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Chapter 6. Matters of Sex. 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.

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Chapter 6

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Chapter 6

Chapter 6

Matters of Sex

Qsr 2

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 _____________________________.

Mendelian inheritance of human traits

MendelianInheritance 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



  • 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

Analyzing pedigrees

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 individual’s parent will have the disease

  • Recessive—parents are normal children are infected

Risk of diseases

Risk of Diseases

  • Use pedigrees

  • Genetic counseling

  • Prenatal testing

    • Amniocentesis/chorionic villi sampling to determine karyotypes

Chapter 6


    • 1. Dominant or Recessive

    • 2. Sex-linked or Autosomal

Chapter 6


    • 1. Dominant or Recessive

    • 2. Sex-linked or Autosomal

    • 3. Tell the genotype of each person

Practice constructing a pedigree

Practice constructing a pedigree:

  • Ben and Jan are married with 4 boys. Ben has dimples as does his 2 oldest boys. Jan’s 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 

Qsr 3 questions for trait a pedigree use the letter b b

QSR#3Questions 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

Inhertitance symptoms


Recessive autosomal heredity

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 blood”—family members may share certain traits or disorders

Recessive autosomal heredity1

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

Chapter 6


Recessive heredity

Recessive Heredity

  • Ex: Tay-Sachs—problem 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

Chapter 6

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.

Recessive heredity1

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

Chapter 6


  • 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

Dominant heredity

Dominant Heredity

  • One gene from either parent and the child is affected

    • Tongue rolling

    • Hapsburg lip

    • Free earlobes

    • Hitchhiker’s thumb

    • Almond shaped eyes

    • Thick lips

    • Hair in the middle section of your fingers

Dominant heredity1

Dominant Heredity

  • Ex: Huntington’s Disease

    • Lethal genetic disorder— AUTOSOMAL DOMINANT

    • Breakdown of certain areas of the brain

    • No treatment

    • Onset is between 30 and 50

    • +++++++++++++++++++++++++++++++++++

Sex linked recessive

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

Sex linked dominant

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

Rett syndrome

Rett Syndrome

Brain disorder – causes the “forgetting” of things previously learned

-- very similar symptoms to Autism

--only found in female – WHY?

Fragile x syndrome

Fragile X syndrome

Missing piece of X chromosome

Mental retardation, large ears, elongated face


Qsr 6

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:____________________-

Incomplete dominance

Incomplete dominance

  • Homozygous Red Snap Dragons x Homozygous White Snap Dragons

    • Pink Snap Dragon

    • RR x R’R’

    • Neither allele is completely dominant over the other one

    • R—protein to make red pigment

    • R’—makes no pigment

    • Pinkish color

    • Does have segregation of alleles

    • What happens in the F2 generation?

When heredity follows different rules

When Heredity Follows Different Rules

  • Mendelian Genetics

    • Simple---dominant or recessive alleles




  • Both phenotypes appears

  • Chickens

  • Black-feathered and white-feathered birds both homozygous

  • BB x WW

  • Produces a chicken with black and white feathers—checkered

  • ++++++++++++++++++++++++++++

Practice problems

Practice problems --

Qsr 8

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 ____________.

Sex determination how bout we review a little o

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

Sex linked traits

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 3:1 ratio because only males had white eyes

Sex linked traits1

Sex-linked traits

  • Color blindness

  • Male pattern baldness

  • hemophilia

Multiple alleles

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.

Polygenic inheritance

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?________________

    • ++++++++++++++++++++++++++++++++++++++

Environmental influences on genes

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)

Environmental influences

Environmental Influences

  • Internal environment

  • Hormones and structural differences between sex

    • Male-pattern baldness

    • hemophilia

Examples of certain disorders

Examples of certain Disorders:

  • 1. Cri du chat

  • 2. Progeria diseases

Cri du chat syndrome

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:

Cri du chat syndrome1

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.

Chapter 6

  • 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.

Progeria syndromes

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

Progeria syndromes1

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

How to solve problems involving pedigrees

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.

Chapter 6

  • If neither parent is affected,

    • the trait cannot be dominant.

    • the trait could be recessive and either parent or both could be heterozygous carriers.

Chapter 6

  • 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

Chapter 6

  • 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

Chapter 6

  • 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

Chapter 6

  • 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

Sexual development

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)

X chromosome

X chromosome

Telomeres: tips of the


Y chromosome

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



  • is the condition in which an organism is born with secondary sex characteristicsor a phenotypethat 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.



  • 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.



  • 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



  • 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



  • 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

Qsr 9

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.

Review before test x linked recessive inheritance

REVIEW BEFORE TEST:**X-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

X linked recessive inheritance

X-Linked Recessive Inheritance

Ichthyosis: an enzyme deficiency

blocks the removal of cholesterol

from skin cells – upper skin can’t

peel off causing a brown scaly


X linked recessive disorder

X-linked recessive disorder

  • Ex: Hemophilia – blood cotting disorder

  • Ex: Color-blindess

  • Ex: male-patterned baldness

  • Most common in males, rare in females

X linked dominant inheritance

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?__________________________________

X linked dominant inheritance1

X-linked dominant inheritance

  • Incontinentia Pigmenti: lesions

  • that look warty and eventually

  • turn into brown splotches that

  • remain for life

  • Males don’t survive to be born

Chapter 6

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