Genetics Ch 3 9/2 - 9/4
Genetics Ch 3 9/2 - 9/4 BIOL 3721 - 01
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This 4 page Class Notes was uploaded by Cherith Notetaker on Saturday September 5, 2015. The Class Notes belongs to BIOL 3721 - 01 at Youngstown State University taught by David K Asch, Chester R Cooper & Heather Elizabeth Lorimer in Fall 2015. Since its upload, it has received 59 views. For similar materials see Genetics in Biology at Youngstown State University.
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Date Created: 09/05/15
Genetics Ch 3 92 94 gt Dominance O Incomplete Dominance is characterized by F1 progeny that express an intermediate phenotype that is distinct from either purebreeding parent I these heterozygous F1 progeny produce offspring that are of 121 phenotypic ratio I 12 Will be intermediate IA Will be homozygous dominant 14 Will be homozygous recessive I the phenotypes re ect genotypes I the biochemical explanation for incomplete dominance is the individual alleles of a gene have an alternative protein Which has an enzyme that in uences pigment production I this enzyme Will be present in the alleles of one trait in a cross but absent in the other I a heterozygote Will have only enough of the pigment enzyme from the one allele to produce the intermediate trait O Codominance is characterized by F1 hybrids expressing traits from purebreeding parents in equal amounts I e g spotted and dotter lentils producing offspring with spots and dots I cross of the F1 produces offspring with a 121 phenotype ratio 0 a dominance series describes a pattern of dominance ranging from most dominant to most recessive gt Multiple Alleles 0 though there may be more than two alleles in a series Mendel s law of segregation still holds true because individuals only carry no more than two alleles for each gene as alleles separate during gamete formation gt Blood Type Alleles 0 AB blood type individuals have red blood cells RBC that are heterozygous IAIB and codominant I they have both A and B sugar polymers on the surface of their RBC thus they do not make antibodies against A or B blood 0 individuals who are A B or O can be heterozygous in the case of A and B ie IAi IBi or homozygous ie IAIA IBIB ii though 0 can only be expressed as a homozygote ii 0 alleles are not inherently dominant or recessive they are relatively dominant or recessive I dominantrecessive is unique to that allele pair 0 Ex IAi produce Type A making IA completely dominant to I but IAIB produce Type AB making IA codominant to IB 0 these dominant relations are responsible for the six possible blood type genotypes gt Mutations 0 Multiple alleles arise due to mutations or alterations in genetic material I the following gene transmission is possible due to mutation I one example of a mutant allele can be found in the agouti gene which is responsible for the coat pattern present in house mice I the wildtype alleles of the agouti gene exist as bands of yellow and black fur that blend together and give the mouse the appearance of a grey coat I wildtype describes alleles that are present in more than 1 of the population I one common allele monomorphic I multiple common alleles polymorphic gt Lethality O Recessive Lethality allele results in the death of the homozygote I Ex in the gene for yellow mice AY one copy of the gene would produce an offspring with a yellow coat but two copies of the gene would result in the prenatal death of the individual 0 Delayed Lethality death of an individual later in life due to a genetic defect gt Conditional Alleles alleles that are expressed or not expressed under certain environmental conditions 0 Conditional Lethality allele that can be lethal under certain conditions I can be effective after birth I Permissive Conditions range of conditions that permit survival I Restrictive Conditions conditions that negatively impact survival Penetrance number of individuals that have a certain genotype and express the expected genotype 0 PartialReduced Penetrance individuals with the mutated gene who do not exhibit symptoms express partialreduced penetrance Pleiotropy when a single genes determines multiple distinct and seemingly unrelated characteristics 0 Ex sicklecell allele that affects hemoglobin in RBC also prevents the sufferer from contracting malaria I the malaria virus can multiply in normal RBC sickled cells break down before the virus can multiply Expressivity degree of expression of a phenotype in regard to a particular genotype 0 Variable Expressivity range of expression among different individuals with the same genetic condition Epistatic Interactions gene masking the alleles of one gene masking the effects of the alleles of another gene 0 Dominant Epistasis one gene s dominant allele masks the effects of the allele of another gene I Ex the color of summer squash B white A green 0 Recessive Epistasis phenotype of the recessive allele masks the effects of the genotype I Ex the coat of colors Labrador Retrievers B black bb chocolate brown ee yellow 0 the presence of ee in combination with black or brown alleles produces a yellow Labrador I Ex individuals with the rare blood type phenomenon the Bombay phenotype have genotype hh in which case they do not produce substance H the sugar polymer that binds to polysaccharides A and B 0 genotype hh with any of the blood type alleles produces an individual who appears to be type 0 I evidence of recessive epistasis is the 934 ratio in the F2 generation between the cross BBEE black X bbee white gt Complementation Test determines whether a trait arises from a mutation or occurs naturally 1 2 3 tested when seemingly recessive phenotype appears in two different breeding lines proves that mutation affects two different genes and that one parent s normal allele can produce the trait that the other parent s mutant allele cannot one affected individual from both lines is crossed with the other I if offspring have a mutation from each parent and express the wildtype then complementation has occurred gt Gene Interactions of Multifactorial Traits 1 2 3 4 5 gene interaction can produce novel phenotypes dominant alleles from two different genes can be necessary to produce a normal phenotype alleles of one gene can mask the effect of alleles of another gene redundant alleles can be masked by dominant alleles of another gene to produce the normal phenotype mutations of alleles from different genes can be produced by the same phenotype