Complex Inheritance and Human Heredity Chapter 11

Basic Patterns of Human Inheritance Chapter 11.1

Recessive Genetic Disorders A recessive trait is expressed when the individual is homozygous recessive for that trait. An individual who is heterozygous for a recessive disorder is called a carrier. Ex) Cystic Fibrosis, Albinism, Tay- Sachs Disease, Galactosemia

Dominant Genetic Disorders Individuals with a dominant disorder will have at least one dominant allele. Ex) Huntington’s Disease, Achondroplasia

Pedigrees A diagram that traces the inheritance of a particular trait through several generations. A pedigree uses symbols to illustrate inheritance of the trait.

Pedigrees

Pedigrees Affected Male Female Affected Male Carrier Female

Analyzing Pedigrees Pedigrees are used to infer genotypes from the observation of phenotypes. If good records are kept within families, disorders in future offspring can be predicted.

Complex Patterns of Inheritance Chapter 11.2

Incomplete Dominance The heterozygous phenotype is an intermediate phenotype between the two homozygous phenotypes. Ex) Snapdragons (Flower) RR (red) x rr (white) 100% Rr (pink)

Codominance Both alleles are expressed in the heterozygous condition. Ex) Sickle-cell disease Individuals will have normal and sickle- shaped cells. AA = normal Aa = sickle cell trait (few symptoms) aa = sickle cell anemia

Multiple Alleles Some forms of inheritance are determined by multiple alleles. Ex) Blood Types ABO blood groups have 3 forms of alleles. I A is blood type A, I B is blood type B, and i is blood type O. i is recessive to I A and I B. I A and I B are codominant resulting in the AB blood type. Rh factors are either positive or negative. Rh+ is dominant.

Multiple Alleles

Epistasis Epistasis is an interaction where one allele hides the effects of another allele. Ex) Coat color in Labrador retrievers

Sex Determination Sex chromosomes: determine an individual’s gender Autosomes: the other 22 pairs of chromosomes Females have 22 pairs of autosomes and one pair of X chromosomes (XX). Males have 22 pairs of autosomes and one X and one Y chromosome (XY).

Sex Determination The X chromosomes is larger than the Y chromosome because it carriers genes that are necessary for the development of both male and females. To balance the “dose” of X-related genes, one of the X chromosomes in females is inactivated (X-inactivation).

Sex-Linked Traits Traits controlled by genes located on the X chromosome are called sex-linked or X-linked traits. Because males only have one X chromosome they are affected by recessive X-linked traits more than females. In females the other X-chromosome will often mask the effect of the recessive trait.

Sex-Linked Traits Red-green color blindness is a recessive X-linked trait. 8% of males in the US are red-green color blind.

Color Blindness

Hemophilia The Royal Family Hemophilia

Polygenic Traits Many phenotypic traits arise from the interaction of multiple pairs of genes and are called polygenic traits. Ex) Skin color, height, eye color, and fingerprint pattern.

Environmental Influences The environment also has an effect on phenotype. Ex) Heart disease is inherited but diet and exercise play an important role in the occurrence and seriousness of the disease.

Twin Studies By studying identical twins, geneticists can separate genetic contributions from environmental conditions.

Chromosomes and Human Heredity Chapter 11.3

Karyotypes Scientists study whole chromosomes by using images of chromosomes stained during metaphase. The staining bands identify or mark identical places on homologous chromosomes. The homologous chromosomes are arranged in decreasing size to produce a micrograph called a karyotype.

Karyotype

Telomeres Chromosomes end in protective caps called telomeres. The cap serves as a protective structure for the chromosome. Scientists believe that telomeres may play a role in both aging and cancer.

Telomeres

Nondisjunction When sister chromatids fail to separate properly during cell division it is called nondisjunction. If this occurs during meiosis I or meiosis II the resulting gametes will not have the correct number of chromosomes.

Nondisjunction Nondisjunction can result in extra copies of a chromosome or only one copy of a chromosome. Trisomy: having a set of three chromosomes of one kind. Monosomy: having only one of a particular type of chromosome.

Down Syndrome Disorder resulting from an extra chromosome 21. Often called trisomy 21. Characteristics include distinctive facial features, short stature, heart defects, and mental disability.

Down Syndrome

Fetal Testing Amniocentesis: diagnosis of chromosome abnormalities and other defects Chorionic villus sampling: diagnosis of chromosome abnormalities and certain genetic defects Fetal blood sampling: diagnosis of genetic or chromosome abnormalities, checks for fell blood problems and oxygen levels