An Introduction to Genetics

Every living thing – plant or animal, microbe or human being – has a set of characteristics inherited from its parent or parents. -

Gregor Mendel - Born 1822 Austrian monk who taught high school and was in charge of the monastery garden. -

The Role of Fertilization -

- Mendel decided to “cross” his stocks of true breeding plants meaning he caused on plant to reproduce with another -

Mendel studied 7 different traits in the pea plants - Shape: round seed vs. wrinkled seed Color: green vs. yellow Height: short vs. tall -

Mendel performed experiments to see what happened when 2 different traits were crossed -

Traits are determined by genes Gene = - Remember…. Human body cell = 46 chromosomes Human sex cell = 23 chromosomes - Example: gene for seed color come in 2 forms: yellow or green

Why didn’t Mendel see a mixture of tall and short pea plants? - Dominate allele = - Ex: Tall is dominate to shortTT or Tt Recessive allele = - Ex: Short tt (have to have both recessive alleles)

Mendel wanted to know what would happen if the F1 generation was mated with each other, would the recessive traits reappear? -

How did this occur?? Mendel suggested that the alleles for tallness and shortness is the F1 plants must have segregated from each other during the formation of the sex cells or gametes

Segregation of Alleles -! Example F = Free earlobe (capital letter = dominant allele) f = attached earlobe (lower case letter = recessive allele) F Mother = Ff to her offspring f

Probability Mendel realized that the principles of probability could be used to explain the results of genetic crosses. PROBABILITY – - What is the probability of flipping heads on a coin? ½ = 50% What is the probability of flipping heads 3 times in a row? ½ * ½ * ½ = 1/8 = 12.5%

Law of Segregation -: Diploid cells have pairs of genes, on pairs of homologous chromosomes. The two genes of each pair are separated from each other during meiosis, so they end up in different gametes. -

Homozygous Vs. Heterozygous Homozygous: - Ex: TT, tt“homo” = same Heterozygous: - Ex: Tt“hetero” = different

Genotype Vs. Phenotype Phenotype: - Tall, short, blue eyes, can roll tongue Genotype: - TT, Tt, tt Organisms can have the same phenotype, but a different genotype! Ex: TT = tallTt = tall

Gene expression - Expressed genes determine traits.

How can a genotype be determined? A testcross is a method of determining genotype -

Monohybrid Experiments - Different alleles of a gene are crossed Example: a purple flower x a white flower

Punnett Squares - Parents genes are placed on the outside and possible offspring allele combination in the squares Cross: Yy x yy

Practice Problems GG x Gg What are the possible genotypes? What are the possible phenotypes?

Practice Problems Cross a pure dominant pea plant with round seeds with a pea plant that has wrinkled seeds

Practice Problems Cross a plant that is heterozygous tall with a plant that is short.

Practice Problems What is the chance of producing a child with attached ear lobes if both parents are known to be heterozygous for free ear lobes?