Beyond Mendel’s Laws
Exceptions to Mendel’s law
A. Mendel’s traits showed two distinct forms
B. Most genes do not exhibit simple inheritance
C. Genotypic ratios persist by phenotypic ratios may vary due to “outside-the-gene” influences
including:
1. Multiple alleles
2. Other nuclear genes (epistasis: standing on top of /one gene is stomping the other)
3. Non-nuclear genes (mitochondria has genetic material)
4. Gene linkage
5. Enviornment
D. Lethal Alleles:
1. A lethal genotype causes death before the individual can reproduce (genes do not appear)
2. This removes an expected progeny class from the gene pool following a specific cross
3. A double dose of a dominant allele may be lethal
4. Examples:
a. Achondroplastic dwarfism (chondro: cartilage) bones do not form regulary –cartilage
forms bones
b. Mexican hairless dogs (chichauas) lethal allel *N2K 2 of the dominant alleles die
E. Multiple Alleles
1. From mutation (different amino acids combine with alleles
2. An individual carries two alleles for each autosomal gene
3. However, a gene can have multiple alleles because its sequence can deviate in many ways
4. Different allele combinations can produce variations in the phenotype
5. CF gene has over 1500 alleles
6. PKU (phenol keto uria) –phenyl alanine (phenol with methyl group-alanine) *insuffeicient
mental development results
7. gene has hundreds of alleles resulting in four basic phenotypes
F. Incomplete Dominance
1. The heterozygous phenotype is between those of the two homozygotes
2. Example: Familial hypercholesterolemia (FH)
a. A heterozygote has approximately half the normal number of receptors in the liver for
LDL cholesterol
b. A homozygous for the mutant allele totally lacks the receptor, and so their serum
cholesterol level is very high
G. Codominence
1. Example with blood type (RBCs)
2. The heterozygous phenotype results from the expression of both alleles
3. The ABO gene encodes a cell surface protein
4. IA allele produces A antigen
5. IB allele produces B antigen
6. I (IO) allele produces no antigens
7. Alleles IA and IB are codominant, and both are completely dominant to i
H. Epistasis
1. The phenomenon where one gene affects the expression of a second gene
2. Example: Bombay phenotype
a. The H gene is epistatic to the / gene
b. H protein places a molecule at the cell surface to which the A or B antigens are attached
c. *hh genotype= no H protein
d. Without H protein the A or B antigens can not be attached to the surface of the RBC
e. All hh genotypes have the phenotype of type O, although the ABO blood group
genotype can be anything (A, B, AB, or O)
I. Penetrance and Expressivity
1. Penetrance refers to the all-or-none expression of a single gene
2. Expressivity refers to the severity or extent
a. A genotype is incompletely penetrant if some individuals do not express the phenotype
for that genotype
b. A phenotype is variably expressive if symptoms vary in intensity among different people
J. Pleiotropy
1. The phenomenon where one gene controls several functions or has more than one effect
(exp: porphyria variegate: test urine turns purple in the sunlight)
2. Affected several members of European Royal families, including King George III
3. The varied illnesses and quirks appeared to be different unrelated disorders
K. The Porphyrias
1. Diseases that result form deficiencies of any of several enzymes required to make heme
2. In each disease, an intermediate biochemical builds up
a. It may be excreted in urine, or accumulate in tissues causing symptoms
b. These symptoms, include reddish teeth and photosensitivity, may have inspired vampire
and werewolf legends
L. Marfan syndrome (N2K)
1. Pectus excavatum (chest sunken in –malformed sternum)
2. Arachnodactyly (long fingers- spider didgits)
3. Lens dislocation
4. Long arms
Genetic Heterogeneity
A. Different genes, but the same picture
B. Different genes can produce identical phenotypes
C. Genes may encode enzymes that catalyze the same biochemical pathway, or different proteins
that are part of the pathway
1. Hearing loss- 132 autosomal recessive forms
2. Osteogenesis imperfect- at least two different genes involved
3. Alzheimer disease- At least four different genes involved (alzheimers: is dementia before
you get old)
4. MIM: Mendelian inheritance of Man
D. Amyvid: a radiopharmaceutical that binds specifically to the amyloid plaques tx Alzheimers
E. Leber congenital amaurosis (caused by 100+ genes)
Genetic Heterogeneity: leber congenital amaurosis
Phenocopy
A. A trait that appears to be inherited but is caused by the environment
B. May have symptoms that resemble an inherited trait or occur within families
C. Examples:
1. Exposure to teratogens: thalidomide causes limb defects similar to inherited phocomelia
2. Infection: AIDS virus can be passed from mother to child, looking like it is inherited
The Human Genome Sequence Adds Perspective:
A. The Human Genome Project has revealed that complications to Mendelian inheritance are more
common than originally thought
B. Thus terms like epistasis and genetic heterogeneity are beginning to overlap and blur –Exp:
Marfan syndrome
C. Interactions between genes also underlie penetrance and expressivity- Exp: Huntington disease
D. Amaurosis: darkness RPE65 (retinal pigment..) can be fixed and cured
E. Misc: (Seal limb: -phoco media)
F. Misc: coreo atheosis- weird dance movements
Chapter 5b
The Mitochondrion
A. Organelle providing cellular energy
B. Contains small circular DNA called mtDNA- 37 genes (n2k) without noncoding sequences (loop
without protein)
C. No crossing over and little DNA repair machinery
D. High exposure to free radicals (love to combine with anything organic)
E. Mutation rate is greater than nuclear DNA (?!) *cramming mutation rate to fit their model
F. Mitochondrial genes are transmitted from mother to all of her offspring (muscles high in
mitochondrial count)
G. A cell typically has thousands of mitochondria, and each has numerous copies of its “minichromosome”
Features of Mitochondrial DNA (N2K all seven)
A.
B.
C.
D.
E.
No crossing over
Fewer types of DNA repair
Inherited from the mother only
Many copies per mitochondrion and per cell
High exposure to oxygen free radicals *bad news (anti-oxidants help this red cranberry, red
wine, dark chocolate)
F. No histones (DNA-associated proteins)
G. Genes not interrupted
Mitochondrial Disorders
A. Mitochondrial genes encode proteins that participate in protein synthesis and energy
production
B. Weak muscles
C. Several diseases result from mutations in mtDNA
D. Examples:
E. Mitochondrial myopathies- weak and flaccid (tone) muscles *distinguish between two
F. Leber optical atrophy- impaired vision *troph (feeding) a *without) –loss of mass in structure
G. **Lose 7% of muscle mass each day by laying in bed
H. Ooplasmic transfer technique can enable woman to avoid transmitting a mitochondrial disorder
I. Oo- egg, ooplasm: stuff that is not in the nucleus *offspring have normal and abnormal
mitochondrial
Heteroplasmy (different plasma)
A. The condition where mt DNA sequence is not the same in all copies of the genome- thus, a
mitochondrion will have different alleles for the same gene
B. Offspring is a mosaic (def
C. At each cell division, the mitochondria are distributed at random into daughter cells
D. If an oocyte is heteroplasmic, differing number of copies of a mutant mtDNA may be
transmitted- the phenotype reflects the proportion of mitochondria bearing the mutation
(different proportions)
Mitochondrial DNA Reveals Past
A. .mtDNA provides a powerful forensic tool used to:
1. Link suspects to crimes
2. Identify war dead
3. Support or challenge historical records- Example: identification of the son of Marie
Antoinette and Louis XVI
B. .mtDNA is more likely to survive extensive damage and cells have copies of it
C. Only 37 genes mitochondrial shorter to analyze
D. (Oj simpson case example)
Romenoas?? Heir to throne: suffered from hemophilia (factor 8) inherited from mom, hypnosis resbutin
(monk) , Anastasia *hemophilia is nuclear DNA (sex linked) x linked recessive
Linkage
A. Genes that are close on the same chromosome are said to be linked (closer they are, less likely
will be separated in the crossover in prophase 1 (N2K)
B. Linked genes do not assort independently in meiosis
C. Rather, they are usually inherited together when the chromosome is packaged into a gamete
D. Therefore, they do not produce typical Mendelian ratios
Recombination
A. *What happens normally when genes from two parents (could be combination, happens every
generation)
B. *Bateria (recombinant dna therapy) two homologs or two species
C. Chromosomes recombine during crossing-over in prophase 1 of meiosis
D. New combinations of alleles are created
E. Parental chromosomes have the original configuration
F. Recombinant chromosomes have new combinations of alleles (b/c of crossing over)
Crossing over disrupts linkage
Allele configuration in a Dihybrid *like in chemistry (on same side vs different sides)
A. Cis= two dominant or two recessive alleles are on each chromosome
B. Trans= one dominant and one recessive allele are on each chromosome
Know linkage vs non-linkage
Frequency of Recombination:
A. the correlation between crossover frequency and gene distance is used to construct linkage
maps
B. Frequency of recombination is based on percentage of meiotic divisions that result in breakage
of linkage between parental alleles
C. The frequency of recombination between two genes is proportional to the distance between
them
Linkage versus non-linkage
Linkage Maps
A. A linkage map is a diagram indicating the relative distance between genes
B. 1% recombination = 1 map unit = 1 centiMorgan (cM)
C. Map distances are additive
Linkage Disequilibrium (LD)
A. Is the non-random association between DNA sequences (more linkage than there ought to be)
B. Inherited together more often than would be predicted from their frequency.
C. The human genome consists of many “LD” (linkage disequilibrium/ ia) blocks” where alleles stick
together
D. These are interspersed with areas where crossing over is prevalent
E. These “LD Blocks” are also called haplotypes (haplo= half), NOT haploid(one)
F. *in a tight package *totally unexpected for genes to cross over
Solving linkage problems
A. The genes for Nail-patella syndrome (N) and ABO blood type (I) are 10 map units on
chromosome 9
B. *Patella (knee cap: little dish)
C. *Syndrome: collection of things (syn with, drome: conduction) *chromotropic and dromotropic:
contration, conduction velocity
D. *Map unit: centimorgan 1/100 of chromosomes
E. I = blood type, i= -…indominant N= n=…
F. Greg and Susan each have Nail-patella syndrome
G. Greg has type A and Susan type B blood
H. What is the probability that their child has normal nail and knees and type O blood?
I. The ni sperm would have to fertilize the ni oocyte. Using the product rule, the probabililty of a
child with nnii genotype is 0.45 x 0.05=0.0225 or 2.25%
Genetic Markers
A.
B.
C.
D.
Are DNA sequences that serve as landmarks near genes of interest
These were used starting in 1980 in linkage mapping
Currently, they are used in genome-wide association studies
Chromosomal: trait appears with unusual chromosome: Duffy blood type and dark area of
chromosome 1
E. SNPs: Single-base differences, genome-wide association studies to identify health-related genes
F. *Disease some: ---LOD Score: Logarithim of the odds
A. Indicates the “tightness” of linkage between a marker and a gene of interest
B. It is the likelihood that particular crossover frequency data suggests linkage rather than
inheritance by chance.
C. LOD scores of 3 or higher signifies linkage- observed data are 1,000 times more likely to be due
to linkage than chance
Haplotype:
A. Is the set of DNA sequences inherited on one chromosome due to linkage disequilibrium
B. Make it possible to track specific chromosome segments in pedigrees
C. Disruptions of a marker sequence indicate crossover sites
Chapter 3 (6?) Matters of Sex
Our Sexual Selves
A. Maleness or femaleness is determined at conception
B. Another level of sexual identity comes from the control that hormones exert on development
C. Finally, both psychological and sociological components influence sexual feelings (identity)
Sexual Development
A. During the fifth week of prenatal development, all embryos develop two sets of:
1. Unspecialized (indifferent) gonads
2. Reproductive ducts –Mullerian (female- specific) and Wolffian (male-specific)- guy is the
wolf
B. An embryo develops as a male or female based on the absence or presence of the Y
chromosome- Specifically the SRY gene (sex-determining region of the Y chromosome)
Sex Chromosomes Determine Gender
A. Human males are the heterogametic sex with different sex chromosomes, (XY).
B. Human females are the homogametic sex, (XX)
C. In other species sex can be determined in many ways- For example, in birds and snakes, males
are homogametic, (ZZ), while females are heterogametic (ZW) *xo in honeybees?
X and Y Chromosomes
A. X chromosome
1. Contains > 1,500 genes (N2K)
2. Larger than the Y chromosome
3. Acts as a homolog to Y in males
B. Y chromosome
1. Contains 231 genes (N2K)
2. Many DNA segments are palindromes and may destabilize DNA. (A man, a canal, Panama!
Revered now, I live on. O did I do no evil, I wonder, ever?) *pallindrome –same frontwards
and backwards. Fatal or infertile if problem in the Y chromosome
Anatomy of the Y chromosome
A. Pseudoautosomal regions (PAR1 and PAR2) –Par: pseudo autosomal region *two alleles one
from each parent
1. 5% of the chromosome
2. Contains genes shared with the X chromosome
B. Male specific region (MSY)
1. 95% of the chromosome
2. Contains majority of the genes including SRY*sex determining region of the Y chromosome*
and AZF *azoosermia factor* (needed for sperm production)
SRY Gene
A.
B.
C.
D.
Encodes a transcription factor- protein SRY
Controls the expression of the other genes
Stimulates male development
Developing testes secrete anti-Mullerian hormone and destroy female structures in the gonadal
ridge
E. Testosterone and dihydrotestosterone (DHT) are secreted and stimulate male structures
F. Epistatic: ***controls the expression of other genes
G. *remember abbreviations (Slide^^)
H.
Abnormalities in Sexual Development
A. Pseudohermaphroditism= presence of male and female structures but at different stages of life
1. Androgen insensitivity syndrome= lack of androgen receptors
2. 5-alpha reductase deficiency=absence of DHT
3. Congenital adrenal hyperplasia= high levels of androgens
B. KNOW FIGURE 6.3
C. Homosexuality
1. Homosexuality has been seen in all cultures for thousands of years
2. Documented in 500 animal species
3. Evidence suggests a complex input from both genes and the environment
4. Research in this area is controversial
5. Studies of identical and fraternal twins
6. Identifying possible markers
7. ***READ: http://www.conservapedia.com/Homosexuality_in_animals_myth
8. Romans 1:26-27
D. Sexual identity (Level: Events: Timing)
1. Chromosomal/genetic: XY=male, XX=female : Fertilization
2. Gonadal sex: Undifferentiated structure begins to develop as testis or ovary: 6 weeks after
fertilization
3. Phenotypic sex: Development of external and internal reproductive structures continues as
male or female in response to hormones: 8 weeks after fertilization, puberty
4. Gender identity: strong feelings or being male or female develop: from childhood, possibly
earlier
5. Sexual orientation: attraction to same or opposite sex: from childhood
6. Androgens: testosterone, DHT etc
7. Cholesterol basic unit to form forms of estrogen/androgens
8. (know slide with pictures) Reticualris layer produces androgens
Sex Ratios
A.
B.
C.
D.
E.
F.
The proportion of males to females in a human population
Calculated by # of males/ # of females multiplied by 1,000
Primary sex ratio- at conception
Secondary sex ratio- at birth
Tertiary sex ratio-at maturity (puberty)
Sex ratios can change markedly with age
Sex determination in Humans
Y-linked Traits
A.
B.
C.
D.
E.
Genes on the Y chromosome are said to be Y-linked
Y-linked traits are very rare
Transmitted from male to male
No affected females
Currently, identified Y-linked traits involve infertility and are not transmitted
X-linked traits
A. Possible genotypes:
1. X+X+ -homozygous wild-type female
2. X+Xm- heterozygous female carrier
3. XmXm- homozygous mutant female
X+Y –Hemizygous wild-type male
XmY –Hemizygous mutant male
B. Table 6.2 Criteria for X linked recessive trait
1. Always expressed in the male
2. … (finish chart)
C. Examples:
1. Ichthyosis= deficiency of an enzyme that removes cholesterol from my skin
2. Ichthyosis: ichthy-fish (skin that looks like a fish)
3. Color blindness= inability to see red and green colors
4. Hemophilia= disorder of blood-clotting
D. Table 6.3 Criteria for an X-linked Dominant Trait
1. Expressed in females in one copy
2. …finish chart
E. X-linked dominant traits: Incontinentia pigmenti
F. Congenital generalized hypertrichosis
&&&&&
Solving Genetic Problems
A. Steps to follow
1. Look at the inheritance pattern
2. Draw a pedigree
3. List genotypes and phenotypes and their probabilities
4. Assign genotypes and phenotypes
5. Determine how alleles separate into gametes
6. Use Punnett square to determine ratios
7. Repeat for next generation
Sex limited traits
A.
B.
C.
D.
E.
Traits that affect a structure or function occurring only in one sex
The gene may be autosomal or X linked
X-linked traits are the great majority
But the gene may be autosomal: examples
Examples:
1. Beard growth (not expressed in the female but fm can still carry the gene)
2. Milk production- marge produces milk with elevated levels of omega-3s and reduced
saturated fat healthier for brain and heart
3. Preeclampsia in pregnancy (influenced by the genes of the dad-too high blood pressure- pee
out protein and seizures result)
Sex influenced traits
A. Traits in which the phenotype expressed by a heterozygote is influenced by sex
B. Allele is dominant in one sex but recessive in the other
C. Example:
1. Pattern baldness in humans
2. A heterozygous male is bald, but a heterozygous female is not (for a female must be
homozygous)
X inactivation:
A. Females have two alleles for X chromosome gene but males have only one (from either dad or
mom-maternal or paternal)
B. In mammals, X inactivation balances this inequality and one X chromosome is randomly
inactivated in each cell
C. The inactivated X chromosome is called a Barr body
D. X inactivation occurs early in prenatal development
E. In is an example of an epigenetic change (not changes in the sequence, but changes on a higher
level outside of the DNA sequence- an inherited change that does not alter the DNA base
sequence
F. The XIST gene (causes the Barr Body to be formed) N2K!! (eXist, X isn’t) encodes an RNA that
binds to and inactivates the X chromosome
G. A female that expresses the phenotype corresponding to an X-linked gene is a manifesting
heterozygote (manifest: to show)
H. X inactivation is obvious in calico cats
Genomic Imprinting (Epigenetic)
A. The phenotype of an individual differs depending on the gene’s parental origin
B. Genes are imprinted by an epigenetic event: DNA methylation
C. Methyl (CH3) groups bind to DNA and suppress gene expression in a pattern determined by the
individual’s sex
D. Imprints are erased during meiosis- then reinstituted according to the sex of the individual
Imprints are erased during meiosis
E. Then reinstituted according to the sex of the individual
Importance of Genomic Imprinting
F. Function of imprinting isn’t well understood, but it may play a role in development
G. Same gene is from mom or dad…
H. Genes are imprinted by an epigenetic event DNA methylation *Cows eat alfalfa produce
methylene *chemical event (expressing)
I. Methyl (CH3) groups bind to DNA and suppress gene expression in a pattern determined by the
individual’s sex
J. Research suggests that it takes two opposite sex parents to produce a healthy embryo
(pronucliei to make a new organism from same sex)
1. Male genome controls placental development (and embryo is deficient if it’s this alone)
2. Female genome controls embryonic development
K. Genomic imprinting may also explain incomplete penetrance (only affects some people)
Imprinting and Human Disease
A. Two distinct syndromes result from a small deletion (inactivation) in chromosome 15 *
functionally it is not (physically it is not) *Rare cases:
1. Prader-Willi syndrome –deletion (inactivation) inherited from father
2. Angelman syndrome- deletion from mother
B. The two syndromes may also result from uniparental disomy
Chapter 7
Genes, Environment and Traits
A. Few, if any, genes act alone
B. Environmental factors and other genes may modify expression of the traits
C. Traits can be described as
1. Mendelian: caused by a single gene
2. Polygenic: caused by multiple genes
D. Both can be multifactoral or complex due to an interaction between genes and the
environment
E. Single-gene traits are discrete or qualitative- often produce an “all-or-none” effect
F. Polygenic traits produce an continuously varying phenotype
1. Also called quantitative traits
2. DNA sequences involved are termed quantitative trait loci (QTLs).
Polygenic Traits
A. Are influenced by interaction of genes and by the environment
B. Examples:
1. Height
2. Skin Color
3. Body weight
4. Fingerprint patterns
5. Behavioral traits
C. Individual genes follow Mendel’s laws, but their expression is hard to predict
D. Effect of genes is addictive or synergistic- however, input of genes is not necessarily identical
E. The frequency of distribution of phenotypes forms a bell-shaped curve!
Fingerprint Patterns
A. Dermatoglyphics is the study of fingerprints
B. The number of ridges is largely determined by genes and prenatal contact
C. The average total ridge count is 145 in a male and 126 in a female
Height
A. The difference in height between the two sets of students is attributed to improved diet and
better overall health
B. Genome-wide association studies have identified dozens of genes that affect height- also,
certain SNP patterns are seen in individuals with periods of rapid height increase
Skin Color
A. Melanin protects against DNA damage from UV radiation, and exposure to the sun increases
melanin synthesis
B. We all have the same number of melanocytes per unit area of skin. –However, we differ in
melanosome number, size, and density distribution
C. Skin color is NOT a reliable indicator of ancestry- overall, 93% of varying inherited traits are no
more common in people of one skin color than any other
D. The definition of race based largely on skin color is a social construct more than a biological
concept
E. It is NOT a biological concept
Investigating Multifactoral Traits
A. Empiric risk measures the likelihood that a trait will recur based on incidence
B. Incidence is the rate at which a certain event occurs
C. Prevalence is the proportion or number of individuals who have a particular trait at a specific
time
D. Cleft lip is more likely in a person who has a relative with the condition
Heritability (H): estimates the proportion of the phenotypic variation in a population due to genetic
differences
A. Researchers use several statistical methods to estimate heritability
B. One way is to compare the proportion of people sharing a trait to the proportion predicted to
share the trait
C. The expected proportion is derived by knowing the blood relationships of the individuals
Coefficients of Relatedness: the proportion of genes shared between two people related in a certain
way
Adopted Individuals
A. Similarities between adopted people and adopted parents reflect mostly environmental
influences
B. Similarities between adoptees and their biological parents reflect mostly genetic influences
C. Therefore, information on both sets of parents can reveal how heredity and the environment
both contribute to a trait
Twins
A. Twin studies have largely replaced adoption methods
B. N2K Concordance measures the frequency of expression of a trait in both members of
monozygotic (MZ) or dizygotic (DZ) twins –twins who differ in traits are said to be discordant for
it
C. For a trait largely determined by genes, concordance is higher for MZ twins
Separating Genetic and environmental influences**N2K
A. State contribution of environment and genes:
B. Dizygotic twins= shared environment and 50% of genes
C. Monozygotic twins= identical genotype and shared environment
D. Twins raised apart= shared genotype but not environment
E. Adopted individuals= shared environment but not genes
N2K!!!
SNP: a single nucleotide polymorphism is a site in the genome that is a different DNA base in > 1% of a
population
CNV: a copy number variant is a tandemly repeated DNA sequence, such as CGTA CGTA CGTA
Gene expression: The pattern of genes that are underexpressed and/or overexpressed in people with a
particular trait or disease,
______:Epigenetic signature (changes of expression by epigome)
SNPs:
A. SNPs (single nucleotide polymorphisms) are sites in a genome anywhere the DNA base varies in
at least 1% of the population
B. In these studies, SNPs span the genome, rather than define a single gene
C. A SNP can be anywhere among our roughly 3.2 billion base pairs
D. SNP examples: Thiourea (sulfur ), Urea, Phenylthiocarbamide (Phenylthiourea) PTC
Genome-Wide Association Studies
A. Older techniques search for known gene variants, typically in only a few people
B. Sequencing of human genome and the HapMap project (which identifies SNPs) have led to a
new tool.
C. HapMap: refers to haploid (one =half of norm)
D. Initially, 269 individuals, several million SNPs
E. Genome-wide association studies seek correlations between SNP patterns and phenotypes in
large groups of individuals
F. Genome-wide association studies seek SNPs that are shared with much greater frequency
among individuals with the same trait than among others
N2K!!
Study Designs:
A. In a cohort study, researchers follow a large group of individuals over time and measure many
aspects of their health. Framingham Heart Study
B. In a case-control study, pairs of individuals are matched so that they share as many
characteristics as possible
C. SNP differences are then associated with the presence or absence of the disorder
D. The “affected sibling pair” strategy scans genomes of siblings for SNPs shared by those with the
condition, but not by those who don’t have it
E. Homozygosity mapping is performed on families that are consanguineous (with the same
blood)- the children in this case are more likely to inherit two copies of the mutation
Limitations of Genome-Wide Association Studies
A. They include so many data points and so are prone to error
B. They reveal associations between two types of information, not causes (assumptions)
C. Bias can be introduced in the way the patient population is selected
D. Their accuracy is affected by complicating factors, such as phenocopy (appears to be genetic,
but is environmental) and epistasis
E. They may miss extremely rare SNPs
Terms used in evaluating Multifactorial traits --N2K
A. Coefficient of relatedness: The proportion of genes shared by two people related in a particular
way. Used to calculate heritability
B. Concordance: The percentage of twin pairs in which both twins express a trait
C. Empiric risk: The risk of recurrence of a trait or illness based on known incidence in a particular
population
D. Genome-wide association study: Detecting association between marker patterns and increased
risk of developing a particular medical condition
E. Heritability: The percentage of phenotypic variation for a trait that is attributable to genetic
differences. It equals the ratio of the observed phenotypic variation to the expected phenotypic
variation for a population of individuals
Body Weight
A. Body weight is a multifactorial trait that reflects energy balance (in the form of adipose tissue)
B. About 35.7% of all adults in the US are obese, and another 37.2 are overweight
C. Scientific studies use a measurement called body mass index (BMI)
D. =weight (kg)/height2 (m2) in meters N2K!!
E. Studies on adopted individuals and twins indicate a heritability of 75% for obesity
F. Lifestyle, including diet and exercise, are environmental or behavioral components impacting
weight
G. Genes influence hunger and metabolism (bacteria in gut increase metabolism)
N2K!
Leptin and Associated proteins:
A. Leptin is a protein hormone produced by fat cells- acts on the brain to decrease appetite
B. Ghrelin is a peptide hormone produced in the stomach- responds to hunger by increasing the
person’s appetite (ghrelin- growling)
C. N2K: PYY (pancreas peptide y), Insulin, Leptin, Ghrelin
D. These and other hormones are important for general weight regulation
E. TABLE 7.8??
Qualitative: either on or off (slide 3)
Over a spectrum- exp :skin color s 3
Loci- (plural place) 3
Height: toxins can harm, 5
Skin: karotene, 5
Fingerprint: contact with the uterus with the amniotic sac, 5
Behavioral: get zapped enough times decide not to do that, 5
Not frequency of mutations , 6
Dermato….. glyphic: writing
N2K numbers on slide 15 (greatest difference is .2%...racial characteristics difference .012%
Only one race-human race
N2K slide 23
P sparks the whole investigation –proband, 24
Stop 26