Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
27 Cards in this Set
- Front
- Back
|
Extensions of Mendelian Genetics
|
There are patterns of inheritance that follow the basicprinciples of Mendelian inheritance but yield different phenotypic forms and/or proportions. •genes are present on homologous chromosomes, which segregate from each other and assort independently with other segregating chromosomes during gamete formation,but:•gene expression does not always adhere to a simpledominant/recessive mode, or: •more than one pair of alleles influences the expression of asingle character |
|
|
Alleles:
|
Alleles are different forms of a gene (e.g. G and g). •if an individual has two variations of a gene, the two genesare said to be allelic (Gg) •if an individual has two copies of the same form of a gene, these two genes are non allelic (because they are identicalgenes) (GG or gg)•for two genes to be considered alleles they must map to the same locus (same position) on homologous chromosomes |
|
|
Wild type and Null Alleles:
|
Wild-type refers to the phenotype of the most common formof a species as it occurs in nature. Null allele: a mutant allele with the effect of either theabsence of gene product or the absence of gene product function. Most null alleles behave as recessive. |
|
|
Alleles: notation
|
e+/e+ homozygous wild-type color e+/eheterozygous e/ehomozygous recessive (ebony) +/+homozygous wild-type color +/eheterozygouse/ehomozygous recessive (ebony) R^1 & R^2 alternative alleles of gene R IA, IB & IO alternative alleles of gene I (blood types) L^M & L^N alternative alleles of gene L C^R & C^W alternative alleles of gene C (eye color: red or white) w^+, w, w^a, six of the 100+ alleles of the white locus w^cf, w^bl, w^e in Drosophila |
|
|
Incomplete dominance (partial dominance):
|
-neither one of the contrasting traits is dominant. The phenotype of heterozygous individuals is an intermediate of the of two contrasting traits. |
|
|
Penetrance and expressivity in tribbles
|
<100% penetrance (all should have had color) 100% penetrance but variable expressivity |
|
|
Variable expressivity of the Drosophilaeyeless mutation
|
All three flies are homozygous for the recessive eyeless mutant allele but show different degrees of eye reduction
|
|
|
Penetrance:
|
the frequency with which individuals of a givengenotype manifest at least some degree of the trait.
|
|
|
Expressivity:
|
the degree or range in which a phenotype for agiven trait is expressed.
|
|
|
Pleiotropy
|
is a condition in which a single mutation causes multiple phenotypic effects.
|
|
|
Marfan syndrome
|
results from an autosomal dominant mutation in fibrillin, a gene that codes for a connective tissue protein present in many tissues in the body.
|
|
|
The Agouti locus in mice
|
AA agouti AAY yellow •A (agouti) is an essential gene •one copy of A is sufficient for survival •A^Y (yellow) is dominant and pleiotropic •AY is also a recessive lethal |
|
|
Lethal alleles
|
An essential gene is defined as a gene that is necessary for growth to a fertile adult. The products of essential genes are necessary for survival, and their absence results inlethality.•if a gene product is necessary for survival, but a single copy of the gene can provide sufficient amount, a null allele behaves as a recessive lethal (the homozygotes die but theheterozygotes survive) •results: modified Mendelian monohybrid ratios |
|
|
The problem with tribbles
|
Normal male tribbles are XY. The n mutant allele is X-linked recessive lethal. Heterozygous individuals have short hair instead of the normal long hair. Use the Punnett square to determine the outcome of a cross between a normal male and a short-haired female, indicating the genotypes and phenotypes of all the individuals in P1 and F1.
|
|
|
Multiple alleles
|
The inheritance of feather patterns in mallard ducks depends on the three alleles of the M locus: M: wild-type mallard M^R: restricted m^d: dusky •restricted is dominant over mallard and dusky •mallard is dominant over dusky |
|
|
Codominance
|
is a mode of inheritance in which the phenotypic effects of two allelic genes are fully and simultaneously expressed in the heterozygous individuals.
|
|
|
The human ABO blood groups
|
The A and B antigens are carbohydrate groups that are bound to lipids on the surface of red blood cells(erythrocytes). •they are controlled by the IA and IB alleles of the ABO locuson chromosome 9 •if both alleles are present in an individual, the two antigenswill be present simultaneously |
|
|
The ABO blood groups
|
Slide 19 Ch4
|
|
|
Extensions of Mendelian genetics:
|
•multiple alleles of the same locus •codominance of blood type alleles: the IA and IB alleles are expressed simultaneously in heterozygous individuals •I^O (i) is recessive to both IA and IB |
|
|
A dihybrid cross with codominance
|
The inheritance of normal skin pigmentation follows simple Mendelian rules. A: normal pigmentation (dominant) a: albino (recessive) P1 Aa x Aa-> F1 -> Genotypes:1/4 AA 2/4 Aa 1/4 aa Phenotypes:3/4 pigmented 1/4 albino |
|
|
Functions of the H and the ABO gene products in the biosynthesis of the A and B antigens
|
•the H gene product is an enzyme that adds a fucose to thecompound H precursor to yield compound H •the IA gene product is an enzyme that adds a terminalN-acetylgalactosamine (AcGalNH) to compound H to yield the A antigen •the IB gene product is an enzyme that adds a terminal galactose to compound H to yield the B antigen |
|
|
The inheritance of the H gene follows simple Mendelian laws:
|
•H (a.k.a. the FUT1 allele) is a dominant allele •the null allele h is recessive •homozygous hh individuals do not produce compound H |
|
|
The Bombay phenotype
|
•no H enzyme (fucosyltransferase) •fucose is not added to compound H precursor •enzymes IA and IB can not recognize the substrate ->O phenotype, regardless of genotype on the ABO locus |
|
|
Epistasis
|
occurs when the effect of one gene masks ormodifies the effect of another gene. •the epistatic locus alters the phenotypic expression ofthe hypostatic locus •result: modified Mendelian dihybrid ratios ->the hh genotype is epistatic over IA_ or IB_ |
|
|
Novel phenotypes
|
are observed when the interactionbetween two loci yields new phenotypes and modified Mendelian dihybrid ratios. Example: two loci control pepper color in Capsicum annum. •if both loci contain at least one dominant allele: red •if both loci contain only recessive alleles: cream •if only one locus contains at least one dominant allele:peach or orange (novel phenotypes) |
|
|
Complementation
|
occurs when two parents that exhibit a recessive phenotype yield offspring that exhibit the dominant phenotype for the character. •it can only occur if the recessive mutant phenotypes of thetwo parents are caused by mutations in two different genes that affect the same character |
|
|
A frequent explanation for complementing loci:
|
enzymes for a metabolic pathway •the two enzymes needed to produce the final product areencoded by separate genes •if either enzyme is absent: same albino phenotype(no pathway product) |
