Chapter 3: Basic Principles of Heredity Flashcards
Who is the founder of modern genetics?
Gregor Mendel
How did Mendel first discover the principles of heredity?
Crossing different varieties of pea plants and analyzing the pattern of transmission of traits in subsequent generations
What did Mendel use in his studies? How many characteristics did it have? What is an interesting fact about these traits? Is it haploid or diploid?
- Pea plant (Pisum sativum)
- Seven characteristics
- All characteristics were controlled by one single gene (one locus, one allele)
- The plant was diploid (2n)
Why was the pea plant successful?
Because it was only diploid, unlike other plants (e.g. wheat)
What were the traits observed in the pea plant?
- Seed color
- Seed shape
- Seed coat color
- Pod color
- Pod shape
- Flower position
- Stem length
Define a gene.
Genetic factor (region of DNA) that helps determine a characteristic
Define an allele.
One of two or more alternate forms of a gene
Define a locus.
Specific place on a chromosome occupied by an allele
Define a genotype.
Set of alleles possessed by an individual organism
Define a heterozygote.
An individual organism possessing two different alleles at a locus
Define a homozygote.
An individual organism possessing two of the same alleles at a locus
Define a phenotype (trait).
The appearance or manifestation of a character
Define a character or characteristic.
An attribute or feature
At each locus, how many alleles does a diploid organism possess, located on different homologous chromosomes?
Two alleles
When peas with two different traits – round and wrinkled seeds – are crossed, will their progeny exhibit one of those traits, both of those traits, or a “blended” intermediate trait? What was Mendel’s experiment to answer this question?
- Removed the anthers from flowers to prevent self-fertilization
- Dusted the stigma with pollen from a different plant
- The pollen fertilized the ova, which developed into seeds, and the seeds grew into plants
- Reproduced the experiment
“Each individual organism possesses two alleles encoding a trait.” Which stage of meiosis does this observation from Mendel’s first law correspond to?
- Before meiosis
- Segregation (First Law)
“Alleles separate when gametes are formed.” Which stage of meiosis does this observation from Mendel’s first law correspond to?
- Anaphase I
- Segregation (First Law)
What constitutes the next generation in Mendel’s experiment?
The seeds (not the plants)
“Alleles separate in equal proportions.” Which stage of meiosis does this observation from Mendel’s first law correspond to?
- Anaphase I
- Segregation (First Law)
“Alleles at different loci separate independently.” Which stage of meiosis does this observation from Mendel’s second law correspond to?
- Anaphase I
- Independent Assortment (Second Law)
What is Mendel’s first law?
Segregation
What is Mendel’s second law?
Independent assortment
What happened when Mendel crossed homozygous round seeds with homozygous wrinkled seeds?
All round seeds
What happens when Mendel self-fertalized the round seeds that he produced from crossing over (F2 generation)?
- 3/4 were round (dominant allele)
- 1/4 were wrinkled (recessive allele)
What did Mendel’s monohybrid crosses reveal?
The principle of segregation and the concept of dominance
Describe the principle of segregation (Mendel’s first law).
- Each individual diploid organism possesses two alleles for any particular characteristic
- These two alleles segregate when gametes are formed, and one allele goes into each gamete
Describe the concept of dominance.
When two different alleles are present in a genotype, only the trait encoded by one of them, the “dominant” allele, is observed in the phenotype
What does Mendel’s second law require to test experimentally?
A dihybrid cross
What is a testcross?
- Breeding a phenotypically recessive plant
- Determines whether a dominant phenotype is homozygous or heterozygous for a specific allele
- One individual of unknown genotype is crossed with another individual with a homozygous recessive genotype for the trait in question
Do traits blend in a diploid organism?
No
What observation can be seen in independent assortment? How many characteristics are needed to prove it? When is it observed?
- Alleles at different loci separate independently
- Two characteristics
- Anaphase I
What is the genotypic ratio? What is the phenotypic ratio?
- Phenotypic: ratio of the traits expressed
- Genotypic: ratio of the letters
The genotypes of parents are Aa and Aa. What is the phenotypic ratio and what is the genotypic ratio?
- Phenotypic: 3:1
- Genotypic: 3/4 A_: 1/4aa
If the genotypes of the parent is RRYY, what are the possible gametes formed?
- RY
- RY
- YR
- YR
If the parents RRYY and rryy reproduce, what is the resulting F1 generation?
RrYy
If RrYy is self-fertalized, what is the resulting phenotypic ratio?
- 9 round, yellow
- 3 round, green
- 3 wrinkled, yellow
- 1 wrinkled green
9: 3:3:1
Differentiate a monohybrid and a dihybrid cross.
- One characteristic: mono
- Two characteristics: di
When does the multiplication rule apply?
To two or more independent events taking place together
When does the addition rule apply?
Applies to any of two or more mutually exclusive events
What is the difference between a locus and an allele?
- Locus: position on chromosome where a specific gene is located
- Allele: one or two more alternative forms of a gene
How are the principles of segregation and independent assortment related?
They both refer to the separation of alleles in anaphase I of meiosis
How are the principles of segregation and independent assortment different?
- The principle of segregation says that these alleles separate
- The principle of independent assortment says that they separate independently of alleles at other loci
Which of the following factors did not contribute to Mendel’s success in his study of heredity?
A) His use of the pea plant
B) His study of plant chromosomes
C) His adoption of an experimental approach
D) His use of mathematics
B) His study of plant chromosomes
What is the difference between a locus an an allele?
- A locus is a place on a chromosome where genetic information encoding a characteristic is located
- An allele is a version of a gene that encodes a specific trait
How did Mendel know that each of his pea plants carried two alleles encoding a characteristic?
The traits encoded by both alleles appeared in the F2 progeny
If the probability of being blood type A is 1/8 and the probability of being blood type O is 1/2, what is the probability of being either blood type A or blood type O?
5/8
