Chapter 5: 5.4 Laws of Inheritance [Mendel's Laws] Flashcards
What is Mendel’s First Law?
Law of Segregation
State:
The Law of Segregation
States that gametes receive only one allele of each gene
Mendel’s most important discovery was the – ——- from parental strains with different traits were not…
- F1 progeny
- True-breeders
What is a true-breeding organism?
Organisms that always pass down their phenotypic traits to its offspring
In Mendel’s Law of Segregation:
Where does the F2 Generation come from?
Comes from the F1 generation self-fertilizing
In Mendel’s Law of Segregation:
What did Mendel discover in the F2 Generation?
The recessive trait reappeared
* Reappeared consistently at a dominant : recessive ratio close to 3 : 1
True or False:
In true breeding parental strains, the two alleles are identical
True
Two identical alleles means the plants are…
Homozygous
True or False:
Each gamete contains two of alleles of one gene
False, each gamete contains just one allele of each gene
What is a reproductive cell known as?
A gamete
Each gamete contains — allele of each gene
One
State:
The Principle of Segregation
When gametes are formed, the two alleles of a gene segregate
* Half of the gametes get one allele, while the other half get the other allele
True or False:
In heterozygous plants, all the gametes will have the same allele
False, in homozygous plants all the gametes will have the same allele
Describe:
- When a zygote is formed
- How it is formed
- Formed after fertilization
- Comprised of the union of two gametes - one from each parent
When the two gametes that formed the zygote carried different alleles for a gene, the resulting zygote…
Is heterozygous
* A hybrid containing two different alleles
How can the resulting progeny of the F2 generation be determined?
Using a Punnett square
True or False:
The dominant phenotype has to be the same genotype
False, since it is dominant the phenotype is the same but the genotype can be different
State:
The Law of Segregation
Alleles must segregate equally into gametes such that the progeny (F2) have an equal likelihood of obtaining one of the two alleles
What can be used to test segregation?
Testcross
How is a testcross done? What will the results show
Cross the F1 progeny with the true-breeding recessive strain instead of allowing them to self-fertilize
* The recessive trait will only be observed if the F1 strain is heterozygous
True or False:
All traits follow the Mendelian rules of dominance
False
List two ways that traits don’t follow the Mendelian rules of dominance
- Incomplete dominance: The phenotype of the heterozygote is somewhere in-between the homozygote phenotypes
- Codominance: When both traits are expressed
What is Mendel’s Second Law?
Law of Independent Assortment
State:
Mendel’s Second Law (Law of Independent Assortment)
Alleles of different genes assort independently of one another during gamete formation
There are — possibilities at meiosis when an individual is…
- Two
- Heterozygous at two loci
How did Mendel find support for the Second Law?
By performing dihybrid crosses
What does the law of independent assortment allow for in trait combinations?
All trait combinations are possible
* Four equally likely gametes in the F2 generation
What would happen if the Law of Independent Assortment was not true?
The progeny would all be heterozygous for both genes
Punnett Square Rules:
How large should the grid be?
Should fit all the alleles from the parents on either side
Punnett Square Rules:
Do the parents have to be placed in specific places on a Punnett Square?
No, it is arbitrary
Punnett Square Rules:
How should alleles be written in a Punnett Square?
- Dominant alleles written first
- In alphabetical order
Define:
Locus
The physical location of a gene on a chromosome
(Plural: Loci)
Define:
Alleles
The different versions of a single gene or locus
In diploid organisms, how many alleles will the individual inherit for each gene?
2 alleles of every gene
* One from mother
* One from father
What are some common short-hands for alleles?
- B and b
- B and B’
- B1 and B2
Define:
Trait
Each variant for a character
Alleles for a given gene affect the same character but…
Can specify different traits
Define:
Genotype
The specific alleles in an individual (the genetic makeup)
Define:
Phenotype
The physical appearance of an individual
True or False:
Phenotype helps determine genotype
Not exactly, genotype helps determine phenotype
What does transmission of alleles depend on?
Depends on events in meiosis and fertilization
Mendel’s Law of Segregation:
— alleles for a heritable character segregate during ——- formation and end up in different gametes
- Two
- Gamete
When do members of an allelic pair segregate during meiosis I come together?
Fertilization
In Mendelian Inheritance:
How many characters are controlled by each gene?
One
In Mendelian Inheritance:
How many alleles do each genes have?
Two
* Each accounts for variations in inherited characters
In Mendelian Inheritance:
What do dominant alleles do?
Determines an organisms appearance
In Mendelian Inheritance:
What do recessive alleles do?
Have no noticeable effect if the two alleles at a locus differ
In Mendelian Inheritance:
When does the segregation of the two alleles for a heritable character occur?
During gamete formation
In Mendelian Inheritance:
The alleles or two different genes are…
Inherited independently (independent assortment)
True or False:
Alleles remain unchanged
Mostly. They can be rarely be mutated
Can a character be affected by the environment?
Yes
In the real-world population, pairs of ——— mate with frequencies that depend on their proportions in the ———-
- Genotypes
- Populations
