Exam 1 Flashcards
- Positive Eugenics
Encourage the ablest and healthiest people to have more children
- Negative Eugenics
Advocated culling the least able from the breeding population to preserve humanity’s fitness;
Defectives” should be prevented from breeding through means like:
Compulsory sterilization
Custody in asylums
Discuss at least one flaw in the research methods in the scientific origins of eugenics
Complex behavioral traits are hard to study with simple mendelian laws of inheritance and complex traits are often poorly defined
There was a tendency to treat the traits as if they were a single entity (not polygenic)
Describe one of the eugenics laws enacted in the United States
Virginia’s Eugenical Sterilization Act: Based off of Laughlin’s Model Eugenical Sterilization Law that authorized sterilization of “socially inadequte” (those who were “feeblminded”, “insane”, “epileptic”, “diseased”, “blind/deaf”, etc
Describe Ernst Rüdin’s role in psychiatric genetics and Nazi Germany’s policies
Rüdin’s work argued for the sterilization of people suffering from mental illness and was based on the idea that metal illnesses were inherited by passing down a single gene. When Hitler took office in Germany he pushed through: The Law to Prevent Hereditarily Sick Offspring by using forced sterilization, this idea was based on Rudin’s work in psychopathology.
Describe one finding suggesting significant environmental influences on IQ
Murray’s assertion that it is hard to raise the IQs of disadvantaged children leaves out the most important data point. Adoption from a poor family into a better-off one is associated with IQ gains of 12 to 18 points
Describe the two major theories of inheritance before Mendel
One parent (the male) contributes the majority of the inherited features in a child (ex: homonuculus theory)
Blended inheritance: the parental genes become mixed and are forever changed in the child (like if you were to mix blue and yellow to get green)
Describe the reasons Mendel was so successful
- He did matings within the same species
- Studied non-complex traits
- Looked at simple, quantatative traits
- Looked at traits with dominance
What are true breeding plants?
A true-breeding plant is one where it will always yield the same result when crossed with the same kind of plant
Ex: Peas with smooth seeds bred with other peas with smooth seeds the offspring will always have smooth seeds
What are F1 and F2 generations
F1: The F1 generation are the offspring of two true-breeding parents (two smooth seed true-breeding parents have offspring with smooth seeds)
F2: The offspring of the F1 generation
Mendel’s results when he crossed true breeding parents (resulting in the F1 generation), and self-fertilized the F1 generation (resulting in the F2 generation)
F1 generation with true-breeding parents: smooth(P1) x smooth(P2) = all offspring are smooth seeded
F2 generation: ¾ of offspring were smooth, ¼ were wrinkled
Showed us that there is dominance of a particular trait (smooth seeds in this case)
The two hypotheses Mendel came up with to explain his results from F1 and F2 generations
- Each parent has two alleles (can be either same or different), but transmits only one of the alleles to each offspring
- When an individual’s two alleles are different, one allele could dominate the other.
What is the difference between heterozygous and homozygous
Homozygous: Individuals with two same alleles
Heterozygous: Individuals with two different alleles
What is the difference between dominant and recessive
Dominant: A particular allele dominates (controls phenotypic expression) over another
Recessive: Need two copies of the allele for a phenotypic trait to be expressed
Name and describe Mendel’s first law of heredity
Law of segregation: States that there are two genes for a trait, offspring inherit one allele (copy of the gene) from each parent because the parent alleles separate during gamete formation and during fertilization the offspring has one allele from one parent and another allele from the other parent. One of these alleles can dominate another
Describe disease and inheritance pattern of Huntington’s Disease
Huntington’s disease: neurodegenerative disorder that general shows up in adulthood and affects males/females of all ethnic backgrounds
Inheritance pattern: Caused by a single gene and dominant allele (H), affected individuals are generally heterozygous because the H allele is rare it is unlikely both parents will pass on the dominant allele. Because the parent generally is heterozygous and usually only one parent is affected the risk for offspring with one affected parent is 50%
Describe disease and inheritance pattern of PKU
PKU: Affected individuals have a deficiency in Phenylalanine hydroxylase that results in the buildup of phenylalanine in the body. Too much build up can lead to toxic levels and cause brain damage (results in mental disability, movement disorders, etc.) Can be treated though by screening for it before birth and then avoiding foods containing phenylalanine (proteins, diet soda, etc.)
Inheritance pattern: Caused by a single gene and is recessive (requires two copies of the allele. If two parents are unaffected (but are carriers, meaning they each have a recessive allele) then the chance their offspring will get the disease is 25%
What is the difference between monohybrid cross and dihybrid cross?
Monohybrid: Mating between individuals that differ in only one trait (ex: mating between wrinkled and smooth seeded parents)
Dihybrid: Mating between individuals who differ in two traits (ex: yellow vs. green seed color AND wrinkled vs. smooth seeds)
Mendel’s results from his dihybrid crosses (F1 and F2 generations)
YYSS (true breeding dominant parent for yellow, smooth seeds) x yyss (true breeding recessive parent for green, wrinkled seeds)— NOTE: for the true-breeding parents yellow always come with smooth and green always with wrinkled
F1 generation: YySs (all offspring were yellow, smooth)
F2 generation: YySs x YySs: result was new recombinant types not seen in parental generation (new types: green, smooth and yellow, wrinkled)
What is the difference between parental types and recombinant types
Parental types: phenotypic combinations seen in the true breeding parents (i.e., the yellow smooth peas and green wrinkled peas)
Recombinant types: new phenotypic combinations not seen before in the true breeding parents (i.e., the yellow wrinkled peas and the green smooth peas)
Name and describe Mendel’s second law of heredity
Law of independent assortment – During gamete formation, different pairs of alleles segregate independently of each other.
Know the fact that Mendel’s second law of heredity is violated when genes for two traits are very close together on the same chromosomes
If genes influencing different (or same traits) are close together on the chromosome then during recombination they may always end up crossing over together just do to the fact they are close together.
How likely are recombinant types when two traits are caused by genes close together on the same chromosome?
Unlikely; if the inheritance pattern of a trait violates Mendel’s 2nd law then it is evidence that the genes are close on the same chromosome
What is phenotypic frequency and how to calculate
Proportion of individuals in a population that have a particular phenotype (e.g., a particular disease)
To calculate:need to know whether a disease is dominant or recessive, then need to know the number of individuals in a sample, then need to know the genotypes of those individuals, count the # of individuals who have a particular trait given their genotype
What is genotypic frequency and how to calculate
Proportion of total individuals in a population that have a particular genotype
To calculate: need to know whether a disease is dominant or recessive, then need to know the number of individuals in a sample, then need to know the genotypes of those individuals, count the # of individuals who have a particular genotype
What is allelic frequency and how to calculate
Proportion of all copies of a gene in a population that are of a given allele type
To calculate: need to know number of people in population, need to know their genotypes, then need to breakdown into each allele, then multiply each allele by the number of copies of each allele there is and divide by total number of alleles in population
EX:
R : 8 people with RR (16 copies) and
2 people with Rr (2 copies)
= 8+8+2 = 18/32 = .56
r : 2 people with Rr (2 copies) and
6 people with rr (12 copies)
= 2+6+6 = 14/32 = .44
Know why we’re interested in the Hardy-Weinberg equilibrium
Many inherited diseases result from disease-causing alleles that are recessive to the wildtype alleles (non-disease-causing allele) whose allele whose frequency is greater than 1%
Know the basics of Hardy-Weinberg equilibrium – i.e., what p and q stand for, the two formulas (p+q = 1; p2 + 2pq + q2 = 1), and the frequency of different kinds of individuals (homozygous dominant, heterozygotes, and homozygous recessive)
- p= the frequency of dominant alleles; the chance that any particular egg or sperm has the dominant allele
- q= the frequency of recessive alleles; the chance that any particular egg or sperm has the recessive allele
- p+q= 1
- p2= frequency of offspring with two dominant alleles (homozygous dominant)
- q2 = frequency of offspring with two recessive alleles (homozygous recessive)
- 2pq= Probability of the heterozygous genotype (heterozygous)
- p2+ 2pq + q2= 1 ; The frequency of the offspring genotypes
- EX: Frequency of PKU individuals (homozygous recessive) in the population is 1/10,000 = q2= .0001
o this means q = .01
o p + q = 1
o p + .01 = 1
o p = .99
o Frequency of individuals who are carriers for PKU (heterozygous)= 2pq = 2 ( .99) (.01) = .02
What is incomplete dominance
The F1 generation resembles neither purebred parent (blended)
Ex:
True-breeding red flowers (AA) x True-breeding white flowers (aa)
F1 generation= Aa= Pink flowers (intermediate phenotype for heterozygotes)
Easy way to tell ratios is that the phenotypic ratio is an exact reflection of genotypic ratios
What is codominance?
F1 generation resembles both true-breeding parents
Ex: Lentils
True-breeding spotted lentils (SS) x True-breeding dotted lentils(ss)
F1 heterozygous generation= Ss= both spots and dots for the heterozygote intermediate genotype
Know the examples involving more than 1 allele we discussed (e.g., human blood types) and be able to complete Punnett squares involving these traits
Blood type has 3 possible alleles (BUT EACH PERSON ONLY HAS TWO ALLELES)
IA= dominant over i and results in adding sugar A to blood (blood type A)
IB= dominant over i and results in adding sugar B to blood (blood type B)
i= recessive and results in carrying neither sugar (blood type O, universal donors)
IAIB= codominant such that an individual with this genotype carries both A and B sugar (can receive either A or B blood type)
What are mutations? What is the difference between monomorphic and polymorphic?
Mutations – chance alterations of genetic material; Arise spontaneously in nature and lead to new alleles. Once they occur in gametes they then get inherited and passed down to other generations
- Monomorphic: Gene with one wild-type allele
- Polymorphic: Gene with more than one wild-type allele
What is pleiotropy?
Pleiotropy – phenomenon of a single gene determining a number of distinct and seemingly unrelated characteristics (Ex: Mendel noticed that specific seed coat colors are always associated with specific flower colors)
What is epistasis?
Example with Labrador coat colors
Epistasis – A gene interaction in which the effects of an allele at one gene hides the effects of alleles at another gene
Bb or BB: B dominant to b = black coat
bb: recessive = brown coat
Second gene (E or e)
EE or Ee= no effect
ee= overrides what is happening at b/B locus and = yellow
This is an example of recessive epistasis
What is complete penetrance? Incomplete penetrance?
Complete penetrance: 100% of population with a particular genotype show the expected phenotype
Ex: Huntington’s disease
Incomplete penetrance - < 100% of population with a particular genotype show the expected phenotype
Ex: Retinoblastoma (75% penetrance)
What is expressivity? Varying expressivity? Unvarying expressivity?
Expressivity: the degree or intensity with which a particular genotype is expressed in a phenotype
Varying:the degree or intensity with which a particular genotype is expressed in a phenotype differs in the population
Ex: retinoblastoma
Unvarying:the degree or intensity with which a particular genotype is expressed in a phenotype does not differ in the population
Ex: pea color
What are the factors that contribute to expressivity?
Modifier genes: alter the phenotypes produced by the alleles of other genes
Ex: mouse tail lengths. Mutant allele makes tail short, but not all mice have same amount of shortness because there is a modifier gene that affects how short it gets
Environmental effects on expressivity:
Ex: alleles that account for dark coat color in cats; “Siamese” allele for coat color produces enzyme that doesn’t function at normal body temperature, so dark pigment only happens in cat’s extremities (dark extremities and light body color)
Chance and expressivity: Some people are less affected just by chance (ex: retinoblastoma only affecting one eye)
What is a phenocopy?
A change in phenotype arising from environmental agents that mimics the effects of a mutation in a gene (not heritable because they do not arise from a change in a gene)
Ex: A sedative called “thalidomide” was being taken by pregnant women and mimicking the effects of a rare dominant trait called phocomelia where limb development is interrupted
Know what the frequency of the disorder is for males and females when the allele frequency is known
Ex: If a disorder is X-linked recessive and frequency of disorder= 10%
Expected frequency of disorder in males= 10%, same as disease frequency
Expected frequency of disorder in females= 10% squared (0.1)2= frequency of disorder squared because they need two alleles that are disordered to get the disease (females have two X chromosomes)
What is nondisjunction? Be able to discuss the examples of nondisjunction we discussed in class
Nondisjunction: failure to apportion the chromosomes equally
Ex 1: Down syndrome- 3 copies of chromosome 21 and is consider trisomy (where there are three, instead of two, copies of a chromosome)
Ex 2: Turner syndrome- example of monsomy (only one copy of a chromosome) and occurs when only one sex chromosome is inherited (XO)— leads to learning problems, people are unusually short, infertile
Ex 3: Klinfelter syndrome: another example of trisomy, but in the sex chromosomes so inherits an extra X (XXY)—leads to learning problems, unsually long limbs, infertile
Why is Down syndrome is more common for children of older mothers?
More common because all female eggs are present at birth, but undergo the last step of cell division each month. Older eggs are then more prone to errors in cell division
What are expanded triplet repeats? What are examples of this discussed in class?
A special form of mutation that involves repeat sequences of DNA
Ex 1: Huntington’s disease: most cases are caused by a repeat sequence of three nucleotide bases, CAG, on chromosome 4
CAG codes for glutamine and this repeat sequence leads to a greater number of glutamines in the middle of a protein
Most people have a repeat sequence at this location of about 11-34
People with Huntington’s disease have a repeat of more than 40 copies of this CAG sequence
Note: expanded triplet repeats are unstable and often increase in subsequent generations make the disease progression faster or earlier onset
Ex 2: Fragile X syndrome: Expanded triplet repeat on the X chromosome that makes the X chromosome fragile. It is more common in males than females, but doesn’t follow traditional X-linkage inheritance patterns because it is do to an expanded triplet repeat, which are often unstable and increase in subsequent generations
A parent with the fragile X expanded triplet repeat may not show signs of mental retardation because they may only have 40-200 copies of triplet repeat.
However, because it is unstable the repeats increase in subsequent generations so offspring may get 200+ copies of this repeat sequence and that does manifest as mental retardation
What is premutation?
When a parent produces expanded repeats that don’t cause an effect (like mental retardation) in their offspring, but then that repeat is unstable and expands further in the offspring’s offspring (and they then have mental retardation)
What is a morbidity risk estimate?
Morbidity risk estimate: Chance of being affected (having a particular disease) during entire lifetime
Be aware of examples of complex traits we discussed in class
- Schizophrenia
- Pea size
- Height
How can multiple genes acting in accordance to Mendel’s laws lead to a complex trait?
Each gene of a polygenic trait is inherited according to Mendel’s laws
But the alleles don’t act in a totally dominant or recessive manner and are additive, where each allele contributes something to the phenotype.
This then leads to continuous variation at the phenotypic level (many varying degrees of a phenotype due to each alleles contribution)
Know the basics of a liability-threshold model
Assumes that the risk for a disorder is normally distributed (due to the additive nature of complex traits), however, most people are below the “threshold” where the disorder occurs
Those who are related to someone with a disorder increase their liability and thus move their distribution curve further to the right
What is DNA?
Deoxyribonucleic acid and is responsible for heredity
What are the four bases in DNA?
- C: Cytosine
- G: Guanine
- T: Thymine
- A: Adenine
Which bases pair together in DNA?
- C and G
- T and A
What are the two functions of DNA?
- Replication
- Synthesis of proteins
Know the steps involved in the replication of DNA
- Occurs during cell division
- DNA double-helix unzips forming two single strands with exposed nucleotide bases
- The now exposed nucleotide bases (that were previously paired) attract their complementary pairs (ex: C attracts G and T attracts A)
- Now you have two double-stranded DNA helices where there was previously one
Know the steps involved in the synthesis of proteins
- Transcription: turns DNA into RNA or mRNA (messenger RNA)
- Translation: mRNA turns the sequence into amino acids and then into proteins
Know steps involved in transcription
DNA double helix unzips and then copying occurs to mRNA which is similar to DNA replication, however, the mRNA strand formed is single-stranded and any thymine gets substituted for a uracil (so all adenines are paired with uracils on mRNA)
Newly formed mRNA strand now leaves the nucleus and enters the cytoplasm and binds with ribosomes where the translation process will occurs
Know steps involved in translation
a. In the ribosome there is a strand of mRNA that is waiting for transfer RNA (tRNA) to come in
b. tRNA enters the cell and has a complementary code of three nucleotides that bonds to the complementary code of three nucelotides in the mRNA
i. The three nucleotide bases on mRNA are called codons
ii. The complementary three nucleotide bases on tRNA are called anticodons
c. The tRNA sequence also has its associated amino acid
d. The ribsome then moves along the mRNA strand while tRNA pieces (and associated amino acids) come in to bond to the complementary bases in the mRNA
e. Once the tRNA anticodon bonds to the complementary mRNA codon it adds its associated amino acid to a growing chain of polypetides (these are what make up a protein)
i. Proteins are generally made up of polypetide chains that are 100-1000 amino acids in length
ii. The order of the amino acids determines the shape and function of the protein
Know the “central dogma” of molecular genetics
- Genetic information flows from DNA to mRNA to protein
- A gene is a DNA segment that is a few thousand to several million base pairs in length
- A DNA molecule contains a linear message of four repeating bases (A, T, C, G)
Understand the difference between DNA, mRNA, and tRNA
- DNA: Contains 4 bases: C, G and A,T ; double-stranded; encodes the sequence to make up amino acids
- mRNA: messenger RNA; 4 bases C, G and A, U (uracil); single-stranded, mRNA leaves the nucleus where DNA lives to allow for translation of genetic sequence into amino acids
- tRNA: transfer RNA; only three bases and these three bases are complementary to three on mRNA; transfer RNA contains its associated amino acid that it then transfers to the ribosome (where the amino acids are assembled into polypeptide chains that make up proteins)
Know what codon and anticodon are
Codon: all 20 amino acids are specified by a list of three sequential mRNA bases (A, C, U, G). This list of three sequential mRNA bases are what is called a codon
Anticodon: each mRNA codon attracts its complementary anticodon that is on the tRNA. This pairing allows the amino acid associated to detach from the tRNA and add to the polypeptide chain
Know the difference between introns and exons
Introns: Pieces of a gene that are transcribed into mRNA, but are spliced out before the mRNA leaves the nucleus
o Vary in length from 50-20,000 base pairs
o Can help regulate transcription of other genes
Exons: Pieces of a gene that are transcribed and spliced together after removing introns. The exons are the code of mRNA that exits the nucleus and gets translated into proteins
o Usually only a few hundred base pairs
Know what alternative splicing is and its role in biological complexity
During the process of removing introns and reassembling exons the combinations of mRNA code can vary and be spliced into different combinations of exons which in turn translate into different amino acid combinations and different proteins
This is necessary to form the complexity of proteins we have with just four nucleotide bases
Know the general characteristics of the human genome – e.g., number of base pairs, number of genes, number of base pairs in genes
- Number of base pairs in human genome: 3.2 billion
- Number of genes in human genome: 21-25 thousand
- 1000 to 2 million base pairs per gene
Know what the three main surprises of the human genome project were
- The majority of the human genome consists of non-coding regions (don’t code for proteins)
- Humans have a small number of protein-coding genes (21-25 thousand compared with rice that may have 37 thousand)
- We share 98% of our DNA with chimpanzees and 99.9% with other humans
Know the different kinds of genetic variation across individuals
- Sequence: Different nucleotide at a given position in the genome
- Structure
Insertions (small number of DNA bases that has been inserted)
Deletions (small number of DNA bases that has been deleted)
Copy number variants (>1000 bases that has been deleted or inserted)
Duplication: piece of DNA that is duplicated - Organization
Inversion: a piece of chromosome that is inverted
Translocation: pieces of non-homologous chromosomes (like chromosome 4 and 20) that exchange info so a piece of chromosome 4 is now on 20 and vice versa
Know what mutations are
Occurs when there is a mistake in copying DNA and result in polymorphisms that lead to different alleles of a gene
Know the characteristics of human chromosomes (e.g., number, sex vs. autosomes, parts of chromosomes) and those of other species (examples we discussed)
Humans have 23 chromosomes
22 autosomal chromosomes
2 sex chromosomes (an X and X or X and Y)
Each chromosome has a short p arm and and longer q arm that are joined at the centromere
Number of chromosomes varies widely with fruit flies having 4, dogs 39, carp 52
Know the difference between gametes and somatic cells
- Gametes: sex cells, like egg and sperm
- Somatic cells: all other cells
