Genetics and Heredity

GENETICS  Study of the passing on of characteristics from one organism to its offspring

HEREDITY  The passing of traits from parents to offspring.

TRAIT  A characteristic of an organism  Examples include: height, skin color, eye color, freckles, nose shape, etc.  Traits are controlled by genes.

GENE The set of information that a controls a traitThe set of information that a controls a trait It is a segment of DNA on a chromosomeIt is a segment of DNA on a chromosome  Genes come in 2 forms (allele-forms of a gene): a. DOMINANT: allele that will always be expressed (shown) in an offspring a. DOMINANT: allele that will always be expressed (shown) in an offspring Tries to PREVENT the expression of Tries to PREVENT the expression of recessive gene recessive gene

b. RECESSIVE: allele that will only be expressed if there are no dominant alleles present b. RECESSIVE: allele that will only be expressed if there are no dominant alleles present Is prevented from showing up if there is a dominant allele presentIs prevented from showing up if there is a dominant allele present

 Example:  Eyecolor- Brown eyes are dominant and blue eyes are recessive.  A person can have a brown allele and a blue allele but still have brown eyes because the brown allele is dominant and hides the blue allele (it’s recessive).

 Dominant alleles are represented with a capital letter.  Recessive alleles are represented with a lowercase letter.  R = Dominant  r = recessive  An organism is represented by two letters for each allele (or gene that comes from mom and dad)

 Homozygous (purebred)-when a species has two identical (genes)alleles for a trait  Represented by the same 2 letters  Ex. BB (dominant) or bb (recessive)  Heterozygous (hybrid)-when a species has two different (genes) alleles for a trait  Represented by 2 different letters  Ex. Bb

 Genotype- genes in an organism that are present  Ex. Bb, bb or BB  Phenotype- an organism’s physical traits (or visible traits)  Ex. Brown eyes, brown hair

MUTATION CCCChange in a gene’s information (like a change in instructions)

Mutations can be:  HELPFUL  HARMFUL Examples include: Down’s syndrome, color blindness, albinism, sickle cell anemia Examples include: Down’s syndrome, color blindness, albinism, sickle cell anemia  NEUTRAL

PUNNET SQUARE  A mathematical model used to predict the chances that offspring will inherit genes from their parents

SAMPLE PUNNET SQUARE

Practice problem #1  Predict the genotypes for the fur color of the offspring of a brown, heterozygous hamster and a white homozygous hamster. Brown is dominant and white is recessive.  Use any letter you like.

Problem #2  Predict the gentoypes of the offspring of 2 white homozygous cows. Black is dominant over white.  Use any letter you like.

#2

Problem #3  Predict the genotypes of the offspring of 2 gray heterozygous rats. Gray is dominant over white, which is recessive.  Use any letter you like.

#3

Practice problem #4  What are the chances of having a girl or a boy baby?  How would you make a punnett square to show it?

#4

Pedigree Charts  Pedigree: a chart of the genetic history of a family over several generations  They are used to find out the probability of a child having a disorder or a certain trait in a family.

Symbols on a Pedigree Female: Male :

Connecting Pedigree Symbols:  Examples of connected symbols:  Married couple  Children 

More symbols in a Ped. Chart:

Example of a ped. Chart:  What does a pedigree chart look like?

Interpreting a Ped. Chart:  1. Determine if the pedigree chart shows an autosomal or X-linked disease/disorder.  If one sex in the pedigree is affected, it is X-linked.  It is a 50/50 ration between sexes, the the disorder/disease is autosomal. Autosomal doesn’t affect just one sex.

Is it autosomal or X- linked?

 Autosomal…why????

Interpreting Ped. Chart cont.  2. Determine whether the disorder is dominant or recessive.  If it is dominant, one of the parents must have the disorder/trait/disease.  It is is recessive, neither parent has to have the trait/disorder because they can be heterozygous (Bb).

Dominant or Recessive?

 Dominant….why????

Dominant or Recessive???

 Recessive…..why???

 You are researching the inheritance of a red colored tongue in a lizard….  Is it autosomal or X-linked?  Is it dominant or recessive?