Genetics Flashcards
What were the 4 reasons that Gregor Mendel chose pea plants as his organism of choice for his experiments?
- There are many varieties with distinct characters or traits.
- Mating of the plants can be controlled.
- Each pea plant has sperm and egg producing organs.
- Cross-pollination can be achieved by dusting one plants pollen to another.
What is a character? How is this different from a trait?
A heritable feature that varies among individuals. Such as flower color.
A trait is each varient of a character, such as purple or white flower color.
What were two critical components of Mendels experimental paradigm?
Only true-breeding varieties of pea plants were cross pollinated.
Only characters that varied in an “either-or” manner were were tracked (EITHER purple OR white).
What is meant by something that is true-breeding?
Plants prduce offspring of same variant (trait) when they self-pollinate.
In Mendels experiment, for pea plant color, what were the two parents in the P generation considered to be? What did they create in the F1 generation after being cross-pollinated?
What was done with the F1 generation after it was produced and what was the outcome?
Both parents were true-breeds of either trait, example is one being true-bred white and other being true-bred purple in color. The offspring created were an F1 generation of hybrid plants that were all purple in color in this case.
The F1 generation was self-pollinated, creating the F2 generation. The outcome was a 3:1 ratio of purple to white plants. This ratio was found in other “either-or” traits examined by creating F2 generation using same process.
What was concluded after the P generation (true-purple and true-white) was cross-pollinated to form the F1 generation that was all purple?
Purple was the only thing affecting flower color for that generation, therefore dominant trait and white was recessive.
What Mendel called a heritable factor we now call what?
gene
What were the four concepts that are described that make make up MEdels model?
- Alternative versions for genes account for variations in inherited characters.
- For each character, an organism inherits two copies (two alleles) of a gene, one from each parent.
- If the two alleles at a locus differ then the dominant allele determines the appearance and the other recessive allele has no affect on the organisms appearnace.
- The law of segregation: two allels for a heritable character segregate (separate) during gamete formation and end up in different gametes.
Describe the first concept of Medels model (alternative versions of genes account for variations in inherited characters) in relation to plant color. What are these alternative versions called? What is the specific location at which a gene resides called?
Example: The gene for flower color in a pea plant exists in two versions (purple or white)
These alternative versions are called alleles.
Locus
Describe the second concept related to Mendels model (for each character an organism inherits two alleles, one from each parent).
The two alleles at a locus on each chromosome may be identical. Like in the true-breeding plants of the P generation in mendels experiment.
These alleles also may differ, like in the F1 hybrid of the medel experiment.
THIS DEDUCTION WAS MADE BEFORE KNOWING ABOUT CHROMOSOMES
Describe the way the allele for purple color vs white color works at a molecular level.
Purple allele - codes for enzyme to be synthesized that produces the purple pigment. .
White allele - a change in one base pair changes the amino acid sequence of protein so enzyme that makes purple pigment is not produced, making white color.
If a breed is a hybrid, is it always the case that if only one dominant allele is present that it will show the trait as the true-bred dominant (2 dominant allele)? For example: the fact that a true-bred dominant pea plant (purple) can’t be distinguished from the hybrid purple.
NO, sometimes only having one allele expressing the dominant trait will result in a different physical appearnace.
Describe the third concept for mendels model (if two alleles at a locus differ, then one (dominant) allele determines appearnace and the other (recessive) has no effect) with an example.
In the F1 generation of pea plants, all of the plants were purple in color because purple is the dominant trait.
Describe the 4th concept of Mendels model, known as the LAW OF SEGREGATION. How is it decided where each allele will go during gamete formation?
Two alleles for an inheritable characteristic are separated during gamete formation and end up in different gametes.
Meaning a sperm or egg gets only one of the two alleles present in the somatic cells of the organism that created them.
The separation of alleles is determined based on the distribution of homologous chromoses in meiosis. Specifically during meiosis I.
How can we determine the possible combinations of a sperm and an egg? What must we know first?
Punnett square
we must know their genetic makeup first.
What In a punnett sqyare, what represents a dominant allele and what represents a recessive allele?
Dominant - capital letter
Recessive - lower-case letter
What would you consider an organism to be if it had two identical alleles for a character? Example?
Homozygous
PP or pp
What would you consider an organism that has two different alleles for a character? Example?
Heterozygous
Pp
Which are true-breeding, homozygous or heterozygous?
Homozygous
Can you always tell the genetic composition just based off of its appearance? Why or why not? Example?
NO, because of the different effects of dominant and recessive alleles.
Purple: can either be PP or Pp. two separate compositions.
Given that appearance doesn’t equate to genetic composition in all cases, how are these two things distinguihed in genetics?
Phenotype: appearnace of organism (purple pea plant).
Genotype: genetic composition (PP or Pp for pruple pea plant)
A plant with one phenotype may have different genotypes, while the same genotype will result in the same phenotype.
How would you determine the genotype of an individual with the dominant phenotype?
Perform a testcross
What is a testcross? Why do we do this? How do you interpret the results?
This is when a individual with the domminant phenotype is bred with an individual that is homozygous recessive.
this is done to figure out the genotype of that individual, whether or not it is homozygous dominant or heterozygous dominant.
If any offspring display the recessive phenotype then the individual is heterozygous dominant.
How was the law of segregation derived?
Following a single character.
What is a monohybrid? What is an example of this?
Individuals that are heterozygous for one character.
The F1 offspring in mendels pea plant color experiment.
How does a dihybrid cross ACTUALLY work and what ratio results? Describe the difference between the hypothesis of dependent-assortment and the independent assortment hypothesis that were created before the expermient was carried out by mendel.
SEE PICTURE: 9:3:3:1
Dependent assortment hypothesis: Dominant allele and recessive allele for each character follows each other as a package. creating same 3:1 as monohybrid
Independent assorment: Each allele for each character are independent of one another
INDEPENDENT ASSORTMENT HYPOTHESIS PREVAILED
Describe the multiplication rule. Use the probability of a coin toss landing tails twice.
probability of landing tails: 0.5 (1/2)
Probability of landing tails twice: 0.5 (1/2) x 0.5 (1/2) = 0.25 (1/4)
So for a heterozygous plant, EACH GAMETE has a 0.5 chance of carrying dominant allele and a 0.5 chance at carrying recessice allele.
How does the addition rule differ from the multiplication rule? Define mutually exclusive.
Addition rule looks at mutually exclusive events and states they occur by ADDING together their individual probabilities.
mutually exclusive meaning that two events that happen independently of each other and result in same combination.
Look at this picture and see the two ways a heterozygote can be formed, received one of each allele from each parent in two combination. Each combination is a mutually exclusive event. So by adding the probability of each you have the total probability of getting a heterozygote from this picture. 1/4 + 1/4 = 1/2 (0.5)
What are the three types of dominance that are a part of the spectrum of dominance?
Complete dominance - phenotype of heterozygote and dominant homozygote are identical.
Codominance - two dominant alleles that affect the phenotype in separate distinguishable ways.
Incomplete dominance - the phenotype of F1 hybrids is somehwere between the phenotypes of the two parental varieties. Like for snadragon color: CrCr (red) and CwCw (white) are both homozygous and are incompletely dominant, when these produce the F1 generation they are CrCw (pink) whihch is between the two parental varieties.
Do genes exist that have more than two alleles? What example does the book give?
YES.
ABO blood typing: SEE PICTURE
What is epistasis? What example is given in the book?
A gene at one locus alters the phenotypic expression of a gene at a second locus.
In mice and other mammals their coat color depends on two genes.
For mice: B (black) and b (brown) are for pigment color and C (pigment) and c (no pigment) control presence of pigment. The gene for pigment is epistatic to the gene for black and brown pigment.
What is meant by the fact that quantitative variation is indicative of polygenic inheritance? What is polygenic inheritance?
Polygenic inheritance - an additive effective of two or more genes on one phenotype (basically the opposite of pleiotropy)
A more simple story in the book covers skin color: 3 genes each have a dark-skin allele (A, B, and C) and is incompletely dominant to the other alleles (a, b, and c).
So these 3 genes all effect this one phenotype and are incompletely dominant, meaning unique mixtures of these genes alleles will make a unique skin color (quantitative variation)
SEE PICTURE
What is a pedigree analysis?
This is when scientists collect information about the family history for a particular trait and make a family tree describing the traits of parents and children across the generations, known as the family pedigree. SEE PICTURE (dominant widows peak allele).
Make sure you know the key for a family pedigree. See the picture in next slide.
