Download single trait crosses

Genetic
Crosses –
single gene
 Genotype
and
Phenotype


Genotype is the
genetic makeup of
the organism.
Phenotype is the
physical appearance
of the organism.
Heterozygous Vs Homozygous
 Homozygous

Same gene or allele for
the pair (AA or aa)
 Heterozygous

Different genes or
alleles in the pair (Aa)
 Capital
letter for
dominant, lower case for
recessive
Probability
 Likelihood
that an event
will occur.
 Can be expressed as a
fraction, decimal, or a
percentage.
 Calculated by:

Prob. = # times event
occurs/ # of times
opportunity occurred.
Crosses Involving 1 Pair of Genes percent
outcomes
P

P

P

= TT x TT
100% tall
= TT x Tt
100% tall
= TT x tt
100% tall
• P = tt x tt
– 100% short
• P = Tt x tt
– 50% tall,
50% short
• P = Tt x Tt
– 75% tall,
25% short
Memorize these crosses – it will
save you time.
Crosses Involving 1 Pair of Genes
P = Tt x Tt
T.5
t.5
T.5
T T T t
t.5
T t
Gametes of 1
parent (1N)
tt
Gametes of the
other parent (1N)
What is
inside the box
are the
prosible
results of
fertilization
(2N)
Test Cross – a breeding experiment
Pair share:
 How could you
determine if a black
guinea pig is
heterozygous or
homozygous?


(black is dominant over
white)
Hint look at the outcomes
of different crosses….
B = Black
b = white
(answer on next slide)
P
= B? x bb
If F1 is 100%
black then
genotype of
unknown parent is
Test Cross
X
BB
If F1 is 50% black and 50% white then unknown
parent is
Bb.