Transcript Les 5-6 Pedigrees

Heredity:
PedigreesWorking Out
Inheritance Patterns
By Lisa Marie Meffert, PhD
Genology - Lee Family of Virginia and Maryland
c1886 Apr. 26.
Prints and Photographs Division,
Library of Congress (LC-USZ62-90145)
Rice University
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How is gender determined? (see text p 318)
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Recall that in humans the diploid # of x’mes is 46 (23
pairs)
There are 22 pairs of homologous x’mes called
autosomes
The 23rd pair of x’mes are different in males and
females
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These two x’mes are called the sex x’mes.
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Indicated by the letters X andY
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Females are homozygous XX
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Males are heterozygous XY
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Gender determination (cont’d)
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Which x’me will determine the gender?
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The male
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Why?
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What is the expected ratio of males to females?
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Complete a punnet square (XX x XY)
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Sex linked inheritance
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Traits controlled by genes located on the sex x’mes are
called sex linked traits.
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Fig 12.2 - Discussion
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Draw a punnet square for each
generation
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Nondisjunction (p 271)
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The events of meiosis usually proceed accurately
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Sometimes homologous x’mes fail to separate properly
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Anaphase I – x’me pairs separate (1 to each daughter
cell)
Nondisjunction – both x’mes of a homologous pair
move to the same pole.
One gamete has an extra x’me and the other is short
one x’me
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Trisomy
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Zygote with one normal gamete and one gamete with
extra x’me
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47 x’mes – Down Syndrome
Organism with an extra x’me usually survive
Organisms one or more x’mes short usually do not
 Monosomy
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E.g. Turner syndrome
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Tetraploid
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Syndromes
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Trisomy 21 – Down syndrome
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Trisomy 13 – Patau’s syndrome
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XO – Turner’s syndrome
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XXX – Trisomy X (metafemales)
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XXY – Klinefelter’s syndrome
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XYY – Jacob’s syndrome
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OY – lethal
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Turner syndrome – XO monosomy.
Dwarfism
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Webbed neck
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Valgus of elbow.
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Amenorrhea
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KLINEFELTER'S SYNDROME - Trisomy XXY
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testicular atrophy
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increase in gonadotropins in urine.
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Jacob’s syndrome
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Jacob's syndrome is a rare chromosomal disorder that
affects males.
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It is caused by the presence of an extra Y chromosome.
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Males normally have one X and one Y chromosome.
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However, individuals with Jacob's syndrome have one
X and two Y chromosome.
Males with Jacob's syndrome, also called XYY males
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Patau’s syndrome
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Factors to Consider in Pedigrees
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Is the trait located on a sex chromosome or an
autosome?
 Autosomal – not on a sex chromosome
 Sex Linkage – located on one of the sex
chromosomes
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Y-linked - only males carry the trait.
X-linked (recessive) - sons inherit the disease from normal
parents
How is the trait expressed?
 Dominant - the trait is expressed in every
generation.
 Recessive - expression of the trait may skip
generations.
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Pedigree Diagrams: I
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Basic Symbols
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Pedigree Diagrams: II
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Basic Symbols for offspring and the expression of a trait.
 The offspring are depicted below the parents.
 Filling the symbol with black indicates the expression
of the studied trait.
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Marfan’s Syndrome: An Example
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Expressed in both sexes.
 Thus, autosomal.
Expressed in every generation.
 Thus, dominant.
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Marfan’s: Genotype the Normal Individuals
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Assign codes for the alleles.
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Code “m” for the recessive normal allele.
Code “M” for the dominant allele for Marfan’s
syndrome.
Normal individuals must be “mm.”
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Marfan’s: Genotype the Affected Individuals
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Affected individuals must have at least one “M.”
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Marfan’s: Parent-Offspring Relationships
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Possibilities for #1 and #2: Heterozygote (Mm)
or homozygous for “M?”
If “MM,” all offspring from a normal mate
should be affected.
Therefore, both must be heterozygotes.
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Marfan’s: Parental Genotypes Known
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“M” must have come from the mother.
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The father can contribute only “m.”
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Thus, the remaining genotypes are “Mm.”
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Albinism: An Example
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Expressed in both sexes at approximately equal frequency.
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Thus, autosomal.
Not expressed in every generation.
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Thus, recessive.
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Albinism: Genotype the Affected Individuals
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Assign codes for the alleles.
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Code “A” for the dominant normal allele.
Code “a” for the recessive allele for albinism.
Affected individuals must be homozygous for “a.”
First generation parents must be “Aa” because they have normal
phenotypes, but affected offspring.
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Albinism: Genotype the Normal Individuals
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Normal individuals must have at least one “A.”
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Albinism: Parent-Offspring Relationships
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#1 must transmit “a” to each offspring.
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The “A” in the offspring must come from the father.
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Normal father could be either heterozygous or
homozygous for an “A.”
**
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Albinism: Parental Genotypes are Known
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Both parents are heterozygous.
Normal offspring could have received an “A” from
either parent, or from both.
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Albinism: One Parental Genotype is Known
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Only the genotype of the offspring expressing albinism
are known.
Normal offspring must have received an “a” from their
affected father.
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Hairy Ears: An Example
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Only males are affected.
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All sons of an affected father have hairy ears.
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Thus, hairy ears is Y-linked.
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Hairy Ears: Female Sex Determination
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All females are XX.
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Hairy Ears: Male Sex Determination
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All males are XY.
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Hairy Ears: Gene on the Y Chromosome
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Code “H” indicates the allele on the Y chromosome for
hairy ears.
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Hairy Ears: Wild-Type Allele for Normal Ears
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Code “+” indicates the allele on the Y chromosome for
normal ears.
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Hemophilia: An Example
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In this pedigree, only males are affected, and sons do
not share the phenotypes of their fathers.
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Thus, hemophilia is linked to a sex chromosome–the X.
Expression of hemophilia skips generations.
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Thus, it is recessive.
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Extensive bruising of
the left forearm and
hand in a patient with
hemophilia.
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Hemophilia:
Expression of the Female Sex Chromosomes
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All females are XX.
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Hemophilia:
Expression of Male Sex Chromosomes
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All males are XY.
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Hemophilia: Genotype the Affected Individuals
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Assign codes for the alleles.
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Code “H” for the recessive hemophilia allele.
Code “+” for the wild-type normal allele.
Affected individuals must have an “H” on an X chromosome.
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Hemophilia: Father-Daughter Relationship
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All daughters of an affected father receive an X
chromosome with the “H” allele.
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Hemophilia: Genotyping the Normal Individuals
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Normal individuals must have at least one X
chromosome with the wild-type allele, “+.”
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Hemophilia: Homozygous or Heterozygous?
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Only males affected
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Not Y-linked
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Skips a generation: recessive
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X-linked
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