Exam 1 Flashcards
Define Genetics
The study of genes/heredity/ and genetic variation (in living organisms)
characteristics of model organisms
short generation time, production of numerous progeny, ability to vary out controlled genetic crosses, ability to be reared in a laboratory environment, availability of numerous genetic variants, already have an accumulated body of knowledge about their genetic systems
Prokaryotes
no membrane bound nucleus or organelles, relatively small, (usually) one circular DNA molecule with NO histones, DNA is organized in a nucleoid region (but no nucleus)
How do prokaryotes replicate?
binary fission
Eukaryotes
has a nucleus, relatively large, multiple linear DNA molecules and have histones, has membrane-bound organelles
Organization of Eukaryotic DNA
tightly packed into linear chromosomes which are further organized into chromatin (DNA wrapped around histones)
Viruses
are composed of proteins as the outer coat and nucleic acid inside (they are not PRO or EUK)
Diploid unreplicated chromosomes
a haploid product of meiosis would only contain ONE of these unreplicated chromosomes. Let’s say the grey one is from mom and the black one is from dad; the products of meiosis will only have 1 (mom’s chromosome OR dad’s, not both (unless nondisjunction occurs))
Diploid replicated chromosomes
Nondisjunction in Meiosis 1
Nondisjunction in Meiosis 2
Karyotype
visual display of an individual’s chromosomes
Genotype
the set of alleles in an individual organism
Phenotype
the observable characteristics in an individual (when one allele gets expressed over the other, we see it in the phenotype)
Gene
Genetic factor that helps determine a trait
Allele
a different form of a gene
Locus
a specific place on a chromosome where an allele takes place
Homologous chromosomes
chromosomes with the same genes (but can have different alleles). One chromosome in each homologous pair is from the mother, and one is from the father.
Which phase in Interphase does the DNA get replicated? G1, S, or G2?
S (synthesis)
In which phase do the homologous chromosomes meet up?
Only in Prophase 1 of meiosis
In which phase do the homologous chromosomes separate?
Only in Anaphase 1 of meiosis
In which phase do the sister chromosomes separate?
In Anaphase of Mitosis, and in Anaphase 2 of Meiosis (the cohesion protein holding them together had to break down in order for the sister chromatids to separate)
Products of Mitosis
produces two cells that are genetically identical to each other (and to the parent cell)
Products of Meiosis
Produces haploid gametes that are genetically different from the original cell (and from each other)
In which phase of Meiosis can crossing over occur?
In prophase 1 of Meiosis (the homologous chromosomes meet up with each other only in prophase 1 of meiosis 1 until the get pulled apart in anaphase 1)
What type of chromatids can crossing over occur in?
Crossing over can only occur between non-sister chromatids
Concept of Independent Assortment
Genes on non-homologous chromosomes will line up independently of each other (for example, chromosome 1 (who contains the alleles A and a) and chromosome 2 (who contains the alleles B and b) will line up at the metaphase plate anywhere regardless of each other)
Law of segregation
The alleles separate (in anaphase 1 of meiosis) as they into the two new cells and form gametes
If an individual has the genotype AaBb for a dihybrid cross, what are that individual’s gametes?
AB, Ab, aB, and ab
If an individual has the genotype Aabb for a dihybrid cross, what are that individual’s gametes?
Ab and ab
If an individual has the genotype aabb for a dihybrid cross, what are that individual’s gametes?
ab only
If we crossed the AaBb and the aabb, how would we set up the Punnett square?
Probability, Multiplication Rule;
When crossing AaBbcc x aabbcc, what is the probability of getting aabbcc?
Probability, Multiplication Rule;
When crossing AaBbcc x Aabbcc, what is the probability of getting aabbcc OR A_B_cc?
the underscore means the second allele can be uppercase or lowercase
Set up the following problem with the formula P = (n!/s!t!)(p^s)(q^t)
In a family of 5 children, what is the probability of getting 5 boys and 0 girls?
Set up the following problem with the formula P = (n!/s!t!)(p^s)(q^t)
In a family of 5 children, what is the probability of getting 2 boys and 3 girls?
Reasons Gregor Mendel chose to study heredity on pea plants
Research already showed pea plant hybrids could be produced, there are many pea plant varieties available, pea plants are small and easy to grow, they can self-fertilize and cross-fertilize
Heterozygote
when an individual possesses two different alleles at a locus (on locus xyz of the maternal chromosome they have the dominant version of that allele, while at the same locus xyz of the paternal chromosome they have the recessive version of that allele)
Homozygote
when an individual possesses two of the same alleles at a locus
If you crossed two individuals with the genotype Bb, what is the probability that the progeny with the black fur will be homozygous for that allele? (B = black fur, b = gray fur)
Is the following Drosophila male or female?
Sex-chromosomes: XX Haploid sets of Autosomes: AA
Female (2 X’s / 2 A’s = 2/2 = 1.0 ratio; female)
Is the following Drosophila male or female?
Sex-chromosomes: XY Haploid sets of Autosomes: AA
Male (1 X / 2 A’s = 2/2 = 0.5 ratio; male)
Is the following Drosophila male or female?
Sex-chromosomes: XXY Haploid sets of Autosomes: AA
Female (2 X’s / 2 A’s = 2/2 = 1.0 ratio; female)
Is the following Drosophila male or female?
Sex-chromosomes: XX Haploid sets of Autosomes: AAA
Intersex (2 X’s / 3 A’s = 2/3 = 0.67 ratio; female)
What genetic condition does the following pair of sex chromosomes lead to?
XO (O = no chromosome)
Turner syndrome (this individual is a female, every human needs at least ONE X to survive)
What genetic condition does the following pair of sex chromosomes lead to?
YO
This individual would die since they have zero X chromosomes
What genetic condition does the following pair of sex chromosomes lead to?
XXY
Klinefelter syndrome (the individual is a male since they have the Y chromosome (which contains the SRY gene (ASSUMING that the SRY gene was not mutated off of the Y chromosome) The SRY gene is the male-determining gene)
What genetic condition does the following pair of sex chromosomes lead to?
XXX
Poly-X female (this individual is a female)
What genetic condition does the following pair of sex chromosomes lead to?
XYY
Jacob’s syndrome (this individual is a male)
Sex-linked genes
Genes located on sex chromosomes (males are hemizygous for these genes since they only have one X (XY))
If a mother is heterozygous for the color blind allele (X+Xc) and the father is not color blind (X+Y), what are the chances of their daughter being color blind? (the colorblind allele is recessive)
P(XcXc) = 0
because the daughter has to get an X from mom and dad, and dad does not have the colorblind allele
If a mother is heterozygous for the color blind allele (X+Xc) and the father is not color blind (X+Y), what is the chances of their daughter CARRYING the blind allele? (the color blind allele is recessive)
Dosage Compensation
Because females have two X chromosomes and the dosage of proteins in males vs females needs to be equal, females have random X-inactivation. The sex-linked genes need to be balanced between males and females. So, on one of the X’s in females, about all but 15% of the genes get inactivated. X-inactivation is random (and it happens after the zygote forms and splits into twins), that’s why twins have different spots of X-inactivation on their body.
Barr bodies
When one of the X sex chromosomes gets inactivated, it becomes a barr body. All except 1 X will be inactivated.
If an individual has the sex chromosomes XX, how many barr bodies will they have?
1
If an individual has the sex chromosomes XY, how many barr bodies will they have?
0
If an individual has the sex chromosomes XXY, how many barr bodies will they have?
1
If an individual has the sex chromosomes XYY, how many barr bodies will they have?
0
If an individual has the sex chromosomes XO, how many barr bodies will they have?
0
Complete Dominance
When the heterozygote child completely represents the homozygous dominant parent
Incomplete Dominance
When only one of the alleles in the heterozygote is expressed, but the child does not completely resemble either parent because that one allele isn’t being fully expressed
Codominance
When the heterozygote displays phenotypes from both homozygotes
(When one parent has blood type A (IAIA), and the other is type B (IBIB), the child will be type AB (IAIB); the child is expressing both alleles from both homozygote parents)
Penetrance
the % of individuals with a particular genotype that express the expected phenotype.
Example: if there is 70% penetrance, and 50% of the progeny have genotype XYZ, then 70% of those 50% will express gene XYZ and it will show up in the phenotype.
*(If we have 100% penetrance, then we get 100% of what we expect of the Mendelian ratio)
Lethal alleles
An allele that causes death if the individual is homozygous for the lethal allele. The lethal phenotype is recessive because you NEED two of the lethal allele for the individual to be affected and die. The individuals who are heterozygous for the lethal allele are safe. (In the example below, the lethal allele is ‘y’)
Epistasis
when one gene masks the effect of another gene
Epistatic gene
the gene that does the masking
Hypostatic gene
the gene whose effect is masked
Recessive epistasis
only masks the effect of another gene when there are two copies of the epistatic allele
Dominant Epistasis
only a single copy of the epistatic allele is required to mask the phenotype of the hypostatic gene
We cross an individual with type IAiHh blood to an individual with type IBihh. (The Bombay blood group is epistatic and when the gene is recessive (hh), the other gene (blood type) gets masked and becomes blood type O). What is the probably the progeny will be blood type O?
Complementation test
determines whether mutations are at the same locus or not
mutations in the same gene = “fail to complement”mutations at a different locus = “complement each other”
Sex-influenced characteristics
autosomal genes (not located on a sex chromosome/ not a sex-linked gene) that are expressed differently in males vs females (then gene for beards on goats is expressed stronger in males than females)
Sex-limited characteristics
Autosomal genes only expressed in one sex (both gender mammals have the genes to lactate, but only female mammals express this gene)
Genetic Maternal Effect
Phenotypes of the offspring that are determined by the genotype of the mother
Continuous Characteristics
continuous distribution of phenotypes; phenotype is determined by interaction of many genes. (many genes feeding into one trait)
Pleiotropy
One gene affects/causes multiple characteristics
Temperature-sensitive allele
an allele whose product is only functional at a certain temperature
Pedigree
Pictorial representation of a family history that outlines inheritance of characteristics
Proband
The person from whom the pedigree is initiated
(pedigree mode of inheritance) X-linked Dominant Traits
Every affected individual on the pedigree has AT LEAST one affected parent
The affected males have only affected daughters and unaffected sons (because the affected father passes on the Y chromosome (which un unaffected) to the sons, and passes on his affected X chromosome to his daughters)
(pedigree mode of inheritance) Autosomal Dominant Traits
Every affected individual on the pedigree has AT LEAST one affected parent
The affected males DO NOT have only affected daughters and unaffected sons (this trait is not linked to a sex chromosome, so both gender children have an equal chance of being affected)
(pedigree mode of inheritance) X-linked Recessive Traits
Every affected individual does not have to have an affected parent (there can be a generation skip, where that generation is totally unaffected (but that doesn’t mean they are not carriers))
There are more affected males than females (males only have one X chromosome (rather than two), so they are much more likely to be affected than females who have two X chromosomes)
(pedigree mode of inheritance) Autosomal Recessive Traits
Every affected individual does not have to have an affected parent (there can be a generation skip)
Both genders of the progeny are about equally affected; the males are not more affected than the females (this trait is not linked to a sex chromosome, so both gender children have an equal chance of being affected)
(pedigree mode of inheritance) Y-Linked Traits
Only males are affected AND an affected father will ALWAYS have an affected son (if he has a son)
