mendelian genetics
DESCRIPTION
Mendelian Genetics. Principles of Heredity. Gregor Mendel: The Father of Genetics. Basics of Heredity: Mendel’s Rules. 1. Traits are controlled by particles 2. Two genes per trait 3. Heterozygous vs. Homozygous 4. Law of Dominance 5. Law of Segregation 6. Law of Independent Assortment. - PowerPoint PPT PresentationTRANSCRIPT
1. Traits are controlled by particles2. Two genes per trait3. Heterozygous vs. Homozygous4. Law of Dominance5. Law of Segregation6. Law of Independent Assortment
Basics of Heredity: Mendel’s Rules
1. Traits are controlled by “particles”
a. The “particles” are solids in the cells
b. “Particles” = genes
c. Genes are…
d. Gene means…
e. Alleles are…
2. Two genes per trait
a. Most biologists thought it was a single gene per trait (in the sperm), but really…
b. One gene from dad and one from momc. Trait: general description of what is being
controlled by the genes (e.g. seed color)d. Phenotype: visible expression of the genes
(e.g. yellow or green)e. Genotype: Actual genes present
3. Heterozygous vs. Homozygous
a. the 2 genes may be the same= homozygous e.g. EE or ee(purebred, true, non-carrier)b. …or different = heterozygous e.g. Ee(hybrid, crossed, mixed breed, carrier)
4. Law of Dominance
a. when it comes to showing up, some genes are more powerful than others = Dominant e.g. E = or
b. Others only show up if both genes are recessive e.g. e =
Antonio Alfonseca (P)
4. Law of Dominance, cont.
d. Some traits are inherited as Recessives:Sickle-cell anemiaHitchhiker’s ThumbAlbinismPhenylketylnuria
5. Law of Segregation
a. “When gametes are made, the two genes for a trait separate and each gamete has only one gene for each trait” This happens in meiosis
b. Punnett squares: A a show the possible
offspring from a
cross
A
a
6. Law of Independent Assortment
a. “The way one pair of genes for a trait is inherited has no effect on any other trait”
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Parent 2: AaBb
Parent 1:
AaBb
b. This allows us to examine multiple traits on a single (larger) Punnett Square. This is called a dihybrid cross and predicts 2 traits at once.
c. Probability II “The chances of two separate events happening at the same time equals the product of their separate probabilities”
d. Solving a Dihybrid Cross
1. Make “Gamete Tree” for both parents
2. Create Punnett Square
3. Insert Gametes along top and side
4. Fill in Punnett Square
I. Linkage A. genes for two traits carried on the same chromosomeB. example: Freckles and alleles for red hair
II. Mutations A. random changes in the genetic codeB. may produce “unexpected” offspring that Mendel
couldn’t account for. C. Ex: achondroplastic kids (Dd) usually come from
two perfectly normal (dd) parents
Exceptions to Mendel’s Rules
III. Polygenic
A. Controlled by multiple alleles on different chromosomes.
B. Best examined at the population level
C. Shown as continuous (bell curve) distribution
D. Ex.: human height, skin and hair color.
IV. Environmental Effects
A. some genes are affected by environmental influence
B. example: BRCA1 Breast Cancer Gene
Exceptions to Mendel’s Rules
Exceptions to Mendel’s Rules
IV. Sex Linkage
A. traits specifically carried on (usually) the X chromosome
B. Work like recessive traits (needs 2 alleles to show)
C. Show up most often in males (XY versus XX genotype)
D. Examples: Hemophilia and Color Blindness
Exceptions to Mendel’s Rules
V. Codominance A. two alleles that express themselves equally in the
presence of each other B. Example: ABO blood grouping, Roan cattle
VI. Multiple Alleles A. some traits have more than two possible phenotypes
because there are more than just two alleles for the traitB. This creates multiple combinations of possibilityC. Example: ABO blood grouping
Multiple Alleles & Codominance: ABO Blood Groups
I. A and B alleles code for glycoproteins (antigens) on red blood cells which can be detected immunochemically:
A. mix blood sample with type A or type B antibodies
B. look for clumping (agglutination) of RBC’s
II. O allele carries neither antigen
ABO Blood Groups
A - A antigen only
B - B antigen only
AB - Both A and B antigens
O - Neither antigen
III. ABO Genotypes and Phenotypes
Genotype Antigen Phenotype
IAIA
IAIOAA
A
IBIB
IBIOBB
B
IAIB A, B AB
IOIO Neither O
Some Important ABO Factoids
IV. IA and IB are codominantV. Both IA and IB are dominant to IO
VI. ApplicationsA. testing compatibility of blood transfusions
A. Who can donate to who?B. What happens in case of incompatibility?
B. disproving parentage of a childC. forensic scienceD. childbirthing (Rhogam and hemolytic disease)
Pedigree Analysis
I. Introduction to Pedigrees
A. Background: What is a Pedigree?“A diagram that shows appearance of phenotypes for a single trait in a group of related individuals from one generation to the next.”
Pedigree Analysis
B. Reading a Pedigree: SymbolsMales (squares or triangles) Females (circles)Marriage/MatingOffspring and SiblingsShaded or UnshadedCrossed outGeneration Labels (Roman)Individual Labels (Arabic)Birth Order (left to right)
Father 1. Mother 2.
Daughter 1. Son 2. Daughter 3.
Marriage line
Siblings
Oldest Child Youngest ChildMarriage into family
I.
II.
Dead
Pedigree Analysis
C. Genotypes in a Recessive PedigreeThere are some rules to follow:1. Shaded people are homozygous recessive. Fill
them in as such.2. Unshaded people are either:
Homozygous Dominant OR Heterozygous So… Assign one Dominant allele to each person
3. Work one generation at a time to determine the “unknown” genotypes. NEVER “skip” generations!!!!!
Pedigree Analysis, continued
II. Advanced Pedigrees: Unknown InheritanceA. First, “flip a coin” i.e. pick a mode ( Dom or Rec) B. Assign known genotypes across pedigreeC. Begin filling in unknowns
Remember to work 1 generation at a time!!! Don’t skip!!!
D. Look for anomalies (matings that don’t work)E. Try the pedigree again with the other mode of inheritanceF. Use colored pencils, different ink pens, or different letters
to help you solve