Genetics Chapter 5: Extensions of Mendelian Genetics

phenotype of the heterozygote is the same as the phenotype of one of the homozygotes

what is complete dominance?

the heterozygote has an intermediate phenotype between the two homozygote phenotypes

what is incomplete dominance?

1:2:1

what is the phenotypic ratio of a cross between two heterozygous parents that exhibit incomplete dominance?

1:2:1

what is the genotypic ratio of a cross between two heterozygous parents that exhibit incomplete dominance?

the same

when a trait displays incomplete dominance, the genotypic and phenotypic ratios of the offspring are ___

expressed, inherited

dominance affects the way genes are ___ not how they are ___

the phenotype of the heterozygote involves the phenotypes of both homozygotes

what is codominance?

codominance

what kind of dominance does human MN blood-group display?

an interaction between genes at the same locus (allelic genes), allelic interaction

what is dominance?

when an individual with a specific genotype does not express the expected phenotype

what is incomplete penetrance?

the percentage of individual organisms having a particular genotype that expresses the expected phenotype

what is penetrance?

the degree to which a trait is expressed

what is expressivity?

under different environmental conditions (like temperature)

how can penetrance and expressivity vary?

causes death at an early stage of development (often before birth) so that some genotypes do not appear among the progeny

what is a lethal allele?

when loci have more than 2 alleles with a series of effects

what is an allelic series?

ABO blood groups in humans

give an example of an allelic series

A

what is the blood type of someone with the genotype IAIA?

A

what is the blood type of someone with the genotype IAi?

B

what is the blood type of someone with the genotype IBIB?

B

what is the blood type of someone with the genotype IBi?

AB

what is the blood type of someone with the genotype IAIB?

O

what is the blood type of someone with the genotype ii?

none

what antigen type does O blood have?

anti-B

what antibodies does someone with A blood type make?

anti-A

what antibodies does someone with B blood type make?

Anti-A and Anti-B

what antibodies does someone with O blood type make?

none

what antibodies does someone with AB blood type make?

an individual who carries two different alleles at a locus that result in a recessive phenotype

what is a compound heterozygote?

because the two loci controlled independent traits

why did Mendel's dihybrid crosses produce a 9:3:3:1 ratio?

a type of interaction between the effects of genes at different loci

what is gene interaction?

gene interaction

when different genes participate in the expression of a single phenotype, there is a potential of ___ ___

homozygous red and cream peppers cross to produce red, peach, orange, and cream peppers (2 phenotypes not found in the parental generation)

what is an example of gene interaction?

a gene interaction where one gene masks the effect of another gene at a different locus

what is epistasis?

the masking gene

what is the epistatic gene?

the masked gene

what is the hypostatic gene?

a recessive allele can mask the effect of another gene

what is recessive epistasis?

one dominant allele in a locus can mask the effect of an allele at another locus

what is dominant epistasis?

two recessive alleles at either of two different loci are capable of suppressing a phenotype

what is duplicate recessive epistasis?

9:7

what phenotypic ratio can be seen in dihybrid cross with duplicate recessive epistasis?

9:3:4

what phenotypic ratio can be seen in dihybrid cross with recessive epistasis?

12:3:1

what phenotypic ratio can be seen in dihybrid cross with dominant epistasis?

whether different mutant alleles for the same characteristic occur at the same locus or at different loci

what does a complementation test determine?

mutant

if mutations are allelic, what phenotype will heterozygotes have?

wild-type

if mutations are not allelic, what is the phenotype of the heterozygous offspring?

if an individual organisms possessing two recessive mutations has a wild-type phenotype, indicating that the mutations are at nonallelic genes

when can complementation take place?

determined by autosomal genes and are inherited according to Mendel's principles, but they are expressed differently in males and females, trait is dominant in one sex and recessive in the other

what are sex-influenced characteristics?

encoded by an autosomal gene that is only expressed in one sex, trait has zero penetrance in the other sex (phenotype only expressed in one sex)

what is a sex-limited characteristic?

the transmission of genetic information located in the cytoplasm, like chloroplasts and mitochondria

what is cytoplasmic inheritance?

both parents

who does a zygote inherit nuclear genes from?

the egg (the mother)

where does a zygote inherit cytoplasmic genes from?

a genetic phenomenon in which the phenotype of the offspring is determined by the genotype of the mother (not cytoplasmic inheritance)

what is genetic maternal effect?

genotype, phenotype

in genetic maternal effect, ___ matters, not ___

the differential expression of genetic material depending on whether it is inherited from the male or the female parent

what is genomic imprinting?

no change in phenotype

if a gene exhibits genomic imprinting and the paternal copy is actively expressed, what happens if the mother's copy is blocked?

a modification of the DNA or chromatin that does not change the DNA sequence (like DNA methylation or histone modification)

what is epigenetics?

epigenetics

genomic imprinting is an example of ___

characteristics that have a few easily distinguished phenotypes (i.e. round vs wrinkled)

what are discontinuous characteristics?

characteristics that exhibit a continuous distribution of phenotypes and must be described in quantitative terms (quantitative characteristics)

what are continuous characteristics?

characteristics encoded by genes at many loci

what are polygenic characteristics?

pleiotropy

what is the converse of polygeny?

when one gene affects multiple characteristics

what is pleiotropy?

phenylketonuria

what is an example of pleiotropy?