GENETICS TEST 5 (FINAL)

At the cellular and genetic levels, cancer is

usually a multistep process

Once a cancerous cellular growth has become malignant

the cells are invasive (that is, they can invade healthy tissues)

Cancerous cells are also

metastatic (that is, they can migrate to other parts of the body)

Oncogene

a mutant gene that is overexpressed or hyperactive and contributes to cancerous growth

Tumor-suppressor gene

a gene that prevents cancer. Loss-of-function mutations in these genes allow cancerous growth to occur

Proto-oncogenes that are involved in the cell cycle can be

mutated to become oncogenes, which causes unregulated cellular division

Tumor-suppressor genes that normally regulate the cell cycle can be

inactivated, which causes unregulated cellular division

Because there are two copies of most genes, only one copy of proto-oncogenes

need to be affected to cause cancer, while both copies of tumor-suppressor genes usually need to be inactivated to cause cancer

Oncogenes promote

abnormal cell growth

Proto-oncogenes are

normal cellular genes that can be mutated into an oncogene

egf

Epidermal growth factor

ngf

Nerve growth factor

sis

Platelet-derived growth factor

erbB

Growth factor receptor for EGF (epidermal growth factor)

fms

Growth factor receptor for NGF (nerve growth factor)

ras

GTP/GDP-binding protein

raf

Serine/threonine kinase

src/abl

Tyrosine kinase

myc/jun/fos

Transcription factor

Tumor-suppressor genes play

a role in preventing the proliferation of cancer cells

rb

The protein is a negative regulator of E2F (see Figure 25.14). The inhibition of E2F prevents the transcription of certain genes required for DNA replication and cell division

p16

a protein kinase that negatively regulates cyclin-dependent kinases. This protein controls the transition from the G1 phase of the cell cycle to the S phase

NF1

The protein stimulates Ras to hydrolyze its GTP to GDP. Loss of function causes the Ras protein to be overactive, which promotes cell division

APC

a negative regulator of a cell-signaling pathway that leads to the activation of genes that promote cell division

p53

a transcription factor that acts as a checkpoint protein and positively regulates a few specific target genes and negatively regulates others in a general manner. It acts as a sensor of DNA damage. It can prevent progression through the cell cycle and also
can promote apoptosis

BRCA-1, BRCA-2

proteins are both involved in the cellular defense against DNA damage. These proteins facilitate DNA repair and can promote apoptosis if repair is not achieved.

Most cancers are caused by

mutations in multiple genes, but the order of the
mutations is not necessarily important

Tumor cells often have

missing, extra and rearranged chromosomes

Inherited mutations in either oncogenes or tumor suppressor genes can

lead to a predisposition for developing cancer

Abnormalities in chromatin modification are

common in cancer cells

morula

16-cell stage

blastula

32-cell stage

gastrula

64-cell stage

The uniformity of the dividing cells in a developing animal clearly start

to differentiate at the gastrula stage

Morphogens

molecules that convey positional information and promote developmental changes

Morphogens can

act at the earliest stage of development in the unfertilized oocyte

homeotic gene

Genes that specify the final identity of a body region

anteroposterior axis

head-tail

dorsoventral axis

up-down or front-back

An adult fly emerges from its pupal case with four definable axes:

anteroposterior axis, dorsoventral axis, left-right axis, and proximodistal axis

proximodistal axis

how the limbs are attached to the body

There are three classes of segmentation genes:

Gap genes, pair-rule genes, and segment-polarity genes

Sequential expression of gap, pair-rule and segment-polarity genes divides the embryo into segments

Maternal effect genes to gap genes to pair-rule genes to segment-polarity genes

homeotic mutant

refers to mutant alleles in which one body part is replaced by another

polycomb genes

represses the expression of homeotic genes in regions of the embryo where they should not act

trithorax genes

promote the expression of homeotic genes in regions of the embryo where they should act

Male (XO) (nematode):

Produce sperm
An adult male is composed of 1,031 somatic cells

Hermaphrodites (XX) (nematode):

Produce sperm and eggs
An adult hermaphrodite is composed of 959 somatic cells

cloned genes from simpler organisms such as Drosophila are used

as probes to identify homologous vertebrate genes

By comparison, plants have two axes:

Root-shoot axis and radial axis

Root-shoot axis

Most plant growth occurs via cell division near the tips of the shoots and the bottom of the roots

Radial axis

A plant shoot gives off the buds that give rise to branches, leaves and flowers

In insects XX are female, XY and X0 are male

The X chromosome dictates femaleness and is governed by the Sxl gene
An insect lacking two X chromosomes is male

In animals, XX and X0 are female, XY and XXY are male

The Y chromosome dictates maleness and is governed by the SRY gene
An animal with a Y chromosome is male and an animal lacking a Y chromosome is female

In Drosophila the Sxl gene dictates

femaleness and is active in females and inactive in males

In male animals

the SRY gene is active

polymorphism

refers to the observation that many traits display variation within a population

At the DNA level:

polymorphism occurs when two or more alleles influence a phenotype

Polymorphic is also used to

describe a gene that commonly exists as 2 or more alleles in a population

The allele frequency formula

look at it

The genotype frequency formula

look at it

For a given trait, the allele and genotype frequencies are

always less than or equal to 1

For polymorphic genes

The frequencies of all of the alleles should add up to 1

Note that the Punnett square analysis gives the

same result mathematically as the Hardy Weinberg equation p2 + 2pq + q2 = 1

Hardy Weinberg equation

look at it

Mechanisms that alter existing genetic variation:

Natural Selection, random genetic drift, migration, and nonrandom mating

Simply stated, natural selection is

the survival of the fittest

Simply stated, beneficial alleles are

favored in a population

Darwinian fitness

a quantitative assessment of the relative likelihood that a genotype will survive and contribute to the gene pool of the next generation

Darwinian fitness or relative fitness values (w)

a measure of reproductive superiority and it should not be confused with physical fitness

Four patterns of natural selection

Directional selection, balancing, disruptive or diversifying selection, and stabilizing selection

Directional selection

Favors the survival of one extreme phenotype that
is better adapted to an environmental condition

Balancing

Favors the maintenance of two or more alleles

Disruptive or diversifying selection

Favors the survival of two or more different phenotypes

Stabilizing selection

Favors the survival of individuals with intermediate phenotypes

Directional selection favors

individuals at one extreme of a phenotypic distribution
that are more likely to survive and reproduce in a particular environment

Directional selection affects

the Hardy-Weinberg equilibrium and allele
frequencies by favoring the extreme phenotype as determined by w, the relative fitness value

The mean fitness of the population, (wU), formula

look at it

There are two types of balanced polymorphisms

Heterozygote advantage and negative frequency-dependent selection

Heterozygote advantage

the heterozygote has a higher fitness than either homozygote

Negative frequency-dependent selection

the fitness level of a genotype decreases when its frequency becomes higher- rare individuals have a higher fitness level than the more common individuals- rare individuals are more likely to reproduce, which produces a balanced polymorphism

The selection coefficient formula

look at it

Complex traits

traits that are determined by multiple genes and influenced by environmental factors

Quantitative traits

traits that can be described numerically

continuous traits

they do not fall into discrete categories (ex. height and weight)

meristic traits

traits that can be expressed in whole numbers (ex. bristle hairs on flys)

threshold traits

traits that are inherited due to the contributions of many genes (ex. often diseases)

Biometrics

the statistical study of biological traits

Variance (VX)

the deviance from the mean for measurable values in a group

Polygenic inheritance

transmission of traits that are governed by two or more genes

Polygenic traits or phenotypes are

influenced by both the genetic makeup and the environment

Environmental impact increasingly skews the

Mendelian inheritance ratio as more and more genes
are involved

Both genetic variance and environmental variance
contributes to

the overall phenotypic variance that is observed for a trait

Heritability

the amount of phenotypic variation within a group of individuals that is due solely to genetic variation

Broad sense heritability (hB2)

takes into account all of the different types of genetic variation that may affect the phenotype

narrow sense heritability (hN2)

The heritability of a trait due solely to the additive effects of alleles (VA)

Can calculate narrow sense heritability as

look at chapter 28

The closer the relationship between genetically related individuals

the higher the rexp becomes

Selective breeding

the modification of phenotypes in plant and animal species of economic importance

Selective breeding is also called

artificial selection