Mendelian Genetics Flashcards
Define the following: Gene Allele Homozygous Heterozygous Dominant Recessive Genotype Phenotype
Gene- a discreet unit of heredity
Allele- the alternate forms of a gene found on chromosomes
Homozygous- when an organism has two copies of the same allele; AA
Heterozygous- When an organism has one copy of two different alleles; Aa
Dominant- an allele that takes precedence over other alleles; presents when homo or heterozygous
Recessive- an allele that does not take precedence over others; only presents when homozygous
Genotype- the genetic constitution of an organism
Phenotype- the physical presentation of a particular genotype
Whet were the two primary views concerning trait inheritance during the 17th and 18th centuries? What was the primary view in the early-mid 19th century? Describe those views.
17th/18th century- believed that small, fully-formed humans called homunculi existed in the sperm or eggs cells and simply grew larger into the size of an infant during pregnancy; Spermists believed that the homunculus was located in the sperm cell, ovists believed it was located in the egg cell.
19th century- believed that offspring were just an equal blend of parents’ physical characteristics, the “blended theory of inheritance”
Who was Gregor Mendel? Why did he work with peas? Describe some key reasons for use of pea plants as a model organism for genetic studies. How did Mendel control mating and prevent self-pollination of pea plants?
Gregor Mendel was an Austrian monk who is considered to be the father of modern genetics. He worked with pea plants because they are small, reproduced relatively quickly, and had lots of trait variability To control pollination, he cut the female parts off of some plants and the male parts off of the others so that he had full control over which plants pollinated which.
What was Mendel;s experimental method? Define the terms character, trait, and true-breeding organism. Why would he start his experiment with true-breeding organisms?
Mendel would use pollen from one plant to fertilize another, then evaluate the resulting progeny.
Character- a heritable feature (eg. pea color)
Trait- each variant of a character (eg. yellow peas)
True-breeding organism- organisms that always pass on certain genetic traits, ie they always pass on the same phenotype.
Mendel would start with true-bred plants so that he knew exactly what was being passed on to the offspring
What is monohybrid cross? What is the P generation? What genotypes did Mendel’s P generations have? What are the resulting progeny of the P cross?
Monohybrid cross- a genetic cross between two plant varieties that differ by ONE trait
P generation: the first cross b/w true-breeding plants, aka the Parental generation
Mendel started out with making P crosses between pants with purple and white flowers- all the progeny had purple flowers
What is meant by an F1 generation? What was the genotype of Mendel’s F1 generations? What is a reciprocal cross?
F1 - first filial generation; the progeny of the P cross
The genotype of Mendel’s F1 cross were all Pp
Reciprocal cross- a genetic cross involving the same parental varieties but with the sex of the parents switched
What is meant by an F2 generation? Why do F2 generations show phenotypic diversity? Be able to describe using the genotypes of the crosses
F2- the generation resulting from the F1 gen reproducing
F2 Gen showed phenotypic diversity because all of the F1s were Pp, so 1/4 of their offspring had a pp genotype, allowing the recessive phenotype to present
What conclusions could be drawn from Mendel’s work on pea plants? What is Mendel’s Law of Segregation? How are dominant and recessive alleles denoted in genotypes?
Conclusions-traits are controlled by genes, not blending inheritance; two copies of each gene- alleles- determine each character, one is received from each parent; when two alleles are present, the dominant one determines the appearance of the trait and masks the recessive allele
Mendel’s Law- the two alleles for a character separate during gamete formation and wind up in different gametes
Dominant allele are denoted with capital letters, recessive are denoted with lowercase
What is a test cross and when might it be used? Whet results for a test cross are expected if the unknown dominant plant is homozygous? Heterozygous?
Test cross- a cross used to determine the genotype of an individual with a dominant phenotype by crossing with a homozygous recessive individual
If the individual is homozygous, all of the progeny will display the dominant phenotype, if heterozygous, half of the progeny will display the recessive phenotype
What are dihybrid crosses? What event of phase during meiosis is responsible for independent assortment?
Dihybrid cross- crosses b/w two true-breeding lines that differ for two traits
Metaphase is responsible for independent assortment
What is Mendel’s law of independent assortment? Why would this law only apply to genes located on heterologous chromosomes or those genes far apart on the same chromosome?
Mendel’s law of independent assortment- a pair of alleles for one trait segregates independently of the alleles for a different trait; thus all alleles are randomly mixed during gamete production.
This only applies for genes on different non-homologous chromosomes or genes far apart on the same chromosome because close together genes form linkages and stay together
What were Mendel’s major contributions to modern genetics?
He came up with the concept of genes, alleles, homozygous, and heterozygous
He came up with the two basic laws of inheritance– segregation and independent assortment– that still exist today
