Cell Cycle & Mendelian Genetics

Genetics Vocabulary Genetics- scientific study of heredity Heredity- information that makes each species unique Trait- any characteristic that can be passed from parent to offspring Gene- units of inheritance Locus- location of a gene on the chromosome

Genetics Vocabulary Allele- alternate form of a gene at a locus Autosomal trait- on chromosomes 1-22 (not sex) X-linked trait- locus on the X chromosome Y-linked trait- locus on the Y chromosome

Theories on Genetics Aristotle’s Pangene Theory Pangenes- found in the blood and carried the “memory” of each structure in a person’s body Blood carried pangenes to reproductive organs and would be passed on Didn’t explain alterations that occurred Where bloodline and blood relative come from Blending Hypothesis of the 1600s Both parents contribute traits to the offspring through sexual reproduction The trait expressed is a blend of the parents Didn’t explain unexpected traits such as brown eyed parents with a blue eyed child

Mendel Gregor Mendel- Father of Genetics Monk who studied math and science, in charge of the monastery garden working with garden peas Mendel knew that the male part of the flower produced pollen and the female produced egg cells, which joined during sexual reproduction Pea flowers are normally self-pollinating with a sperm fertilizing an egg on the same flower Pea plants have a single parent that produces offspring identical to itself (clones)

Mendel Mendel prevented the peas from self-pollinating by removing the male reproduce organs For his experiments, Mendel would cross-pollinate 2 different plants by dusting pollen on the female structures Mendel studied seven different traits and each trait had two contrasting characteristics Flower color, flower position, seed color, seed shape, pod shape, pod color, stem length Mendel cross plants with each of the 7 contrasting traits and studied their offspring

Mendel Each original pair of plants is the P (parental) generation The offspring is the F1 (first filial) generation He called the observed trait dominant and the trait that disappeared recessive Always use the same letter for different forms of the trait (alleles) Capital letter shows dominance, lowercase recessive Ex- stem height tall allele T, short allele t

Mendel The way an organism looks and behaves is its phenotype Ex- tall, short The allele combination or genetic make up is its genotype Ex- TT, Tt, or tt An organism’s genotype can’t always be known by its phenotype An organism is homozygous (pure bred) for a trait if the two alleles are the same Ex- TT, tt An organism is heterozygous for a trait if the two alleles are different Ex- Tt

Experiment 1 P generation- Pure-bred tall plants crossed with pure-bred short plants

Experiment 1 Phenotype: dominant – when allowed to self-fertilize, each produced only offspring with parental trait 1 st filial generation (F1)- all offspring were hybrid (heterozygous) tall plants Principle of Segregation - all received different genetic information from each parent

Experiment 1 Mendel didn’t get a blend of the parents which was expected with the blending hypothesis He concluded that biological inheritance was determined by factors passed from one generation to the next We now know these factors as genes and alleles are different forms of the genes

Experiment 1 Mendel created from this the Principle of Dominance, that some alleles are dominant and some recessive A dominant allele for a trait will always exhibit that trait and the recessive allele will be exhibited when the dominant allele is absent Pea plants will be tall unless the allele for shortness is absent TT- ? Plant Tt- ? Plant tt - ? Plant

Experiment 2 After his first cross of the pure-bred tall and short plants, Mendel did not know if the recessive allele had disappeared completely. Mendel crossed the F1 plants to produce the F2 generation by letting the F1 plants self-pollinate. F2 generation produced 3 tall plants and 1 short plant

Experiment 2 The recessive allele reappeared, all of the traits ( including height) showed a 3:1 ratio of 3 dominant alleles to 1 recessive allele In the second cross, the recessive allele had separated from the dominant allele Mendel concluded from his second experiment that alleles segregate (separate) from each other so that each gamete carries only a single copy of a gene

Experiment 2 When each F1 plant flowers and produces gametes, those with the allele for the tallness and those with the allele for shortness From this he created his second principle: Principle of Segregation: each pair of alleles segregates during meiosis and half of an organism’s gametes have one allele from each pair of chromosomes and half the gametes have the other

Punnett Squares Used to make phenotype and genotype predictions to predict and compare the genetic variations that will result from a cross.

Punnett Squares Rules: Determine the alleles in the gametes of the parents Place alleles of the gametes of 1 parent along the top & those of the other parent along the left side Combine the alleles in the boxes of the Punnett square Determine the genotype and phenotype of the offspring inside the boxes

Monohybrid Cross 1 trait

Test Cross Used to distinguish between homozygous and heterozygous organisms Unknown organism is crossed with a homozygous recessive individual If unknown is heterozygous, then ½ of offspring will be dominant and ½ will be recessive If unknown is homozygous, then all offspring will be dominant

Test Cross Example: Unknown vs. homozygous recessive A breeder has a yellow cat and wants to know if it is a purebred. To determine what the cat’s genotype is the breeder does a test cross with a brown cat (homozygous recessive). All of the offspring turn out yellow. What is the genotype of the original yellow cat?

Dihybrid Cross Mendel wanted to know if alleles segregated independently when the gametes were formed or if the alleles stayed together. He performed an experiment to follow two different genes as they passed from 1 generation to the next. The 2-Factor Cross-(Dihybrid Cross) two traits

Dihybrid Cross Mendel crossed true breeding plants that produced only round, yellow peas (RRYY) with plants that produced wrinkled green peas (rryy) P: RRYY X rryy F1: RrYy- round yellow peas This showed that round and yellow was dominant over green and wrinkled, but it didn’t show whether genes segregated independently RrYy x RrYy

Dihybrid Cross F2 genotype and ratio: 9:Round, Yellow 3: round, Green 3: wrinkled, Yellow 1: wrinkled, green Mendel’s found that genes for different traits—for example, seed shape and seed color—are inherited independently of each other, so one does not influence the other This conclusion is known as the Principle of Independent Assortment

Probability Probability is the likelihood an event will occur The principals of probability can be used to predict the outcomes of genetic crosses A Punnett square can be used to determine the probability of the number of desired outcomes by the total number of possible outcomes

Probability Probability scale ranges from 0 to 1 If an event is certain to happen, it has a probability of 1 If an event is certain NOT to happen, it has a probability of 0, getting heads on a coin toss is ½ (one out of two)

Probability Product Rule “And” To determine the chance that two or more independent events will occur together in a specific combination, compute the probability for each independent event and then multiply the individual probabilities to get the overall probability Example: Rolling two dice and rolling 3 on each 1/6 X 1/6= 1/36

Probability Sum Rule “Either/Or” The probability of an event that can occur in two or more different ways is the sum of the separate possibilities of those ways Rolling an odd number using a dice: 1/6 + 1/6 + 1/6= 3/6 (or 1/2)