Hour
Finger
Hair –
yes
1
Tongue
Widow’s
roll - yes Peak
Free
Earlobe
Hitchhiker
Finger
Thumb - yes Length
Different
11/12 11/12 3/12
11/12
2/12
10/12
3
18/21 17/21 8/21
20/21
11/21
10/21
5
23/25 19/25 15/25
17/25
16/25
14/25
Total:
52/58 47/58 26/58 48/58 29/58
34/58
2
Mendel’s Laws of Heredity
 Mendel artificially pollinated
plants to produce crosses and
documented results.
 All offspring were identical to
parents – unexpected finding.
 Crosses of offspring yielded: 3/4
showed phenotype of dominant
gene.
3
Mendel’s Laws of Heredity
Law
of Dominance:
when an organism has 2
different alleles for a given
trait, the allele that is
expressed is considered
dominant. The other
allele is recessive.
4
Mendel’s Laws of Heredity
Law
of Segregation: when
gametes are formed by a
diploid organism, the alleles
that control a trait separate
from one another into
different gametes, retaining
their individuality.
5
Mendel’s Laws of Heredity
Law
of Independent
Assortment: Members of
one gene pair separate
from each other
independently of the
members of other gene
pairs.
6
Probability vs. Possibility
Probability:
chance that
an event will happen, can
be quantified, i.e.
mathematical expression.
This is not the same as
possibility.
7
Single-Factor Crosses

Single cross: single trait is followed from
one generation to the next. AKA Monohybrid
 To
solve single-factor crosses:
1. Assign a symbol for each allele.
2. Determine genotype of parents and
indicate a mating.
3. Determine all possible types of gametes.
4. Determine all possible gene combinations.
5. Determine phenotypes of each gene
combination.
8
Single-Factor Crosses
 Example:
Tourette Syndrome
 autosomal
dominant allele, 11q23
 if both parents are heterozygous for
this allele:
 do
the parents have signs/symptoms of
Tourette’s?
 what is the probability that the
offspring will have s/s?
9
Punnett Square

Tool to help determine probability of
genotypes and phenotypes of progeny of a
cross. Example: Tourette’s
T
t
T
t
10
Punnett Square

Tool to help determine probability of
genotypes and phenotypes of progeny of a
cross. Example: Tourette’s
T
T
t
TT
Tt
t
11
Punnett Square

Tool to help determine probability of
genotypes and phenotypes of progeny of a
cross. Example: Tourette’s
T
t
T
TT
Tt
t
Tt
tt
12