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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
-Construct / Interpret PEDIGREES
READING Q’s
1-IDENTIFY
-Check 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
-aa
READING Q’s
2-CATEGORIZE:
The following genetic disorders as RECESSIVE or DOMINANT
a-albinism
b-Huntington's
c-cystic fibrosis
recessive dominant
recessive dominant
recessive dominant
READING Q’s
3-EXPLAIN
-For what purpose is a genetic pedigree used?
-study genetic relationships
-trace inheritance of a trait generation to generation
READING Q’s
4-DRAW
The symbols that are used to represent a male AND female in
a pedigree
MALE-
FEMALE-
READING Q’s
5-EVALUATE
-Circle the carriers in the second generation
READING Q’s
6-CALCULATE
-What percentage of the children in this family inherited TaySachs disease?
-1/4=25%
READING Q’s
7-IDENTIFY
-Do any grandchildren in this family have polydactyly?
-NO
READING Q’s
8-EXPLAIN
-Why are recessive traits difficult to study?
-Not all people who carry the recessive allele have the trait
GROUP WORK: APPLICATION NOTES
-As a group complete the areas below using your knowledge
from the reading/discussion.
MAIN IDEA
REVIEW VOCAB
RECESSIVE / DOMINANT GENETIC DISORDERS
VOCAB
-carrier
-pedigree
MAIN IDEA
-PEDIGREESinheritance of traits over several generations
REVIEW VOCAB
DEFINE: gene
-segment of DNA on chromosome
DEFINE: homozygous
-2 identical alleles [TT / tt]
DEFINE: heterozygous
-2 different alleles [Tt]
RECESSIVE/DOMINANT GENETIC DISORDERS
COMPARE/CONTRAST:
recessive and dominant genetic disorders
RECESSIVE
-expressed when indv HOMO recessive [tt]
DOMINANT
-expressed when indv HOMO dominant [TT] or HETERO [Tt]
RECESSIVE/DOMINANT GENETIC DISORDERS
EXPLAIN why recessive disorders are more common than
dominant disorders.
-DOMINANT: only one allele must be inherited to be affected
-if DOM trait interferes w/ survival- no pass on
-RECESSIVE: carriers do NOT display the disorder
-many carriers are unaware they carry an affected gene
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
-HUNINGTON’S
-DOMINANT
-affects mucus-producing glands, digestive enzymes, sweat
glands
-CYCTIC FIBROSIS
-RECESSIVE
-affects height and body size
-ACHONDROPLASIA
-DOMINANT
RECESSIVE/DOMINANT GENETIC DISORDERS
PREDICT: what are the chances of 2 carriers of cystic fibrosis
having a child with cystic fibrosis?
F
f
F
FF
Ff
f
Ff
ff
¼= 25%
RECESSIVE/DOMINANT GENETIC DISORDERS
Positive Exposure
Positive exposure video clip Rick Guidotti - PART 2
Positive Exposure Inside Edition Part I - YouTube
PEDIGREE BASICS
[the FAMILY TREE of genetics]
WHAT is it:
-diagram explaining genetic history
WHO uses it:
-scientist
-genetic counselors
WHY use it:
-probability of child having disorder/condition
-determine disorder/condition as autosomal/sex linked
PEDIGREES
SUMMARIZE: pedigree symbols
MALE
CARRIER
-sqaure
-
-half shaded symbol
/
FEMALE
-circle
-
PARENTS/OFFSPRING
-line down from parent,
circles/squares on second row
AFFECTED MALE
-shaded square
AFFECTED FEMALE
-shaded circle
PARENTS
-circle joined to square
GENERATIONS
-I, II , III, IV,V
STEPS for INTERPRETING PEDIGREES
1- DETERMINE if the pedigree chart is showing:
AUTOSOMAL or X-LINKED disorder
-autosomal:
-If it is a 50/50 ratio between men and women
-x-linked:
-If most of the males in the pedigree are affected
2- DETERMINE if disorder is DOMINANT or RECESSIVE
-dominant:
-one of the parents must have the disorder.
-recessive
-neither parent has to have the disorder because they can be heterozygous.
Connecting Pedigree Symbols
 Married Couple
 Siblings
EX- PEDIGREE CHART
PRACTICE INTERPRETING
1. Determine if the pedigree chart shows an
autosomal or X-linked disease.
-If most of the males in the pedigree are affected the
disorder is X-linked
-If it is a 50/50 ratio between men and women the
disorder is autosomal.
PRACTICE: Interpreting
 Is it Autosomal or X-linked?
Answer
 Autosomal
Interpreting a Pedigree Chart
2. Determine whether the disorder is
dominant or recessive
-If the disorder is dominant, one of the parents must
have the disorder.
-If the disorder is recessive, neither parent has to have
the disorder because they can be heterozygous.
PRACTICE: Interpreting
 Dominant or Recessive?
Answer
 Dominant
PRACTICE: Interpreting
• Dominant or Recessive?
Answer
• Recessive
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:
-individuals I-1 and I-2 are unaffected
but have affected child
RECESSIVE
DOMINANT
X
-SPECIFIY if parents II-1 and II-2, who have an affected child, are
carriers of that trait
X
CARRIER
NOT A CARRIER
-TELL whether there is a dominant gene in the genotype of II-4
X
NONE
A 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 like 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.
[TONGUE ROLLING = DOMINANT / T]
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%
PEDIGREE CHART PRACTICE
PEDIGREE PRACTICE A
PEDIGREE PRACTICE B
PEDIGREE PRACTICE C
PEDIGREE PRACTICE 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