COMPLEX INHERITANCE AND HUMAN HEREDITY

*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, CRR for red flowers & CW for the white flower. A heterozygous flower color is written CRCW

*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 = IA

*B = IB

*AB = IAIB

*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: XB = normal vision; Xb = colorblind; Y chromosome

*X-Linked colorblind Punnett square

XB Y

XB

Xb

XBXB XBY

XBXb XbY

*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

*20th 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