Human Heredity

Chapter 11.1 & 11.3

RECESSIVE GENETIC DISORDERS

• may be passed on to children without “knowing”

• both parents are CARRIERS of recessive alleles – Aa x Aa

• passed like any recessive trait – offspring must get

recessive allele from mother + father – aa

Cystic Fibrosis (CF)AlbinismGalactosemiaTay SachsPrimordial DwarfismPhenylketonuria (PKU)Xeroderma Pigmentosum (XP)

CYSTIC FIBROSIS (CF)– affects the mucus producing glands, digestive enzymes and sweat glands

Cause:

• recessive allele that is defective

Effects:

• excessive mucus production

• respiratory system is compromised; high risk of infection

• digestive and respiratory system failure

• life expectancy 36.8 years

Cure/Treatement:

• no cure

• daily breathing treatments

• mucus-thinning drugs

• pancreatic enzyme supplements

Cystic Fibrosis - http://www.youtube.com/watch?v=PjoE-yzyDNk

ALBINISM

– partial or total lack of pigment (melanin)

in hair, skin and eyes Cause:• recessive allele that is defective

Effects :• do not produce normal amounts of melanin• skin susceptible to UV damage• higher risk of skin cancer and eye damage• occurs in humans and other mammals

Cure/Treatment:• no cure• protect eyes and skin from sun

GALACTOSEMIA

– an inability to digest galactose (milk sugar) Cause:

• recessive allele that is defective

• lack of enzyme that breaks down galactose

Effects :

• enlarged liver and kidney failure

• galactose builds up in the cells and becomes toxic

• usually causes no symptoms at birth

• if not detected immediately results in liver disease, mental retardation and death 

Cure/Treatment:

• no cure

• children diagnosed early can have a normal, healthy life

• treatment is the restriction of galactose and lactose from the diet

TAY-SACHS DISEASE

– an inability to break down fatty acids: only affects people of Jewish descent

Cause:• recessive allele that is defective• lack of enzyme

that breaks down fatty substances

Effects • inability to break down fatty acids • fatty deposits build up in the brain • brain cells deteriorate• mental capacity is diminished• death by age 5

Cure/Treatment• no cure or treatment

Xeroderma Pigmentosum (XP)• recessive genetic disorder

• inability to repair damage caused by UV light

• in extreme cases, all exposure to sunlight must be forbidden, no matter how small

• individuals with the disease are often referred to as Children of the Night

• suffer from basal cell carcinomas and other skin malignancies (such as

malignant melanoma and squamous cell carcinoma)

Primordial Dwarfism

• form of dwarfism that results in a smaller body size in all stages of life beginning from before birth

• proportionate dwarfism, in which individuals are extremely small for their age, even as a fetus

• caused by inheriting a mutant gene from each parent

Kenadie - born February 13, 2003 2 lbs 8oz and 11 inches long

Phenylketonuria (PKU)

• Caused by a mutation in the gene for a liver enzyme called PAH

• this enzyme is necessary to metabolize the amino acid phenylalanine

Effects of untreated PKU…

• children normal at birth but fail to attain early developmental milestones

• microcephaly, progressive impairment of mental function seizures, learning disabilities nd other serious medical problems,

Cure/Treatment of PKU…

• there is no cure

• treatment with restricted diet supplemented by amino acids and other nutrients

• PKU is commonly included in newborn screenings performed just after birth

Dominant Genetic Disorders

• one dominant allele (AA or Aa) to inherit the disorder• NO CARRIERS• either you have the disorder or you don’t

Huntington’s DiseaseAchondroplasiaProgeriaTreacher CollinsMarfan Syndrome

- the genetically programmed degeneration of brain cells

Cause:• dominant allele that affects neurological function

Effects:• symptoms appear between age 30 - 50 • degeneration of brain cells (neurons) • loss of intellectual faculties• uncontrollable movements • emotional disturbances

Cure/Treatment:• none

Huntington’s - http://www.youtube.com/watch?v=xguyxdmeUK8

woman with Huntington’s Disease at age 48

HUNTINGTON’S DISEASE

ACHONDROPLASIA

- a common form of dwarfismCause:• dominant allele that affects bone growth

Effects:• short arms and legs • 75 % of individuals with achondroplasia

are born to parents of average size…• this means that most cases of achondroplasia

occur “out of the blue” and are the

result of a new mutation in the gene

Cure/Treatment:• none; normal life expectancy

Achondroplasia - http://www.youtube.com/watch?v=d8B-rdUrO9U

Progeria • extremely rare genetic disease wherein symptoms resembling

aspects of aging are manifested at an early age

• typically live to their mid teens and early twenties

• occurs as a result of a dominant, new mutation

• rarely inherited

Progeria - http://www.youtube.com/watch?v=T8eaD6FdFJw

Treacher Collins• rare, congenital disorder characterized by craniofacial deformities

• caused by a defective protein called treacle

Physical Features Include ….

• downward slanting eyes

• micrognathia (a small lower jaw)

• conductive hearing loss

• absent cheekbones

• malformed or absent ears.

Cure/Treatment…

• No cure - only affects physical features

• physical features can be made less obvious by plastic surgery

Treacher Collins - http://www.youtube.com/watch?v=tYYMRd39wcE

Marfan Syndrome

• disoder of connective tissue

Effects…

• unusually tall, long limbs and long, thin fingers

• range of expressions - from mild to severe

• defects of the heart valves and aorta, lungs, skeleton, hard palate

Cure/Treatment….

• no cure

• medications to slow progression of disease

• new treatments being developed

• life expectancy today - similar to that of the average person

Codominance and Red Blood Cells

Codominance occurs when…

• both alleles are dominant

• both alleles are fully expressed – NO BLENDING

Red Blood Cells (RBCs) can be….

• disc shaped (D) NORMAL –

easily flow through blood vessels

• crescent shaped (C) ABNORMAL

clump and block blood flow

DD = all RBC’s normal shaped

DC or CD = some RBC’s normal + some abnormal

CC = all RBC’s abnormal – causes SICKLE CELL ANEMIA

SICKLE CELL ANEMIA - results from misshapen RBC’sCause:

• recessive allele that is defective

• both mom and dad are “carriers”

Effects:

• causes RBCs to be misshapen – “sickle” or “C” or “crecsent” shaped

• misshapen RBCs break down prematurely, cannot effectively transport oxygen, are stiff and sticky and block blood flow

• pain, organ damage, increased risk of infection

Cure/Treatment:

• bone marrow transplant – finding matching donor is difficult and procedure has risks – may work for some

• regular medical care, pain medicine, fluids, oxygen therapy

Sickle Cell Anemia - http://www.youtube.com/watch?v=LlF_8oRs6Bw

Videos – Genetic Disorders

• Cockayne - http://www.youtube.com/watch?v=6QeXF3d9jY8

• Brittle Bone - http://www.youtube.com/watch?v=6b7cWvMlw8Y

• Ectodermal Dysplasia - http://www.youtube.com/watch?v=cAl6ZoQ7Mes

• Duchenne MD - http://www.youtube.com/watch?v=CT3CsVoxWs0

Tetra-Amelia SyndromeNick Vujicic

• rare disorder characterized by the absence of all four limbs

LOOK AT YOURSELF http://www.youtube.com/watch?v=Gc4HGQHgeFE

PEDIGREE

chart which shows theinheritance of a trait from one generation

to the next

Allows geneticists to trace the transmission of a trait through a family.

square = malecircle = female

colored shape = has traithalf colored shape = carrier

slash = deceased

How many generations are represented?How many males? afflicted males? normal males?

How many females? afflicted females? normal females?Any carriers?

Sex-linked or autosomal trait?Dominant or recessive trait?

Any twins? deceased individuals?

Victoria…(born into the British Monarchy in 1819)• 1837 - became Queen of England • 1840 - married her 1st cousin Prince Albert – which was the custom• she was a carrier of HEMOPHILIA• had 9 children and PASSED HEMOPHILIA ON TO SEVERAL OF THEM• ALL OF HER CHILDREN MARRIED INTO THE ROYAL FAMILIES OF EUROPE• HEMOPHILIA BECAME KNOWN AS THE ROYAL DISEASE

Princess Alexandrina Victoria…o the granddaughter of Queen Victoriaowas born into the British Monarchy in 1872

She was also a CARRIER OF HEMOPHILIAohemophilia is an X-linked recessive traitoresults in an inability to clot the blood

Princess Alexandrina Victoria…• married her 2nd cousin, Nicholas Romanov II, Tsar of Russia• they had 5 children …

– 4 girls - Olga, Tatiana, Maria, Anastasia – 1 boy - Alexei - heir to the throne - had HEMOPHILIA

• 1918 - Russian Civil War• Tzar Nicholas II, his wife and their 5 children

disappeared

• 1991 - the remains of Tzar Nicholas, his wife, and 3 of the children were found and exhumed for DNA testing

HUMAN CHROMOSOMESHuman somatic cells contain….

46 individual chromosomes

or 23 chromosome pairs

Of these 23 pairs…

SEX CHROMOSOMES (1 pair)

• determine the sex

of an individual

AUTOSOMES (22 pairs)

• do not determine the sex

of an individual

KARYOTYPEphotomicrograph of the chromosomes in a dividing

cell

chromosomes are grouped and placed into (23)pairs

female - 46 XX

male - 46 XYnonhomologous

Telomeresprotective caps on ends on chromosomes

made of protein and DNAmay play a role in cancer and aging

telomeres are like…

aglets on the ends

of a shoe string

Mutations

What is a mutation? a change in the DNA it is interesting that mutations can be helpful, harmful or

may have no effect

mutations – are a source of genetic variation in LT

MutationsWhat causes a mutation? a mutagen

….anything that can cause

a change in the DNA

Some mutagens are….

viruses, chemicals, toxins, UV light,….

Mutations can also happen as a result of …

DNA being copied incorrectly

Types of Mutations

SOMATIC cell mutations - affect body (somatic) cells will affect individual, but not offspring

GERM cell mutations - affect germ (sex) cells will affect offspring, but not the individual

LETHAL mutations will cause death either before or shortly

after birth

Types of Chromosome

Mutations

Deletion– A piece of a chromosome is LOST

Inversion– A piece of a chromosome breaks off, FLIPS OVER + REATTACHES

Translocation– A piece of a chromosome breaks off and attaches

to ANOTHER chromosome

Nondisjunction– Homologues DO NOT SEPARATE PROPERLY DURING CELL

DIVISION - results in too many or too few chromosomes

loss of a portion of a chromosome

Williams Syndrome

• caused by spontaneous deletion of genes on chromosome 7

• rare, neurodevelopmental disorder

• characterized by, "elfin" facial appearance, low nasal bridge, cheerful demeanor and ease with strangers

• developmental delays and cardiovascular problems

Inversion – a section of a chromosome breaks off, flips over and reattaches

Translocation – a portion of a chromosome detaches and reattaches to a nonhomologous chromosome

Let’s Practice – What type of mutation?

NONDISJUNCTION - when chromosomes don’t separate properly during CELL

DIVISION

(CAN OCCUR IN mitosis or meiosis)

nondisjunction means

“not coming apart”

Nondisjunction in Meiosis…can lead to …

monosomy (45) – missing a chromosome of a pair (having only 1 chromosome of the pair)

trisomy (47) – having an extra chromosome in a pair (having 3 chromosomes in the pair)

Conditions resulting from Nondisjunction

• Down’s Syndrome

• Turner’s Syndrome

• Klinefelter’s Syndrome

DOWN SYNDROME

male or female having an extra chromosome in pair #21

(3 chromosomes instead of 2) - 47 XX or 47 XY

Down Syndrome (onosomy)

nondisjunction on #21 = Trisomy 21

Characteristics of Down Syndrome

• almond shaped eyes

• flat nose bridge

• large tongue

• ears are set a bit lower on the head

• shorter in stature

• simean crease on the palm of the hand

• possible congenital heart defects

• lat feet, sandal toe (large gap between big toe and the next)

• lower IQ

• developmental delays

Turner Syndrome (Monosomy)• female missing a sex chromosome; 45

XO• nondisjunction on #23; monosomy

Klinefelter Syndrome (Trisomy)

• male having an extra sex chromosome• 47 XXY or 48 XXXY; nondisjunction on #23;

trisomy

Jacob’s or XYY Syndrome (Trisomy)

• male having an extra Y (sex) chromosome

• 47 XYY; nondisjunction on #23; trisomy• clinical phenotype is normal

Fetal (genetic)Testing

– pre-pregnancy: DNA testing & genetic counseling– post-pregnancy: PKU testing– during pregnancy:

• Amniocentesis

• Chorionic Villi Sampling (CVS)

• Fetal Blood Sampling

Amniocentesis - a small amount of amniotic fluid (containing fetal tissues and cells) is extracted from the amniotic sac surrounding the developing fetus - the DNA is examined for genetic abnormalities

Chorionic Villi Sampling (CVS) - the removal of a small piece of the placenta (chorionic villi) during early pregnancy to screen for genetic defects – the placenta has the same genetic makeup as the fetus

Fetal Blood Sampling (FBS) - the collection of fetal blood from the umbilical cord or fetus – the blood is tested genetic defects or other abnormalities