Mendelian Genetics

Mendelian GeneticsChapter 10

A Bit of VocabularyAllele -alternative form that a single gene may have for a particular trait (dominant & recessive)Dihybrid - cross involving two traits e.g. flower color & plant heightDominant -stronger of two genes expressed in the hybrid; represented by a capital letter (R). Masks recessive alleles.Codominance Pattern where phenotypes of both homozygote parents are produced in heterozygous offspring so that both alleles are equally expressed. F1 generation - the first-generation offspring in a breeding experiment. (1st filial generation, your parents)

A Bit of VocabularyF2 generation - the second-generation offspring in a breeding experiment. (2nd filial generation, you)Gene - a unit of heredity; a sequence of DNA nucleotides that determines a single characteristic.Genetics -science of heredityGenotype -gene combination for a trait (e.g. RR, Rr, rr)Heredity - passing of traits from parent to offspringHeterozygous(heh tuh roh ZI gus)or Hybrid - gene combination of one dominant & one recessive allele (e.g. Rr)

A Bit of VocabularyHomozygous(ho muh ZI gus)or true breeding (pure) -gene combination involving 2 dominant or 2 recessive genes (e.g. RR or rr)Karyotype Chart of chromosome pairs used to identify unusual chromosome numbers in cellsIncomplete Dominance Pattern where one allele is not completely dominant over the other. Generally displays a new trait. ( Parents = Red Flower, RR and White Flower, rr; Offspring are all Rr with Pink flowers)Law of Independent Assortment -Mendelian law stating that a random distribution of alleles occurs during the formation of gametes.Law of Segregation -Mendelian law stating that two alleles for each trait separate during meiosis

A Bit of VocabularyMonohybrid a cross involving a single trait e.g. flower color Parental P1 Generation - the parental generation in a breeding experiment.(your grandparents)Pedigree Graphic representation of genetic inheritance used by geneticists to map genetic traits.Phenotype -observable characteristic that is expressed as a result of genotype (e.g. red, white)Polygentic Traits traits controlled by two or more genes; genes may be on the same or different chromosomes

A Bit of VocabularyPunnett Square - a diagram showing the gametes that can be produced, including the joining of gametes, to produce offspring. The resulting diagram shows the possible genotypes and phenotypes of the offspring and the ratios of each produced.Recessive -gene that shows up less often in a cross; represented by a lowercase letter (r). Is not seen if a dominant allele is present.Sex Linked Traits traits controlled by genes located on sex chromosomes ( X and Y chromosomes)Trait characteristic that is inherited; can be either dominant or recessive

Gregor MendelKnown as the father of geneticsAustrian MonkStudied the inheritance of traits in pea plantsDeveloped the rule of dominance and laws of inheritanceMendel's work was not recognized until the turn of the 20th century

Why Peas, Pisum sativum? Can be grown in a small area Produce lots of offspring Produce pure plants when allowed to self-pollinate several generations Can be artificially cross pollinated

Reproduction in Flowers Pollen contains sperm which is produced by the stamen Ovary (found inside the flower) contains eggs

stamenpistolovary Pollen carries sperm to the eggs for fertilization Self-fertilization can occur in the same flower Cross-fertilization can occur between flowers

Mendels Experiments Mendel cross-pollinated flowers using a paintbrush He could snip the stamens to prevent self-pollination He traced traits through the several generations

Mendels ExperimentMendel produced pure strains by allowing the plants to self-pollinate for several generations

Eight Pea Plant TraitsSeed shape --- Round (R) or Wrinkled (r)Seed Color ---- Yellow (Y) or Green (y)Pod Shape --- Smooth (S) or wrinkled (s)Pod Color --- Green (G) or Yellow (g)Seed Coat Color ---Gray (G) or White (g)Flower position ---Axial (A) or Terminal (a)Plant Height --- Tall (T) or Short (t)Flower color --- Purple (P) or white (p)

He studied only one trait at a time to control variables, and he analyzed his data mathematically.

Mendels Monohybrid CrossMendels first experiments are called monohybrid crosses because mono means one and the two parent plants differed from each other by a single traitheightGenerationsMendel cross-pollinated a tall pea plant with pollen from a short pea plant (P1 generation; both true breed)All of their offspring were as tall or taller than the parent plants. (F1 generation)These plants were allowed to self pollinateThree-fourths of the plants were as tall as the tall plants in the parent and first generations and One-fourth of the offspring were as short as the short plants in the parent generation. (F2 generation)

Generations

P1Short pea plantTall pea plantF1All tall pea plantsF23 tall: 1 short In the second generation, tall and short plants occurred in a ratio of about three tall plants to one short plant.(3:1)Mendels Continued Research

Mendels Continued ResearchIn every case, he found that one trait of a pair seemed to disappear in the F1 generation, only to reappear unchanged in one-fourth of the F2 plants.Mendel concluded that each organism has two factors that control each of its traits.We now know that these factors are genes and that they are located on chromosomes.

The Rule of DominanceAn organisms two alleles are located on different copies of a chromosomeone inherited from the female parent and one from the male parent.

Mendel called the observed trait dominant and the trait that disappeared recessive.

The Rule of DominanceWhen recording the results of crosses, it is customary to use the same letter for different alleles of the same gene. An uppercase letter is used for the dominant allele and a lowercase letter for the recessive allele. The dominant allele is always written first.

Tall plantTTTTShort planttttt