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56 terms

chapter 4

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meiosis produces
haploid gametes
fertilization produces
diploid zygotes
autosomes
nonsex chromosomes
the letter O signifies the
absence of a sex chromosome
heterogametic sex
when males produce two different types of gametes with respect to the sex chromosomes
homogametic sex
when females produce gametes that are all the same with respect to the sex chromosomes
pseudoautosomal region
small region of the X and Y chromosomes that contains homologous gene sequences
genic sex determination
sex determination in which the sexual phenotype is specified by genes at one or more loci, but there are no obvious differences in the chromosomes of males and females
genomic imprinting
differential expression of a gene that depends on the sex of the parent that transmitted the gene. If the gene is inherited from the father, its expression is different from that if it is inherited from the mother
genic balance system
sex determining system in which sexual phenotype is controlled by a balance between genes on the X chromosome and genes on the autosomes
Turner Syndrome
1. females
2. underdeveloped secondary sex characteristics
3. sterile
4. chromosome complement - XO
Klinefelter Syndrome
1. feminine males
2. small testes, sterile
3. reduced facial hair
4. chromosome complement - cells have one or more y chromosome, XXY, XXXY, XXYY
Poly-X females
1. females
2. few are sterile, most menstruate regularly
3. severity of mental retardation increases with the amount of X chromosomes
4. chromosome complement - XXX+
Barr Body
condensed, darkly staining structure that is found in most cells of female placental mammals and is an inactivated X chromosome
When does random X inactivation takes place?
Early in development, within the first weeks of development
dominance
the idea that an individual organism possesses two different alleles for a characteristic, but the trait encoded by only one of the alleles is observed in the phenotype
incomplete dominance
an intermediate phenotype between two homozygotes
codominance
the heterozygote expresses the phenotypes of both homozygotes (think AB blood type)
Dominance
Phenotype of the heterozygote is the same as the phenotype of one of the homozygotes.
Incomplete Dominance
Phenotype of the heterozygote is intermediate (falls within the range) between the phenotypes of the two homozygotes
Codominance
Phenotype of the heterozygote includes the phenotypes of both homozygotes
dominance is an __________ ______________
allelic interaction
an allelic interaction is
the interaction between the products of genes
Incomplete Penetrance
Refers to a genotype that does not always express the expected phenotypes. When an individual will possess the genotype but does not always express the phenotype - EX. polydactyly
Penetrance
Percentage of individuals with a particular genotype that express the phenotype expected of that genotype
Expressivity
the degree to which a character is expressed
(T or F) Incomplete Penetrance and variable expressivity are due to the effects of other genes and to environmental factors that can alter or completely suppress the effect of a particular gene.
T
lethal allele
causes the death of an individual organism, often early in development, and so the organism does not appear in the progeny of a genetic cross. Recessive lethal alleles kill individual organisms that are homozygous for the allele; dominant lethals kill both heterozygotes and homozygotes
An example of a dominant lethal allele is:
Huntington's Disease
Multiple Alleles
presence in a group of individuals of more than two alleles at a locus
gene interaction
type of interaction between the effects of genes at different loci (genes that are not allelic)
epistatic gene
a gene that does the masking
epistasis
type of gene interaction in which a gene at one locus masks or suppresses the effects of a gene at a different locus
hypostatic gene
gene that is masked or suppressed by the action of a gene at a different locus
when a probability associated with the chi-square value is >.05
there is a good fit between the observed results and the ratio
complementation test
test designed to determine whether two different mutations are at the same locus (are allelic) or at different loci (are nonallelic).
complementation
two different mutations in the heterozygous condition are exhibited as the wild-type phenotype; indicates that the mutations are at different loci
cytoplasmic inheritance
inheritance of characteristics encoded by genes located in the cytoplasm, because cytoplasm is usually contributed entirely by only one parent, most cytoplasmically inherited characteristics are inherited from a single parent
sex-influenced characteristics
encoded by autosomal genes that are more readily expressed in one sex.
sex-limited characteristics
characteristic determined by a gene or genes on sex chromosomes
genetic maternal effect
determines the phenotype of an offspring. offspring inherits genes for the characteristics from both parents, but the offspring's phenotype is determined not by its own genotype but by the nuclear genotype of its mother
epigenetics
Phenomena due to alterations to DNA that do not include changes in the base sequence; often affect the way in which DNA sequences are expressed. Alterations are often stable and heritable in the sense that they are passed from one cell to another
Norm of Reaction
range of phenotypes produced by a particular genotype in different environmental conditions
Sex-linked characteristics
Genes located on the sex chromosome
Sex-influenced characteristics
Genes on autosomal chromosomes that are more readily expressed in one sex
Sex-limited characteristics
Autosomal genes whose expression is limited to one sex
Genetic maternal effect
Nuclear genotype of the maternal parent
Cytoplasmic inheritance
Cytoplasmic genes, which are usually inherited entirely from only one parent
Genomic imprinting
Genes whose expression is affected by the sex of the transmitting parent
Phenocopy
phenotype that is produced by environmental effects is the same as the phenotype produced by a genotype
discontinuous (meristic) characteristics
have a few easily distinguished phenotypes (blood type)
continuous characteristics
characteristics that exhibit a continuous distribution of phenotypes (height, weight)
continuous characteristics are also called
quantitative characteristics
polygenic characteristics
characteristics that are encoded by genes at many loci
pleiotropy
one gene affects multiple characteristics
multifactorial characteristics
many continuous characteristics both polygenic and influenced by environmental factors