16: Inheritance of Genetic Information I Flashcards
Module 3, Lesson 5
The first detailed experiments on genetic inheritance were performed by…
Gregor Mendel
Mendel’s experiments used ____ plants.
Pea
List three reasons why Mendel used pea plants for his experiments.
- They have multiple traits
- They are small and easy to grow
- They can either cross-fertilize or self-fertilize
Why was it important that pea plants can either cross-fertilize or self-fertilize?
This enables plant mating to be closely controlled
Mendel’s initial experiments used the ____ experimental design.
Monohybrid cross
Mendel’s ____ exhibited true-breeding strains of two variations of interest.
Parent variation
In order for a parent to be “true-breeding”, all its offspring must…
Exhibit the trait of interest
Mendel’s ____ were created by cross-fertilizing the true-breeding parents.
F1 generation
What percentage of the F1 generation exhibited the dominant trait (purple flowers)?
100%
Mendel’s ____ was created by self-fertilizing the F1 plants.
F2 generation
True or false:
All of the F2 plants exhibited the dominant trait (purple flowers).
False
What percentage of the F2 plants exhibited the dominant trait?
75%
What percentage of the F2 plants exhibited the recessive trait (white flowers)?
25%
Mendel’s ____ were created by self-fertilizing the F2 plants.
F3 generation
True or false:
The F2 and F3 generations had the same ratio of dominant-to-recessive phenotypes.
True
What percentage of the recessive F2 plants were true-breeding?
100%
What percentage of the dominant F2 plants were true-breeding?
33%
(one-third)
What percentage of the F2 plants were not true-breeding?
66%
(two-thirds)
The F2 plants had a phenotype ratio of 3:1 but a genotype ratio of…
1:2:1
(one true-breeding dominant,
two not true-breeding dominant,
one true-breeding recessive)
Today, we call the “true-breeding” plants…
Homozygous
Today, we call the “not true-breeding” plants…
Heterozygous
List the two main conclusions Mendel came to from his initial experiments.
- Parents transmit discrete factors to their offspring
- A gene may have different variations called alleles
We now know that the “discrete factors” Mendel identified are…
Genes
An organism with two copies of the same allele is…
Homozygous
An organism with one copy of the dominant allele and one copy of the recessive allele is…
Heterozygous
The total set of alleles an organism contains make up its…
Genotype
An organism’s physical appearance is its…
Phenotype
True or false:
Two organisms with different genotypes can have the same phenotype.
True
The principle of segregation states that…
Each individual receives one copy of each allele from each parent because the chromosomes segregate during meiosis
True or false:
Mendel knew about chromosomes and meiosis when he developed his theories.
False
When writing a Punnett square, a capital letter (“P”) represents a ____ allele.
Dominant
When writing a Punnett square, a small letter (“p”) represents a ____ allele.
Recessive
True or false:
The offspring of homozygous parents will always be heterozygous.
True
Each parent can only give its offspring one kind of allele.
Each parent donates ____ allele(s) to each individual in the new generation.
One
Each box of a Punnett square shows the offspring’s…
Genotype
The left and top edges of a Punnett square represent…
Haploid parent cells
The boxes in a Punnett square represent the…
Diploid offspring cells
List the possible genotypes of offspring of parents whose genotypes are both Pp.
One PP
Two Pp
One pp
A ____ experimental design follows the behavior of two different traits in a single cross.
Dihybrid cross
What question was Mendel aiming to answer with his dihybrid cross experiments?
Do different traits behave independently in hybrids?
Organisms that are doubly heterozygous (heterozygous for two different traits) are called…
Dihybrid
Mendel’s dihybrid parent generation was ____ for both traits.
Homozygous
Which two traits was Mendel observing in his dihybrid cross experiments?
The shape and color of pea plants’ seeds
Mendel’s dihybrid ____ generation were doubly heterozygous.
F1
What percentage of Mendel’s dihybrid F1 plants had seeds that were yellow and round?
100%
If each trait behaves independently during a dihybrid cross experiment, ____ different types of gametes should be produced.
Four
Plants in Mendel’s dihybrid ____ generation had one of ____ possible phenotypes.
Four
What was the ratio of phenotypes in Mendel’s dihybrid F2 plants?
9:3:3:1
What fraction of F2 dihybrid plants had round and yellow seeds?
9/16
What fraction of F2 dihybrid plants had round and green seeds?
3/16
What fraction of F2 dihybrid plants had wrinkled and yellow seeds?
3/16
What fraction of F2 dihybrid plants had wrinkled and green seeds?
1/16
The results of Mendel’s dihybrid cross experiments ____ the idea that each allele behaved independently.
Supported
The principle of independent assortment states that…
The segregation of different allele pairs is independent
Why is the segregation of allele pairs independent?
Different homologous chromosomes align independently during metaphase 1 of meiosis.
In humans, it is often more practical to use ____ instead of Punnett squares.
Pedigrees
List three reasons why pedigrees are often more practical than Punnett squares for humans.
- Humans tend to have fewer offspring
- Humans are highly selective about mate choices
- Most of our knowledge of human genetics depends on analyzing family histories
A ____ is a graphical representation of mating history over several generations.
Pedigree
Each individual in a pedigree is represented by a…
Shape
On a pedigree, biological males are indicated by ____ and biological females are indicated by ____.
Squares ; circles
On a pedigree, a single horizontal line indicates…
Mating
On a pedigree, a vertical line indicates…
Two individuals’ offspring
On a pedigree, shaded shapes represent…
Affected individuals
(show the phenotype of the trait)
On a pedigree, unshaded shapes represent…
Unaffected individuals
A dominant pedigree tracks…
A dominant allele
True or false:
The expression of dominant alleles may skip generations.
False
True or false:
Parents who are both affected by a dominant allele can have unaffected offspring.
True
Dominant pedigrees can be used to predict…
The genotypes and phenotypes of future offspring
A recessive pedigree tracks…
A recessive allele
On a pedigree, a double horizontal line represents…
Mating between related individuals
On a recessive pedigree, a half-shaded shape indicates…
A heterozygous carrier
In order to be affected by a recessive allele, an individual must be…
Homozygous recessive
True or false:
Parents who are affected by a recessive allele can have offspring who are unaffected.
False
True or false:
The expression of recessive traits can skip generations.
True
In order to express a recessive trait, an individual must inherit the recessive allele from ____ parent(s).
Both
Affected offspring become more frequent when…
The parents are related
List the three assumptions that must be true for Mendel’s original model to work.
- Each trait is controlled by a single gene
- Each gene has only 2 possible alleles
- A clear dominant-recessive relationship exists between the alleles
True or false:
Most human genes can be explained using Mendel’s model.
False
True or false:
There may be more than two alleles for a gene in a population.
True
Human ABO blood typing is an example of both ____ and ____.
Multiple alleles and co-dominance
Which allele(s) for expressing antigens on the surface of red blood cells are dominant?
A and B
Which allele(s) for expressing antigens on the surface of red blood cells are recessive.
O (denoted i)
How many different genotypes are there for human ABO blood types?
Six
(AA, Ai, BB, Bi, AB, ii)
How many different phenotypes are there for human ABO blood type?
Four
(A, B, AB, and O)
Type ____ blood has no sugars on the outside of blood cells.
O
(ii)
Type ____ blood has two types of sugars on the surface of the red blood cells.
AB
(both A and B sugars present)
Type AB blood is an example of…
Codominance
The dominant allele for the Rhesus factor…
Codes for surface proteins on red blood cells
The recessive allele for the Rhesus factor…
Does not code for any surface proteins on red blood cells
A “positive” blood type is a result of expressing the ____ Rh allele.
Dominant
____ occurs when multiple genes control the expression of a single trait.
Polygenic inheritance
In a population, traits controlled by polygenic inheritance usually…
Show continuous variation and a normal distribution over a range
Human height is an example of…
Polygenic inheritance
True or false:
Polygenic traits can be affected by an individual’s behavior and environment.
True
Traits that use polygenic inheritance are also sometimes called…
Quantitative traits
____ occurs when a single gene affects multiple phenotypes.
Pleiotropy
List two reasons why the affects of pleiotropy can be difficult to predict.
- The gene often affects other unknown traits
- The allele may be dominant with respect to one trait but recessive with respect to another
Cystic fibrosis is an example of…
Pleiotropy
____ occurs when a heterozygous phenotype is an intermediate form of the homozygous phenotypes.
Incomplete dominance
A cross between red and white flowers that produces pink flowers is an example of…
Incomplete dominance
____ occurs when a heterozygote shows aspects of both homozygous phenotypes.
Codominance
True or false:
Mendel’s model assumed that the products of genes do not interact.
True
____ occurs when genes that code for different traits show some form of dependence at the level of function.
Epistasis
What happens to a dihybrid cross if the two alleles are involved in/affect the same pathway?
The expected ratio of phenotypes changes
____ occurs when the expression of one gene is in some way controlled, altered, or dependent on the expression of another.
Epistasis
True or false:
Phenotypes can be influenced by the environment.
True
Why is a Siamese cat’s head and torso white while its extremities are dark?
The protein that affects coat color is heat-sensitive and is only active in the cooler extremities.
