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Genetics Cheat Sheet (DRAFT) by

Chapter 9: Fundamentals of Genetics

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Section 1&2 Summaries

The study of how charac­ter­istics are transm­itted from parents to offspring is called genetics.
The genotype is the genetic makeup of an organism. The phenotype is the appearance of an organism.
Mendel observed seven charac­ter­istics of pea plants. Each charac­ter­istic occurred in two contra­sting traits.
Probab­ility is the likelihood that a specific event will occur. A probab­ility may be expressed as a decimal, a percen­tage, or a fraction.
Self-p­oll­ina­tion, in which pollen is transf­erred from the anthers of a flower to either the stigma of the same plant, normally occurs in pea plants. Cross-­pol­lin­ation occurs when pollen is transf­erred between flowers of two different plants.
A Punnett square can be used to predict the outcome of genetic crosses.
Mendel concluded that inherited charac­ter­istics are controlled by factors that occur in pairs. In his experi­ments on pea plants,one factor in a pair masked the other. The trait that masked the other was called the dominant trait. The trait that was masked was called the recessive trait.
A cross in ehich one charac­ter­istic is tracked is a monohybrid cross. The offspring of a monohybrid cross are called monohy­brids.
The law of segreg­ation states that a pair of factors is segreg­ated, or separated, during the formation of gametes. Two factors for a charac­ter­istic are then combined when fertil­ization occurs and a new offspring is produced.
A testcross, in ehich an individual of unknown genotype is crossed with a homozygous recessive indivi­dual, can be used to determine the genotype of an individual whose phenotype expresses the dominant trait.
The law of indepe­ndent assortment states that factors for individual charac­ter­istics are distri­buted to gametes indepe­nde­ntly. The law of indepe­ndent assortment is observed only for genes that are located on separate chromo­somes or are far apart on the same chromo­some.
Complete dominance occurs when hetero­zygous indivi­duals and dominant homozygous indivi­duals are indist­ing­uis­hable in phenotype.
We now know that the factors that Mendel studied are alleles, or altern­ative forms of a gene. Each of two or more altern­ative forms of a gene is called an allele. One allele for each trait is passed from each parent to the offspring.
Incomplete dominance occurs when two or more alleles influence the phenotype and results in a phenotype interm­ediate between the dominant and the recessive trait.
 
Codomi­nance occurs when both alleles for a gene are expressed in a hetero­zygous offspring. Neither allele is dominant or recessive, nor do the alleles blend in the phenotype as they do in incomplete dominance.
 
A cross in which two charac­ter­istics are tracked is a dihybrid cross. The offspring of a dihybrid cross are called dihybrids.
 

Vocabulary

Genetics
The field of biology devoted to unders­tanding how charac­ter­istics are transm­itted from parents to offspring. Founded by Gregor Johann Mendel.
Heredity
The transm­ission of charac­ter­istics from parents to offspring.
Trait
Geneti­cally determined variant of a charac­ter­istic, such as yellow flower color.
Pollin­ation
Occurs when pollen grains produced in the male reprod­uctive parts of a flower are transf­erred to the female reprod­uctive part of a flower.
Self-P­oll­ination
Occurs when pollen is transf­erred from the anthers of a flower to the stigma of either that flower or another flower of the same plant.
Cross-­Pol­lin­ation
Occurs between flowers of two plants.
True-b­reeding
pure
P Generation
True breeding parents
F1 Generation
Offspring of the P Generation
F2 Generation
Offspring of the F1 Genera­tion.
Dominant
Masked the factor for the other trait in the pair.
Recessive
Trait that does not appear.
Law of Segreg­ation
States that a pair of factors is segreg­ated, or separated, during the formation of gametes.
Law of Indepe­ndent Assortment
States that factors separate indepe­ndently of one another during the formation of gametes.
Molecular Genetics
Study of the structure and function of chromo­somes and genes.
Genotype
Organism's genetic makeup
Phenotype
Organism's appearance
Homozygous
Both alleles of a pair are alike
Hetero­zygous
Two alleles in the pair are different
Probab­ility
Likelihood that a specific event will occur.
Monohybrid Cross
Only one charac­ter­istic is tracked.
Punnett Square
Diagram used to aid in predicting the probable distri­bution of inherited traits in the offspring.
Genotypic Ratio
Ratio of the genotypes that appear in the offspring.
Phenotypic Ratio
Ratio of the offspr­ing's phenotype.
Testcross
An individual of unknown genotype is crossed with a homozygous recessive indivi­dual.
Complete Dominance
One allele is completely dominant over another.
Incomplete Dominance
Phenotype of a hetero­zygote is interm­ediate between the phenotypes determined by the dominant and recessive traits.
Dihybrid Cross
Two charac­ter­istics are tracked
 

Questions

Describe what a true-b­reeding plant is.
Plants that are true-b­ree­ding, or pure, for a trait always produce offspring with that trait when they self-p­oll­inate. For example, pea plants that are true-b­reeding for the trait of yellow pods self-p­oll­inate to produce offspring that have yellow pods.
Outline how Mendel produced plants that had genes contra­sting traits of a charac­ter­istic.
Mendel cross-­pol­linated pairs of plants that were true-b­reeding for contra­sting traits of a single charac­ter­istic. True-b­reeding parents are called P genera­tion, or F1 genera­tion. He cross-­pol­linated by transf­erring pollen from the authors of one plant to the stigma of another plant. When the plant matured, he recorded the number of each type of offspring produced by each cross.
Define the terms dominant and recessive.
In genetics, dominant describes an allele that is fully expressed whenever the allele is present in an individual while recessive describes an allele that is expressed only when no dominant allele is present in an indivi­dual.
State in modern termin­ology the two laws of heredity that resulted from Mendel's work.
The law of segreg­ation states that a pair of factors is segreg­ated, or separated, during the formation of gametes. The law of indepe­ndent assortment states that factors separate indepe­ndently of one another during the formation of gametes.
Differ­entiate Genes from alleles.
A gene is the segment of DNA on a chromosome that controls a particular hereditary trait. Because chromo­somes occur in pairs, genes also occur in pairs.
How did Mendel's F1 Generation plants differ from his F2 Generation plants?
The F1 generation was the result of cross-­pol­lin­ation. It was controlled by a dominant factor. The F2 generation was the result of self-p­oll­ination of the F1 genera­tion. The trait (recessive factor) reappeared in a ratio of about 3:1 in the F2 genera­tion. This pattern emerged in thousands of crosses and led Mendel to conclude that one factor in a pair may prevent the other from having an effect
Many inherited disorders of humans appear in children of parents who do not have the disorder. How can you explain this?
A trait controlled by a recessive factor had no observable effect on an organism's appearance when that trait was paired with a trait controlled by a dominant factor. An affected child inherits a recessive allele from each parent
During meiosis, what allows genes located on the same chromosome to separate indepe­ndently of one another?
Crossi­ng-over during synopsis allows genes located on the same chromosome to separate indepe­ndently of one another.
Explain why a phenotype might not always indicate genotype.
An organism's appearance is its phenotype. A phenotype does not always indicates genotype as the phenotype of a PP or a Pp pea plant is purple flowers whereas of a pp pea plant is white flowers. In addition to recessive alleles, certain enviro­nmental factors can affect phenotype.
Identify the equation used to determine probab­ility.
Probab­ility= number of times an event is expected to happen divides number of times an event could happen - may be expressed as a decimal, a percen­tage, or a fraction
Explain how you might go about determ­ining the genotype of a purple­-fl­owering plant.
A pea plant homozygous for purple flowers that is crossed with a pea plant homozygous for white flowers will produce only purple­-fl­owering offspring. All of the offspring, called monohy­brids, are hetero­zygous for flower color
Illustrate in the form of a punnett square the results of crossing a pink-f­low­ering four o'clock with a white-­flo­wering four o'clock.
50% pink flowering, 50% white flowering
Explain the difference between a monohybrid cross and a dihybrid cross and give and example of each.
A monohybrid cross is a cross in which only one charac­ter­istic is tracked. An example of a monohybrid cross is between a pea plant that is true-b­reeding for producing purple flowers and one that is true-b­reeding for producing white flowers. A Punnett square is used to predict the probable distri­bution of inherited traits in the offspring. On the other hand, a dihybrid is a cross in which two charac­ter­istics are tracked. Predicting the results of a dihybrid cross is more compli­cated than predicting the results of a monohybrid cross because more combin­ations of alleles are possible. Both seed texture and seed color can be used to track
The offspring of two short-­tailed cats have 25 percent chance of having no tail, a 25 percent chance of having a long tail, and a 50 percent chance of having a short tail. Using this inform­ation, what can you hypoth­esize about the genotypes of the parents and all the way in which tail length is inherited?
The genotype consists of the alleles that the organism inherits from its parent­s.P­arents have alleles that are dominant. Their own short-­tailed offspring give away equally chance of being either a long tail or no tail.
If you crossed two purple­-fl­owering pea plants and all of the F1 offspring were purple­-fl­owe­ring, what could you say about the genotypes of the parents? If some of the F1 offspring were white-­flo­wering, what could you say about the genotypes of the parents?
The genotype of the two purple­-fl­owering pea plant may be either PP or Pp, which means they can be homozygous dominant or homozygous recessive. In the second case, the parents are hetero­zygous for their charac­ter­istic. They have a genotype of Pp.