Lab Biology Chapter 9 - Genetics Mrs. Nemanic

I. Mendel’s Legacy Genetics – study of heredity A. Gregor Mendel 1. Researched heredity – the passing of traits from parents to offspring. 2. Observed 7 characteristics of garden peas. a. when he planted seeds from purple flowers, he noticed most offspring were purple but some were white. b. seeds from tall plants produced mostly tall but some short.

3. Mendel’s Methods a. pollination – occurs when pollen grains produced in (anthers) male reproductive parts of flower are transferred to (stigma) female reproductive parts. b. Self-pollination – when flower is pollinated by same plant. c. Cross-pollination – when flower is pollinated by a different plant.

B. Mendel’s Experiments 1. Trait – different forms for a characteristic. 2. Pure – always produce offspring with that trait. 3. Strain – denotes plants that are pure 4. P1 Generation – parental generation 5. F1 Generation – first filial generation (offspring of P1) 6. F2 Generation – second filial generation (offspring of F1)

C. Mendel’s Results & Conclusions 1. Recessive & Dominant Traits a. Dominant – it “masked” the other ‘factor’ ( gene). b. Recessive – it is not expressed if with dominant gene. Recessive traits did not appear in F1 but reappeared in F2.

2. Law of Segregation – a pair of ‘factors’ ( genes) is segregated, or separated, during gamete formation. 3. Law of Independent Assortment – ‘factors’ ( genes) for different characteristics are distributed to gametes independently.

D. Chromosomes and Genes 1. Molecular Genetics – study of structure & function of chromosomes & genes 2. Gene – a segment of DNA that controls a trait 3. Allele – alternate forms of a gene (Mendel’s factors) a. capital letters refer to dominant genes b. lowercase letters refer to recessive genes

II. Genetic Crosses A. Vocabulary 1. Genotype – genetic makeup of an organism - consists of alleles the organism inherits 2. Phenotype – appearance of an organism as a result of its genotype

3. Homozygous – when both alleles of a pair are alike a. dominant homozygous Ex: TT b. recessive homozygous Ex: tt 4. Heterozygous – when 2 alleles in a pair are different or hybrid Ex: Tt

B. Probability 1. Probability – the likelihood that a specific event will occur. a. expressed as a decimal or percentage or fraction. b. probability = # of times an event is expected to happen # of opportunities for an event to happen c. the results predicted by probability are more likely to occur when there are many trials.

C. Predicting Results of Monohybrid Crosses 1. Monohybrid – a cross between individuals involving one pair of contrasting traits. 2. Punnett Square – a diagram used to predict results of crosses.

Homozygous x Homozygous Ex: TT x tt

Homozygous x Heterozygous Ex: TT x Tt

Heterozygous x Heterozygous Ex: Tt x Tt

a. Ratios: – Genotypic Ratio – ratio of genotypes in offspring – Phenotypic Ratio – ratio of phenotypes in offspring b. Testcross – individual of unknown genotype is crossed with homozygous recessive.

C. Dominance: Complete Dominance – one allele is completely dominant over another. (Heterozygous and dominant homozygous plants are indistinguishable in phenotype)

Incomplete Dominance – two or more alleles influence the phenotype, resulting in intermediate phenotype. Codominance – both alleles for a gene are expressed in heterozygous offspring. Neither allele is dominant or recessive; nor do they blend in the phenotype.

D. Predicting Results of Dihybrid Crosses Dihybrid Cross – cross between individuals that involves 2 pairs of contrasting traits.

a. Homozygous x Homozygous Ex: RRYY x rryy

b. Heterozygous x Heterozygous Ex: RrYy x RrYy Likely to result in 9 different genotypes & 4 different phenotypes