INTRODUCTION TO GENETICS

Ms. Wassum

Traits

• Traits are the different forms of a characteristic that you may exhibit• Ex: Blue or Brown Eyes

• Traits are inherited from our parents

• Therefore, when we talk about genetics, we are talking about sexual reproduction

Chromosomes

• Every cell in a human body has 23 pairs of chromosomes – half from our mother, half from our father

• Genes are found on chromosomes• We have about 20,000-25,000 genes

• Each gene holds a code that tells our body to make

a certain protein• The protein that is made determines a

Specific trait. Ex: Blue eye pigment or

Brown eye pigment

Alleles

• The different forms of a gene that can exist• Ex: Curly hair gene or straight hair gene

• Dominant – ‘Strongest Allele’ – If it is present, you will have that trait. We use upper case letters for dominant alleles

• Recessive – ‘Weakest Allele’ – This won’t show up unless there are two of them. We use lower case letters for recessive alleles

Genotype

• The actual alleles you have for a trait• Ex: For eye color, you inherit B from dad and b from

Mom• Your genotype is Bb• If there is a dominant allele, the genotype is written

with the upper case first. (Never write bB)

• Your genotype is the genes you have

Genotype (Cont’d)

• If you have two copies of the same allele for a trait (BB or bb), then you are HOMOZYGOUS for that trait

• If you have two different alleles for a trait (Bb), then you are HETEROZYGOUS for that trait

Phenotype

• How the genes actually show up, or how they are expressed

• So, if your genotype is Bb,• Where B is brown• And b is blue

• The phenotype would be Brown eyes

• Phenotype is the physical appearance

Karyotype-Normal

A picture of the chromosomes found in an individual. Used to determine abnormalities.

Karyotype - Abnormal

There are three copies of chromosome 21 – there should only be two copies. This is a karyotpe of a female with Down’s Syndrome.

Quiz Time

• You inherit the gene for freckles (F) from dad, and the gene for no freckles (f) from mom

1. What would your genotype be? • Ff

2. What would your phenotype be?• You would have freckles

3. Which allele is dominant?• F (freckles)

Quiz Time

• You inherit the gene for no allergies (a) from dad, and the gene for allergies (A) from mom

1. What would your genotype be? • Aa

2. What would your phenotype be?• You would have allergies

3. Which allele is dominant?• A (allergies)