BISC 200 001 Exam 2

Professor James White of Louisiana Tech University

What are alleles?

Alternate forms of the same gene

What are Neo-Mendelian genetics?

Different patterns of inheritance or gene interactions were discovered after Mendelian’s genetics

What are some factors of wild-type alleles?

* Generally, dominate
* Responsible for the corresponding phenotype
* Change (mutations) is compared to it

Variants of the wild-type alleles create what?

Mutant alleles

What are mutations the source of?

New alleles

How are mutations usually expressed?

As a loss of the specific wild-type allele function

How do you find the symbols for alleles?

You use the initial letter, or a combination of two or three letters, of the name of the mutant trait.

What is the scientific name for fruit flies?

Drosophila melanogaster

What is incomplete or partial dominance?

An expression of the heterozygous phenotype which is distinct from, and often intermediate, to that of either parent.

What is an example of incomplete or partial dominance?

A red and white flower breeding to create pink flowers.

What does incomplete or partial dominance mean in breeding?

None of the genes that are bred have dominance over each other.

There are two versions of the gene that specify hair texture, but how many phenotypes are there?

Three phenotypes

What are the three phenotypes of hair?

* Curly
* Straight
* Wavy

What is codominance?

Two alleles of a single gene are responsible for producing two distinct, detecable gene products.

Joint expression, or phenotypic expression, of both allees in a heterozygote is called what?

Codominance

H is what in hair?

Curly

h is what in hair?

Straight

Hh is what in hair?

Wavy

What is an example of codominance in humans?

Blood type

What blood type(s) are dominant?

A and B

What blood type(s) are recessive?

O

What are multiple alleles?

Alternate forms of a single gene

How are multiple alleles studied?

Using population genetics/in a population

What are lethal alleles?

An allele that results in the death of an organism

The gene involved in forming lethal alleles is known as what?

Essential Gene

What is an example of a recessive lethal allele?

Yellow mice

What is an example of a dominant lethal allele?

Huntington disease

What are essential genes?

Genes needed for survival.

A mouse that is non-yellow is known as what?

An “agouti”

Why are there no homozygous yellow mice (aa)?

It causes lethality, or death.

Huntington disease typically appears in what age?

Middle-aged

What gender is more at risk for Huntington’s disease?

Neither; there is equal risk

What are the allele(s) for Huntington’s disease?

HH or Hh

Does Huntington’s disease ever skip a generation?

No/rarely

If one parent has Huntington’s…

approximately 1/2 (50%) of offspring will be similarly affected.

Is Huntington’s autosomal or sexual?

Autosomal, which is why it has an equally rate of affecting men and women.

In 1983, what was discovered?

The gene causing Huntington’s was located on chromosome 4

If Huntington’s develops before age 15, it is primarily inherited from…

the father.

How does Huntington’s disease form?

A repetition of a trinucleotide sequence

What is anticipation?

When the signs and symptoms of some genetic conditions tend to become more severe and appear at an earlier age as the disorder is passed from one generation to the next.

What is epistasis/an epistatic gene?

When a gene masks another gene

What is a hypostatic gene?

A gene that is masked by the epistatic gene

What is an example of an epistatic gene?

Yellow fur in labrador retrievers. If an ee is present, despite a BB/bb/Bb, the dog will still be yellow.

What is an example of novel phenotypes?

The shapes of squash

* Long
* Disk
* Sphere

What is pleiotropy?

The ability of a single gene to have multiple effects/phenotypes

The development of a zygote is a direct result of…

* It’s genomes
* It’s environment

Genomes and the environment have…

regulated growth and differentiation interact to form an organism.

What is penetrance?

The frequency with which an organism with a particular genotype displays the corresponding phenotype in a population

Penetrance depends on what?

Both genotype and environment

Penetrance can be both…

…complete or incomplete.

What is complete penetrance?

When a gene or genes for a trait are expressed in all the population who have the genes

What is incomplete penetrance?

The genetic trait is expressed in only part of the population. 

What is an example of incomplete penetrance in humans?

Brachydactyly is a gene that forms shorted or deformed fingers and toes.

What is expressivity?

The degree to which a penetrant gene or genotype is phenotypically expressed in an individual.

What is constant expressivity?

100% expected phenotype

What is variable expressivity?

A range of phenotypes

What is an example of variable expressivity in humans?

Osteogenesis imperfecta, which causes fragile bones and blueness of the whiteness in the eyes.

Some genes can have incomplete penetrance with variable expressivity. What is an example of this in humans?

Neurofibromatosis, which shows 50-80% penetrance and variable expressivity.

What is the age of onset?

The age of the organism creates internal environment changes that can influence gene function.

What is an example of “the age of onset” in human conditions?

* Male-pattern baldness
* Muscular dystrophy

What are telomeres?

The structures that “cap” the end of chromosomes

Cancer cells and germ cells produce…

telomerase.

What is the Programmed Life Span Hypothesis?

Telomeres keep the chromosomes from coming apart, but once they break down, aging begins and cells are to stop dividing.

What are free radicals?

Oxygen-containing molecules with an uneven number of electrons that can adversely alter lipids, proteins, and DNA and trigger a number of human disease

What is Werner’s syndrome associated with?

A mutation in a helicase enzyme

What are sex-linked conditions?

Characteristics that are determined by genes located in the sex chromosomes

Sex-influenced traits are…

Encoded by autosomal genes that are more readily expressed in one sex.

Sex-limited traits inheritance is…

Encoded by autosomal genes and expressed in ONLY one sex.

What is dosage compensation of X-linked genes?

A problem of dosage of genes on the X chromosome, making it more common in females than males.

What is an example of dosage compensation of X-linked genes?

During early development of the embryo, one X chromosome remains genetically active, and the other does not. This is known as X inactivation.

X-chromosome inactivation has two consequences.

* Dosage compensation (single-active-X-principle)
* Genetic mosaic

What is a genetic mosaic?

An individual that has cells of two or more different genotypes

Women who are heterozygous for an X-linked recessive mutation have…

an absence of sweat glands.

The calico cats’ different colored spots are an example of what?

X-chromosome inactivation

Genetics can be altered by temperature. What is an example?

The dark fur of Siamese cats develops in areas that need to stay warmer.

Genetics can be altered by chemicals. What is an example?

Phenylketonuria, which is the metabolism of the amino acid phenylalanine in humans.

What is the Norm of Reaction?

The range of potential phenotypes that a single genotype could produce if exposed to a range of environmental conditions.

What is continuous variation?

A variation in a population showing an unbroken range of phenotype rather than discrete categories

What is an example of continious variation?

Human height

What is a polygenic trait?

A characteristic that is influenced by two or more genes.

What is multifactorial inheritance?

Traits that are caused by a combination of gene and environmental interaction.

What is pleiotropy?

A single gene that affects two or more characteristics

What are the haploid gametes?

Egg and sperm

Sexual reproduction depends on what?

Sexual differentiation

What is sexual dimorphism?

Distinct difference in size or appearance between the sexes in addition to difference between the sexual organs themselves.

What is sexual differentiation?

The process of development of the sex differences between males and females from an undifferentiated zygote.

Heterogametic

Individuals of a species in which the sex chromosomes are not the same (XY).

Homogametic

Individuals of a species in which the sex chromosomes are the same (XX).

What is XX - XO sex determination?

Females have two X chromosomes and males simply carry a single X, the “O” in “XO” indicates the absence of the second sex chromosome.

What is ZZ - ZW sex determination?

The sperm determines the sex. Males are the homogametic sex (ZZ), while females are the heterogametic sex (ZW).

What is the function of pseudoautosomal reigions?

They allow the X and Y chromosomes to pair and properly segregate during meiosis in males.

X and Y chromosomes are not homologous. However, they typically act as if…

…they are homologus.

The male-specific region of the Y is known as what?

The MSY

The sex-determining region of the Y is known as what?

SRY

What is environmental sex determination? 

A mechanism in which an individual's sex is decided after conception, according to its immediate environment, such as temperature.

What is a genic sex-determining system?

Sex is genetically determined, but there are no sex chromosomes, and the sexual phenotype is determined by genes at one or more loci.

What is an example of a genic sex-determining system?

Some plants and protozoans

What is an example of an environmental sex determination system?

Reptiles, such as alligators or turtles.

What are Poly-X females?

47, XXX

What is Jacob’s syndrome?

47, XYY