Heredity Genetic problems –Apply rules of probability Multiplication rule Key terms 1. Gene  the genetic material on a chromosome that contains the instructions for creating a particular trait (codes for a trait) 2. Allele  one of several varieties of a gene 3. Locus  location on a chromosome where a gene is located

Heredity Key terms 4. Homologous pair  every cell contains two copies of each chromosome, one inherited from each parent. 5. Dominant/ Recessive 6. Homozygous dominant 7. Homozygous recessive 8. Heterozygous 9. Phenotype 10. Geneotype

Heredity Law of segregation –Random segregation of alleles (and their chromosomes) to separate gametes. –Occurs during meiosis I. Law of independent assortment –The migration of homologues within one pair of homologous chromosomes to opposite poles does not influence the migration of homologues of another homologous pair.

Heredity Mendel –Crossed (mated) two varieties of pea plants to form offsprings, or hybrids. –Monohybrid cross  involves a gene for only one trait Flower color (Purple and White) P generation  parents F 1 generation  offspring from the parents F 2 generation  offspring produced from crosses among the F 1

Heredity Monohybrid Crosses –Genotypic ratios –Phenotypic ratios Test cross A test cross is a mating of an individual whose genotype you are trying to determine with an individual whose genotype is known. You will always know the genotype of the individual that expresses the recessive trait.

Heredity Dihybrid Crosses –Genes for two different traits are observed at the same time. Incomplete Dominance –The alleles for a gene do not exhibit the dominant and recessive behaviors. –Instead, the combined expression of two different alleles in the heterozygous condition produces a blending of the individual expressions of the two alleles.

Heredity Codominance –Both inherited alleles are completely expressed Multiple alleles Epistasis –Occurs when one gene affects the phenotypic expression of a second gene. –Ex. mice hair color One gene codes for the presence or absence of pigmentation Second gene codes for the color of pigmentation (black or brown) Phenotypic expressions: CCBB, CCBb, CcBB, CcBb CCbb, Ccbb ccBB, ccBb

Heredity Polygenic inheritance –The interaction of many genes to shape a single phenotype. –Example: human height Linked genes –Genes that reside on the same chromosome and cannot segregate independently. –Genes that are linked are usually inherited together.

Heredity Sex-Linked Inheritance –Sex chromosomes –Sex-linked or X-linked –Examples Hemophilia –Inability to code for all factors required to form normal blood clots. Color-blindness –Inability to distinguish red from green Duschenne’s Muscular Dystrophy (MD) –Absence of an essential muscle protein called dystrofin. –Results in deteriorating muscles and loss of coordination.

Heredity X-inactivation –During embryonic development in female mammals, one of the two X chromosomes in each cell does not uncoil into chromatin. –Barr body- dark, compact body –Example: female calico cat Yellow, black, and white hair. –Yellow and black colors are coded by a gene on the X chromosome. –White color is coded by a different gene.

Heredity Nondisjunction –Chromosomes do not properly separate –Example Down syndrome (trisomy-21) –Mental retardation –Heart defects –Respiratory problems –Deformities in external features Turner syndrome –Female  XO –Physically abnormal and sterile Klinefelter syndrome –Male  XXY –Sterile and often mental retarded

Heredity Human Genetic Defects –Caused by: inheritance of an allele Chromosomal abnormalities –Results when the inherited genome is missing a chromosome, or has an extra chromosome, or when one or more chromosomes have portions: »Deletion »Duplication »Translocation »Inversion

Chromosomal Mutations

Common Genetic Defects Phenylketonuria Autosomal recessive Inability to properly breakdown phenylalanine. Causes mental retardation and death. Tay-Sachs disease Autosomal recessive Inability to properly breakdown certain lipids. Causes progressive nervous system dysfunction and is usually fatal by age four. Huntington’s disease Autosomal dominant Expression begins in middle age with mild mental illness and loss of motor control progressing to total physical and mental incapability. Cri du chat Deletion in chromosome 5 Physical and mental retardation and catlike cry

PKU

Tay-Sachs Disease

Huntington’s Disease

Common Genetic Defects Cystic FibrosisAutosomal Recessive Abnormal chloride transport Sickle-cell DiseaseCodominantAbnormal Hemoglobin AchondroplasiaAutosomal Dominant Form of dwarfism

Cystic Fibrosis

Sickle-cell Disease

Sickle-cell

Polydactyl- Right Hand

Polydactyl- Left Foot