Chapter 12 Flashcards
Purple or White petals are determined but different _______.
Alleles
What are all the possible gamete combinations between a Pp and pp cross?
Pp, pp
Prior to Mendal, how did people think that inheritance worked?
The basis for ideas about heredity involved blending
Define: True-breeding, self-crossing, progeny, hybrid, dihybrid
True-breeding -
Self-crossing -
Progeny - offspring
Hybrid - crossing two different lines or varieties
Dihybrid -
What did the work of TA Knight demonstrate?
Why did Mendel choose to work with Peas?
- Other research showed that pea hybrids could be produced
- Many pea varieties were available
- Peas are small plants and easy to grow — quick generation time
- Peas can self-fertilize or be cross-fertilized
Outline the basic structure of Mendel’s experimental design.
Three stages:
1. Produce true-breeding lines for each trait he was studying
2. Cross-fertilize true-breeding strains having alternate forms of a trait
3. Allow the hybrid offspring to self-fertilize for several generations and count the number of offspring showing each form of the trait
Mendel worked with 7 specific traits, why did he choose these traits?
- Easily observable
- Minimal variation
- “Either or” exclusive traits
- Existed in alternate forms (e.g., purple vs. white flower; wrinkled vs. smooth seed)
In a monohybrid cross, what % of F1 have the dominant phenotype?
100%
Why are true breeding lines always homozygous?
CONCEPT QUESTION: How can different genotypes result in the same phenotype? Or why does the 1:2:1 genotype ratio appear as the 3:2 phenotype ratio?
The 1:2:1 genotypic ratio appears as the 3:1 phenotypic ratio because the genotype is homozygous dominant: 2heterozygous: homozygous recessive. Heterozygous genotype displays the dominant phenotype because it has one dominant allele and one recessive. The dominant allele takes priority in the phenotype. For that reason different genotypes can result in the same phenotype. Homozygous dominant and heterozygous genotype both appear as the dominant phenotype.
Different genotypes can produce the same phenotype due to dominant and recessive alleles. In a 1:2:1 genotype ratio (like AA, Aa, and aa), the dominant allele (A) masks the effect of the recessive allele (a) in heterozygous individuals (Aa). This results in a 3:1 phenotype ratio because both AA and Aa display the dominant trait, while only aa shows the recessive trait. So, three have the dominant phenotype, and one has the recessive.
What does it mean for two alleles to segregate? When does this happen?
What is the principle of segregation?
Two alleles for a gene segregate during gamete formation and are rejoined at random, one from each parent during fertilization
CONCEPT QUESTION: Can individuals have more than two alleles for a gene? Why or why not?
No.
Monohybrid cross
cross that follows a single trait with two variations
First filial generation
offspring resulting from a cross between a parental generation (P)
Dominant
An allele that is expressed when present in either the heterozygous or the homozygous condition
Recessive
An allele that is expressed only when present in the homozygous condition, but is “hidden” by the expression of a dominant allele in the heterozygous condition
Second filial generation (F2)
offspring resulting from a cross between members of first filial (F1) generation
What is the monohybrid phenotyptic ratio?
3:1
What is the monohybrid genotypic ratio?
1:2:1
1:2:1 ratio
1/4 true-breeding dominant (homozygous dominant)
1/2 non-true breeding dominant (heterozygous)
1/4 true-breeding recessive (homozygous recessive)
Alleles
different forms of a gene
Genotype
total set of alleles an individual contains
Phenotype
physical appearance of an individual
Dihybrid cross
single genetic cross involving two different traits
Principle of Independent Assortment
In a dihybrid cross, the alleles of each gene assort independently –> The segregation of different allele pairs is independent
Testcross
unknown genotype is crossed with homozygous recessive genotype
T or F: Dominant phenotype can only be heterozygous
F: Dominant phenotype can be either homozygous or heterozygous
Polygenic inheritance
more than one gene can affect a single trait
In polygenic inheritance, the phenotype has
continuous variation
Continuous variation
Variation in a trait that occurs along a continuum
Quantitative traits
A trait that is determined by the effects of more than one gene
Quantitative traits are traits with a ________ distribution
Continuous
What are examples of quantitative traits?
Height, weight, eye color in humans
The more genes involved in determining a phenotype, the more …
Continuous variation there is
Pleiotropy
A single gene can affect more than one trait
Allele has more than one effect on phenotype
What are examples of diseases in human that are the result of pleiotropic alleles?
Sickle cell anemia
Cystic fibrosis
Cystic fibrosis cause?
Mutation in a gene that encodes a chloride ion transmembrane channel
Patients with cystic fibrosis exhibit the following symptoms:
Clogged blood vessels
Sticky mucus
Salty sweat
Liver and pancreas failure
Incomplete dominance
two or more alleles of a gene do not display clear dominance
phenotype of heterozygote is intermediate between the two homozygotes
Complete dominance
two or more alleles of a gene are each dominant to other alleles but not to each other
The phenotype of a heterozygote for codominant alleles exhibits characteristics of each of the homozygous forms
