Terms in this set (94)
Continuos Population Variation, controlled by multiple Loci, Phenotypes are measured in population, Phenotypic Traits are distributed over a range in the population.
Simple Polygenic Inheritance
Two or more Loci lead to phenotype, no environmental influence on the phenotype, strictly genetic. Ex. Eye Color & Skin Color
SPI: Number of Loci
The number of loci can be determined if we make the following assumptions:
The different Loci are not linked (assort independently). Dominant alleles contribute equally to the phenotype.
Assume some baseline phenotype, then each dominant Allele adds equally to that phenotype. Recessive alleles make no contribution to the phenotype beyond the baseline.
# of Loci Determine the # of Phenotype Classes, (2n+1) N=# of Loci
3 Loci = 7 Phenotypic Classes
4 Loci = 9 Phenotypic Classes
Variation in the population will approach a bell shaped distribution as the # of loci increases.
Human Eye Color
Example of 2 Loci, 5 Classes of Eye Color=
Brown, Hazel, Green, Grey, Blue
Phenotype is a result of multiple loci, and environmental interactions. No direct relationship between # of Loci and # of phenotypic classes. Most complex human traits are multifactorial:
Height, Weight, Personality, IQ
Complex Human Diseases are Multifactorial
Disease phenotype is determined by the interaction of genes and the environment
Genes: Some increase risk, Some decrease risk
Environmental Factors: Some increase risk, Some Decrease risk
Multifactorial Threshold Inheritance
Genetic Predisposition: Must inherit minimal number of defective genes - genetic threshold
Environmental Trigger: Must have exposure to the correct environment - non-genetic trigger
The phenotype is only expressed when the genetic threshold is present and the correct physical environment is present
Phenotypic variation among individuals with the same genotype in the population - variation is due to differences in environmental factors not genetics Ex. Height of cloned trees where trees are planted in different types of soil
Phenotypic Variation among individuals in a population where the environment remains constant or has no affect on this phenotype - the variation in the population can be directly attributed to variation in the genotypes of the individuals Ex. ABO blood type
Measure of the genetic variance(how much of the variation is due to genetics)...this implies the extent of genetic contribution to the phenotype
H is ranged from 0 to 1 and is interpreted as a percent - limitations: the calculated H value is only valid for the population being studied under the environmental conditions present at that time
H = 0
100% of the phenotypic variation in the population is due to differences in the environment - genetic factors play no role
H = 1
100% of the phenotypic variation in the population is due to differences in the genotypes of the individuals in the population - genes are entirely responsible for the characteristic - finger print
Suggest genetic component of multifactorial traits
Indirect Evidence Only
Does not demonstrate cause and effect
population size is important (statistical validation)
Both twins have phenotype
Only one twin has phenotype
Monozygous Twins (MZ)
Single fertilized zygote splits
genetically identical (share 100% of genes)
If phenotype is totally genetic, both twins will share phenotype
Concordance if phenotype is entirely genetic = 1 (100%)
Dizygotic Twins (DZ)
Two separate ova are fertilized by different sperm
No more genetically related than normal siblings
Share 50% of genes
All twins will not share phenotype
Concordance if phenotype is entirely genetic = 0.5 (50%)
MZ Concordance vs. DZ Concordance
MZ concordance should always be higher than DZ concordance if the genetic contribution is higher than the environmental contribution
Animal Studies and Obesity
Ob gene: leptin hormone (fat cells secrete)
Db gene: leptin receptors in hypothalamus
Leptin tells hypothalamus to signal increased metabolism
-mutation in either gene ob or db gene result in fat mice
Human Obesity and Genetic Variance
Indirect Evidence: H = range from 0.3 to 0.7 from twin concordance studies, human ob or db genes are mutated in only 5% of obese individuals studied
Phenotypes that fall into two or more distinct, non-overlapping categories.
A distribution of phenotypic characters that is distributed from one extreme to another in an overlapping, or continuous fashion.
Traits controlled by multiple genes, the interaction of genes with each other, and with environmental factors where contributions of genes and environment are undefined.
Traits controlled by two or more genes.
Traits that result from the interaction of one or more environmental factors and two or more genes.
Regression to the Mean
In a polygenic system, the tendency of offspring of parents with extreme differences in phenotype to exhibit a phenotype that is the average of the two parental phenotypes.
Measures the degree of interdependence of two or more variables.
Both Types of Variance
Deals with variation of phenotypes in population
Neither Type of Variance
Deals with variation of phenotypes in an individual
Individuals in the population have the same genotype but show phenotypic variation
Neither Type of Variance
Individuals in the population have identical phenotypes but show genetic variation
Individuals in the population show phenotypic variation and genotypic variation
A measure of genetic variance
Share 50% of their genes
Responsible for making leptin
Contribute equally to the phenotype (additive)
Contribute nothing to the phenotype
2 Loci are Involved
(2N+1) 5 Phenotypic Classes
3 Loci are Involved
(2N+1) 7 Phenotypic Classes
The more Loci involved
The more the phenotype distribution will approach a bell shape
Determined by 2 Loci
Usually Seen in Single Gene Traits
Usually Seen In Simply Polygenic Traits
Threshold Effect Shows This Kind of Variation in the Population
Club foot shows this type of Variation in the Population
Phenotypes are Either/Or in the Population
A complete set of chromosomes from a cell that has been photographed during cell division and arranged in a standard sequence.
Treat metaphase spread with trypsin, an enzyme that digests part of chromosomal protein. Stain with Giemsa stain. Observe banding patterns with light microscope.
Treat metaphase spreads with the chemical quinacrine mustard. Observe fluorescent banding pattern with a special ultraviolet microscope. Same as G-Band.
Heat metaphase spread at high temperature to achieve partial denaturation of DNA. Stain with Giemsa stain Observe with light microscope. Pattern is reverse of G-band
Chemically treat metaphase spread to extract DNA from the arms but not the centromere regions of chromosomes. Stain with Giemsa stain and observe with light microscope. Good for observing centromere region, only centromeres show dark bands.
A method of sampling the fluid surrounding the developing fetus by inserting a hollow needle and withdrawing suspended fetal cells ands fluid; used in diagnosing fetal genetic and developmental disorders; usually performed in the 16th week of pregnancy.
A method of sampling fetal chorionic cells by inserting a catheter through the vagina or abdominal wall in the the uterus. Used in diagnosing biochemical and cytogenetic defects in the embryo. Usually performed in the 8th or 9th week of the pregnancy.
The failure of homologous chromosomes to separate properly during meiosis or mitosis.
A chromosomal number that is not an exact multiple of the haploid set. Can be cause by nondisjunction.
A condition in which one member of a chromosomal pair is missing; having one less than the diploid number (2N-1)
A condition in which one chromosome is present in three copies, whereas all other are diploid; having one more than the diploid number (2N+1)
A Chromosomal number that is a multiple of the normal haploid chromosomal set.
A chromosomal number that is three times the haploid number, having three copies of all of the autosomes and three sex chromosomes.
A chromosomal number that is four times the haploid number, having four copies of all of the autosomes and four sex chromosomes.
Sex Chromosome Aneuploidy
Aneuploidy involving the X and Y sex chromosomes
A monosomy of the X chromosome (45,X) that leads to fertility. Females only, wide chest, short stature rudimentary ovaries and puffy hands and feet.
Males with an extra X Sex chromosome, causes fertility issues,caused by maternal disjunction, reduced intelligence, tall stature, may include female sexual characteristics.
Normal Appearance, slightly taller, slightly lower IQ, used to be believed that it caused impulse control, new data suggests this is not true.
Trisomy 13 Patau Syndrome
Condition is lethal, avg. survival rate is 6 months, severe congenital malformations, CNS and heart malformations lead to death, parental age is a known factor
Trisomy 21 Down Syndrome
Aneuploidy involving the presence of an extra copy of chromosome 21, resulting in down syndrome.
Trisomy 18 Edwards Syndrome
Small at birth, grow very slowly, and are mentally retarded. similar to trisomy 13, more females affected
Autosomal Aneuploidy Monosomy
Always lethal, rarely seen in miscarriages and live births. Majority are lost very early even before pregnancy is recognized.
Aneuploidy Risk Factor
Older Maternal Age - Older Oocytes and Reduced implantation selection
Chromosomal Structure Abnormalities
May lead to clinical syndromes due to gene disruption, correct number of chromosomes but banding patterns indicate changes in chromosome structure
Chromosomal Disruption Agents
X-Rays, Cosmic Rays, UV radiation, clastogens (caffeine), viruses
Duplication of part of chromosome
Part of chromosome is missing
Obesity, compulsive eating 15q- Chromosome deletion
Cri du Chat
Infants have cat like cry, sever mental retardation 5p- Chromosome deletion
Part of Chromosome is rearranged and is now inverted, can turn genes on and off that should not be, moves genes away from control center
One part of chromosome is transferred to another chromosome (nonhomologous exchange) very different from crossing over
No gain or loss of genetic material, balanced exchange of material, gametes may be unbalanced, may lead to monosomy or trisomy
Inherited form of down syndrome, carrier is phenotypically normal, carrier is missing acrocentric area, unbalanced gametes lead to down's syndrome in offspring
No gain or loss of genetic material, gametes may be unbalanced, may lead to monosomy or trisomy
Part of chromosome is rearranged and is now inverted, just arms
Part of chromosome is rearranged and is now inverted, just centromere
Both copies of a chromosome are inherited from one parent-Prader Willi and Angelman Syndrome
Usually involves deletion of 15q11, 40% have no deletion of 15q11, both 15 chromosomes are maternal
Usually involves del of 15q11 (mental retardation, seizures, bouts of laughter) 40% have no deletion of 15q11 both 15 chromosomes are paternal
Fragile X Syndrome
Most common form of mental retardation, fragile site at the tip of X (q arm) affects primarily males, FMR-1 gene is involved CGG repeat region > 50
Hardy Weinberg Law
Allele frequency for a given locus (single gene trait) within a population will stabilize and remain constant
Pop must be Large >100
No Allele Selection
Migration is rare
mutation is rare
Simple Dominant/Recessive Inheritance
Frequency of Dominant Allele
Frequency Recessive Allele
P + Q
P2 +2PQ + Q2