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Chapter 11 . Human Heredity. 11-1 “It Runs in the Family”. How are human traits transmitted from parents to offspring? What are sex chromosomes, autosomes, gametes, and zygotes? What impact does the environment have on gene expression?. 11-1 “It Runs in the Family”.

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chapter 11

Chapter 11

Human Heredity

11 1 it runs in the family
11-1 “It Runs in the Family”
  • How are human traits transmitted from parents to offspring?
  • What are sex chromosomes, autosomes, gametes, and zygotes?
  • What impact does the environment have on gene expression?
11 1 it runs in the family1
11-1 “It Runs in the Family”
  • Many human traits are inherited by the action of dominant and recessive genes
  • Other traits are determined through more complicated gene interactions
  • Why is it important to understand human genetics?
the human organism
The Human Organism
  • How many chromosomes does a diploid cell have?
  • There are 3 billion nucleotide pairs of DNA in our chromosomes
  • In humans the gametes or reproductive cells, contain a single copy of each gene

What is the process that forms gametes?
    • Meiosis
  • Each egg and sperm contain 23 chromosomes (haploid)
  • During fertilization the sperm and egg unite to form a zygote, or fetilized egg
  • How many chromosomes does the zygote contain?
    • 46

Simplest form of inheritance are by traits influenced by one gene

human traits
Human Traits
  • Is the genotype the only affect on the phenotype of an organism?
    • No the environment is a factor
  • Example: advancements in infant and childhood nutrition has increased average height
Environmental effects in gene expression are not inherited; genes are
  • Genes that are not expressed because of the environment could be expressed in a different generation with a different environment
11 2 the inheritance of human traits
11-2 The Inheritance of Human Traits
  • What are multiple alleles?
  • What are some examples of dominant, recessive, and polygenic traits in humans? How are they inherited
human blood groups
Human Blood Groups
  • Multiple alleles-three or more alleles of the same gene that code for a single trait
  • Although many alleles may exist, two alleles are present in diploid organisms
  • ABO and Rh blood groups are examples of human traits determined by multiple alleles
abo blood groups
ABO Blood Groups
  • 4 blood groups A, B, AB, and O
  • Blood groups carry 2 different antigens called A & B. Antigens are molecules that can be recognized by the immune system
Type A = has A antigen
  • Type B = has B antigen
  • Type AB = has both
  • Type O = has neither
  • Important with blood transfusions
  • AB blood are universal receivers
  • Type O are universal donors…Why?
These are determined by three alleles IA, IB, and i
  • ii = O
  • IAIA or IAi = A
  • IBIB or IBi = B
  • IAIB = AB
rh blood groups
Rh blood Groups
  • Another antigen on cells called Rh antigen
  • If you have it you are Rh+
  • If you don’t Rh-
  • 8 alleles code for this
huntington disease
Huntington Disease
  • Huntington disease is produced by a single dominant allele
  • Doesn’t show up till 30’s or 40’s when their nervous system begins to become damaged
  • Painful loss of muscle control and mental function until death occurs
sickle cell anemia
Sickle Cell Anemia
  • Genetic disorder where the red blood cells are sickle shaped instead of a round-flattened disk
  • Caused by a change in one of the polypeptides found in hemoglobin (protein that carries oxygen in blood)
These blood cells are more rigid and get stuck in blood vessels in the body
  • Causes damage to cells and tissues
  • Serious death or injury may result
  • The allele for normal hemoglobin (HA) is codominant with the sickle cell allele (HS)
(HAHS) are sickle cell carriers, these people suffer few ill effects of the disorder
  • (HSHS) are sickle cell sufferers because all hemoglobin molecules are affected
polygenic traits
Polygenic Traits
  • Polygenic traits-human traits that are controlled by a number of genes
  • Examples: height, body weight, skin color
  • Humans have at least four genes that control skin color and these genes have multiple alleles

Children of the same mother and father may have quite different patterns of skin color
  • Melanin, is a dark-colored pigment present in skin cells
  • The more of the pigment the darker your skin is
  • Dark-skinned people have alleles that code for the production of melanin in most of their skin cells and vise versa
11 3 sex linked inheritance
11-3 Sex-Linked Inheritance
  • How is sex-determined in humans?
  • What are some disorders that result from nondisjunction of the sex chromosomes?
  • What are some examples of sex-linked disorders in humans?
  • How are sex-influenced traits inherited?
  • What chromosomes determine the sex of an organism?
    • XY
  • What does meiosis produce for males and females?
    • Males: half Y chromosome 22 autosomes, half X chromosome 22 autosomes
    • Females: 22 autosomes and an X chromosome
  • How is the sex of a person determined?
    • Whether an X or Y carrying sperm fetilizes an egg
sex determination the human xy system
Sex determination: The Human XY System
  • Errors do sometime take place in meiosis
  • What is nondisjunction?
    • Failure of chromosomes to separate properly during meiosis
  • This can result in gametes that carry two sex chromosomes or no sex chromosomes
  • Results in abnormal number of sex chromosomes during fertilization
nondisjunction disorders
Nondisjunction disorders
  • 1/1000 births are affected by sex chromosome nondisjunction
  • The two most common abnormalities are Turner Syndrome and Klinefelter syndrome
turner syndrome
Turner syndrome
  • Are female in appearance but their female sex organs do not develop at puberty
  • Sterile (unable to have children)
  • Abbreviated 45X or 45XO
klinefelter syndrome
Klinefelter Syndrome
  • Male in appearance and sterile
  • Abbreviated 47XXY

No instances of babies being born missing an X chromosome
  • The human body does not develop properly because it is missing important genetic info
  • X chromosome is essential for survival
  • Sex is determined by presence or absence of Y chromosome
  • Have been males with genotypes 48XXXY and 49XXXXY
Y chromosome contains a gene that switches on the male pattern of growth during development
  • If gene is absent the baby follows a female pattern of growth
sex linked genetic disorders
Sex-Linked Genetic Disorders
  • Genes on the X or Y chromosomes are Sex-linked
  • X chromosome contains many vital genes, Y doesn’t contain much
  • Why are X alleles more commonly expressed in males?
X-linked alleles are expressed in males, even if they are recessive
  • Their must be two copies of the alleles for recessive genes to be expressed in females
  • If one X contains a dominant allele is masks the recessive
  • Recessive disorder where people can’t distinguish colors
  • Usually caused by sex-linked genes on the X chromosome
  • Red-green colorblindness is the most common type
  • Have difficulty distinguishing light reds and greens (8% of males & 1% of females)
Color vision depends on the sensitivity of cones (specialized cells) in the retina
  • Dominant for color = XC
  • Recessive for red-green Xc
  • Females: Normal-XCXC or XCXc (Carrier)


  • Males: Normal-XCY



  • Recessive X-chromosomes disorder
  • The protein AHF necessary for blood clotting is missing
  • 1/10,000 males & 1/100,000,000 Females
  • Can bleed to death from normal cuts or can internally bleed from bruises
  • Treated by injecting AHF into donated blood
hemophilia genetics
Hemophilia genetics

muscular dystrophy
Muscular dystrophy
  • Inherited disease that results in the breakdown of skeletal muscle
  • Children who have it rarely live past to adulthood
  • Most common is a defect that codes for the muscle protein dystrophin (on X chromosome)

sex influenced traits
Sex-Influenced Traits
  • Male-pattern baldness is thought to be a sex linked trait but it is actually an autosomal linked trait
  • But why does it show up more in men than women?
  • It is a sex-influenced trait which means it is caused by a gene whose expression is different in males and females
Baldness is controlled by a single gene with two alleles: Normal (B), baldness (b)
  • BB = Normal hair
  • bb = bald whether male of female
  • Males who are heterozygous (Bb) tend to be bald where females aren’t
  • Has to do with male sex hormones
11 4 diagnosis of genetic disorders
11-4 Diagnosis of Genetic Disorders
  • What is Down syndrome? How is it inherited?
  • How can genetic disorders be diagnosed before birth?
a chromosomal abnormality down syndrome
A Chromosomal Abnormality – Down Syndrome
  • Nondisjunction affects autosomes too
  • Example of this is Down Syndrome (trisomy 21)
  • There is an extra copy of chromosome 21
  • This can be seen by a careful examination of the chromosomes
This causes a person to have a wide range of mental problems
  • Also causes increased susceptibility to diseases
  • (1/800) babies born with Down syndrome in the US
  • There are multiple other chromosome disorders as well
prenatal diagnosis
Prenatal Diagnosis
  • Many genetic disorders like Down syndrome can now be analyzed before birth
  • Amniocentesis-requires the removal of a small amount of fluid from the sac surrounding the developing baby

Cells are carefully grown for a few days and then examined by scientists
  • A karyotype is then prepared where the scientists are able to look at problems with the chromosomes if there are any
  • Chronic villus biopsy-a sample of embryonic cells is removed directly from the membrane surrounding the baby
chronic villus biopsy
chronic villus biopsy

This is much faster than amniocentesis
  • These are able to detect down syndrome and other chromosomal problems
  • They are both considered safe for the mother and baby
  • They have gotten much better at looking at genes of the cells and seeing other disorders as well