Genetics Exam 1

genetics

the study of heredity in all its manifestations

• revolves around genes

genetics is important because

• it unifies the study of biology

• it has a profound impact on human affairs

history of genetics

• domestication of animals began 13,000 BC

• cultivation of plants began around 8,000 BC

• ancient greek philosphers were the first to provide formal explanations of heredity and variation

hippocrates

“Of the semen, however, I assert that it is secreted

by the whole body healthy by healthy parts, sick

by sick parts. Hence as a rule, bald-headed

begets bald-headed, blue-eyed beget blue-eyed”

Democritus

“more people become able by exercise than by their natural prediposition”

plato

advocated the selection of spouses to produce children who will develop into bodily and ethically eminent personalities

aristotle

The male semen was only formed from the blood

„ It provides a “form”

The menstrual blood contains the “matter” for offspring

The “form” controls and shapes the “matter” into the mature offspring

William Harvey

• proposed that all living things originate from an egg

• introduced the theory of epigenesis

  • all parts of the embryo are present potentially in the egg

  • the organism evolves by gradual building up and aggregation of these parts

Antonie van Leeuwenhoek

• discovered spermatozoa

• speculated that the sperm provides the essential life-giving properties and the egg merely furishes the proper environment for the embryo’s nutrition and development

Theory of Preformationism

• the organism is contained in one of the sex cells as a fully developed (albeit miniature) homunculus

• with proper nourishment the homunculus unfolds into its adult proportions

• the spermists believed the homunculus was found in the sperm

• the ovists believed the homunculus resided in the egg

Caspar Wolff

discredited the theory of preformationism

Jean Baptiste de Lamarck

-proposed the first theory of evolution

The Theory of the Inheritance of Acquired Characteristics consists of two major laws:

„ I. Change in the environment

„ => change in the needs of the organism

„ => change in their behavior

„ => excess use or disuse of an organ orstructure

„ => increase or decrease in the size of theorgan or structure

„ II. All changes of such nature are inherited

charles darwin

proposed the theory of organic evolution by natural selection

The theory can be summarized as follows:

„ Variation is characteristic of animals & plants

„ Variation can be inherited

„ Every organism group overproduces offspring

„ A struggle for survival ensues

„ Individuals with the most favorable variations are more likely to survive and leave offspring

„ Passing on favorable variations leads to evolution of populations

Darwin’s Pangenesis

• Cells of the developing organism are capable of producing gemmules, which are exact but minute copies of each body part

• These are carried by the blood to the reproductive organs where they are assembled into gametes

• With fertilization, the combined gemmules then separate out to different parts of the body during development

August Weismann

• disproved Darwin’s Pangenesis and proposed the Germplasm Theory of Heredity

Multicellular living organisms are made up of two

types of tissue

„ - Somatoplasm = Body tissues

„ - Essential for functioning of the organism

„ Germplasm = Hereditary material

„ Set aside for reproductive purposes

There was a continuity of Germplasm between successive generations

The Germplasm is associated with the nucleus

Hybridists before Mendel

• Joseph Kolreuter

• Karl Gaertner

• Both obtained results similar to those Mendel would later record, but they failed to realize the significance of their work

Johann Gregor Mendel

• a priest who worked with garden peas in the garden of his monastery

• used the results of cleverly-designed experiments to propose The Particulate Theory of Inheritance

• his work went largely unnoticed for 34 years

William Bateson

• first to demonstrate experimentally the extension of Mendel’s Laws to animals

• coined the term Genetics to describe the science of heredity

eugenics

• term coined by Francis Galton

• refers to the improvement of a population by selecting its best specimen for breeding

• Galton believed that many human traits are inherited and thus subjects to selection

francis galton

was concerned by the “differential fertility” of the “genetically-inferior”

advocated for

• positive eugenics: encouraging the reproduction of those with beneficial traits

• negative eugenics: discouraging the reproduction of those with undesirable traits

eugenics movement

• had a strong impact on US public policy in the early 20th century

  • compulsory sterilization of “eugenically unfit” individuals

  • Laws invalidating marriages between “eugenically-unfit” individuals

  • immigration restriction act

  • started floundering in the 1930s

blending theory

factors that control hereditary traits are maleable

• they can blend together generation after generation

• gregor mendel’s experiments refuted this theory

mendel’s experimental system

• used pure-breeding lines of garden peas

• selected 7 traits to study (each had two distinguishable appearances)

• carefully designed his experiments and gathered mathematical data

Law of Segregation

paired factors segregate randomly so that half of the gametes received one factor and half of the gametes received the other

• union of male and femal gametes reestablishes the paired units

phenotype

the physical appearance of an individual and is a product of the genotype and the environment

test-cross

• an orgnaism with known phenotype but unknown genotype is crossed with an organism that has the recessibe phenotype

Law of Independent Assortment

the segregation of any pair of hereditary determinants is independent of the segregation of other pairs

• phenotypic ratio (9:3:3:1)

modern genetics

• are interested in the relationship between the molecular expression of genes and the outcome of traits

loss-of-function alleles

the defective copies of genes

• commonly inherited in a recessive manner

product rule

the probability of the occurrence of independent events is the product of their respective probabilities (AND)

sum rule

probability of the occurrence of one of several mutually exclusive events is the sum of their respective probabilities (OR)

Binomial expansion equation

probability of the occurrence of unordered mutually exclusive events is defined by the binomial theorem

Chi-square test

a statistical method used to determine “goodness of fit”

• refers to how close the observed data are to those predicted from a hypothesis

• low: observed deviations could be due to random chance alone

• high: low probability that the observed deviations are due to random chance alone

monozygotic twins

identical twins that are formed from the same sperm and egg

• share the disease more often than fraternal twins

Dizygotic twins

fraternal twins formed from separate pairs of sperm and egg

concordance

degree to which a disorder is inherited

the percentage of twin pairs in which both twins exhibit the disorder or trait

• actual is often less than theoretical

observation 1

when an individual exhibits a disease, the disorder is more likely to occur in blood relatives than in the general population

observation 2

identical twins share the disease more often than fraternal twins

observation 3

the disease does not spread to individuals sharing similar environmental situations

observation 4

different populations tend to have different frequencies of the disease

observation 5

the disease tends to develop at a characteristic age

• many genetic disorders exhibit a specific age of onset

observation 6

the human disorder may resemble a genetic disorder tha is already known to have a genetic basis in an animal

observation 7

a correlation is observed between a disease and a mutant human gene or a chromosomal alteration

pedigrees

diagrams that show the relationship among members of a family, as well as their status with respect to a particular hereditary condition

autosomal dominant

• trait is usually present in every generation

• members of both sexes affected equally

• unaffected parents produce unaffected offspring

huntington disease (HD) (autosomal dominant)

degeneration of certain types of neurons in the brain, leads to personality changes, dementia and early death

• result of a mutuation in a gene that encodes a protein termed huntingtin

autosomal dominant disorders

• achondroplasia

• polydactyly

• brachydactyly

• syndactyly

haploinsufficiency

heterozygote has 50% of the normal protein

not sufficient for a normal protein

gain-of-function mutations

mutation changes protein so it gains a new function

dominant negative mutations

the altered gene product acts antagonistically to the normal product

autosomal recessive

• trait tends to skip generations

• members of both sexes affected equally

• unaffected parents can have an affected child

• two affected parents cannot have an unaffected child

albinism (autosomal recessive)

absence or partial deficiency of melanin in the skin, eyes and hair

• occurs in a wide variety of animals

cystic fibrosis (autosomal recessive)

most common lethal genetic disease among caucasians

• mutant allele creates an altered CFTR protein that ultimately causes ion imbalance

• average life expectancy is about 50 years

Tay-Sachs Disease

• affected individuals appear healthy at birth but then develop neurodegenerative symptoms at 4 to 6 months

• patients typically die at 3 or 4 years of age

x-linked recessive

• trait may skip generations

• most affected individuals are male

• affected males result from affected mothers or mothers who are carriers

• affected females come from affected fathers and affected or carrier mothers

• affected females will have affected sons

hemophilia (x-linked recessive disorders)

blood cannot clot properly when a wound occurs

common accidental injuries pose a threat of severe internal or external bleeding

called “royal disease” as it has affected many members of european royal families

hemizygous

males only have a single copy of most x-linked genes

• females heterozygous for an x-linked recessive gene will pass this trait to half her sons

x-linked dominant

• trait does not skip generations

• affected males must come from affected mothers

• affected females come from affected mothers or fathers

• males are often more severely affected

y-linked traits

trait only affects males

• affected males get it from their fathers and give it to their sons

locus heterogeneity

a disease can be caused by mutations in two of more different genes

penetrance

proportion of individuals with a specific genotype who manifest the corresponding phenotype

phenocopy

an organism whose phenotype has been modified to resemble the phenotype of a different mutant organism

incomplete dominance

the phenotype of the heterozygote is intermediate between that of the homozygotes (partial dominance)

codominance

the phenotype of the heterozygote is a mixture of the phenotypes of the homozygotes

multiple alleles

more than 2 alleles for the same gene

agglutination

donor’s RBC will clump in the recipient’s bloodstream

• could lead to death

• occurs from incompatible blood samples coming together in the humman body

Type A

can donate to: Type A and Type AB

can recieve from: Type A and Type O

Type B

can donate to: Type B and Type AB

can recieve from: Type B and Type O

Type AB

can donate to: Type Ab

can recieve from: all

Type O

can donate to: all

can recieve from: Type O

lethal allele

allele that has the potential to cause the death of an organism

• typically the result of mutations in essential genes

• usually inherited in a recessive manner

essential genes

genes that are absolutely required for survival

nonessential genes

those not absolutely required for survival

recessive lethal allele

the heterozygous state is tolerated

dominant lethal allele

if the heterozygous state leads to death

conditional lethal alleles

may kill an organism only when certain environmental conditions prevail

semilethal alleles

kills some individuals in a population, but not all of them

• environmental factors and other genes may help prevent the detrimental effects of semilethal genes

temperature-sensitive lethal

• a developing drosophila larva may be killed at 30 degrees but will survive if grown at 22 degrees celsius

pleiotropy

a genetic phenomenon where a single gene or locus influences two or more distinct, and often seemingly unrelated, phenotypic traits

pleiotropy occurs for several reasons

• The gene product can affect cell function in more than one way

• The gene may be expressed in different cell types

• The gene may be expressed at different stages of development

overdominance

phenomenon in which a heterozygote is more vigorous than both of the corresponding homozygotes

• aka heterozygote advantage

antigen

a substance that stimulates the immune system to produce antibodies

sickle cell anemia (autosomal recessive)

defect is a mutation in the chain for the B chain of hemoglobin

Sickled red blood cells are destroyed by liver.

 Anemia causes impaired growth and weakness

Odd-shaped cells clump

 Partial or complete blocks in capillary circulation.