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Word & Picture Definition

Carrier

This is when a recessive allele is possessed by the parent but not

expressed as a phenotype. This parent is heterozygous and has a 50% chance of

passing that recessive trait to their offspring. If both parents demonstrate

this condition they have a 25% of having offspring that are affected by this

phenotype or condition. These parents would be considered

____________________

Codominance

When you have two dominant alleles that both show up in the phenotype of

the individual. Not a blending of phenotypes but both independently

expressed in different areas.

Dihybrid cross

This is a cross of alleles when two traits are considered simultaneously.

Its major importance is… I can remember it by…


When this type of allele is present in the genotype (homozygous or heterozygous) it will

be directly visible in the phenotype.

F1 generation

This is the offspring of the parental generation. In standard Mendelian crosses, pure breeding parents have

offspring which are 100% heterozygous.

F2 generation

This is the offspring of the F1 generation. In a standard Mendelian

cross this will create a 1:2:1 ratio for the genotypes and a 3:1 ratio for the

phenotypes.

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Gene Pool

The collection of all alleles present within a population that could be used

to create the next generation.

GenotypeThese are the two alleles that an

individual possesses. This may be expressed as a homozygous or

heterozygous condition for each set. These alleles determine what the

individual will look like when the genes are expressed.

Homozygous

This word describes when both alleles being carried are coding for the same

phenotype. This can be a dominant(BB) or recessive(bb) condition.

B B b b


Heterozygous

This word describes when the two alleles being carried are each coding for

a different phenotype (Bb).

Incomplete dominanceThis describes a situation when both

alleles are dominant but neither is fully expressed in its original form. There is a

blending of phenotypes.

Multiple AllelismThis describes a situation where 3 or

more different alleles contribute to the phenotype of the individual. Human

blood types are an example of this type of inheritance.

B b


Parental GenerationIn a standard Mendelian cross these are

the individuals that create the F1 generation. By saying that these individuals are pure-breeding, we

indicate that they are both homozygous for the alleles in question.

Pedigree

This shows the gender and phenotype of several members or generations of the same family. These trees can be

used to determine genotypes and predict disorders in future generations.

Phenotype

This is the physical expression of the organisms genotype.


Polygenic Inheritance This is when 3 or more genes are controlling the appearance of a trait.

Traits controlled in this fashion demonstrate continuous variation.

Examples of human traits that demonstrate continuous variation

would include height, weight, intelligence, skin color, and hair color.

ProbabilityThis describes the measure of the likeliness that an event will occur.

Example: You have a 1 in 6 chance of getting a 5 every time you roll standard

dice. We will be also discussing The Sum Rule and The Product rule when

using this idea in Biology.

Purebred

This indicates that the parents are only containing one type of alleles for a given trait. Their offspring are guaranteed to

be pure in terms of this genotype / phenotype.


RecessiveThis phenotype hides when the

genotype is heterozygous.

Sample Size When increased this factor generally leads to increased precision when

estimating the unknown. For example, if we wish to know the proportion of a certain species of fish that is infected

with a pathogen (disease), we would generally have a more precise estimate

of this proportion if we sampled and examined 200 rather than 100 fish.

Sex linkageThis indicates that the gene for a trait in

question is carried on the X chromosome. This means that it will

affect the genders unequally.

(Men will be affected more if the condition is recessive and woman will be more affected if the

condition is dominant.)


Test CrossThis is done when the genotype is

unknown and the dominant phenotype is displayed for an individual. Based on the offspring produced, the unknown parent’s genotype can be deduced.

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