4.3&10.2 Theoretical Genetics IB Biology HL I Mrs. Peters Spring 2014

Genetic History Genetic History: Gregor Mendel: Austrian monk who worked with garden peas in the 1860’s, developed fundamental principles of inheritance Mendel’s Laws: Law of segregation: two alleles for a specific character are packaged into separate gametes Law of Independent Assortment: pairs of alleles for different characters segregate independently of each other in the formation of gametes (they line up at the metaphase plate in metaphase I randomly)

Important Terms Genotype: all alleles of an organism Phenotype: the characteristics of an organism Allele: one specific form of a gene Homozygous: having two identical alleles of a gene Heterozygous: having two different alleles of a gene

Important Terms Dominant Allele: an allele that has the same effect on the phenotype whether it is present in the homozygous or heterozygous state Recessive Allele: an allele that only has an effect on the phenotype when present in the homozygous state Codominant alleles: pairs of alleles that both affect the phenotype when present in a heterozygote (formerly incomplete dominance)

Practice Determine if these are genotypes or phenotypes: Red hairbrown eyeshitchiking thumb TTttTt Determine if these are homozygous or heterozygous: TtttTT Determine if these are dominant or recessive traits: TtttTT

Practice Answers Determine if these are genotypes or phenotypes: Red hairbrown eyeshitchiking thumb TTttTt Determine if these are homozygous or heterozygous: TtttTT Determine if these are dominant or recessive traits: TtttTT Tt will show the dominant trait, but carries the recessive trait also.

Genetic Crosses Monohybrid cross: a cross involving the inheritance of a single character (only one trait) Each parent provides two alleles which are separated during meiosis A cross looks at the possible combinations of alleles are for the next generation Punnett square: a diagramming device used to predict simple genetic crosses

Genetic Crosses Monohybrid Cross Trait: Seed Shape Alleles: R: round; r: wrinkled Parents: RR x Rr Offspring??? Let’s find out! 1: draw a chart with 4 sections 2: separate each parent’s alleles RR= R; R Rr = R; r 3: place alleles at top and left side of chart 4: Fill in each inner box, with two letters, the one from the top and the one from the left 5. Determine the possible offspring ratios: Genotype: 2RR:2Rr Phenotype: all round RRrRr RRrRr R r R R

Genetic Crosses Dihybrid Crosses: A cross involving the inheritance of two characters (two traits) This is looking at two traits that are generally not located on the same chromosome. Looking at the possible combinations of two traits or 4 alleles in the next generation.

Genetic Crosses Dihybrid Cross Traits: Seed Shape & Seed Color Alleles: R: round; r: wrinkled; Y: yellow; y: green Parents: RrYy x RrYy Offspring??? Let’s find out! 1: draw a chart with 4 columns and 4 rows 2: separate each parent’s alleles RrYy = RY; Ry; rY; ry 3: place alleles at top and left side of chart 4: Fill in each inner box, with two of each letter, the one from the top and the one from the left (alpha/cap order) 5. Determine the possible offspring ratios: Genotype: 1RRYY, Phenotype: RRYYRRYYRRYyRRYyRrYYRrYYRrYyRrYy RRYyRRyyRrYyRryyRryy RrYYRrYyrrYYrrYy RrYyRrYyRryyrrYyrrYyrryy RY Ry rY ry RY Ry rY ry

Practice Time!

Genetic Crosses Codominance: (the old incomplete dominance) Two alleles If homozygous produce a certain color, if heterozygous produce a combined color Ex: Alleles for Red (RR) and White (WW) flowers, when heterozygous (RW) are Pink

Genetic Crosses Multiple Alleles: genes that exist with more than 2 alleles Blood Type Alleles: A, B, O iAiiAiiBiiBi iAiiAiiBiiBi i A i B i

Genetic Crosses Sex Linked Traits: genes located on X or Y chromosomes color blindness and hemophilia in humans are sex linked traits Seeing color is dominant and not seeing certain colors is recessive Hemophilia is a recessive trait Both are carried on the X chromosome XBXbXBXb XbYXbY XBXbXBXb XbYXbY X B Y XbXbXbXb B is not color blind, b is color blind

Genetic Crosses Polygenic Inheritance: when two or more genes are part of the phenotype Skin color and height in humans At least three genes contribute to determining skin color

Genetic Crosses Test Cross: testing a suspected heterozygote by crossing it with a known homozygote recessive

Important Terms Locus: the particular position on a homologous chromosome of a gene Pedigree: a family tree with the history of a particular trait shown across generations Carrier: an individual that has one copy of a recessive allele that causes a genetic disease in individuals that are homozygous for this allele

Pedigrees Members without trait are usually not colored in Members with a trait are colored in Carriers can either be left without color, have a lighter color, or have a split box half colored in Always look at all the information provided before making statements about pedigrees

Pedigree for Hemophilia

Genetic Testing Testing for disorders Amniocentesis A needle is inserted into the uterus and extracts about 10ml of amniotic fluid, cells in the fluid are cultured and analyzed using karyotyping (takes several weeks to get results) Chorionic villus sampling (CVS) A narrow tube is inserted through the cervix of the uterus and a tiny tissue sample from the placenta is suctioned out, karyotyping can happen immediately (takes a few hours to get results, more advantageous procedure)