Genetics Lecture 3, 9/3: Mendelian Genetics

Today's audio. NOTE: I have included the apx. times of when he goes over particular topic in the notes. Ex. He goes over Mendels monohybrid cross at (19:10))

• Practice problems (due before next fridays exam)
• 2,9,17,23,33,35
• Gregor J. Mendel -1866-
• Laid the foundation for the science of Genetics. Thus this form of genetics is called Mendelian Genetics or transmission Genetics. This is study of how traits are passed from generation to generation. Genotype to phenotype.
• Brief bio
• born in 1822 in central europe @Heinzendorf
• 1843 admitted to Augustinian Monastary - St. Thomos Brno.
• spends time as a pastor but in 1849 is relieved
• begins teaching and then went to school from 1851-1853. He studied physics and botany at the U of Vienna
• 1854 he returns to the monastary and teaches physics and natural science for 16 years
• 1856 he performs first experiment. Continues this research until 1868.
• In 1868 he becomes the abbott (top guy)
• 1884 he dies.
• Why was Mendel successful? (slide 2 chap 3)
• chose a good organism - common pea plant
• easy to grow
• can produce lots of data in one growing season
• control of its mating - which parents are for which offspring
• chose a series of traits to study with relatively straightfoward inheritance patterns
• all of the traits came in two varieties and in all of his relationships you have one trait that is completely dominant over a second trait.
• mendel had access to a variety of seed types.
• true breeding strain --> a strain that, when fertilized, you produce offspring that are all identical to the parent.
• Mendel took GREAT records. Allowed him to have a large amount of data. Enough so he could do quantitative analysis on. This gave creedence to Mendel's conclusions.
• Mendels monohybrid cross. Monohybrid cross and follow one trait at a time. (19:10)
• His experiment. Take tow pairs (true -breeding) with opposing characteristics.
• Tall cross that with a short plant. P generation --> parental generation
• produce and examine the offspring, called the F1 generation or First filial generation.
• F2 generation is the second filial generation and the F2 generation is a result of self-crossing a member of the F1 generation. Or crossing two identical members of the F2 generation.
• Results
• F1 generation all of the offspring are tall. In all of the crosses --> one trait appears and masks the second trait
• He then self fertilizes a member of the F1 generation and produces F2's. He gets 787 tall plants and 277 dwarf plants, 3:1 ratio of one trait to the 2nd trait. This phenomenon was not sex dependent. He did the cross two ways: tall sperm and dwarf on the egg and he got 3/4 tall and 1/4 dwarf. He switched and the numbers were the same.
• From his work he developed a series of postulates on the nature of inheritance.
• Genetic characteristics are controlled by unit factors (genes) which exist in pairs in individuals. Two copies of each gene one from mom and one from dad.
• When you have different forms of the same unit factor (alleles) in an individual one of the traits dominates over the other. Referred to as the dominant trait. In Mendels experiments it appeared solely in the F1 generation and 3/4 in the F2 generation. Recessive trait which appears as 1/4 of the F2.
• this is true for a lot of situations but it is not universally true.
• During gamete formation the unit factors (genes) segregate independent of each other. Roughly an equal likelihood of a gamete receiving a particular trait. Basically if an individually has both genes (an allele for tall and one for short) 50% of gametes will be tall and the other half will be dwarf.
• Genotype - refers to the nature of the genes for a particular trait. Are you "tall tall" "tall dwarf" or "dwarf dwarf" (36:25)
• Phenotype - physical appearance. Different genotypes lead to different phenotypes which means they can either be homozygous or heterozygous.
• homozygous - two identical copies of the same gene. You can be homozygous dominant (two alleles for tall) or you can be homozygous recessive.
• Heterozygous - two different alleles for a particular trait (heterozygous dominant). Can't be heterozygous recessive because by the nature of the relationship between the dominant and recessive allele the heterozygous individual will end up with the dominant phenotype. To figure this out you do a mono-hybrid cross on a punnet square.
• A true breeding plant is homozygous by nature. A heterozygous plant will produce offspring with both characteristics. SIDE NOTE: capital letter=dominant cell . . . lower case letter=recessive allele
• Homozygous tall x homozygous dwarf. (start as a diploid organism and your gametes are haploids with one allele each, shown here)

• 	D	D
  d	Dd	Dd
  d	Dd	Dd

• In the F1 generation all of the offspring are Dd-->Heterozygous (all tall)
• F2 generation production (46:45)
• Self fertilize tall x tall
• 1/4 offspring are homozygous
• 1/2 are heterozygous
• 1/4 are homozygous recessive
• This is how you end up 3/4 tall (homozygous dominant plants and heterozygous dominant plants will show the tall phenotype) and 1/4 (homozygous recessive) dwarf.
• SIDE NOTE: Gene vs. allele.
• gene: unit factor of inheritance. Passed down from generation to generation
• allele: you have alleles of a gene (different forms of a gene). Ex. Your gene is a pea plant and your allele is whether you are tall or short.
• You have a dominant plant in the F2. How do you know if its homozygous or heterozygous? (slide 4 chap 3)
• Do a test cross.
• Cross your dominant individual with a homozygous recessive individual. Two possibilities homozygous dominant or heterozygous dominant.
• If your F2 plant is homozygous dominant --> all Dd --> all tall
• If it is heterozygous dominant then --> 1/2 tall Dd and 1/2 homozygous recessive dwarf dd
• In a test cross if your individual is heterozygous that individual will produce the recessive phenotype.

Genetics Lecture 2 8/31: Regulation of Cell Cycle, Meiosis

Here is the audio for lecture on 8/31

http://www.archive.org/details/GeneticsLecture2831

• • Cell cycle is genetically regulated. WHY?
• o Too many cells = not enough food
• o Avoid mutations
• o Avoid cancer
• • Cell is built in with 3 checkpoints to control growth
• o G1 S Checkpoint → occurs at the end of G1 phase (prior to entering into S phase). Integrity of the DNA . . . are there any errors in the DNA. Also check the size of the cell.
• o G2 M Checkpoint → occurs at the end of G2 phase. Check two things:
• • Integrity of DNA – no mutations occurred during the previous round of division
• • Environmental conditions – can the environment support the cells
• o M Checkpoint → occurs early in Mitosis and ensures that the mitotic spindle has attached to the DNA correctly. If it is not attached correctly then things may come apart incorrectly and things such as down syndrome occurs.
  
• • Meiosis
• o Occurs in diploid (us) organisms. Functions to create haploid gametes, they have half of the chromosomal content.
  
• o Meiosis is a two step process.
• • At the beginning of meiosis I you have 4 copies of each chromosome
• • At the end of meiosis I you have two cells each of which have two copies of each chromosome.
• • At the end of Meiosis II you have 4 cells each of which have one copy of each chromosome
• o MEIOSIS I - Stages
  
• • Prophase I: genetic recombination occurring. In genetic recombination you take your parental chromosomes and you exchange information between one maternal chromosome (from Mom) and one paternal chromosome. End result is the production of a new chromosome that is a unique DNA sequence. Facilitates genetic diversity.
• - --5 subdivisions-- -
  
• Leptonema → chromatin condenses
• Zygonema → your homologous chromosomes pair with each other.
• Pachynema → chromosomes condense further. Process of synapsis → chromosomes in a homologous pair are intimately linked.
• Diplonema → tetrads appearing. Two pairs of homologous chromosomes come together to make a group of 4 chromosomes. IN this process genetic exchange occurs . . . essentially a different arrangement.
  
• Diakinesis → chromosome pairs begin to separate and exchange is completed. The important end result is 4 unique copies of the chromosome. (When you started you only had two)
  
• • Prometaphase I
• Like prometaphase in mitosis. (see 8/27 notes)
• When you get to meiosis II you start with a diploid cell. End point is two haploid cells per diploid cell.
• This is the process of meiosis as it is actually done in the body
  
• o Oogenisis → process of egg production in females. (slide 7, chap 2)
• • Begin with the oogonium, it has 4 copies of each chromosome. The oogonoium grows through a period of growth and maturation to produce the primary oocyte. It is the primary oocyte that enters meosis I. (The oogonium will not begin division until it has matured enough to become a primary oocyte.) Divide the primary oocyte in two.
• Secondary oocyte (diploid cell).
• First polar body → will not become an egg (endpoint)
• • This happens during oogenisis because during the physical division of cells in meiosis (oogenisis) the DNA is divided in two. When you get to cytokinesis you have an eneven cleavage of the cytoplasm. The primary oocyte gets the majority of the cytoplasm. The first polar body gets a small amount of cytoplasm. This occurs because the egg is the major donor to the cytoplasm of the zygote.
• • Another division occurs and the secondary oocyte splits into the ootid and second polar body. The ootid differentiates into the ovum which is a fully mature gamete.
• • HOW THIS ALL WORKS:
• In a human female meiosis I occurs during the embryonic period. A newborn girl has all of the secondary oocytes that she will ever produce.
• Meiosis II occurs during the menstrual cycle. Meiosis II only completes when fertilazation occurs.
• o Spermatogenesis - production of sperm in males (slide 7, chap 2)
• • Spermatogenium → undergoes growth and differentiation.
• • Primary spermatocyte then has 4 copies of each chromosome. Go through meiosis I and you produce two secondary spermatocyts. The sperm is not responsible for cytoplasmic delivery you can produce two secondary spermatocytes, they are diploids.
  
• • Then there is meiorsis II and there are 4 spermatids, haploid. Next is growth differentiation. Result is 4 functional spermatozoa.
• • In the human male this is an ongoing process after the onset of puberty.
• • SIDE NOTES: During meiosis you can have nondisjuntion events. This means that during anaphase when your chromosome pairs should split they fail to separate. This, in turn, can lead to a gamete with either too few or too many chromosomes. If these gametes are fertilized the end result is a trisomy on a monosomy.
• • Meiosis is critical for sexual reproduction and genetic diversity. It produces the necessary haploid gametes. The genetic recombination leads to an increase in diversity. The average person can produce 8 million unique gametes. Multiplied by the 8 million the other person has you will get 64x10^13 unique offspring.