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Explore the basics of genetics, including traits, genes, alleles, and mutations. Understand how Punnett squares predict offspring traits and read pedigree charts to analyze family genetic history. Dive into the inheritance of traits like fur color and use practice problems to solidify your knowledge.
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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 trait • It is a segment of DNA on a chromosome • Genes come in 2forms (allele-forms of a gene): a. DOMINANT: allele that will always be expressed (shown) in an offspring • Tries to PREVENT the expression of recessive gene
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 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 • 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 • NEUTRAL
PUNNET SQUARE • A mathematical model used to predict the chances that offspring will inherit genes from their parents
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.
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.
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?
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
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.
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).
You are researching the inheritance of a red colored tongue in a lizard…. • Is it autosomal or X-linked? • Is it dominant or recessive?
