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Genes and Inheritance Chromosome Genes contain the information for the production of proteins, which specify traits. Gene Protein Since genes are inherited, traits are also inherited. Trait Location of Genes In sexually reproducing organisms, cells have a homologous pair of chromosomes (one from each parent). Chromosome from egg (mom) Chromosome from sperm (dad) Chromosomes from a homologous pair have the same genes but can have different alleles. Allele: different form of a gene May be dominant or recessive. Homologous pair of chromosomes Gregor Mendel: Father of Genetics Genetics: branch of biology dealing with heredity Gregor Mendel (1822-1884) was an Austrian monk who is regarded as the father of genetics. Mendel used pea plants to study the inheritance patterns of many traits. Mendel’s View of Inheritance Parent A Parent B Parent A Parent B Offspring Offspring Old Idea New Idea (Mendel) Blending of parental traits Inherited traits behave as discrete units Mendel’s Pea Experiments Mendel examined a small number of phenotypic characters or traits in peas. Dominant alleles masked recessive alleles. Seed color yellow dominant over green Pod color green dominant over yellow Seed shape round dominant over wrinkled Pod shape inflated dominant over constricted Using a Punnett Square: Monohybrid Crosses X Parents Pp Pp Each parent provides two gametes for the grid Calculates outcomes of genetic crosses. Important vocabulary: P Homozygous dominant Gametes p Heterozygous P Gametes Homozygous recessive PP Pp Pp pp p Offspring Genotype and Phenotype Genotype Phenotype PP Purple (homozygous) Pp The genotype of an organism refers to its genetic make-up. The phenotype of an organism refers to its observable features or traits. (heterozygous) Pp Purple Purple (heterozygous) pp (homozygous) White Results of Mendel’s Experiments Seed shape Round Wrinkled Seed color Yellow Green Pod color Green Yellow Flower position Axial Terminal Pod shape Inflated Constricted Stem length Tall Dwarf 5474 1850 7324 Round Wrinkled TOTAL 2.96 : 1 6022 2001 8023 Yellow Green TOTAL 3.01 : 1 428 152 580 Green Yellow TOTAL 2.82 : 1 651 207 858 Axial Terminal TOTAL 3.14 : 1 882 299 1181 Inflated Constricted TOTAL 2.95 : 1 787 277 1064 Tall Dwarf TOTAL 2.84 : 1 Mendel’s Law of Segregation Each pair of alleles is separated into different gametes and into different offspring. Gametes contain only one copy of a gene since they only receive one chromosome from each homologous pair. Homologous pair of chromosomes, each has a copy of the gene on it (A or a) Gametes (sperm Or egg cells) Law of Independent Assortment Genotype: AaBb Alleles for different traits are sorted independently of each other. All combinations of alleles are distributed to gametes with equal probability. Intermediate Cells Gametes Ab Ab aB aB Selected Hereditary Traits Dominant Recessive Right handedness Left handedness Hitch-hiker’s thumb Normal thumb Polydactylism (extra digits) Normal digits Pattern baldness Normal hair Free ear lobes Attached ear lobes Hitch-hiker’s thumb Free ear lobe Handedness Polydactylism is a dominant trait Attached ear lobe In this crowd of men, almost all show some degree of pattern baldness, a dominant trait. Human Tongue Roll The ability to roll the tongue into a U-shape when viewed from the front is controlled by a dominant allele. Dominant Recessive Phenotype: Can roll tongue Phenotype: Cannot roll tongue Allele: T Allele: t Punnett Square Practice 1. Brown hair (B) is dominant over lighter hair colors (b). If two heterozygotes for this trait mate, what are the: a. genotype frequencies b. phenotype frequencies of the offspring? Punnett Square Practice 2. Dwarfism (D) is dominant over normal height (d). If a person of normal height and a dwarf who is homozygous dominant mate, what are the chances of having a child that is also a dwarf? Punnett Square Practice 3. Polydactyly, or having extra digits (P) is dominant over having five digits on each limb (p). If a woman with polydactyly mates with a normal male, then: a. What are the possible genotypes of the woman? b. What is the genotype of the male? c. Create two Punnett Squares displaying their possible children. Punnett Square Practice 4. Tallness in pea plants (T) is dominant to shortness (t). Round seeds (R) are dominant to wrinkled seeds (r). Set up a Punnett Square showing the mating results of two plants that are heterozygous for both traits.