Gregor Mendel • Father of Genetics • Born in 1822 in the Czech Republic • Priest in monastery • Fertilization by testing pea plants • Cross pollination
Genes and Dominance • Gene: a specific characteristic that varies from one individual to another. • Alleles: different forms of a gene.
Principle of Dominance • Dominant trait: overshadows the recessive trait • Recessive trait: only can be seen when with another recessive trait
Homozygous: organisms that have two identical alleles for a particular trait.(TT) • True breeding • Heterozygous: organisms that have two different alleles for a particular trait. (Tt) • Hybrid
Terms for Genetic Crosses • Phenotype: physical characteristics • Genotype: genetic makeup • P group: parental group • F1: First offspring or generation • F2: second generation
Rules for Punnett Squares • Determine the symbols for the traits • Determine the genotype of the parents. • Make the cross • Answer the questions
Practice Problem #1 • Mendel found that the allele for tall (T) pea plants is dominant to the allele for short (t). What offspring phenotypes would be expected from the following parents: • Male: TT Female: tt • Male: Tt Female: tt • Male: Tt Female: Tt
Practice Problem #2 • The allele for axial flowers (A) in peas is dominant to the allele for flowers borne terminally (a). What phenotypic ratios would you expect among the offspring of a cross between a known heterozygous axial-flowered plant and one whose flowers are terminal?
Practice Problem #3 • Two drosophilas (fruit flies) with normal wings are crossed. Among 123 progeny, 91 have normal wings and 32 have dumpy wings. • A. which trait is dominant? • B. what were the genotypes of the parents?
Practice Problem #4 • Black fur in guinea pigs is a dominant trait and white is the recessive trait. When a homozygous black (BB) guinea pig is crossed with a homozygous white one (bb), what is the phenotype and genotype of the F1 generation?
Law of Segregation • Alleles segregate from each other during the formation of gametes • EX: allele for tall separates from allele for short
Incomplete Dominance • Cases in which one allele is not completely dominant over another • Heterozygous phenotype is somewhere between the two homozygous phenotypes.
Incomplete Problem • A homozygous red flower is crossed with a homozygous white flower. This produces pink flowers in their offspring. What would the offspring look like if a pink flower cross-pollinated with a red flower?
Codominance • Both alleles contribute to the phenotype. • Both show
Codominance Problem • In certain varieties of chickens, the allele for black feathers is codominant with the allele for white feathers. Offspring are speckled with white and black. What would happen if a chicken who is homozygous black feathers is crossed with a chicken who is speckled.
Multiple Alleles • Genes that have more than two alleles • EX: coat color in rabbits. Determined by a single gene that has at least four different alleles.
Polygenic Traits • Traits controlled by two or more genes • EX: wide range in skin color in humans comes about because more than four different genes control this trait.