Biology DMA 1/5/05 Biology DMA 1/6/2005 Prepare an entire piece of paper for notes like this: Mendelian Genetics Vocabulary Main topics Details, pictures, examples will go here will go here
allele: Short for Allelomorph (from Greek allos “other” and morph “form”). Any of a group of possible mutational forms of a gene. Generally used in reference to one form (dominant or recessive) of a characterisitic or trait. In the tall pea plant Tt, T is the allele for tall and t is the allele for short.
genotype: The genetic makeup of an organism. Genotype is communicated as a list of the alleles for a specific trait in an organism. In a pure bred tall pea plant, the genotype is TT. In a hybrid tall pea plant, the genotype is Tt.
phenotype: The genetically and environmentally determined physical appearance of an organism. Phenotype is communicated as a description of the physical appearance of an inherited genotype. The phenotype of TT is a tall pea plant. The phenotype of Tt is also a tall pea plant. The phenotype of tt is a short pea plant.
homozygous: Having identical alleles for a particular trait. Being pure bred for a particular trait. TT, tt, RR, rr, AA, BB, OO, etc.
heterozygous: Having two different alleles for a particular trait. Being hybrid for a particular trait. Tt, Rr, AB, etc.
P generation: The first two organisms crossed in a genetics experiment; the parent organisms.
F1 generation: (from Latin filius “son”) The offspring produced by the genetic crossing of the parent generation; the “children” of the P generation. The offspring of a cross between a homozygous tall pea plant and a homozygous short pea plant: T T t Tt Tt t Tt Tt
F2 generation: The offspring produced by crossing two members of an F1 generation; the “grandchildren” of the P generation. Choosing any two of the offspring of the cross TT x tt, the subsequent offspring produced: T T T t t Tt Tt T TT Tt t Tt Tt t Tt tt F1 F2
hybrid cross: A genetic cross of two parent organisms that are heterozygous for a particular trait. A cross between two hybrid parents. A cross that produces a 3:1 (75%/25%) phenotypic ratio. G g G GG Gg g Gg gg
test cross: A cross performed to identify if an organism is heterozygous or homozygous. The organism is crossed with another organism that is homozygous recessive for the same trait. Analysis of the F1 generation will reveal the genotype of the unknown parent.
Is it homozygous or heterozygous? f f f f F Ff Ff F Ff Ff ? ?f ? f F Ff Ff f f F Ff Ff If all of the offspring are fuzzy? f ff ff If 14 offspring are fuzzy and 15 offspring are scaly?
dihybrid cross: A cross between two organisms that involves two different sets of alleles. A cross between a tall wrinkled pea and a short round pea. TTrr x ttRR
Tr Tr Tr Tr tR TtRr TtRr TtRr TtRr tR TtRr TtRr TtRr TtRr tR TtRr TtRr TtRr TtRr tR TtRr TtRr TtRr TtRr
FOIL and dihybrid crosses First TTrr TrttRR tR Outer TTrrTrttRRtR Inner TTrr Tr ttRR tR Last TTrrTr ttRRtR
Dihybrid cross practice Complete a dihybrid cross between a homozygous short heterozygous round pea and a heterozygous tall homozygous wrinkled pea. Write out the fraction of each different genotype. Write out the fraction of each different phenotype.
sex-linked trait: Genetic characteristics that are carried on sex chromosomes. Characteristics that are generally carried only by the x chromosome. Red-green color blindness is a common sex linked trait. Homozygous recessive genotypes exhibit the color blindness phenotype. Males are statistically more likely to be affected than females.
A color blind male is crossed with a normal female: Xn Y XN XN Xn XNY XN XN Xn XNY A normal male is crossed with a “carrier” female: XN Y XN XN XN XNY Xn XN Xn XnY
incomplete dominance: Failure of a dominant phenotype to be fully expressed in an organism carrying a dominant and a recessive allele. The result is usually a phenotype that is intermediate between the homozygous dominant and the homozygous recessive forms.
Incomplete Dominance A cross between red snapdragons (RR) and white snapdragons (rr) makes pink snapdragons. R R r Rr Rr r Rr Rr
Incomplete Dominance A cross between pink snapdragons (Rr) and pink snapdragons (Rr) makes pink snapdragons, white snapdragons, and red snapdragons. R r R RR Rr r Rr rr
Incomplete Dominance A cross between pink snapdragons (Rr) and white snapdragons (rr) makes pink snapdragons and white snapdragons. R r r Rr rr r Rr rr
Incomplete Dominance A cross between pink snapdragons (Rr) and red snapdragons (RR) makes pink snapdragons, and red snapdragons. R r R RR Rr R RR Rr
TLTL is the genotype for a long tailed cat. TNTN is the genotype for a no tailed cat. A test cross between a long tailed cat and a no tailed cat is performed. TL TL TN TLTN TLTN TN TLTN TLTN The genotypeTLTN produces the medium length tail phenotype.
codominance: Both alleles of a pair are fully expressed in heterozygous organisms.
A is a dominant allele for human blood type. B is a dominant allele for human blood type. O is a recessive allele for human blood type. A test cross is performed between homozygous A and homozygous B. B B A AB AB A AB AB All offspring would have type AB blood.
A test cross is performed between a person with type AB blood and type O blood. A B O AO BO O AO BO The offspring would have either type A blood or type B blood.
A child has type O blood. The mother has type A blood and the father has type B blood. What are the actual genotypes of both parents? A ? B AB ?B ? A? OO
pedigree: A diagram setting forth the ancestral history or genealogical register. A chart that is used to trace the movement of alleles through a group of related organisms.
Biology DMA 1/7/05 Prepare a piece of paper for today’s quiz. Number from one to ten. Leave ample space for setting up Punnett squares. Some of your answers will actually be Punnett squares.
A cross is performed between a black guinea pig and a white guinea pig. Some time passes. Five baby guinea pigs are born, and they all end up with black fur. • What is the genetics term that is used to describe both the mother and father guinea pigs? • What is the genetics term that is used to describe the physical appearance of all five of the baby guinea pigs? • Based on the physical appearance of all of the babies, what is the genetics term that describes the allele for black fur?
Two of the “second generation” black guinea pigs of opposite gender are placed in a separate cage and given some privacy. Some time passes. Eight babies are born. Five of the babies have black fur and three have white fur. • What is the genotype of both parents for the “second generation”? (write two answers) • What is the genotype of the three white babies? • What is the correct genetics terminology for “second generation”?
A 7. What are the genotypes for the labeled guinea pigs? This pedigree is set up to display phenotypes (fur color). B C F D E
Two pink flowering roses are crossed. The seeds are harvested and planted. Several years later, three types of offspring are obvious: many pink roses, a few white roses, and a few red roses. In general, red roses are much more common than white roses. Create a Punnett square that illustrates this cross. 9. What genetics term describes the inheritance of the alleles in this case of the pink roses?
Penelope has type AA blood. She has several boyfriends scattered around the country: Theseus, with type AB blood, Daedalus with type OO blood, and Agamemnon with type BB blood. Penelope gives birth to Icarus, who has type A blood. Icarus marries Hailey, who has type B blood. They have four kids: Stan (AB), Dan (O), Fran (A), and Hailu (B). Who was the father of Icarus?
Biology DMA 1/10/05 How is codominance different from incomplete dominance?
Biology DMA 1/13/05 Prepare an entire piece of paper for notes like this: 1800 1850 1900 1950 2000 1825 1875 1925 1975 Modern Genetics Vocabulary Main topics Details, pictures, examples will go here will go here
gene: A hereditary unit that occupies a specific location (locus) within the chromosome. A unit that has one or more specific effects on the phenotype of an organism. A unit that can mutate to various allelic forms.
epistasis: The nonreciprocal interaction of non-allelic genes. A situation arising when expression of one type of gene masks or covers up the expression of another gene.
Agouti (A) is dominant to albino (a). Agouti (B) is dominant to black (b).
Possible genotypes and phenotypes: AABB AABb AAbb AaBB AaBb Aabb aaBB aaBb aabb
AaBb x AaBb AB Ab aB ab AB AABB AABb AaBB AaBb Ab AABb AAbb AaBb Aabb aB AaBB AaBb aaBB aaBb ab AaBb Aabb aaBb aabb
lethal allele: An allele that is lethal to the organism in a homozygous form. Heterozygous forms do not display the lethal allele. It produces 2:1 phenotypic ratios.
The Case of the Tailless Cats Mm x Mm M m M MM Mm m Mm mm
Gregor Mendel Working with pea plants, Mendel discovered dominant and recessive traits are passed from one generation to another in predictable ratios. He published his results in the paper Versuche über Pflanzen-Hybriden in 1865.
Independent Research Confirms Mendel’s Discoveries Hugo de Vries works with primroses. 1900 Carl Correns works with peas. 1900 Erich von Tschermak works with peas and primroses. 1900