Chapter 12 Flashcards
Mendelian Genetics
Parental generation P0
plants used in the initial crosses
F1
first generation of plants resulting from the original cross
F2
seeds resulting from the self pollination of F1
Trait
variation in the physical appearance of a heritable characteristic
reciprocal cross
breeding plants with the contrasting traits
allele
gene variants
phenotype
observable physical trait expressed by the organism
genotype
the underlying genetic alleles (visible and non-expressed)
incomplete dominance
a heterozygote is a mix between the parental phenotypes
codominance
both alleles in a heterozygote are fully expressed
wild-type
most common combination of alleles in a population (+)
variants
other alleles besides the wild type
X-linked
gene is present of the X chromosome but not the Y
Hemizygosity
only one allele for the X-linked genes
Carriers
heterozygous for the trait
lethal allele
mutation that results in a non-functional allele for an essential gene
linkage
genes that are close together are likely to be inherited together
hypostatic
allele that is being masked
epistatic.
allele doing the masking
Who is Johann Gregor Mendel and what is he known for?
Teacher, scientist, and abbot of a monastery, conducted experiments with pea plants which forms the basis of genetics
What type of plant did Mendel work with and why?
Pea plants, self-fertilize and can cross-fertilize
Understand and describe the experiments performed by Gregor Mendel at the P0, F1, and F2 levels.
True breeding is parental, one cross in F1, self pollination from F1 makes F2
What does it mean if plants are bred “true” for a trait?
When self fertilized, all of the offspring had the same trait
In Mendel’s crosses between true breeds that differed in one trait, what were the genotypic and phenotypic characteristics of the F1 generation?
100 percent of the plants had the dominant phenotype
When Mendel then allowed the F1 generation to self-pollinate, what were the genotypic and phenotypic characteristics of the F2 generation?
the genotypic was 1:2:1 and phenotypic was 3:1
What was the purpose of performing the reciprocal crosses for each of the seven traits?
this showed that the trait did not disappear as it was found in the F2 generation
What are dominant and recessive traits and how did Mendel demonstrate this?
expressed are dominant and latent are recessive this was shown by recessive being seen in F2
How did Mendel know that the traits were “discrete” and separate from one another?
Recessive was found in F2
How did Mendel come to understand that his plants possessed two copies of each of the seven traits, and that one parent transmitted one of its copies to the next generation?
some plants were able to produce all dominant when self fertilized while others were a mix and some were only recessive offspring
The fact that each of his plants possessed two copies of each trait meant that plants showing the recessive trait had what genotype? What did Mendel conclude about
the genotypes of plants showing the dominant trait?
rr, they could either be Rr or RR
What are alleles and how do they arise in a population?
gene variants that arise by mutation and lead to different characteristics of the same trait
How is an organism’s phenotype related to it’s genotype?
the genotype codes for the phenotype
What does it mean if an organism is homozygous or heterozygous? How does this relate to Mendel’s P0, F1, and F2 generations?
all parental were homozygous, F1 were heterozygous, and F2 was a mixture of the two
Name and describe the two genotypic conditions under which an organism could display the dominant characteristic.
RR or Rr
When is a test cross used? How is it performed?
a way to figure out if homozygous or heterozygous, cross unknown individual with a homozygous recessive
What is the Law of Segregation? When is it physically manifested during meiosis?
paired genes segregate equally into gamete such that offspring have an equal likelihood of inheriting either one (meiosis I division)
What is the Law of Independent Assortment? When is it physically manifested during meiosis?
every possible combination of alleles for every gene is equally likely to occur (metaphase one)
What is incomplete dominance? How does it differ from the simple dominant/recessive inheritance pattern?
a heterozygote is an intermediate phenotype between the two parent types (Red+White=pink)
What is codominance? How does it differ from the simple dominant/recessive inheritance pattern?
A heterozygote results in a phenotype where both alleles are fully expressed (blood groups)
What is a “wild-type” and what are “variants?” How do they relate to one another?
most common in a population is the wild type (+) and variants are other genotypes and phenotypes; the two can be either dominant or recessive to each other
What are sex-chromosomes? How are they different from autosomes?
X and Y, shorter and determine the sex
How are the X and Y chromosomes the same? How are they different?
determine sex but Y is much smaller
What does it mean if a trait is X-linked?
it is more likely that men will have it and women can be carriers
What is hemizygosity? Do males or females display hemizygosity and why?
only one allele for X-linked genes, males are hemizygotes
What is a female “carrier?”
a female where one x has the allele and the other does not
What is lethality? Under what types of conditions might these alleles survive in a population?
results in a nonfunctional allele for an essential gene; if the presence of a wild type allele functions well enough to maintain life and is dominant to the lethal allele
How do situations of recessive lethal alleles differ from dominant lethal alleles?
if dominant, one lethal allele would be deadly
What law is supported by the fact that a dihybrid cross may be broken down into two separate monohybrid crosses with the same frequencies of genotypes?
independent assortment
What are linked genes and how do they cause exceptions to the Law of Independent Assortment?
genes that are close to each other on homologous chromosomes
Understand the concept of epistasis. Why did Mendel not see patterns of epistasis in his work?
the interaction of one gene masks or interferes with the expression of another, it did not occur with the traits he was examining
What is the relationship between hypostatic and epistatic alleles?
The hypostatic alleles are being masked while the epistatic alleles are doing the masking
