HUMAN HEREDITY

ONE OF THE MOST IMPORTANT AND

USEFUL FORMS OF BIOLOGY

 

•      HUMANS CONTAIN DIPLOID CELLS

–    46 CHROMOSOMES; 23 PAIRS

•      EACH CELL CONTAINS 6 BILLION NUCLEOTIDE PAIRS

–    IF WRITTEN IN A TEXT BOOK IT WOULD HAVE 1 MILLION PAGES

•      EACH PARENT CONTRIBUTES 1 COPY OF EACH GENE THEREFORE THE GAMETES (SEX CELLS) CONTAIN 1 COPY OF EACH. THEY ARE HAPLOID

•      THE SEX CELL CHROMOSOMES ARE X AND Y

•      TRAITS ARE CARRIED ON TO THE NEXT GENERATION BY SINGLE TRAITS, DOMINANT ALLELES, SEX-LINKED ALLELES, OR ANY NUMBER OF OTHER WAYS

INHERITANCE OF HUMAN TRAITS

•     THERE ARE OVER 1000 GENES THAT HAVE BEEN STUDIED AND DESCRIBED

Making A Pedigree

•     A map of genetic traits from generation to generation

 

 

Pedigree Example w/ Colorblindness

BLOOD GROUPS

•      Blood groups are coded by multiple alleles (3 or more)

•      ABO blood

–    blood types are determined by proteins and chemical substances

–    blood contains antigens (molecules in the immune system found in the blood)

•    antigen A and antigen B

–    4 different blood types exist

•    blood type A: contains antigen A, but not B

•    blood type B: contains antigen B, but not A

•    blood type AB: contains both antigen A and B

•    blood type O: contains neither antigen A or B

–    Opposite blood types can’t mix during transfusions

•    AB can receive any blood

•    A can receive O and A and give to A and AB

•    B can receive O and B and give to B and AB

•    O can receive from O and give to all

BLOOD GROUPS CONT.

•     BLOOD TYPES ARE DETERMINED BY A SINGLE GENE WITH 3 ALLELES

–   IA, IB, i

•     ii = O

•     IAIA, IA = A

•     IBIB,IB = B

•     IAIB = AB

 

BLOOD GROUPS CONT.

•     Rh factor:

–   another antigen present in blood which determines whether blood transfusions will agglutinate (clump)

•   Rh+ : antigen is present

•   Rh-  : antigen is not present (recessive)

–   determined by multiple alleles (8 or more)

–   problems that occur are with pregnancies (1 in 300-400)

•   Rh- female x Rh+ male: child may inherit Rh+

•   if second Rh+ child occurs antibodies from mother will attack babies blood

Genetic disorders

•     Huntington disease:

–   produced by a single dominant allele (H)

–   symptoms appear at age 30-40

–   damage to nervous system, loss of muscle control, mental disfunction, DEATH usually w/in 12 years

 

Sickle Cell Anemia:

–   causes a deformity in shape of red blood cells

–   changes protein structure in the cells

–   cells lose their ability to carry oxygen

–   single nucleotide mutation

Cystic fibrosis:

•     defective protein in the plasma membrane that causes an accumulation of thick mucus in the lungs and digestive tract

Tay-Sachs disease:

•     recessive disorder of the central nervous system, caused by an absence of an enzyme that normally breaks down a lipid produced and stored in tissues of the CNS

•     Leads to neuronal swelling, and death

Phenylketonuria (PKU):

–  A recessive disorder that results from the absence of an enzyme that converts one amino acid (phenylalanine) to a different amino acid (tyrosine)

•   Phenylalanine builds up in the body and damages the CNS

 

 

SEX LINKED INHERITANCE

•     X chromosome is essential for survival

•     Y chromosome determines the sex of the individual ( all fetuses start out female, but the Y chromosome switches when the embryo develops)

SEX LINKED INHERITANCE

•     THE SEX OF A PERSON IS DETERMINED BY WHETHER THE MALE IS X OR Y CARRYING

–   NORMAL:        XX = FEMALE (46XX)

                              XY = MALE (46XY)

–   ABNORMAL:   NONDISJUNCTION DURING MEIOSIS IN WHICH THE CHROMOSOMES FAIL TO SEPARATE COMPLETELY

 

•    1 IN 1000 PROBABILITY: RESULTS IN OFFSPRING WITH  EXTRA SEX CHROMOSOMES OR NOT ENOUGH

–   IF THEY DON’T HAVE ENOUGH THEY DIE
–   IF THEY HAVE TOO MANY THEY INHERIT A GENETIC DISEASE

SEX LINKED INHERITANCE GENETIC DISORDERS

•     TURNER SYNDROME:

–   female in appearance but lacks developed sex organs; therefore they are sterile

–   45X or 45XO

–   lacks second sex chromosome

KLINEFELTER SYNDROME:

 

–  male in appearance, but sterile

–  47XXY

–  has an extra X chromosome

 

SEX LINKED INHERITANCE GENETIC DISORDERS

•     Sex linked - genes carried on the sex chromosomes

–   Y: small, few genes carried

–   X: larger, more genes carried

•     Recessive defects located on the X chromosome are more common in males

•     All X-linked genes are expressed in males even if they are recessive

COLOR BLINDED CONDITIONS

•     Recessive disorder located on the X chromosome

•     most common: red-green colors

•     most affected: males (8 to 1)

•     XC = dominant (normal)

•     Xc = recessive (colorblind)

•     XCXC = normal female           XcXc = colorblind female

•     XCXc = normal female but a carrier 

•     XCY = normal male                XcY = colorblind male

 

HEMOPHILIA

•     Recessive gene disorder - causes bleeding disorders

•     very rare: 1 in 10,000 males, 1 in 100,000,000 females

•     very serious disease

•     treatable by adding missing AHF factor (antihemophilic)

MUSCULAR DYSTROPHY

•     Progressive wasting away of skeletal tissue

•     most often carried on the X chromosome

•     kills in early adulthood

DOWN SYNDROME

•     Non-disjunction of an autosome (non sex cells)

–   extra copy of chromosome #21

•     causes mental retardation

•     increased susceptibility to many diseases

•     1 in 800 in the U.S.

•     can diagnose with a microscope

DIAGNOSIS OF GENETIC DISORDERS

•     AMNIOCENTESIS:

–   TAKING OF FLUID FROM THE SAC AROUND THE EMBRYO AND GROWING A CULTURE

 

 

 

 

•     MICROSCOPES:

–   VIEWING SAMPLES UNDER A MICROSCOPE CAN IDENTIFY SOME DISEASES