Presentation on theme: " 3.a.3 – The chromosomal basis of inheritance provides an understanding of the pattern of passage (transmission) of genes from parent to offspring (14.1-14.4)."— Presentation transcript:
3.a.3 – The chromosomal basis of inheritance provides an understanding of the pattern of passage (transmission) of genes from parent to offspring ( ). 4.c.2 – Environmental factors influence the expression of the genotype in an organism – (14.3). 4.c.4 – The diversity of species within an ecosystem may influence the stability of the ecosystem (14.3).
Blending Theory 1. Blending Theory - traits were like paints and mixed evenly from both parents Incubation Theory 2. Incubation Theory - only one parent controlled the traits of the children Ex: Spermists and Ovists Particulate Model their 3. Particulate Model - parents pass on traits as discrete units that retain their identities in the offspring
Father of Modern Genetics Mendel’s paper published in 1866, but was not recognized by science until the early 1900’s Died prior to his “fame”
experimental Used an experimental approach (scientific method) mathematics Applied mathematics to the study of natural phenomena Ratios and probability good records Kept good records and observations Large test Large test sample/size
1. Short life span 2. Bisexual *Both sexes in one flower/plant *Stamens and carpels 3. Many traits known *Easy to see/observe traits 4. Cross- and self-pollinating *Easy to control reproduction 5. You can eat the failures
two different parents Cross between two different parents Results in hybrid offspring ◦ The offspring may be different than the parents.
Cross with only one flower ◦ Stamens/carpels fertilize each other! Naturally occurring event in pea plants Results in pure-bred offspring where the offspring are identical to the parents Is this asexual reproduction??? NO…you still have gametes
Used seven characters, each with two expressions or traits Example Example: ◦ Character - height ◦ Traits - tall or short
Mono = one single character Crosses that work with a single character at a time ◦ Example - Tall X short
Parental The Parental generation or the first two individuals used in a cross ◦ Example - Tall X short Mendel used reciprocal crosses, where the parents alternated for the trait
F1 - first filial generation ◦ Filial – Latin for “son” F2 - second filial generation, ◦ Bred by crossing two F1 plants together or allowing a F1 to self-pollinate
Notice Notice: only ONE plant shown (self-fertilz.) Notice Notice: TWO P1 plants shown (cross fertilz.)
P1 P1 Tall X short (TT x tt) F1 F1 all Tall (Tt) F2 F2 3 tall to 1 short (1 TT: 2 Tt: 1 tt) TallShort
Mendel observed SAME pattern in ALL 7 characters ◦ F1 generation showed only one of the traits (regardless of sex) ◦ The other trait reappeared in the F2 at ~25% 3:1 ratio; 3 dominant – 1 recessive Remember: the % are estimates (still have mutations that could change %)
1. Genes can have alternate versions called alleles 2. Each offspring inherits two alleles, one from each parent He made this conclusion without having knowledge of chromosomes/DNA makeup
** Remember: Each diploid cell has a pair of homologous chromosomes -Therefore, any gene has 2 loci *one on maternal chromo *one on paternal chromo
3. If the two alleles differ, the dominant allele is expressed The recessive allele remains “hidden” (unseen) unless the dominant allele is absent Mendel’s Law of Dominance Now called Mendel’s Law of Dominance
4. The two alleles for each trait separate during gamete formation (meiosis) Mendel's Law of Segregation This now called Mendel's Law of Segregation
Law of Segregation
Phenotype Phenotype - the physical appearance of the organism Genotype Genotype - the genetic makeup of the organism, usually shown in a code ◦ T = tall ◦ t = short
Homozygous Homozygous - When the two alleles are the same (TT/tt) Heterozygous Heterozygous- When the two alleles are different (Tt) Notice (for single-gene traits Notice (for single-gene traits: ◦ Three choices for genotypes ◦ Homo Dom (TT), Homo Rec (tt), Hetero (Tt)
Cross Genotype Phenotype TT X tt all Tt all Dom Tt X Tt 1TT:2Tt:1tt 3 Dom: 1 Res TT X TT all TT all Dom tt X tt all tt all Res TT X Tt 1TT:1Tt all Dom Tt X tt 1Tt:1tt 1 Dom: 1 Res Notice the 3:1 ratio!!!
Cross of a suspected heterozygote with a homozygous recessive ◦ Goal: to determine genotype of unknown Ex: T? X tt *If TT - all Dominant *If Tt - 1 Dominant: 1 Recessive
two Cross with two genetic traits ◦ Di = two 4 letters Need 4 letters (two for each trait) to code for the cross ◦ Ex: TtRr (Mono = Tt OR Rr) Each Gamete Each Gamete - Must get 1 letter for each trait ◦ Ex. TR, Tr, etc. (when combine = 4 letters)
Critical to calculating the results of higher level crosses heterozygous traits Look for the number of heterozygous traits
The formula 2 n can be used, where “n” = the number of heterozygous traits. Ex Ex: TtRr, n=2 (2 heterozygous traits) ◦ 2 2 or 4 different kinds of gametes are possible (TR, tR, Tr, tr) Ex: Ex: TtRR, n = ? ◦ 2 1 or 2 different gametes are possible
TtRr X TtRr Each parent can produce 4 types of gametes. (n=2; 2 2 =4) ◦ TR, Tr, tR, tr Cross is a 4 X 4 = 16 possible offspring
9 Tall, Red flowered 3 Tall, white flowered 3 short, Red flowered 1 short, white flowered Or: 9:3:3:1 ratio
The inheritance of 1st genetic trait is NOT dependent on the inheritance of the 2 nd trait ◦ Ex: Inheritance of height is independent of the inheritance of flower color This relates to dihybrid crosses – one character’s inheritance is NOT connected to the inheritance of another!
Ratio of Tall to short is 3:1 Ratio of Red to white is 3:1 The cross is really a product of the ratio of each trait multiplied together. (3:1) X (3:1) = 9:3:3:1 ◦ *Use FOIL method to attain ratio
Genetics is a specific application of the rules of probability Probability Probability - the chance that an event will occur out of the total number of possible events
The monohybrid “ratios” are actually the “probabilities” of the results of random fertilization Ex: 3:1 75% chance of the dominant 25% chance of the recessive
The probability that two alleles will come together at fertilization, is equal to the product of their separate probabilities Steps to determining probability: ◦ 1) Determine ratios for each character/trait How? Do “little” Punnett squares for EACH trait ◦ 2) Multiply ratios together
The probability of getting a tall offspring is ¾. The probability of getting a red offspring is ¾. (use same Punnett square as above – only with R/r) The probability of getting a tall red offspring is ¾ x ¾ = 9/16
Product Rule Use the Product Rule to calculate the results of complex crosses rather than work out the Punnett Squares Ex: TtrrGG X TtRrgg
TtrrGG X TtRrgg “T’s” = Tt X Tt = 3:1 “R’s” = rr X Rr = 1:1 “G’s” = GG x gg = 1:0 Product is: (3:1) X (1:1) X (1:0 ) = 3:3:1:1
When the F1 hybrids show a phenotype somewhere between the phenotypes of the two parents Ex. Red X White snapdragons F1 = all pink F2 = 1 red: 2 pink: 1 white NOT BLENDING!!!!!
Not enough red pigment made
No hidden recessive 3 phenotypes and 3 genotypes (Hint! – often a “dose” effect) ◦ Red = C R C R ◦ Pink = C R C W ◦ White = C W C W
Both alleles are expressed equally in the phenotype NOT an intermediate (like incomplete dominance Ex. MN blood group ◦ MM, MN, NN Ex: Rooster/chicken feathers Ex: flower petal color
No hidden recessive 3 phenotypes and 3 genotypes (but not a “dose” effect)
When there are more than 2 alleles for a trait ◦ *Remember: only 2 alleles exist for Mendel’s pea plants Ex. ABO blood group ◦ I A - A type antigen ◦ I B - B type antigen ◦ i - no antigen
Multiple genotypes and phenotypes Very common event in many traits
Phenotypes Genotypes A I A I A or I A i B I B I B or I B i AB I A I B O ii
I A and I B are dominant A and B are CODOMINANT A and B are the names for two different carbohydrates found on the surface of RBCs ◦ Blood types are actually ways of differentiating the type of antigens on a person's red blood cells
Rh blood factor is a separate factor from the ABO blood group Rh+ = dominant Rh- = recessive
Wife is type A Husband is type AB Child is type O Question - Is this possible? Comment Comment - Wife’s boss is type O…There’s some explaining to be done!
Factors that are expressed as continuous variation Lack clear boundaries between the phenotype classes Ex: skin color, height
Several genes govern the inheritance of the trait Ex: Skin color is likely controlled by at least 4 genes ◦ Each dominant gives a darker skin
Mendelian ratios fail Traits tend to "run" in families Offspring often intermediate between the parental types Trait shows a “bell-curve” or continuous variation
Often done by Pedigree charts Why? ◦ Can’t do controlled breeding studies in humans ◦ Small number of offspring ◦ Long life span
Most common inherited disease among African-Americans Single amino acid substitution results in malformed hemoglobin Reduced O 2 carrying capacity Codominant inheritance
Only affects Eastern European Jews Brain cells unable to metabolize type of lipid; accumulation of the lipid causes brain damage Death in infancy or early childhood
Most common lethal genetic disease in the U.S. Most frequent in Caucasian populations (1/20 a carrier) Produces defective chloride channels in membranes
Usually rare Skips generations Occurrence increases with consaguineous matings (people descended from the same ancestor) Often an enzyme defect Affects males and females equally
Less common then recessives Affects males and females equally Ex: ◦ Huntington’s disease ◦ Achondroplasia ◦ Familial Hypercholesterolemia
Each affected individual had one affected parent. Doesn’t skip generations. Homozygous cases show worse phenotype symptoms. May have post-maturity onset of symptoms.
Blood tests for recessive conditions that can have the phenotypes treated to avoid damage Genotypes are NOT changed Ex: PKU ◦ Required by law in all states ◦ Tests 1- 6 conditions ◦ Required of “home” births too
Where Genetic and Environment Factors interact to cause the disease Ex: Heart Disease factors ◦ Genetics ◦ Diet ◦ Exercise ◦ Bacterial infections
Recognize Mendel's experiments and their role in the scientific discovery of genetic principles. Identify Mendel's Laws of Genetics. Recognize the use and application of probability in genetics. Recognize the basic Mendelian crosses and genetic terminology. Recognize various extensions of Mendelian genetics and their effect on inheritance patterns. Identify human traits that exhibit Mendelian inheritance patterns. Recognize methods used in genetic screening and counseling.