1. Genetics II
Pedigrees and patterns of
inheritance
Mr. Hunter
Kennedy High School
Biology
03/15/2011

2. Mr. Hunter
Biology 03/06/2013
• Objective(s)
• SWBAT
• Explain the concept of linked genes.
• Define chromosome map.
• Explain the purpose and analysis of a pedigree.
• Distinguish between autosomal and sex-linked traits.
• Bell Ringer – What is the difference between a genotype and
a phenotype?

3. • In the early 1900s, Thomas Hunt
Fruit Flies and Morgan experimented with the
Chromosomes small fruit fly Drosophila
melanogaster.
• They live for approximately 7-10
days and their entire genome has
been recently sequenced.
• Based on his experiments with fruit
flies, Morgan determined that if
genes are inherited together they
must be on the same chromosome.
They are linked genes.
• Question: What are linked genes?

4. • The farther apart genes are located
Fruit Flies and on a chromosome, the more likely
Chromosomes that crossing-over will occur.
• A chromosome map is a diagram
that shows the linear order of genes
on a chromosome.
• The percentage of crossing-over for
two traits is proportional to the
distance between them on a
chromosome.
chromosome
• Question: What determines if
crossing over of genes will occur?
• Question : What is the percentage
of crossing over for two traits equal
to?

5. • Pedigree: A family history that
Family Pedigrees can be
used to study how traits
that shows how a trait is
are inherited inherited over several
generations.
• Very helpful if the trait is a
genetic disorder.
• Family members want to know if
they are carriers or if their
children will be infected.

6. • A carrier of the disorder will be
Family Pedigrees can be
used to study how traits
heterozygous. Ex : Aa, Bb or Pp.
are inherited They will have the genotype -
genes, but will not display the
phenotype – physical condition
• Carriers can pass the allele for the
disorder to their offspring.
• If the genotype is homozygous
recessive, then the offspring will
be infected. aa, bb , cc etc.
• Question: What is a pedigree?

7. • If a trait is autosomal, it will appear
Autosomal or sex linked in both sexes equally.
traits • If a trait is sex-linked, it usually
appears only in males.
• A sex-linked trait is a trait whose
allele is located on the X
chromosome.
• Most sex-linked traits are recessive.
Because males have only one X
chromosome, a male who carries a
recessive allele on the X
chromosome will exhibit the sex-
linked condition.
• Question: What is the difference
between an autosomal and sex-
linked trait?

8. • A female who carries an allele on the
Autosomal or sex linked X chromosome will not exhibit the
traits condition if there is a dominant
allele on her other X chromosome.
• She will express the condition only if
she inherits two recessive alleles.
• Her chances of inheriting and
exhibiting the condition are
significantly less than a male.
• Question : When will a female
display the phenotype of a sex-
linked trait?

9. • If the trait is autosomal dominant,
Autosomal dominant and every individual with the trait will
recessive have a parent with the trait.
• If the trait is recessive, an individual
with the trait can have one, two or
neither parent exhibit the trait.

10. 1. What is a pedigree and how is it
Review 03/06/2013 useful?
2. What is the difference between a
carrier of a genetic disorder and an
individual who is actually affected by
a disease.
3. What is the difference between an
autosomal and sex-linked trait?
4. When will women display the
phenotype of a sex-linked trait?
5. What is the difference between
genotype and phenotype?
6. If a genetic trait is autosomal
dominant, will the parents and
children have the trait? – Explain.

12. • Traits can be influenced by several
Complex Patterns of genes. These traits are called
Heredity polygenic traits.
• The genes may be scattered along
the same chromosome or located on
different chromosomes.
• Many different combinations appear
in the offspring. Examples include:
eye color, height, weight, hair and
skin color.

13. • A trait that is intermediate between
Intermediate Traits two parents results in a condition
known as incomplete dominance.
dominance
• For the snapdragon flower neither
the red or white allele is completely
dominant over the other allele. The
flowers are pink because they have
less red pigment.

14. 1. What is a pedigree and how is it
useful?
2. What is the difference between a
carrier of a genetic disorder and an
individual who is actually affected by
a disease.
3. What is the difference between an
autosomal and sex-linked trait?
4. When will women display the
phenotype of a sex-linked trait?