7. 1． Widow’s Peak
The gene contains 2 alleles: one for
straight hairline, which is recessive
and the other for widow’s peak,
which is dominant.
8. 2． Bent Pinkie
If you are able to bend your
5th finger (pinkie) inwards
towards the 4th finger, it
means you have the
dominant version of the gene
responsible for the distal
segment of the finger to bend.
10. 3． Crossing of Thumbs
When you are interlocking your fingers, observe your
thumbs. If your left thumb crosses your right thumb, this
means you have inherited one or two of the dominant
allele. If your right thumb crosses your left thumb, then
you have a pair of the recessive genes.
11. 4． Earlobe Attachment
People have their ear lobes either attached to the
sides of their heads or hanging free. Those with
unattached earlobes have the unattached earlobe
gene as the dominant gene and the attached
earlobe as the recessive gene.
12. 5． Tongue Rolling
If you are able to raise the sides of your tongue
together, then you have inherited the dominant gene.
Those who are unable to do this have the recessive
tongue rolling gene.
13.
14. Variation
Task 4: Write down 5 physical differences you have with
someone on your table. Write down what you think causes the
difference.
15. Variation
Living organisms differ in several ways, even when they are
offspring of the same parents. These differences are called
variation.
Variation can be determined by genes,
the environment
or both.
16. Variation Variation can be determined by genes, the
environment or both.
Task 5: Copy this table and complete it with examples.
Genetic Environmental Both
17. The Punnet Square
Male
female
T t
T
t
Some people can roll their tongue. This is a
dominant trait (T) Let’s imagine that we cross
two people who are heterozygous. We can show
the phenotypic ratio of traits in the offspring
(F1 generation) using a punnet square.
Gametes
contain half
the genes, so
at the
top/sides of
the punnet
square, we
show the
possible
gametes we
can produce
18. The Punnet Square
T t
T TT
t
Some people can roll their tongue. This is a
dominant trait (T) Let’s imagine that we cross
two people who are heterozygous. We can show
the phenotypic ratio of traits in the offspring
(F1 generation) using a punnet square.
19. The Punnet Square
T t
T TT Tt
t
Some people can roll their tongue. This is a
dominant trait (T) Let’s imagine that we cross
two people who are heterozygous. We can show
the phenotypic ratio of traits in the offspring
(F1 generation) using a punnet square.
20. The Punnet Square
T t
T TT Tt
t Tt
Some people can roll their tongue. This is a
dominant trait (T) Let’s imagine that we cross
two people who are heterozygous. We can show
the phenotypic ratio of traits in the offspring
(F1 generation) using a punnet square.
21. The Punnet Square
T t
T TT Tt
t Tt tt
Some people can roll their tongue. This is a
dominant trait (T) Let’s imagine that we cross
two people who are heterozygous. We can show
the phenotypic ratio of traits in the offspring
(F1 generation) using a punnet square.
22. The Punnet Square
T t
T TT Tt
t Tt tt
Genotypic ratio:
25% TT
50% Tt
25% tt
Phenotypic ratio:
75% roller
25% non-roller
Some people can roll their tongue. This is a
dominant trait (T) Let’s imagine that we cross
two people who are heterozygous. We can show
the phenotypic ratio of traits in the offspring
(F1 generation) using a punnet square.
Remember that
you might not
always get
what you
predict – NOT
because of
mutations, but
because it is
purely due to
chance which
gametes fuse!
23. Looking at whole chromosomes
instead of single genes
X X
X
Y
Some genetic diseases like red-green colour
blindness are due to a faulty allele on the x-
chromosome. Why might this disorder be
more common in men than in women?
Chromosome pair 23 are
known as the sex
chromosomes. Men have
and X and Y chromosome,
and women have two X
chromosomes. What is the
phenotypic ratio of offspring
for a cross between a man
& woman?
24. 1. The ability to tongue roll is a
dominant trait. What are the
phenotypes for a cross
between someone Tt
(tongue roller) and someone
TT (also a tongue roller)
2. Brown eye colour (B) is
dominant to having blue eye
colour (b). What are the
possible genotypes of
someone with brown eyes?
3. Give the % of each
phenotype possible if a
homozygous dominant with
brown eyes mated with a
blue-eyed person?
25. Monohybrid inheritance
Monohybrid inheritance is the inheritance of a single gene.
Genetic diagrams and punnett squares can be used to
describe patterns and predict probabilities of outcomes of
monohybrid crosses.
27. This is a cute little black guinea pig. I want to know the genotype and
phenotype. Why can you only tell me one of them confidently?
Test Cross
Cross an organism with an unknown dominant
genotype (parent 1) with an organism that is
homozygous recessive for that trait (parent 2).
Reveals if unknown individual tested
is homozygous dominant (pure bred)
or heterozygous dominant (hybrid).
If any offspring show the recessive phenotype,
then they must have inherited one recessive
allele from parent 2, but more importantly, parent
1 MUST have had a recessive allele to pass on,
therefore making it heterozygous
34. Albinism
a albino trait
A normal allele
Task 10:
1. What are the genotypes of parents A (3 & 4)? Explain how you know...
1. What are the genotypes of 15,16 and 17? Explain how you know....
35. Try and solve as
many of these
pedigree problems
as you can
