11.1 BASIC PATTERNS OF HUMAN INHERITANCE
WHAT YOU WILL LEARN
-How to determine if an inherited trait is dom/rec
-Examples of DOMINANT/RECESSIVE disorders
-How a PEDIGREE shows a particular trait in families
MAIN IDEA
The inheritance of a trait is shown over several generations in
a pedigree.
READING Q’s
REVIEW VOCAB:
enzyme
-PROTEIN that speeds up biological reactions
READING Q’s
IDENTIFY
-CIRCLE the term that describes the genotype of a person
who expresses a recessive trait
-homozygous:
organism with 2 of the same alleles for a particlular trait
-DETERMINE the genotypes:
recessive genetic disorder
dominant genetic disorder
DD Dd dd
X
X
DD
Dd
dd
X
READING Q’s
EXPLAIN
-Why do ganglioslides build up in the brain of people with TaySachs disease?
-ENZYME missing that breaks down ganglioslides—fatty acids
READING Q’s
EXPLAIN
-How scientist determine if achondroplasia developed from a
new mutation
-achondroplasia is a dominant disorder: dwarfism
-if BOTH parents are average height it dev from MUTATION
Parents would be homozygous recessive so could only pass
on a recessive allele—dominant allele would have to be a
mutation
READING Q’s
EXPLAIN the purpose of a genetic pedigree
-track a trait or disorder throughout several generations
DRAW the symbols used in a pedigree for:
MALE=
FEMALE=
READING Q’s
EVALUATE
-Circle the carriers in the second generation
READING Q’s
CALCULATE
-What percentage of the children in this family inherited TaySachs disease?
-1/4=25%
READING Q’s
IDENTIFY
-Do any grandchildren in this family have polydactyly?
-NO
READING Q’s
EXPLAIN
-Why are recessive traits difficult to study?
-Not all people who carry the recessive allele have the trait
-Don’t know if you are a carrier unless___
-1 parent shows the trait = homozygous recessive
-offspring shows trait = both parents carriers
GROUP WORK: APPLICATION NOTES
-As a group complete the guided note sheet using your
knowledge from the reading.
REVIEW VOCAB
DEFINE:
gene
-segment of DNA on chromosome
carrier
-heterozygous for a recessive disorder--Aa
RECESSIVE/DOMINANT GENETIC DISORDERS
COMPARE:
RECESSIVE GENETIC DISORDERS
-only present if homozygous recessive
-parents are carriers if don’t have disorder
DOMINANT GENETIC DISORDERS
-present if have at least 1 dominant allele
-must have a parent with the disorder
[mutations are exceptions]
-don’t always appear until later in life
RECESSIVE/DOMINANT GENETIC DISORDERS
IDENTIFY:
1-four examples of recessive genetic disorders in humans
1-CYSTIC FIBROSIS
2-TAY-SACHS
3-ALBINISM
4-GALACTOSEMIA
5-ALKOPTONURIA
2-two examples of dominant genetic disorders in humans
1-HUNTINGTON’S
2-ACHONDROPLASIA
RECESSIVE/DOMINANT GENETIC DISORDERS
EXPLAIN why recessive disorders are more common than
dominant disorders.
-don’t always know there are carriers of disorder
-parents may not know the disorder is in the family
------------------------------------------------------------------------------parents with a dominant disorder may choose to not have
children or may not survive to age of procreation
===========================================
a recessive trait may be more functional than the dominant,
therefore a dominant trait could be eliminated over many
generations
RECESSIVE/DOMINANT GENETIC DISORDERS
IDENTIFY:
the disease for each dominant/recessive disorders
-caused by altered genes; results in lack of skin pigmentation
-ALBINISM
-recessive
-characterized by body’s inability to tolerate galactose
-GALATOSEMIA
-recessive
-gene found on chromosome 15;characterized by lack of
enzyme that breaks down fatty acids
-TAY SACHS
-recessive
RECESSIVE/DOMINANT GENETIC DISORDERS
IDENTIFY:
the disease for each dominant/recessive disorders
-affects the nervous system; no treatment; breaks down part
of brain
-HUNTINGTON’S
-dominant
-affects mucus-producing glands, digestive enzymes, sweat
glands
-CYCTIC FIBROSIS
-recessive
-affects height and body size
-ACHONDROPLASIA
-dominant
RECESSIVE/DOMINANT GENETIC DISORDERS
-SHOW a cross between 2 carriers
-what is the probability 2 carriers of cystic fibrosis will have a
child w/CF?
F
f
F
FF
Ff
f
Ff
ff
-25%
RECESSIVE/DOMINANT GENETIC DISORDERS
PREDICT:
-can 2 normal height parents have a child w/achondroplasia?
a
a
a aa
aa
a aa
aa
RECESSIVE/DOMINANT GENETIC DISORDERS
PREDICT:
-can 2 individuals w/achondroplasia have a child that is normal
height?
A
a
A AA Aa
a Aa
aa
PEDIGREES
SUMMARIZE: pedigree symbols
MALE
CARRIER
-square
-
-half shaded symbol
/
FEMALE
--circle joined to square
-circle
-
PARENTS
AFFECTED MALE
PARENTS/OFFSPRING
-shaded square
-
-line down from parent/
circles/squares on second row
-
AFFECTED FEMALE
-shaded circle
-
PEDIGREE CHART
PEDIGREE CHART
GRANDPA X GRANDMA
MOM X DAD
GRAMPS X GRANNY
ANALYZING PEDIGREES
EVALUATE:
the inheritance of achondroplasia shown in the pedigree
-parent w/ disorder
-father
-#children with disorder
-1 / 1st born son
-genotype of younger son
-homozygous recessive / aa
ANALYZING PEDIGREES
ANALYZE and RESPOND:
-RECALL if the trait is rec or dom
based on the following information:
-In the pedigree, individuals I-1 and I-2
are unaffected -- have affected child
RECESSIVE
DOMINANT
X
-SPECIFIY if parents II-1 and II-2, who have an affected child, are
carriers of that trait
CARRIER
NOT A CARRIER
X
-TELL whether there is a dominant gene in the genotype of II-4
NONE
A
X LEAST ONE
-Individual II-1is in generation 2
X
TRUE
FALSE
ANALYZING PEDIGREES
THINK BACK and RESPOND:
-A scientist uses a pedigree to study family history
TRUE
FALSE
X
-A pedigree traces the inheritance of a particular trait
through only two generations
MANY
TRUE
FALSE
X
-In a pedigree, one who does not express the trait is
represented by a darkened circle/square
TRUE
FALSE
X
-In a pedigree, a horizontal line between 2 symbols shows
that these individuals are the parents of the offspring
X
TRUE
FALSE
ANALYZING PEDIGREES
DIAGRAM:
Suppose both parents can roll their tongues but their son cannot.
IDENTIFY this trait as: dominant recessive
DRAW a pedigree showing this trait LABEL each symbol with the appropriate genotype
What was the probability that they would have a non-tongue roller offspring?
(hint: punnet square)
-both parents carry recessive gene
-parent genotype Tt
-son genotype tt
-probability of child tt= 25%
Connecting Pedigree Symbols
 parents
 offspring
EX- PEDIGREE CHART
Interpreting a Pedigree Chart
1-
Determine whether the trait/disorder is
dominant or recessive
-If the trait/disorder is dominant, one of the parents
must have the disorder
-If the trait/disorder is recessive, neither parent has to
have the disorder because they can be heterozygous
PRACTICE: Interpreting
• Dominant or Recessive?
Answer
• Recessive
PRACTICE: Interpreting
 Dominant or Recessive?
Answer
 Dominant
Interpreting a Pedigree Chart
2-
Determine if the pedigree chart shows an
autosomal or X-linked trait/disorder
-If most of the males in the pedigree are affected the
trait/disorder is X-linked
-If it is a 50/50 ratio between men and women the
trait/disorder is autosomal.
PRACTICE: Interpreting
 Is it Autosomal or X-linked?
Answer
 Autosomal
Summary
-Pedigrees are family trees that explain your genetic history.
-Pedigrees are used to find out the probability of a child
having a trait/disorder in a particular family.
-To begin to interpret a pedigree
-determine if the trait/disorder is:
1-dominant or recessive
2-condition is autosomal or X-linked
PEDIGREE PRACTICE 1-A
PEDIGREE PRACTICE 1-B
PEDIGREE PRACTICE 1-C
PEDIGREE PRACTICE 1-D
PEDIGREE PRACTICE 2-A
PEDIGREE PRACTICE 2-B
PEDIGREE PRACTICE 2-C
PEDIGREE PRACTICE 2-D
INVESTIGATING HUMAN PEDIGREES
-USE the information provided in the transcript to construct
a pedigree showing hairy earlobes* in a family *HE
-DETERMINE the oldest couple in the family
-DRAW their pedigree symbols—include names
-CONTINUE with other members in the family
-DETERMINE genotypes as you gather enough information