*

* CH. 11.1 BASIC PATTERNS OF HUMAN
INHERITANCE
* MAIN IDEA – THE INHERITANCE OF A
TRAIT OVER SEVERAL GENERATIONS
CAN BE SHOWN IN A PEDIGREE.
* QUESTION: If someone looks more like one parent than the other, did that person inherit more genes from that parent?

* RECESSIVE GENETIC DISORDERS
* Mendel’s work was ignored for 30 years until scientists began looking at heredity.
* Recessive traits are expressed when the individual is homozygous recessive for that trait.
* Individuals with at least one dominant trait will NOT express the recessive trait.
*
An individual who is heterozygous for a recessive disorder is called a carrier.
* Examples of recessive genetic disorders are:
*
Cystic fibrosis
* Albinism
* Galactosemia
*
Tay-Sachs disease

* RECESSIVE GENETIC DISORDERS CONTINUED
* CYSTIC FIBROSIS
* One of the most common recessive genetic disorders among
Caucasians is cystic fibrosis, which affects the mucus producing glands, digestive enzymes and sweat glands.
* People develop a thick mucus that clogs the ducts in the pancreas, interrupts digestion, and blocks the tiny respiratory pathways in the lungs.
* People with cystic fibrosis are at a higher risk of infection because of the mucus in their lungs
* Treatments are physical therapy, medication, special diets, and the use of replacement digestive enzymes.
* Genetic tests are available to determine if a person is a carrier.

* RECESSIVE GENETIC DISORDERS
* ALBINISM
* Albinism is caused by altered genes, resulting in the absence of the skin pigment melanin in hair and eyes.
* Albinism is also found in animals.
* People with albinism have white hair, very pale skin, and pink pupils.
* Lack of pigment in eyes causes vision problems.
* TAY-SACHS DISEASE
* Gene for Tay-Sachs disease (TSD) is located on chromosome
15.
* Disease is predominantly among Jews of eastern European descent.
* TSD is caused by the absence of the enzymes responsible for breaking down fatty acids, which build up in the brain, inflating brain nerve cells and causing mental deterioration.

* DOMINANT GENETIC DISORDERS
* Some genetic disorders are caused by the dominant allele. So if you do not have the disorder you are homozygous recessive for the trait.
* Some types of dominant genetic disorders include:
* Huntington’s disease affects the nervous system with systems first appearing between the ages of 30 and 50 years old.
* Systems include: loss of brain function, uncontrollable movements and emotional disturbances.
* Genetic tests are available to detect this dominant allele, but there are no preventive treatment or cure for this disease.

* DOMINANT GENETIC DISORDERS CONTINUED
* Achondroplasia (most common form of dwarfism) have a small body size and limbs that are short.
* Individuals with achondroplasia have a normal life expectancy and will reach a height of about 4 feet.
* 75% of individuals with achondroplasia are born to parents of average size.
* Believed to be caused by new mutation or a genetic change.

* PEDIGREES
* Pedigree is a diagram that traces the inheritance of a particular trait through several generations of a family.
* Symbols are used to illustrate the inheritance of a trait.
* Males are represented by squares =
* Females are represented by circles =
* Person who expresses the trait being studied is represented by a filled in square or circle =
* Person who does not express the trait is represented by an unfilled square or circle. =
* Half-filled square or circle means the person is a carrier. =

* PEDIGREES – Continued
*
Horizontal line between 2 symbols shows that the individuals are married
* Brackets show the offspring of the parents.
Offspring are listed in descending birth order from left to right and are connected to each other and their parents.
* Pedigree uses a numbering system where
Roman numerals represent generations and individuals are numbered by birth order using
Arabic numbers.

* PEDIGREE

* INFERRING GENOTYPES
* Pedigrees are used to help figure out the genotypes
* Pedigrees are also used to help figure out dominant and recessive traits.
* Dominant traits are easier to recognize because they are expressed
* Recessive traits are only seen if the person is homozygous recessive for the trait
* Need to follow the recessive trait for several generations to figure out which parents & grandparents were the carriers of the recessive allele.

* SECTION 11.2 – COMPLEX PATTERNS OF
INHERITANCE
* MAIN IDEA – Complex inheritance of traits does not follow inheritance patterns described by Mendel
* QUESTIONS: What possible eye colors are there?
* Do you think that eye color is inherited by a simple dominant/recessive manner?

* INCOMPLETE DOMINANCE
*
REVIEW – dominant/recessive traits the dominant trait is expressed, even if the organism is heterozygous.
* Incomplete dominance is when a heterozygous organism shows a blending of the dominant and recessive trait.
* Ex: cross a red flower with white flower and the heterozygous flower will be pink.
*
Written: C=color for the trait, C R for red flowers & C W for the white flower. A heterozygous flower color is written C R C W

* INCOMPLETE DOMINANCE PUNNETT SQUARE

* CODOMINANCE
* In codominance both alleles are expressed in the heterozygous condition.
* EX: Homozygous black chicken & homozygous white chicken will produce heterozygous black and white chickens.
* SICKLE CELL DISEASE
* Sickle cell disease is a codominant inheritance
* Common in people of African descent and affects the red blood cells ability to carry oxygen
* Ex: if you are heterozygous for sickle cell disease your body produces both normal blood cells and sickle cells
* People living in malaria areas being heterozygous for sickle cell disease also have a higher resistance to malaria
* Allows the sickle trait to continue to be passed down.

* MULTIPLE ALLELES
* Some forms of inheritance are determined by more than 2 alleles. This is referred to as multiple alleles.
* EX: blood
* BLOOD GROUPS IN HUMANS
* The different types of blood that humans can have are: A, B,
AB, and O
* A & B are dominant to O; but A & B together are codominant
* Blood type is written:
* A = I A
* B = I B
* AB = I A I B
* O = ii
* Rh factors are either + or - & written Rh+ or Rh- and + is dominant over -

* SEX DETERMINATION
* Each cell in your body, except gametes, contains 46 chromosomes or 23 pairs of chromosomes.
* One pair of chromosomes, the sex chromosomes, determines an individual’s gender.
* There are 2 types of sex chromosomes, X & Y.
* XX chromosomes = girls
* XY chromosomes = boys
* Males determine sex of the baby
* The other 22 pairs of chromosomes are called autosomes

* DOSAGE COMPENSATION
* Human females have 22 pairs of autosomes and 1 pair of X chromosomes.
* Human males have 22 pairs of autosomes and 1 X and
1 Y
* There are a lot of genes on the X chromosomes, but Y chromosomes only contain genes that pertain to male characteristics
* In female body cells one X chromosome is randomly chosen to be turned off or X-inactivation
* Turned off X chromosome is referred to as a Barr body

* SEX-LINKED TRAITS
* If a trait is located on the X chromosome it is called a sex-linked trait or X-linked.
* Males only have 1 X chromosome, so if that trait is dominant or recessive it is expressed.
* Females have 2 X chromosomes, so their traits follow the dominant recessive pattern.
* COLORBLINDNESS (Red/Green)
* Colorblindness is a recessive X-linked trait.
* Punnett squares for X-linked traits are written:
* EX: X B = normal vision; X b = colorblind; Y chromosome

* X-Linked colorblind Punnett square
X B
X B Y
X B X B X B Y
X b X B X b X b Y

* HEMOPHILIA
*
Hemophilia is a recessive sex-linked disorder.
People with hemophilia have a delayed clotting of their blood.
* Hemophilia was passed through a lot of the royal families
* Men died more frequently and at an early age because of the absence of clotting factors
* 20 th century learned about the clotting factors
& now it is given to people with hemophilia.

* POLYGENIC TRAITS
* Polygenic traits are traits that are controlled by multiple pairs of genes.
* EX: skin color, height, eye color, and fingerprint patterns
* When looking at the frequency of polygenic traits the results you see will be a bell shaped curve.

* ENVIRONMENTAL INFLUENCES
*
Environment also has an effect on phenotypes.
* EX: you may inherit a gene that gives you the tendency to have heart disease.
* Environment factors such as diet and exercise can contribute to the occurrence and seriousness of the disease.
* Other environmental factors that can affect phenotype are:
*
Sunlight
* Water
* Temperature

* Ch. 10.3 – CHROMOSOMES AND HUMAN HEREDITY
* KARYOTYPE STUDIES
* Karyotypes is a study used by scientists to study the whole chromosomes using images of chromosomes stained during metaphase (mitosis).
* Sister chromatids are arranged by looking at their length, centromere location, and the banding.
*
Arranged by decreasing size of the sister chromatids.
* 22 autosome chromosomes are arranged first
* Sex chromosomes X’s & Y’s are placed last
* Information that karyotypes can give us are:
* Sex of the individual
* Different genetic disorders

* KARYOTYPE

* TELOMERES
* At the ends of each chromosomes are protective caps called telomeres.
* Scientists believe that the telomeres might be involved in both aging and cancer

* NONDISJUNCTION
* Nondisjunction is when the sister chromatids fail to separate.
* If nondisjunction occurs either during Anaphase I or
Anaphase II the gametes will not have the correct number of chromosomes.
* Results: gametes either have an extra chromosome or is missing a chromosome
* Trisomy is when you have a set of 3 chromosomes of one kind.
* In humans, altering the # of chromosomes is associated with serious human disorders or death.

* DOWN SYNDROME
*
Down Syndrome occurs when there is an extra #21 chromosome
(trisomy 21)
* Characteristics for Down Syndrome include:
* Distinctive facial features
* Short stature
* Heart defects
* Mental disability
* Frequency of Down Syndrome increases with the age of the mother.
* SEX CHROMOSOME
* Nondisjunction with the sex chromosomes can result in the following conditions:
* Turner’s syndrome = XO
* Klinefelter’s syndrome = XXY
* Death = OY
* Other abnormalities with the sex chromosomes include: XXX, XYY