Intro to Genetics
Inheritance
 An individual’s characteristics are determined by factors that are passed from one ____________________
generation to the next.
o The delivery of characteristics from parent to offspring is called _____________________.
 Genetics
o The scientific study of heredity, known as:
Experiments of Gregor Mendel
 Mendel carried out his work with ordinary garden ______________, partly because:
o Peas are _______________ and easy to grow
o A single pea plant can produce __________________ of offspring
o Observable ________________________
Fertilization
 A trait:

Mendel decided to “cross” his stocks of ______________-breeding plants—he caused one plant to
reproduce with another plant.
Hybrids
 Mendel crossed plants with each of the seven _____________________ characteristics and then studied their
offspring.
 The offspring of crosses between parents with different traits are called _______________________.
Genes & Alleles
 When doing genetic crosses, we call the ___________________ pair of plants the:


Their offspring are called:
For each trait studied in Mendel’s experiments, all the offspring had the ______________________ of only
one of their parents, as shown in the table.
 In each cross, the nature of the other parent, with regard to each trait, seemed to have
_______________________.
 From his experiments, Mendel drew two conclusions:
o An individual’s characteristics are determined by factors that are ________________ from one
parental generation to the next.
o Scientists call the factors that are passed from parent to offspring __________________.
Genes & Alleles
 Each of the traits Mendel studied was controlled by one ________________ that occurred in two
contrasting varieties.
 These gene variations produced different _____________________, or forms, of each trait.
 The different forms of a gene are called __________________.
Dominant & Recessive Traits
 Mendel’s second conclusion is called the principle of ______________________.
o This principle states that
o In Mendel’s experiments, the allele for ______________ plants was dominant and the allele for
short plants was recessive.
Segregation
 During gamete formation, the ___________________ for each gene segregate from each other, so that each
gamete carries only one allele for each gene.
 Mendel wanted to find out what had happened to the ____________________ alleles.
 To find out, Mendel allowed all seven kinds of F1 hybrids to self-___________________. The offspring of an
F1 cross are called the F2 generation.
 When Mendel compared the F2 plants, he discovered the traits controlled by the recessive alleles
_____________________ in the second generation.
 Roughly __________ _______________ of the F2 plants showed the trait controlled by the recessive allele.
 Mendel assumed that a dominant allele had __________________ the corresponding recessive allele in the
F1 generation.
 The reappearance of the recessive trait in the F2 generation indicated that, at some point, the allele for
shortness had __________________ from the allele for tallness.
Probability and Genetics
 Punnett squares use mathematical ____________________ to help predict the genotype and phenotype
combinations in genetic crosses.
 Probability is the ______________________ that a particular event will occur.
 There is ____________ possible outcomes of a coin flip: The coin may land either heads up or tails up.
 The chance, or probability, of either outcome is equal. Therefore, the probability that a single coin flip
will land heads up is 1 chance in 2. This amounts to 1/2, or _________ percent.
 Consider a couple examples:
o If you flip a coin once in the air, what is the chance that you will get a tails?
o If you flipped the coin again, what are the chances of getting tails again?
 Although we can use probability to predict future traits in offspring, the numbers do not always work
out in reality.
 Consider an example:
o If you flip a coin once in the air, what is the chance that you will get tails?
o If you flipped the coin again, what are the chances of getting tails again?
o What are the chances of flipping tails three times in a row?
 __________________________
 Remember, each coin flip is an ______________________ event with a ½ probability of landing tails up each
time.
Probability Rules
 If “x _____________ y will happen”
o Then __________________ the probability of x by the probability of y
o (probability of x)*(probability of y)
Probability Example
 What are your chances of rolling a 1 twice in a row on a normal die?
o ________________________________
 What is your chance of rolling a 5 the first time you roll a die and a 6 the second time?
 You ____________________ your chances –
o _____________________________________________
More Probability Rules
 If “x __________ y will happen”
o Then _______________ the probability of x to the probability of y
o (probability of x) + (probability of y)
 What is your chance of rolling a 1 or a 6 the first time you roll a die?
o ____________________________

What is your chance of rolling a 1, a 3, or a 6 the first time you roll a die?
o _______________________________________________
 What is your chance of rolling a 1 or 2 twice in a row?
o _________________________________ – first roll
o _________________________________ – second roll
o ___________________________
Probability cont’
 Past outcomes do not affect the ________________________!
 Just because you flipped a tails before, does not mean you will __________________ time.
 Independent events will have the same _______________________ as others, but when there is more than
one trait we are testing for, there are more possible outcomes.
 The way in which alleles ___________________ during gamete formation is every bit as random as a coin
flip or a dice roll.
 Therefore, the principles of probability can be used to __________________ the outcomes of genetic
crosses.
 Probabilities predict the average outcome of a _______________ number of events.
 The ____________________ the number of offspring, the closer the results will be to the predicted values.
 If an F2 generation contains just three or four offspring, it may __________ match Mendel’s ratios.
 When an F2 generation contains hundreds or thousands of __________________, the ratios usually come
very close to matching Mendel’s predictions
Genotype & Phenotype
 Genotype – ____________________ makeup
o Ex: _______
 Phenotype – ___________________ traits
o _______________ plant or short plant
Homozygous & Heterozygous
 Organisms that have two ____________________ alleles for a particular gene—TT or tt in this example—are
said to be homozygous.
 Organisms that have two ____________________ alleles for the same gene—such as Tt—are heterozygous.
Predicting Phenotypes
 Using _________________ Squares
o Cross true-breeding strains.
 Genotype – 100% _______
 Phenotype – 100% _____________
 Using Punnett Squares
o Cross F1 generation
 Genotype – 25% _______
 50% _________
 25% _________
o Genotypic ratio – ____________
o Phenotype –
 75% - ___________
 25% - ___________
o Phenotypic ratio- _______________
Summary of Mendel
 The inheritance of biological characteristics is determined by individual units called ______________,
which are passed from parents to _________________.
 Where two or more forms (_______________) of the gene for a single trait exist, some forms of the gene
may be dominant and others may be recessive.

In most sexually reproducing organisms, each adult has two copies of each gene—one from each
parent. These genes ____________________ from each other when gametes are formed.
Codominance
 Codominance: when both alleles are ____________________.
 The heterozygous individual shows ______________ alleles expressed.
 A capital letter represents one of the __________________ alleles.
 A different capital letter represents the other ___________________ allele.
 In horses, gray horses (GG) are codominant to white horses (WW). The heterozygous horses(GW) is an
appaloosa horse (a white horse with gray spots on the rump and loins).
 Cross a white horse with an appaloosa horse.
o What is the phenotypic ratio?
 ______________________
Multiple Alleles
 A single gene can have many possible ___________________.
 A gene with more than two alleles is said to have _________________ ________________.
 Many genes have multiple alleles, including the human genes for _____________ type.
Codominant and Multiple Alleles
 ______________ blood type is determined by mutiple alleles and codominance.
o The ABO blood group is determined by a gene with _______________ alleles: IA, IB, and i.
o IA and IB are both dominant blood types and therefore ______________________.
o i is _______________________
o Individuals with alleles IAIA or IAi produce only the A _________________, making them blood type
A.
o Those with IBIB or IBi alleles produce only the B __________________, making them blood type B.
o Those homozygous for the i allele (ii) produce no __________________ and are said to have blood
type O.