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PCB3063 Test Two
Terms in this set (56)
Genes exhibit independent assortment but do not act independently in their phenotypic expression.
The effects of genes at one locus depend on the presence of genes at another loci. The products of genes at different loci can produce new phenotypes.
In gene interaction, genes at different loci contribute to the expression of one single phenotypic characteristic.
The effect of gene interaction in which gene masks (hides) the effect of another gene at a different locus. Similar to dominance BUT dominance is the masking of genes at the SAME locus (allelic genes).
The gene that does the masking. May be dominant or recessive in their effects.
The gene whose effect is masked.
Color in labrador retrievers
One locus determines the coat color and the other locus determines whether or not pigment gets expressed, affect the deposition. e is the recessive epistatic allele because two copies are needed/must be present to mask the expression of pigment.
The expression of pigment.
color in squash
Only a single copy of an allele is required to inhibit the expression of an allele at another locus.
Allele W is epistatic to y, it suppresses the expression of these pigment producing genes. Allele W is dominant epistatic allele because a single copy is sufficient to inhibit the pigment production.
Duplicate Recessive epistasis
Duplicate dominant epistasis
Dominant and recessive epistasis
Used to determine whether two mutations occur at the same locus (are allelic) or at different loci.
Sex influenced characteristics
Determined by autosomal gene and are inherited according to Mendel's principles but they are expressed differently in males and female. A particular trait is more readily expressed in one sex.
Trait has a higher penetrance in one of the sexes.
Sex limited characteristic
extreme form of sex influenced characteristic. encoded by autosomal genes that are expressed in only one sex. Trait has zero penetrance in the other sex. Example breasts and chest hair.
Sex linked vs sex limited and sex influenced
Sex linked are on the x chromosome. Not somatic, reproductive.
somatic cells. not sex genes. Autosomal chromosome. Limited is an extreme version of influenced. Limited has zero penetrance in one sex.
Influenced - one sex has higher penetrance.
Characteristics are encoded by genes located in the cytoplasm. Frequently exhibit extensive phenotypic variation because no mechanism analogous to mitosis or meiosis ensures that cytoplasmic genes are evenly distributed during cell division. Recognized by Carl Correns as an exception to mendel's laws - variegation in four o'clocks
Present in Males and females
Usually inherited from one parent, typically the maternal parent
Reciprocal crosses give different results
Exhibit extensive phenotypic variation even within a single family.
Mitochondrial diseases linked to this
Organelles containing DNA
chloroplasts, mitochondria, and cytoplasm
Genetic Maternal Effect
The phenotype of the offspring is determined by the genotype of the mother. Genes are inherited from both parents but offsprings phenotype is determined not by its own genotype but by the genotype of its mother.
The differential expression of genetic material depending on whether or not it is inherited from the male or female parent . Form of epigenetics
In mice and humans Igf2
Whether the gene passes through the egg or sperm determines how much methylation of the DNA takes place. The pattern of methylation on a gene is copied when the DNA is replicated and therefore remains on the gene as it is passed from cell to cell through mitosis. Methylation can be modified or removed when DNA passes through the gamete. Amount of methylation determines whether or not gene is expressed in offspring.
Genomic imprinting is one form of this phenomenon. Traits that are caused by alterations to the DNA that do not effect the DNA base sequence but affect the way in which the DNA sequences are expressed. example: the addition of a methyl group to some of the DNA bases (DNA methylation). Alterations are often stable and heritable.
Reversible changes to DNA that do not alter the base sequence but may effect how the gene is expressed.
Temperature Sensitive allele
An allele whose product is functional only at certain temperatures. The expression of many genes is modified by the environment
Environmental factors alone that can produce a phenotype that is the same as the phenotype produced by the genotype.
Characteristics which have a few easily distinguished phenotypes. example ABO
Continuous Characteristics/Quantitative Characteristics
Characteristics that exhibit a continuous distribution of phenotypes. Must be described in quantitative terms because they have so many possible phenotypes. example height
frequently arise because genes at many loci interact to produce the phenotypes.
Single locus, two alleles - three possible genotypes
Two loci, four total alleles - 9 possible genotypes
3^n n being number of loci with two alleles.
Characteristics encoded by genes at many loci
opposite of polygenic. One gene affects multiple characteristics
many factors help determine the phenotype.
Results from independent assortment. The sorting of alleles into new combinations, different than parental genotype.
Rarely occurs. No crossover takes place. Test cross reveals these results. Test cross requires a plant heterozygous for each trait. Linked genes do not assort independently. The closer the gene the more linked it is. Complete linkage means no independent assortment which means no recombination. All offspring exhibit parental genotypes
Three point test cross
An individual heterozygous at three linked loci is crossed with an individual that is homozygous recessive at all three loci to gain information about the location and number of crossovers in the gametes that produce the progeny so that genes can be mapped.
Number of phenotypic classes possible from a three point test cross
2^n ; n being the number of loci, 2 being the number of classes of progeny that are possible. Because a heterozygote is cross with a recessive homozygote there are only two possibilities (heterozygous dominant or homozygous recessive). answer is 8
Middle Locus of a three point cross//determining gene order
Compare double crossover progeny with the non-recombinant progeny to determine where the crossover takes place. Where the crossover takes place. Double cross progeny have two of three same alleles as the parents and one different. This one allele difference is the key to determining order.
Double crossover recombinant progeny
Produced least frequently. Compared to non-recombinant parents to determine the middle locus of the three point cross.
Produced from non-recombinant gametes. Genetically the same as parents. Most frequently produced.
Used to determine the frequencies of recombination which tells us map distance. Must include all crossovers that take place between two genes.
(Number of recombinant progeny/ total progeny) x 100
Steps to gene mapping
Determine gene order
Recombination frequency Farthest to farthest
Recombination frequency End to middle
Recombination frequency Middle to end
Coefficient of coincidence
number of observed double crossovers/number of expected double cross overs
Less than one = only seeing a percentage (seeing less than) expected
More than one = more than expected
Indicates the degree that one crossover interferes with another
= 1 - coefficient of coincidence
Tells us the percentage of double cross progeny that are not observed due to interference. Most eukaryotic organisms exhibit interference which causes crossovers to be more widely spaced along the chromosome than would be expected on a random basis, more space less likely to double cross?
When interference is complete and no double cross progeny are observed the interference =1 and the coefficient of coincidence = 0
Sometimes crossing over increases the chance of a second cross over taking place. Meaning we see more than the expected number of double cross progeny making the coefficient of coincidence greater than 1 and interference negative.
Genome wide association studies
examine the non-random association of genetic markers and phenotypes to locate genes that contribute to the expression of traits.
A specific set of linked alleles. the accumulation of SNP's
Single Nucleotide Polymorphism
positions in the genome in which people vary in a single nucleotide base.
Variation in number and morphology/structure of chromosomes. Frequently play a role in agriculture and evolution.
centime is located in the middle. has two arms of equal length
centromere is displaced toward one end creating a long arm and a short arm. Short arm designated by letter p and long arm q
centromere is near one end producing a long arm and a knob/satellite
centromere is ar or very near the end of the chromosome
The complete set of chromosomes possessed by an organism. Usually presented in a picture of metaphase chromosomes lined up in descending order of their size. Treated with a chemical that prevent them from entering anaphase.
Mutations that change the structure of individual chromosomes. Four basic types:
Many of these originate when double strand breaks occur in the DNA molecules found within the chromosome. These breaks typically cause cell death so organisms have evolved elaborate mechanisms to repair breaks by connecting the broken ends of DNA.
Does not occur if the two broken ends are rejoined and restored correctly
Mutation in which part of the chromosome has been doubled. Leads to unbalanced gene dosage (imbalances in the amount of gene products) creating abnormal phenotypes. Developmental processes depend on the proper gene dosage (ratio). Duplicated gene (three copies) makes 1.5 times the product encoded in an individual with the normal two copies
when the duplicated segment is immediately adjacent to the original segment
if duplicated segment is located some distance from the original segment either on the same chromosome or a different one.
when duplication is inverted. mirror image
mutation in which part of the chromosome has been deleted
human genome contains numerous duplications greater than 1000 base pairs. Usually found on the same chromosome.
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