midterm 2 bio 97

hypomorphic

Refers to a mutation that reduces but does not eliminate the activity of a particular gene product.

loss of function type of mutation

Make less of a gene product

null or amorphic mutation

null alleles produce no functional product

loss of function type of mutation

Or nothing at all

dominant negative mutation

A heterozygote produces a nonfunctional altered protein that also prevents the normal gene product from functioning

loss of function mutation

One copy of a disfunctional allele can destruct the other ones

characterized as negative due to the spoiler effect of the abnormal polypeptide on the multimeric protein

hypermorphic mutation

enhanced gene function (protein functions more efficiently)

-extremely rare

-usually dominant

gain of function mutation

Make more of a gene product

neomorphic mutation

a mutant expressing a new or novel function not seen in the wild type

gain of function mutation

Like insulin being produced in your toe

nonpenetrant

the phenotype is not consistent with the genotype

Sometimes an organism with a particular genotype fails to produce the corresponding phenotype

healthy individuals who are heterozygous for diseased mutations

penetrant

when the phenotype is consistent with the genotype

Showing the disease

haplosufficient

describes a gene that, in a diploid cell, can promote wild-type function in only one copy (dose)

1 copy is enough

haploinsufficient

when a single copy of a gene is not sufficient to produce a wild-type phenotype

a single copy of an allele is not enough to be healthy

incomplete penetrance

indicates that less than 100% of individuals with a mutant genotype have the mutant phenotype.

traits that are nonpenetrant in some individuals are characterized as displaying __________

e.g. polydactyly (many digits)

variable expressivity

indicates that the severity of a mutant phenotype differs among individuals with the same mutant genotype.

Epistasis

2+ genes have control over one trait

when it's NOT a 9:3:3:1 ratio

Pleiotropy

1 gene has control over many traits

somatic cells

cells in the body other than sperm or egg cells

totipotent cells

Stem cells with the potential to differentiate into any type of cell.

Pluripotent

Able to give rise to multiple, but not all, cell types.

differentiated cells

a cell is no longer able to differentiate into any type of tissue

hox genes

Class of homeotic genes. Changes in these genes can have a profound impact on morphology.

hox genes are a subset of homeobox genes which only regulate the formation of axes and appendages in organisms.

homeobox

homeobox genes are mainly involved in the regulation of the entire morphogenesis process, while hox genes are a subset of homeobox genes which only regulate the formation of axes and appendages in organisms.

Antennapedia complex

Cluster of five homeotic genes in fruit flies that affects the development of the adult fly's head and anterior thoracic segments.

bithorax complex

cluster of homeotic genes in Drosophila that control development of structures in the thorax & abdomen of the embryo

homeodomain

A conserved sequence of 60 amino acids used in the binding to DNA. Usually found in transcription factors, it is used to express genes that are related, more specifically in development to make tissues associated with one another.

the part of the protein that attaches (binds) to specific regulatory regions of the target genes

Complementation

Two different mutations in the heterozygous condition are exhibited as the wild-type phenotype; indicates that the mutations are at different loci.

testcross

cross between an organism with an unknown genotype and an organism with a recessive phenotype

1:1:1:1

aabb x ?

dihybrid cross

A cross between individuals that have different alleles for the same gene

AaBb x AaBb

can only see epistasis in a _______

how do hox genes regulate embryonic development in drosophila?

Hox gene expression marks the boundaries of parasegments. Each parasegment expresses a unique combination of Hox gene products that give rise to the identity of each parasegment.

homeotic mutation

a mutation that causes a change in the placement of body parts, like causing a developing fly's antenna to be replaced by a leg

transcription factors

Collection of proteins that mediate the binding of RNA polymerase and the initiation of transcription.

Most of the genes controlling development encode either signal molecules or transcription factors

complementation group

all mutations present in any single gene

lethal allele

an allele whose expression results in the death of the individual organism expressing it

Some genes have alleles that prevent survival when homozygous or heterozygous.

results in 1/3 of progeny with dominant phenotypes and 2/3 recessive

allelic series

describes the dominance hierarchy of multiple alleles

a group of alleles of a gene that display a hierarchy of dominance relationship among them

Delayed age of onset

symptoms usually are not seen until 40 years of age or later

the abnormalities they produce do not appear until after affected organisms have had an opportunity to reproduce and transmit the mutation to the next generation.

e.g. Huntington's disease

temperature-sensitive allele

an allele whose product is functional only at certain temperatures

Penetrance

The percentage of individuals with a particular genotype that actually displays the phenotype associated with the genotype.

gene-environment interactions

influence of environmental factors (i.e., nongenetic factors) on the expression of genes and on the phenotypes of organisms.

e.g. arctic mammals coat color changes in winter (white), spring and summer (brown)

expressivity

the degree to which a trait is expressed

wildtype

original nucleotide sequence

law of independent assortment

Each member of a pair of homologous chromosomes separates independently of the members of other pairs so the results are random

incomplete dominance

Cases in which one allele is not completely dominant over another

heterozygotes with a novel phenotype between the dominant and recessive homozygotes

Need two functional red pigment copies, but if there's only one then there will be a pink flower

sex linkage

the presence of a gene on a sex chromosome

Genes carried on sex chromosomes, such as the X chromosome of humans, show different inheritance patterns than genes on autosomal (non-sex) chromosomes.

variations from classic mendelian genetics

multiple alleles, incomplete dominance, codominance, pleiotropy, lethal alleles, sex linkage

penetrance

the probability that a mutation will manifest its phenotype

rabbit allelic series order of dominance

C > c^ch > c^h > c

full color > chinchilla > himalayan > albino

brown rabbit is dominant to

chinchilla, himalaya, and albino

chinchilla rabbit is partially dominant to

himalayan and dominant to albino

himalayan rabbit is dominant to

albino

Wildtype

Unaffected

Codominance

both traits are fully and separately expressed

null hypothesis

the normal hypothesis that COULD be proven wrong

it assumes that there is no real difference between the observed and expected values

chi squared test

it is a goodness of fit test

does the observed match the expected?

if it is a really good fit then you will have a very low x^2 value (not random chance)

the higher the chi-squared value, the lower chances are of it being random chance (it is random chance)

test cross

the crossing of an individual of unknown genotype with a homozygous recessive individual to determine the unknown genotype

back cross

cross between an offspring (usually the F1) genotype and one of the parental genotypes

monohybrid cross

A cross between individuals that involves one pair of contrasting traits

Aa x Aa

wild-type allele

natural or most common allele in a population

gain of function mutation

a mutation causing a gene to be overexpressed, to be expressed at the wrong time, or to encode a constitutively acting protein; usually inherited as a dominant mutation

certain gain of function mutations are lethal in a homozygous state

hypermorphic and neomorphic mutations

loss of function mutation

causes a complete or partial loss of function

both null and hypomorphic loss-of-function mutations are often recessive and homozygous lethal

multimeric proteins

A protein with more than one polypeptide chain; also said to have a quaternary structure.

particularly subject to dominant negative mutations

dimer

a molecule or molecular complex consisting of two identical molecules linked together.

phenotypic ratio for complete dominance

3:1

phenotypic ratio for incomplete dominance

1:2:1

Antigen

A protein that, when introduced in the blood, triggers the production of an antibody

H antigen

flagellar antigen

locus

Location of a gene on a chromosome

fully penetrant

when the genotype is always expressed in the phenotype

genetic heterogeneity

mutations in different genes can produce the same or very similar mutant phenotypes

genetic complementation analysis

An experimental analysis of crosses designed to test alternative genetic explanations of an abnormal phenotype

Results can determine whether mutant organisms carry mutations of different genes that produce the abnormal phenotype or if the abnormal phenotype occurs due to allelic mutations on the same gene

Number of complementation groups = the number of genes

done by crossing pure breeding mutants for a recessive mutation and observing the phenotype of F1 progeny. If the F1 progeny have the wild type phenotype, genetic complementation has occurred, and the conclusion is that the mutant alleles are of different genes. But if the mutant alleles are of the same gene, the progeny of two pure-breeding mutants will have a mutant phenotype.

genetic complementation

(1) The observation of a wild-type phenotype in an organism or cell containing two different mutations.

(2) The cross of two pure-breeding mutants that yields progeny that are exclusively wild type.

syntenic genes

genes that are located on the same chromosome

Iinked genes are always

Syntenic

genetic linkage

tendency for genes located close together on the same chromosome to be inherited together

homologous recombination

Exchange of genetic information between homologous DNA molecules.

recombinant chromosomes

A chromosome created when crossing over combines the DNA from two parents into a single chromosome.

recombination frequency

The rate of occurrence of recombination between a pair of linked genes.

r = number of recombinants/total number of progeny

hemizygous

A gene present on the X chromosome that is expressed in males in both the recessive and dominant condition

Proto-oncogenes

the corresponding normal cellular genes that are responsible for normal cell growth and division

tumor suppressor genes

encode proteins that help prevent uncontrolled cell growth

normal function involves preventing cell division

Dysplasia

abnormal development or growth of cells, tissues, or organs

Benign cell masses

noncancerous

SNP

Single nucleotide polymorphism, change of base of single DNA nucleotide, makes up 90% of all human genetic variation

occurs every 300 bases in the human genome on average

there are about 10 millions SNPs in the human genome - most don't actually do anything

despite this, human genomes are very similar - they have 7x less genetic variation than in chimpanzees our closest relatives

number of SNPs where you match another person can therefore be used to tell how closely related you are

"typos" in the DNA sequence

dedifferentiated

loss of specialized cell characteristics, seen in cancer

act more like primordial cells than specialized cells

proliferation

active cell reproduction and tissue growth

primordial cells

undifferentiated cells (stem cells) that have the capacity to form into various systems

Hyperplasia

the enlargement of an organ or tissue because of an abnormal increase in the number of cells in the tissues

before cells become cancerous, they begin to look and grow abnormally

abnormality can first appear as hyperplasia

then progress to dysplasia

Neoplasia

dysplastic cells can progress to neoplasia - a general term for a cancerous condition or tumor

malignant tumor

cluster of cells that are cancerous

metastisis

The spread of cancer cells beyond their original site

proto-oncogenes and tumor suppressor genes

proto-oncogenes: start cell division, "gas"

tumor-suppressor genes: switch off cell division - "brake" mutations of these genes are like brake failure

Oncogenes

genes that cause cancer by blocking the normal controls on cell reproduction

"stuck accelerator"

sporadic

a term describing 90% or more of all cases of cancer, that develop as the result of the accumulation of multiple somatic mutations; these cancers occur without the inheritance of a specific mutation that increases an individual's susceptibility of cancer

germ-line mutation

a mutation occurring in gametes; passed on to offspring

leads to familial or hereditary cancer

de novo mutation

A new mutation that was not inherited from either parent

hereditary retinoblastoma

40% of retinoblastoma cases.

Onset typically is earlier than sporadic cases.

Multiple tumors involving both eyes.

Consistent pedigrees; siblings and offspring develop the same type of tumors.

two hit hypothesis

Tumor suppressor genes typically require both copies to be inactivated before an effect is seen.

Genotype of a normal cell in the retina in a person who has sporadic retinoblastoma?

RB1+ RB1+

What is the normal cell genotype if the person has hereditary retinoblastoma?

RB1+ RB1-

Hypermethylation

inactivates transcription of DNA

Methylation makes DNA mute

p <= 0.05

reject the null hypothesis

conclude that the observed experimental results are due to chance and the variable being tested had no effect. the results are "not significant" (due to chance)

little chance that the null hypothesis is true

null hypothesis assumes that there is no real difference between the observed and expected data

smaller X^2 value means that there are higher chances of it being due to random chance

p > 0.05

fail to reject (accept) the null hypothesis. The two groups are not statistically different.

big chance the null hypothesis is true

null hypothesis assumes that there is no real difference between the observed and expected data

bigger X^2 value means that there are lower chances of it being due to random chance