Matters of Sex

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Chapter 6

• Matters of Sex

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QSR 2

• 1. A trait that is __________________, will be
  found mostly in males while ___________________
  traits will be spread out evenly between males
  and females.
• 2. _________________ are the tips of the
  chromosomes only about 5 of the entire
  chromosome.
• 3. The blood-clotting disorder,
  __________________, is a ____________ trait since
  its found mostly in males.
• 4. The nucleus of a cell in a female, during
  interphase, has one dark-staining X chromosome
  called a _____________________________.

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Mendelian Inheritance of Human Traits

• Family trees
• Pedigree
• a graphic representation of genetic inheritance
  thru a family.
• Looks similar to a family tree
• Uses symbols
• Male
• Female
• Children
• relationships

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Pedigrees

• Family history of traits recorded over
  generations
• Can tell if the trait is dominant
• Recessive
• Sex-linked
• Autosomal
• Circles females
• Squares males
• Marriage horizontal lines
• Vertical lines children

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Analyzing Pedigrees

• Sex-linked vs autosomal
• Only seen in males ---sex linked
• Both sexes equally---autosomal
• Dominant vs recessive
• Trait is dominant then every infected
  individuals parent will have the disease
• Recessiveparents are normal children are
  infected

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Risk of Diseases

• Use pedigrees
• Genetic counseling
• Prenatal testing
• Amniocentesis/chorionic villi sampling to
  determine karyotypes

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• ON THE FOLLOWING SLIDE, BE SURE TO LABEL
• 1. Dominant or Recessive
• 2. Sex-linked or Autosomal

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• ON THE FOLLOWING SLIDES, BE SURE TO LABEL
• 1. Dominant or Recessive
• 2. Sex-linked or Autosomal
• 3. Tell the genotype of each person

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Practice constructing a pedigree

• Ben and Jan are married with 4 boys. Ben has
  dimples as does his 2 oldest boys. Jans parents
  do not have dimples. Their youngest son married a
  female with dimples and together they have 2
  daughters and a son all of who have dimples ?

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QSR3Questions for Trait A pedigree(use the
letter B/b)

• 1.  Does a dominant or recessive allele produce
  the trait?  Explain. 2.  Is it autosomal or
  sex-linked?  Explain. 3.  What are the genotypes
  of all the individuals in the pedigree?  (Write
  them on the pedigree.) 4.  What is the genotype
  of individual IV-2?  Explain. 5.  What is the
  genotype of individual IV-6?  Explain. 6.  What
  is the genotype of individual I-1?  Explain

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InhertitanceSymptoms
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Recessive Autosomal Heredity

• Offspring must have 2 traits before the disorder
  will show up must be passed down from both
  parents
• If the parents do not show signs of the
  disorder, they are considered to be CARRIERS
• This is why blood relatives should not have
• children together no incest!!!!
• Consanguinity shared bloodfamily members may
  share certain traits or disorders

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Recessive Autosomal Heredity

• 1. males and females are equally affected
• 2. Affected males and females can transmit the
  gene, unless it causes death before reproductive
  age
• 3. The trait can SKIP generations
• 4. Parents of an affected child are heterozygous
  or carriers

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CANCER
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Recessive Heredity

• Ex Tay-Sachsproblem with chromosome 15
• Recessive disorder of the central nervous system
• An enzyme that breaks down lipid produced and
  stored under tissues is not made and this lipid
  accumulates in the cells
• Survival rate 4-5 years
• Occurs in many Jews

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• Infants with Tay-Sachs disease appear to develop
  normally for the first few months of life. Then,
  as nerve cells become distended with fatty
  material, a relentless deterioration of mental
  and physical abilities occurs. The child becomes
  blind, deaf, and unable to swallow. Muscles begin
  to atrophy and paralysis sets in. A much rarer
  form of the disorder which occurs in patients in
  their twenties and early thirties is
  characterized by unsteadiness of gait and
  progressive neurological deterioration. Patients
  with Tay-Sachs have a "cherry-red" spot in the
  back of their eyes. The condition is caused by
  insufficient activity of an enzyme called
  hexosaminidase A that catalyzes the
  biodegradation of acidic fatty materials known as
  gangliosides.

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Recessive Heredity

• Ex Phenylketonuria (PKU)
• Recessive disorder that results from the absence
  of an enzyme that converts one amino acid,
  phenylalanine to a different amino acid tyrosine
• Affects the CNS
• Common among Nordic or Swedish people

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PKU

• Normal at first
• Then the baby begins to drink milk which has high
  amounts of phenylalanine
• Mental retardation occurs
• Special diets until brain is fully developed
• Chromosome 12

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Dominant Heredity

• One gene from either parent and the child is
  affected
• Tongue rolling
• Hapsburg lip
• Free earlobes
• Hitchhikers thumb
• Almond shaped eyes
• Thick lips
• Hair in the middle section of your fingers

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Dominant Heredity

• Ex Huntingtons Disease
• Lethal genetic disorder AUTOSOMAL DOMINANT
• Breakdown of certain areas of the brain
• No treatment
• Onset is between 30 and 50

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Sex-LinkeD Recessive

• Found on the X chromosome
• Females XX 2 copies
• Males XY 1 copy
• Ex colorblindness Females XcXc
• Males XcY
• Others hemophilia and male-pattern baldness

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Sex-Linked Dominant

• Ex Rett Syndrome
• This type is rarely found in males because many
  types are fatal or cause them to die before the
  reproductive age
• EX Fragile X Syndrome

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Rett Syndrome
Brain disorder causes the forgetting of
things previously learned -- very similar
symptoms to Autism --only found in female WHY?
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Fragile X syndrome
Missing piece of X chromosome Mental retardation,
large ears, elongated face

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QSR 6

• 1. Explain why DOMINANT, x-linked disorders are
  more commonly found in females.
• 2. __________________ is a disorder with
  chromosome 15 that prevents the body from
  producing an enzyme needed to break down lipids
  around nerves of the CNS.
• 3.___________________ means shared blood and is
  shown by the symbols____________________-

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Incomplete dominance

• Homozygous Red Snap Dragons x Homozygous White
  Snap Dragons
• Pink Snap Dragon
• RR x RR
• Neither allele is completely dominant over the
  other one
• Rprotein to make red pigment
• Rmakes no pigment
• Pinkish color
• Does have segregation of alleles
• What happens in the F2 generation?

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When Heredity Follows Different Rules

• Mendelian Genetics
• Simple---dominant or recessive alleles
• NOT ALWAYS THIS SIMPLE!!!!!!

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Codominance

• Both phenotypes appears
• Chickens
• Black-feathered and white-feathered birds both
  homozygous
• BB x WW
• Produces a chicken with black and white
  featherscheckered

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Practice problems --
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QSR 8

• 1. If both parents carry the recessive allele
  that causes cystic fibrosis (autosomal recessive
  trait), whats the chance that their child will
  have it?
• 2. PKU is a recessive disorder that results from
  the absence of an enzyme that turns
  _________________ into tyrosine.
• 3. Tay-sachs occurs mainly in ____________.

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Sex determination (how bout we review a little
O)

• Autosomes
• Chromosomes that are not involved with
  determining sex
• 1-22 pairs
• Sex chromosomes
• X and y chromosomes that determine the sex of
  individuals

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Sex-linked traits

• Traits that are found on the x and y chromsomes
• X and y are not homologous
• Found by Thomas Hunt Morgan
• Used flies and noticed that the male had white
  eyes crossed red x white and got red did not
  get the 31 ratio because only males had white
  eyes

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Sex-linked traits

• Color blindness
• Male pattern baldness
• hemophilia

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Multiple Alleles

• Traits that are controlled by 2 or more alleles
• Pigeon feathers
• Ash-red
• Wild type blue feathers
• Chocolate feather
• Blood types A and B are codominant, O is
  recessive.

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Polygenic Inheritance

• Is the inheritance pattern of a trait that is
  controlled by two or more genes
• Genes maybe on the same chromosome or on
  different chromosomes
• When a trait is produced by main gene
  interactions
• Ex Skin color
• Dominant genes A,B,C control dark pigmentation
• Recessive genes a,b,c has lowest amount of
  pigmentation
• EX AaBbCc would be what skin color?______________
  __

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Environmental Influences (on genes)

• External Environment
• Temperature, nutrition, light, chemicals, and
  infectious agents all can influence gene
  expression
• What can TEMP do to proteins? (hormones for
  example, insulin, ect)

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Environmental Influences

• Internal environment
• Hormones and structural differences between sex
• Male-pattern baldness
• hemophilia

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Examples of certain Disorders

• 1. Cri du chat
• 2. Progeria diseases

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Cri-du-Chat Syndrome

• SymptomsThe syndrome gets its name ("cat's cry")
  from the characteristic cry of infants born with
  the disorder. The infant sounds just like a
  mewing kitten, due to problems with the larynx
  and nervous system. This cry identifies the
  syndrome. About 1/3 of children lose the cry by
  age 2. Other symptoms of cri-du-chat syndrome may
  include

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Cri-du-Chat Syndrome

• Feeding problems because of difficulty swallowing
  and sucking
• Low birth weight and poor growth
• Severe cognitive, speech, and motor delays
• Behavior problems such as hyperactivity,
  aggression, tantrums, and repetitive movements
• Unusual facial features which may change over
  time
• Diagnosis is based on the distinctive cry and
  accompanying physical problems. Genetic testing
  (FISH) can confirm the diagnosis.

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• A deletion is caused by a break in the DNA
  molecule that makes up a chromosome. In most
  cases, the chromosome break occurs while the
  sperm or egg cell (the male or female gamete) is
  developing. When this gamete is fertilized, the
  child will develop cri-du-chat syndrome. The
  parent, however, does not have the break in any
  other cells of the body and does not have the
  syndrome. In fact, the break is usually such a
  rare event that it is very unlikely that any
  other children will have this disorder.

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Progeria Syndromes

• At birth, a child with Hutchinson-Gilford
  progeria appears normal. The syndrome begins to
  show around 6-12 months of age, when the baby
  fails to gain weight and skin changes occur. Over
  time, the child begins to look like an elderly
  person. Some of the characteristic symptoms are
• Head and face baldness, prominent scalp veins
  and eyes, small jaw, delayed tooth formation
• Bones thin limbs with prominent joints, short
  stature, joint stiffness, hip dislocations
• Heart disease and artery disease

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Progeria Syndromes

• Werner syndrome is a less well-known but more
  common form of progeria, occurring in about 1 in
  1 million individuals. Typically, Werner syndrome
  is identified when an adolescent fails to have a
  normal growth spurt. Over time, the young person
  begins to look elderly. Some of the
  characteristic symptoms are
• Striking difference between the person's
  appearance and his/her real age
• Head and face gray hair and/or balding,
  wrinkling of the face, cataracts, sunken cheeks
  and small jaw, a high-pitched voice
• Bones osteoporosis, small stature, muscle
  weakness
• Diabetes and cancer common

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How to Solve Problems Involving Pedigrees

• Since the pedigrees presented are simple
  pedigrees, the following assumptions can be made
  
• No new mutations occur in the families. This
  means that a dominant trait must occur in a
  parent if it appears in a child. This also means
  that if a recessive trait appears in a child but
  does not occur in either parent, both parents
  must be heterozygous carriers for the trait.
• All traits are 100 penetrate. This means that if
  the genotype for the trait occurs in an
  individual, the trail will appear.

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• If neither parent is affected,
• the trait cannot be dominant.
• the trait could be recessive and either parent or
  both could be heterozygous carriers.

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• If one parent is affected,
• the trait could be dominant and the affected
  parent could be heterozygous while the unaffected
  parent is not a carrier
• the trait could be recessive and the affected
  parent is homozygous while the unaffected parent
  could be a heterozygous carrier

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• If both parents are affected
• the trait could be dominant and both parents
  could be heterozygous carriers which means that
  some of the children could be unaffected
• the trait could be recessive meaning that both
  parents would have to be homozygous and all the
  children would have to be affected

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• Consideration of X-linked or Y-linked traits
• X-linked recessive
• affected male children must have, at least, an
  heterozygous mother
• an affected female will transmit the trait to all
  male children
• X-linked dominant
• affected males transmit the trait to all
  daughters
• affected sons must have an affected mother
• Y-linkage
• male to male transmission only
• no affected females

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• Mitochondria associated traits
• affected females transmit the trait to all
  children
• affected males do not transmit the trait to any
  children
• Mitochondria contain their own DNA but only the
  mother can pass down mitochondrial DNA to her
  offspring

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Sexual Development

• Females are homogametic they have the same sex
  chromosomes (XX)
• Males are heterogametic they have different sex
  chromosomes (XY)
• Other species can be different
• Ex male snakes are ZZ and females are ZW
• The X chromosome carries 1500 genes, the Y
  chromosome can only carry approx 230 (much
  smaller)

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X chromosome
Telomeres tips of the chromosome
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Y Chromosome

• Pseudoautosomal region
• The tips of the Y chromosome
• that compromise 5 of the
• entire chromosome
• They have counterparts on the
• X chromosome and can cross
• over with them

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Pseudohermaphroditism

• is the condition in which an organism is born
  with secondary sex characteristics or a phenotype
  that is different from what would be expected on
  the basis of the gonadal tissue (ovary or
  testis).
• In some cases, the external sex organs look
  intermediate between the typical clitoris or
  penis.
• In other cases, the external sex organs have an
  appearance that does not look intermediate, but
  rather has the appearance that would be expected
  to be seen with the "opposite" gonadal tissue.

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Pseudohermaphroditism

• Because of this, pseudohermaphroditism is
  sometimes not identified until puberty. It is
  possible for the condition to be undetected until
  adulthood.
• The term "male pseudohermaphrodite" is used when
  a testis is present
• The term "female pseudohermaphrodite" is used
  when an ovary is present.

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Pseudohermaphroditism

• The term "true" hermaphrodite is reserved for the
  very RARE cases where both ovarian and testicular
  tissue is present.
• A person would be XY but look phenotypically like
  a female

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Transgender

• Very poorly understood does NOT mean
  transvestite
• When an individual has the phenotype and sex
  chromosomes of one gender, but feels strongly
  that he or she is the other gender
• Genetic of physical basis is not known
• Many undergo surgery so their physical selves
  match their gender

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Transgender

• Very poorly understood does NOT mean
  transvestite
• When an individual has the phenotype and sex
  chromosomes of one gender, but feels strongly
  that he or she is the other gender
• Genetic of physical basis is not known
• Many undergo surgery so their physical selves
  match their gender

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QSR 9

• 1. Y-linked genes on the ______ chromosome
• Rare since the Y chromosome has very little genes
• 2. X-linked genes on the ______chromosome
• 3. Females traits on the X chromosome have to
  come in ______ copies to show up
• 4. Males traits on the X chromosome only have to
  come in _____ pair
• 5. The male is said to be _____________for
  X-linked traits since they only need 1 copy
• 6. Explain the main difference between a
  hermaphrodite and a person who is trasngender.

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REVIEW BEFORE TESTX-Linked Recessive
Inheritance

• Females must have 2 copies
• Males only have to have 1 copy
• Common for an unaffected mother (carrier) to pass
  it on to an affected son even if the father is
  NOT a carrier

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X-Linked Recessive Inheritance
Ichthyosis an enzyme deficiency blocks the
removal of cholesterol from skin cells upper
skin cant peel off causing a brown scaly
apperance
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X-linked recessive disorder

• Ex Hemophilia blood cotting disorder
• Ex Color-blindess
• Ex male-patterned baldness
• Most common in males, rare in females

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X-linked dominant inheritance

• Very rare
• 1. Females get the illness, only has to have 1
  copy
• 2. Males more severely affected because there
  are no other alleles to offset it
• 3. high rates of miscarriage due to early
  lethality in males
• 4. passed from male to all daughters but to no
  sons.WHY?__________________________________

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X-linked dominant inheritance

• Incontinentia Pigmenti lesions
• that look warty and eventually
• turn into brown splotches that
• remain for life
• Males dont survive to be born

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• Pedigree Test Page