INTRODUCTION TO GENETICS

TRAITS Traits are the different forms of a characteristic that you may exhibit Ex: Blue or Brown Eyes Traits are inherited from our parents – mother and father 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

   

Human cells contain ____ chromosomes 23 46 12 2

DNA contains a code that tells your body to make _____________ fat carbohydrate protein

______________ traits won’t show up unless you have two copies of the gene. Recessive Dominant Generic Terrific

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) Always use the same letter for both alleles 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

BB Heterozygous Homozygous

Rr Heterozygous Homozygous

Freckles No freckles Ff FF You inherit the gene for freckles (F) from your mother, and the gene for no freckles (f) from your father. What is your genotype? Freckles No freckles Ff FF

Freckles No freckles Ff FF You inherit the gene for freckles (F) from your mother, and the gene for no freckles (f) from your father. What is your phenotype? Freckles No freckles Ff FF

Blue is dominant to white Blue is dominant to white. What would the genotype be for a white flower? BB Bb bb

Blue is dominant to white Blue is dominant to white. What would the genotype be for a heterozygous blue flower? BB Bb

Karyotype – Normal/Male A picture of the chromosomes found in an individual.  Used to determine abnormalities.

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