biol 3301 - genetics ch4a - extending mendelian genetics1st
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BIOL 3301 - Genetics Ch4A - Extending Mendelian Genetics1stTRANSCRIPT
Extending Mendelian Genetics
• Incomplete dominance• Codominance• Multiple alleles• Lethal alleles• Gene Interaction• Polygenic inheritance
or quantitative trait
• Pleiotropy• Effect of environment• Linkage• Sex-linked traits
Alleles and Symbols
• A – __________; a – ______________• + ; a+ - _________, a – mutant• Leu+, leu- ; leu+ is wild typeGene: Gal; galProtein coded:GAL1, GAL2, etc
Modifications of Dominant Relationships
Incomplete Dominance
• Snapdragons:AA - red; aa – whiteAa – pinkP: __________________F1: _________________
• Neither allele is dominant
Coat Color in Horses
CC – light chestnut (sorrel)CCcr – yellow or cream (palomino)CcrCcr – very light (cremello)
Plumage Color In Chicken
P: black x whiteF1: bluish grey (Andalusian blues)F2: 1 black : 3 blue : 1 whiteCB CB – black, ______________________CW CW – white CB CW – __________________________
Pigmentation in Birds and Mammals
• PIGMENTATION in birds and mammals is based on the synthesis of two different types of melanin, brown/black eumelanin and yellow/red pheomelanin.
• Tyrosinase is the rate-limiting enzyme of melanin biosynthesis, which takes place in melanosomes within melanocytes. Tyrosinase and the tyrosinase-related proteins Tyrp1 and Tyrp2 (Dct) are involved in the production of eumelanin.
• ________________ is associated with synthesis of eumelanin whereas _______________ results in the production of pheomelanin.
• The spherical pheomelanin premelanosomes are less organized than the rod-shaped eumelanin premelanosomes and contain less melanin
Intermediate Level of Gene Expression
• Tay-Sachs disease –fatal lipid-storage disorder (lipid accumulates in lysosomes in brain cells, eventually killing the brain cells)
• TT – _____________________________• tt – _______________________________• Tt - ?
Codominance
Heterozygote exhibits the phenotypes of both homozygotes
Codominance• Products of ______________________________; clearly detected for
biochemical phenotypes• Biochemical phenotype - a phenotype that is revealed by biochemical
experimentation; examples are – DNA markers (RFLPs); – protein markers (isozymes); – quantity of a metabolite; – immunological reaction
• MN blood group; autosomal locus, Chr4– Glycoprotein M; glycoprotein N– _____________________________________
Codominance
Genotypes can also be assigned to DNA fragments •A1 = 3.0 kb fragment; A2 = 2.0 kb fragment •Parent 1 = A1A1 •Parent 2 = A2A2. •F1 = A1A2 (heterozygous). •F2 generation will segregate 1 A1A1:2 A1A2:1 A2A2
Multiple Alleles
Can be more than two variants of a gene Each diploid organism can only have two alleles present
Multiple alleles: white Locus in Drosophila
• The recessive eye mutation• Discovered by Thomas Morgan and Calvin
Bridges in 1912• More than 100 alleles: allelic series• Red w+>wa>we>wt > w, white
Test for Allelism: Complementation Analysis
• To find if a mutation is coded by an allele of a gene or by another gene:– Cross with
____________________________________– If F1 is wild type – _____________________– If F1 is mutant phenotype –
__________________________________
Coat Color In Rabbits
• cc – white over the entire body or albino• chch – himalayan, black hair on extremities• cchcch – chinchilla,white hair with black tips• c+c+ - wild type, colored hair• c for
________________________________
Coat Color In Rabbits
• c+ > cch >ch > ca;
• P: c+cch x cchca full color x himalayan
c+ cch
cch
ca
Multiple Alleles – Blood Groups
• There are four different blood groups: O, A, B, AB
• The ABO Blood group alleles: IA, IB, IO or i• Genotypes:
Antigens
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
ABO Blood Groups: biochemical basis
• Cell membrane proteins, _________________• H substance plus fucose plus one more sugar added
(galactose or N-acetylgalactosamine)• IA codes for enzyme (glycosyltransferase) responsible
for adding N-acetylgalactosamine (AcGALNH) – ____________________
• IB codes for enzyme that can add galactose, but not AcGALNH – ____________________
• Allele i – no enzymes, no added sugars• IAIB -?
ABO Blood Groups: biochemical basis
The Bombay Phenotype
• A x AB parents• Woman O• Children AB, A, B
The Bombay Phenotype
• Genetically B, functionally O• Homozygous for fut1/fut1 – no
fucosyltransferase, ________________________________
• Not recognised by glycosyltransferase, no sugar added, ____________________
• Actually two genes system
ABO blood groups and paternity testing
• For example, child with blood type O must be genotype i/i.
• The parents could be___________ • However, they could not be__________ • May be used to suggest paternity,
additional analyses are often needed
Lethal Alleles
Determine conditions that are lethal, usually in homozygous state
Lethal Alleles
• 1904, Lucien Cuenot – color of mice– Yellow mice x wild type ; F1 1:1– Yellow mice x yellow mice– F1 – ___________________________
Lethal Alleles• Loss of function – can survive as Aa, but
not aa – homozygous recessive lethal• In mice:AA – agouti; AAY – yellow• AAY x AAY
A AY
A
AY
Figure 4-4 Copyright © 2006 Pearson Prentice Hall, Inc.
Why Some Alleles Are Dominant and Some Recessive?
• Abnormal protein leads to abnormal cell form and function – _________________________
• Other mutations may lead to – gain of function; – inhibit, antagonize or limit activity of wild-type
allele
Yellow Coat Color In Mice – Molecular Analysis
Merc gene coding region Regulatory coding region
A gene (Agouti)
Deletion (AY)
Merc – critical in embryonic development
Manx Mutation In Cats
Dominant Lethal Genes
• Spontaneous dominant mutation– normal height – _________________– Dwarfs – _______________________– AA – _____________________________– affects less than 200,000 people in the US
population
Huntington Disease
• Chromosome 4• Mutation of the gene causes Huntington
chorea, dominant, ____________________________ (1:10,000)
• _________ of the gene – Wolf-Hirschhorn syndrome, carriers die young
Pleiotropy
Multiple effects of one gene
Pleiotropy
• One gene – multiple phenotypic effects– Sickle cell anemia –
• ________________________________________– Marfan syndrome
Marfan Syndrome
• Marfan's syndrome is a genetic (inherited) disorder that affects the body's connective tissue.
• Connective tissue is the tough, fibrous, elastic tissue that connects one part of the body with another. It is a major part of tendons, ligaments, bones, cartilage and the walls of large blood vessels.
• In Marfan's syndrome, the body can't produce enough _____________ an important building block of connective tissue
Marfan Syndrome
• The problem in Marfan's syndrome is caused by a _______________________.
• In many families with inherited Marfan's syndrome, the mutation affects the FBN1 gene on ________________, although a second gene on chromosome 5 may be involved in some cases.
Sickle Cell Anemia
• Disease caused by __________________________ in the sequence of DNA coding a hemoglobin protein
• Leads to – ____________________________– Abnormal cell form– Abnormal RBC function