Probability and Punnett Squares
Probability
 _____________________is the likelihood that a specific ________will ___________.
 For example, if you flip a coin, the probability that it will land on heads is _______, or ______ out of
_________.
 We can use _____________________ to predict the probability of ______________ outcomes.
Dominant and Recessive Alleles
 _________________ alleles are expressed in _______________ ________________.
 Ex: T B A C X
 Dominant alleles can ___________ recessive alleles. This means you might have a recessive allele, but you
can’t see the ________________ trait if the ________________ allele is present.
 Recessive alleles are represented by __________________ _________________.
 Ex: t b a c x
 Recessive alleles are __________ by ____________________ alleles.
Homozygous and Heterozygous
 An organism is _______________________ if both alleles are __________________ (both dominant or
both recessive).
 Ex: TT, BB, aa, cc, tt
 An organism is ____________________if the alleles are ____________________ (one dominant and one
recessive).
 Ex: Tt, Bb, Rr, Xx
 A heterozygous organism ____________________ the _______________ trait, but is a
_________________ of the _____________________trait.
 TT = ___________________________________
 tt =
 Tt =
Genotype and Phenotype
 _________________________ is the ________________ ____________________ of the trait.
 Ex:
.
 _____________________ is the _________________ _______________ of the organism, or what the
_______________ actually are.
 Ex: BB, Tt, Rr, rr
 Example:
A plant is tall, but has heterozygous alleles for height. What is the genotype?
 A dog is homozygous dominant for a straight tail. What will be the genotype if the letter that represents
tail straightness is S?
Punnett Squares
 A
is a simple
that can be used to predict
the outcome of a
.
 Punnett squares use
to predict possible
and
__________________________.
 In a
cross only one trait is studied at a time.
 Example:
 A brown mouse (Bb) is mated with a white mouse (bb).
 What trait is dominant—brown or white? Which is recessive?
 What is the probability of producing a white mouse?
 In beagles the trait for droopy ears (D) is dominant to the trait for perky ears (d). What would be the
expected offspring if two heterozygous droopy-eared dogs were mated?
Incomplete Dominance
 Some alleles are neither
nor
. In these, a
of the two traits is
.
Codominance

is situation in which both alleles are
.
 In a codominant individual, the
from both alleles are clearly
Multiple Alleles
 Many genes exist in several different
and are said to have
 A gene with more than
alleles is said to have
 In human,
is determined by multiple alleles. A and B are codominant, while O is
recessive.
 A woman with AB blood has a child with a man who has type O blood (OO). What are the possible blood types
of the child?
Sex-Linked Traits
 Humans have ________ pairs of chromosomes.
 We have 22 pairs of
, called _____________.
rd
 The 23 pair determines _______________. Females have an _________ genotype. Males have an
_________ genotype.
 The X and the Y chromosomes are not ___________________. The X chromosome is much bigger than the
Y, so there are some ________ on the X-chromosome that are not on the _______________________.
 The ____________ for sex-linked traits are written as ____________________ of the X-chromosome.
 __________________________ is a sex-linked trait carried on the X-chromosome.
 Because boys only have one X-chromosome, they are more likely to get color blindness. If they only get one
bad copy of the gene, they have the disorder. Girls have to get two bad copies of the gene to have the
disorder.
Polygenic Inheritance
 Traits controlled by two or more genes are said to be ____________________
 These traits often show a wide range of ____________________.
 More than _________different genes code for skin color.