seen such as eye or hair color Behavioral traits demonstrate the way

one acts such as “the fetching behavior of golden retrievers”.

Phenotype Phenotype is another word for physical

trait (in other words, it describes how someone looks)

Examples of phenotypic words are:tall, short, brown hair, straight hair, fat, skinny, fair skin, freckles, etc.

Can you think of anymore? On your notes, write at least 4 phenotypic

words that describe YOU!

REMEMBER!! Phenotype describes things you can see!!!

What do you think person’s phenotype would be?

How would you describe this phenotype?

Remember?? REMEMBER: Mom gives you one half of your genes, and your dad gives you the other half….

sperm + egg = YOU!

Together, these two genes (one from mom and one from dad) represent your genotype

Each gene is represented by one letter.

Genotype Genotype is the genetic makeup of an

organism’s traits represented by letters

Genotype codes for phenotype

T = tall

t = short

Two different forms of the same gene =

The factors that carry all traits =

Example

Gene = height Alleles = tall; short

Example

Gene = eye color Alleles = green, blue, brown

Example

Gene – hair texture Alleles – straight, wavy, curly

Example

Gene – thumb Alleles – hitchhiker’s thumb, straight thumb

Dominant vs. Recessive Think of a person who never lets you

talk during a conversation – that person DOMINATES the conversation.

A Dominant Allele: allele that is expressed (the one that you see).

A Recessive Allele: allele that is masked or hidden (not shown)

Which allele is expressed over another and represented by a capital letter?

Which allele is usually masked or appears less in the population and represented by a lowercase letter?

Dominant or Recessive?

A

F

r

h

G

t

d

Check Yourself

A – dominant

F - dominant

r – recessive

h - recessive

G - dominant

t - recessive

d - recessive

When both alleles are the SAME it is called

When the alleles are DIFFERENT it is called

B = brown hair b = red hair

homozygous for brown hair

heterozygous for brown hair

homozygous for red hair

HOMOZYGOUS HETEROZYGOUS

Homozygous or Heterozygous?

RRJjttHhaa

Check Yourself

RR - homozygousJj - heterozygoustt - homozygous

Hh - heterozygousaa - homozygous

You inherit two alleles for each gene (trait).

1 from MOM! 1 from DAD! PHENOTYPE –

physical characteristics that you SEE

Ex. Straight hair, red hair, freckles, lactose intolerant, tall, blue eyes

GENOTYPE – genetic makeup represented by letters

Ex. RR, Tt, Ffgg, YyEePp

Principle of Dominance: when there is a dominant allele and a recessive allele inherited together for a particular gene, the dominant allele will ALWAYS be expressed.

Mendel’s 1st Law of Inheritance

Dominant Brown

hairallele

Recessiveredhair

allele

Express the dominant allele for brown hair