Observable Patterns of Inheritance Mendelian Genetics & Monohybrid Crosses

Mendel’s First Experiment He crossbred pure tall and pure short plants. These plants were called the parental generation (P). This experiment is called a monohybrid cross because it focuses on only one inherited characteristic.  Mendel's Hypothesis: Mendel expected to see offspring plants of medium height.

Mendel’s First Experiment The hybrid offspring from P were called first filial generation (F1)‏ Mendel's Observations: all of the offspring were tall  Mendel's Conclusion: dominant trait = tallness, recessive trait = shortness, the recessive trait is not expressed in first generation

Principle of Dominance When an organism is hybrid (cross bred) for a pair of contrasting traits, it shows only the dominant trait.

Mendel’s Second Experiment Mendel allowed the F1 plants to mature and self-pollinate. Their offspring were called the second filial generation (F2). Mendel's Observations: ¾ of the plants were tall, ¼ of the plants were short

Mendel’s Second Experiment Mendel's Conclusion: offspring inherit two “factors” for each characteristic (e.g. height), one from each parent, the F1 DID inherit contrasting factors only the dominant factor is expressed

Principle of Segregation Hereditary characteristics are determined by distinct factors (genes) that occur in pairs. These paired factors segregate from one another and are distributed into different sex cells. Each sex cell has an equal probability of possessing either of the pair.

Tracking Generations Parental generation P mates to produce First-generation offspring F1 mate to produce Second-generation offspring F2

Genes Units of information about specific traits Passed from parents to offspring Each has a specific location (locus) on a chromosome

Alleles Different molecular forms of a gene Arise by mutation Dominant allele masks a recessive allele that is paired with it

Allele Combinations Homozygous having two identical alleles at a locus AA or aa Heterozygous having two different alleles at a locus Aa

Genotype & Phenotype Genotype refers to particular genes an individual carries Phenotype refers to an individual’s observable traits Cannot always determine genotype by observing phenotype

Impact of Mendel’s Work Mendel presented his results in 1865 to a small Austrian audience Paper received little notice Mendel discontinued his experiments in 1871 Paper rediscovered in 1900 and finally appreciated

Mendel’s work applied today MONOHYBRID CROSSES Monohybrid crosses are used to determine the probability of certain genetics outcomes in offspring. Mendel is famous for his discovery that there are 2 factors for each trait called alleles. Genes can be dominant or recessive 15

4 Expectations for Genetic Problems After reading the problem, determine the genotype of the parents Indicate the different possible gametes Show possible combinations using a punnett square and state the genotypic and phenotypic ratios Answer the questions in sentence form 16

Capital letters represent the dominant trait Rules for Crosses Capital letters represent the dominant trait Small letters represent the recessive trait Usually the first letter of the allele is used (ie. T (tall) 17

Let’s Practice: Monohybrid Cross problems 1) a) Mendel crossed a purebred tall (TT) plant with a purebred dwarf (tt) plant. What are the possible genotypes for this cross?   F1 P1 P2 Genotype Phenotype Possible Gametes 18

b) If two F1 plants are crossed, what is the probability of having a dwarf plant? 19

2) In humans, the allele A, for pigment formation is dominant to the allele a, for inability to form pigment. aa individuals are albino. Determine the expected genotypic and phenotypic ratios expected from a cross between two individuals heterozygous for this trait. F1 20

3). Some people are PTC tasters (T) and some are non-tasters (t) 3) Some people are PTC tasters (T) and some are non-tasters (t). What is the probability of a grandchild being a non-taster if his paternal grandfather is a homozygous dominant taster, his paternal grandmother is a non-taster and his mother a non-taster? Start with the known info: paternal grandfather = TT (taster) paternal grandmother = tt (non-taster) Father = Mother = tt (non-taster) P1 P2 Geno tt Pheno non-taster Gametes t F1 21