COMPLEX INHERITANCE AND HUMAN HEREDITY CHAPTER 11 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, CR for red flowers & CW for the white flower. A heterozygous flower color is written CRCW

INCOMPLETE DOMINANCE PUNNETT SQUARE

Allows the sickle trait to continue to be passed down. 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