Chapter 9 – Patterns of Inheritance

 Primitive civilizations -- domestication of plants and animals, important demonstration of early genetic engineering, lead to agricultural development  Gregor Mendel -- laid down the foundation for the field of genetics (early 1800s) ( )  Morgan (1900s) – used fruit flies to identify chromosomes as region of cell where genes are stored in the cell

 Modern Genetics  Populations Genetics - Evolution  Oncology, oncogenes and Cancer  Genetic Disease and Gene Therapy  Recombinant Technology (e.g., crop resistance, animal breeding, etc...)  DNA Fingerprinting

 Genetics – the study of inheritance (the transmission of traits from one generation to the next)  Mendel’s Experiments:  He performed controlled breading experiments  Pea plants have distinct characteristics that are passed on from one generation to the next in determined mathematical ratios  Traits : (see picture)

 He experimented on peas with monohybrid crosses (following the inheritance of one single trait when two heterozygous parents are crossed).

 Different morphological traits come in two's (e.g., smooth or wrinkled seed), must be 2 particles inside the cell that determine the morphological trait, (Today we know theses are alleles = alternative forms of a gene)  Relationships exist between alleles, most common is dominance (an allele that is more powerful than the other allele of the same gene). Recessive alleles are masked by the dominant ones  Law of segregation - alleles segregate on gametes (today we know – because the gametes are haploid, they carry only one copy of each gene)  Law of independent assortment – during gamete formation (meiosis), alleles of DIFFERENT traits are arranged independently from one another

 Solving monohybrid problems with dominant and recessive inheritance

 Solving dihybrid cross problems (crossing two traits at a time where the parents are heterozygous to both traits)

 To study human inheritance, human pedigrees are used – a chart to follow a certain trait over several human generations.

 You must be able to determine the type of inheritance by using human pedigrees

 Recessive disorders:  Albinism – lack of pigment in skin, hair and eyes  Cystic fibrosis – excess mucus in lungs, digestive tract and liver  Tay-Sach’s disease  Sickle-cell disease – sickled blood cells, damage to many tissues (Pamela’s story: The disease: )  Dominant disorders:  One type of Alzheimer’s disease – mental deterioration  Huntington’s disease – mental deteioration, uncontrollable movements

 More often the inheritance patterns are more complex than simple dominant and recessive inheritance.  Incomplete dominance – a form of intermediate inheritance in which one allele for a specific trait is not completely dominant over the other allele. This results in a combined phenotype. (ex.: red and white snapdragons will have pink flowered offspring)

 Codominance – It occurs when both of the contributions of both alleles are visible and do not over power each other in the phenotype (ex.: A and B blood groups)  Pleiotropy -- occurs when a single gene influences multiple phenotypic traits (ex. Sickle cell disease)

 Polygenic inheritance – A simple phenotypic characteristic is inherited by the interaction of at least two genes. (Ex. Skin color in humans)  The frequency of the traits with polygenic inheritance follow the shape of a bell curve.

 Many characteristics result from the combination of heredity and environment (skin color, weight, height)

 Genes occupy specific loci on chromosomes and it is the chromosomes that undergo segregation and independent assortment during meiosis.  Because of the chromosomal theory, if genes are located on the same chromosome, they are inherited together and not independently from one another – linked genes

 Chromosomes that are responsible for the determination of the gender – sex chromosomes  In humans and most mammals XX determines a female and XY determines a male.  In other organisms there may be a different system of sex chromosomes.

 Genes that are located on either the X or Y chromosomes are sex linked  These genes are inherited differently in males and females because the X and Y chromosomes do not carry the same genes.  Genetic disorders that have genes on the X chromosome show up more frequently in males than females. While Y-linked disorders only show up in males.  Males get their X chromosome from their mother.

 You must be able to solve genetic problems with sex-linked inheritance in traditional genetic problems and in pedigrees.