MENDEL’S LEGACY

 Entered monastery age 21 in Austria  Tended garden therefore saw many plants grow  Later entered college studying math and science  Did much research on Heredity: transmission of characteristics from parents to offspring  Did much research on garden peas when he returned to monastery

 Observed 7 characteristics of pea plants › Height, flower position, pod appearance, seed texture, seed color (yellow, green ), flower color (purple, white)  Each characteristic occurred in two contrasting traits  Used his knowledge of statistics to analyze observations of characteristics  Collected seeds from pea plants, recording characteristics of plant from which each seed was collected  The following year he planted these seeds › Saw purple flowers grew from purple flower containing seeds › Also saw some white flowers grew from purple flower containing seeds

 Able to document traits of each generation’s parent by controlling how pea plants were pollinated  Pollination: occurs when pollen grains produced in the male reproductive part (anther) of a flower are transferred to the female reproductive part of a flower (stigma) › Self-pollination: occurs when pollen is transferred from the anthers of a flower to the stigma of either the same flower or a flower on the same plant  Pea plants usually do this › Cross-pollination: involves flowers of two separate plants  Self-pollination can be interrupted and cross-pollination performed (remove anther and manually transfer pollen to stigma of another plant) › By doing this Mendel was able to protect his flowers from receiving any other pollen via wind or insects  controlling the experiment

 Grew plants “pure” for each trait › Pure: always produce offspring with that trait › Ex. Pea plants pure for trait of yellow self-pollinate to produce offspring with yellow pods  Strain: denotes plants that are pure for a specific trait  Mendel produced strains by allowing plants to self-pollinate for several generations, eventually obtaining 14 strains (one for each of the 14 traits)  each strain = Parental generation (P 1 )

 He then cross-pollinated these strains  When plants matured, he recorded the number of each type of offspring produced by each P 1 plant  Offspring of P 1 generation = F 1 generation  F 1 were allowed to self-pollinate creating F 2 generation

 In one experiment Mendel crossed a plant pure for green pods with a plant pure for yellow pods › F 1 generation was all green  Next, Mendel allowed F1 to self-pollinate and planted the resulting seeds › F 2 generation plants grew and ¾ were green, ¼ yellow pods  3:1  He hypothesized that something within the pea plants controlled the characteristics he observed (called these controls, “factors”)  He reasoned that there must be a pair of factors controlling each trait (not just one factor)

Green-poddedYellow-podded ALL GREEN-PODDED OFFSPRING Self-pollinated F1F1 P F2F2 ¾ green, ¼ yellow (3:1) X

 Whenever Mendel crossed strains, one of the P1 traits failed to appear in the F1 plants  Trait reappeared in F 2 generation in 3:1  Concluded that one factor in a pair may prevent the other from having effect  Hypothesized that trait appearing in F 1 generation was controlled by dominant factor because it masked (dominated) the other factor for specific trait  Trait not appearing in F 1 generation but reappeared in F 2 was controlled by recessive factor

 Mendel concluded that paired factors separate during formation of reproductive cells  each gamete receives only one factor of each pair (when two gametes combine  offspring have two factors controlling specific trait)  LoS: a pair of factors is segregated, or separated, during the formation of gametes

 Mendel crossed plants that differed in two characteristics (ex. Flower color and seed color)  proved that traits produced by dominant factors do not necessarily appear together  Factors for different characteristics are not connected  LoIA: factors for different characteristics are distributed to gametes independently

 Molecular genetics: study of the structure and function of chromosomes and genes  Genes occur in pairs › Each of several alternative forms of a gene is called an allele › Mendel’s “factors” = alleles  Letters used to represent alleles › Capital letter = dominant allele › Lowercase letter = recessive allele › Ex. GG, Gg, gg (one allele from each parent)

 List the steps involved in Mendel’s experiments on garden peas  Define the terms dominant and recessive  Differentiate genes from alleles  State in modern terminology the two laws of heredity that resulted from Mendel’s work.  How might Mendel’s conclusions have differed if he had studied two traits determined by alleles carried on the same chromosomes?  What happens during meiosis that would allow genes located on the same chromosome to separate independently of one another?

 List the steps involved in Mendel’s experiments on garden peas: He first produced pure strains of plants by allowing the plants to self-pollinate over several generations. He then crossed plants that were pure for two contrasting traits. He then allowed the F 1 generation plants to self-pollinate.  Define the terms dominant and recessive: Trait controlled by a dominant allele masks the effects of other alleles for the same characteristic. A trait controlled by a recessive allele has no observable effect on an organism’s appearance when it is paired with a trait controlled by a dominant allele.  Differentiate genes from alleles: Gene = segment of DNA on a chromosome that controls a particular hereditary trait. Allele = an alternative form of a gene pair.  State in modern terminology the two laws of heredity that resulted from Mendel’s work: The law of segregation states that pairs of alleles are separated during meiosis. The law of independent assortment states that alleles located on separate chromosomes or far apart on the same chromosome separate independently of one another during meiosis.  How might Mendel’s conclusions have differed if he had studied two traits determined by alleles carried on the same chromosomes? Mendel would not have observed independent assortment occurring for all traits, so he probably would not have formulated his hypothesis of independent assortment.  What happens during meiosis that would allow genes located on the same chromosome to separate independently of one another? During crossing-over, homologous chromosomes exchange pieces of DNA, enabling alleles to move form one chromosome to a homologous chromosome.

GENETIC CROSSES

 Genotype: the genetic makeup of an organism › The alleles the organism inherits from its parents › Ex. PP, Pp, pp  Phenotype: the physical makeup of an organism  Homozygous: when both alleles of a pair are alike › Ex. PP, pp  Heterozygous: when two alleles of a pair are different › Ex. Pp

 The likelihood that a specific event will occur  Can be expressed as a decimal, percentage, fraction  Determined by following equation: Probability = # times an event is expected to happen # opportunities for an event to happen

 Example: Mendel’s experiment: › dominant trait of yellow seed color appeared in F 2 generation 6,022 times. › The recessive trait of green seed color appeared 2,001 times. › Total number of individuals was 8,023 (6, ,001) 6,022 = 0.75 = 75% = 3/4 8,023 DOMINANT TRAIT RECESSIVE TRAIT 2,001 = 0.25 = 25% = 1/4 8,023

 Monohybrid Cross: cross btwn individuals that involves one pair of contrasting traits  Punnett square: used to aid biologists in predicting probability that certain traits will be inherited by offspring

Pea plant homozygous for purple flower color (PP) and pea plant homozygous for white color (pp) P pppp Pp 100% Heterzygous offspring

 BB X Bb B B Bb Bb Bb BB Bb 50% BB 50% Bb

 Bb X Bb BbBb BbBb BB Bb bb 25% BB 50% Bb 25% bb

How might you determine whether a black guinea pig is homozygous (BB) or heterozygous (Bb)  perform a test cross: an individual of unknown genotype is crossed with a homozygous recessive individual BBBB BbBb b b b Bb bb Bb bb 100% Bb (all black) 50% Bb, 50% bb ( you will get some white)

 Sometimes F1 offspring will have phenotype in btwn that of parents = Incomplete dominance › Occurs when two or more alleles influence phenotype, resulting in phenotype intermediate btwn dominant trait and recessive trait › Ex. Pink flowers that come from parents that are either red or white flowers

INCOMPLETE DOMINANCE

 Occurs when both alleles for a gene are expressed in heterozygous offspring › Neither allele is dominant or recessive, nor do the alleles blend in the phenotype › Example roan horses: horses with coats that consist of white hairs and red hairs when heterozygous for coat color (came from parents that were either only red or only white)

 Dihybrid cross: cross btwn individuals that involves two pairs of contrasting traits  Predicting results is more complicated than monohybrid crosses because there are more possible combinations of alleles to work out

 You want to predict results of cross btwn a pea plant homozygous for round, yellow seeds and one that is homozygous for wrinkled, green seeds  Round seed (R)  Wrinkled seed (r)  Yellow seed (Y)  Green seed (y)

rryy X RRYY RY ry RrYy

RrYy X RrYy RY Ry rY ryry RYRyrYry RRYY RRYy RrYY RrYy RRYyRrYYRrYy RRyyRrYyRryy RrYyrrYY rrYy RryyrrYyrryy

 Explain how you might go about determining the genotype of a purple-flowering pea plant.  What is the equation used to determine probability? In what ways can probability be expressed?  If you were to cross pink-flowering four o’clocks with white-flowering four o’clocks, what results would you expect? Provide a Punnett square to support your answer.  Explain how you would use a Punnett square to predict the probable outcome of a monohybrid cross.  Explain the difference btwn a monohybrid cross and a dihybrid cross. Give an example of each.  The offspring of two short-tailed cats have a 25% chance of having no tail, 25% chance of having a long tail, and 50% chance of having a short tail. Based on this information, what can you hypothesize about the genotypes of the parents?

 Explain how you might go about determining the genotype of a purple-flowering pea plant: First, cross the purple-flowering pea plant with a white-flowering pea plant. If the offspring produced by the cross include white-flowering pea plants, chances are that the plant in questions is heterozygous for flower color.  What is the equation used to determine probability? In what ways can probability be expressed? The equation is as follows: number of times an event is expected to happen divided by the number of opportunities for an event to happen. Probability can be expressed in fractions, percentage, decimals, or ratios.  If you were to cross pink-flowering four o’clocks with white-flowering four o’clocks, what results would you expect? Provide a Punnett square to support your answer: 50% pink-flowering plants, 50% white-flowering plants.  Explain how you would use a Punnett square to predict the probable outcome of a monohybrid cross: Divide a square into four boxes. Place symbols representing one parent’s alleles on the left side and those representing the other parent’s alleles across the top. Fill in each box with the appropriate two symbols. The boxes reveal all possible genotypes.  Explain the difference btwn a monohybrid cross and a dihybrid cross. Give an example of each: A monohybrid cross involves one pair of contrasting traits, such as brown or blue eyes. A dihybrid cross involves two pairs of contrasting traits, such as round and green peas or wrinkles and yellow peas.  The offspring of two short-tailed cats have a 25% chance of having no tail, 25% chance of having a long tail, and 50% chance of having a short tail. Based on this information, what can you hypothesize about the genotypes of the parents? Each short-tailed parent has two incompletely dominant alleles, one for a long tial an done for no tail