BIO-457 Exam 1 Flashcards

Thomas Hunt Morgan

the father of modern genetics, does groundbreaking work using Drosophila melanogaster

Frederick Sanger

DNA sequencing technique developed by

The study of the human genome provides

-How many genes we have
-How cells develop into complex tissue
-How defective genes cause disease

DNA, the molecule of life

-46 human chromosomes, found in 23 pairs
-2 meters of DNA
-Approximately 22,000 genes coding for proteins that perform most life functions
-Approximately 3 billion DNA base pairs per set of chromosomes, containing the bases A, T, G and C

The gene is classically defined

as a 'unit' of heredity

Catabolic enzymes

-Involved in the breakdown of large molecules into smaller ones
-Provide energy for the activities of the cell

Anabolic enzymes

-Involved in the synthesis of large molecules from smaller ones
-Provide components for the construction of the cell

Transcription

The genetic information in DNA is copied into a nucleotide sequence of ribonucleic acid (RNA)

Translation

The nucleotide sequence in RNA provides the information (using the genetic code) to make the amino acid sequence of a protein

Morphological traits

Affect the appearance of the organism
Example: The color of a flower

Physiological traits

Affect the function of the organism

Morphs

Contrasting forms within a single species are termed

Genetic variation is a result of

-Gene mutations
-Changes in chromosome structure
-Changes in chromosome number

Traits are

a result of the interaction between genes and the environment

Homologs

-The two copies of a chromosome are termed
-Homologs contain the same genes

True-breeder

A variety that produces the same trait over several generations is termed

Empirical approach

believed that a quantitative analysis of crosses may provide mathematical relationships that govern hereditary traits

Particulate theory of inheritance

the genetic determinants that govern traits are inherited as discrete units that remain unchanged as they are passed from parent to offspring

Mendel's Law of Segregation

During gamete formation, the paired factors for a given character segregate randomly so that half of the gametes receive one factor and half of the gametes receive the other

Alleles

are different versions of the same gene

homozygous

An individual with two identical alleles

heterozygous

An individual with two different alleles

Genotype

refers to the specific allelic composition of an individual

Phenotype

refers to the outward appearance of an individual

Nonparentals

The F2 generation contains seeds with novel combinations (i.e.: not found in the parentals)
Round and Green
Wrinkled and Yellow

If the genes, assort independently,
Then the predicted phenotypic ratio in the F2 generation would be

9:3:3:1

law of Independent Assortment

During gamete formation, the segregation of any pair of hereditary determinants is independent of the segregation of other pairs

Loss-of-function alleles

Defective copies of genes

Prokaryotes

Bacteria and Archaea

Eukaryotes

Protists, fungi, plants and animals

Locus

The physical location of a gene on a chromosome is called

During the G1 phase

a cell prepares to divide

The S phase

-where chromosomes are replicated
-The two copies of a replicated chromosome are termed chromatids

End of S phase

a cell has twice as many chromatids as there are chromosomes in the G1 phase
-A human cell for example has
46 distinct chromosomes in G1 phase
46 pairs of sister chromatids after S phase

During the G2 phase

the cell accumulates the materials that are necessary for nuclear and cell division

M phase

cycle where mitosis occurs

The primary purpose of mitosis

to distribute the replicated chromosomes to the two daughter cells

By the end of interphase

the chromosomes have already replicated

Interphase

Prophase

Nuclear envelope dissociates into small vesicles
Chromatids condense into more compact structures
Centrosomes begin to separate
The mitotic spindle apparatus is formed

Prophase

Prometaphase

Centrosomes move to opposite ends of the cell, forming the spindle

Prometaphase

Metaphase

Pairs of sister chromatids align themselves along a plane called the metaphase plate

Metaphase

Anaphase

The connection holding the sister chromatids together is broken
Each chromatid, now an individual chromosome, is linked to only one pole

Anaphase

Telophase and Cytokinesis

Chromosomes reach their respective poles and decondense
Nuclear membrane reforms to form two separate nuclei
In most cases, mitosis is quickly followed by cytokinesis

Telophase and Cytokinesis

Mitosis and cytokinesis ultimately produce

two daughter cells having the same number and complement of chromosomes as the mother cell
The two daughter cells are genetically identical to each other

Meiosis

-Parents (diploid) make gametes with half the amount of genetic material (haploid)
-begins after a cell has progressed through interphase of the cell cycle

Prophase 1 of meiosis is further subdivided into five stages known as

Leptotene
Zygotene
Pachytene
Diplotene
Diakinesis

Mitosis

-produces two diploid daughter cells
-produces daughter cells that are genetically identical

Meiosis

-produces four haploid daughter cells
-produces daughter cells that are not genetically identical
The daughter cells contain only one homologous chromosome from each pair
The daughter cells contain many different combinations of the single homologs

Sexual reproduction

is a common way for eukaryotic organisms to produce offspring
Parents (diploid) make gametes through the process of gametogenesis with half the amount of genetic material (haploid)

Isogamous

-Some simple eukaryotic species
-They produce gametes that are morphologically similar

Heterogamous

Most eukaryotic species are
These produce gametes that are morphologically different
Sperm cells (male gametes)
Relatively small and mobile
Egg cell or ovum (female gametes)
Usually large and nonmotile
Stores a large amount of nutrients (animal spec

Spermatogenesis

A diploid spermatogonial cell divides mitotically to produce two cells
One remains a spermatogonial cell
The other becomes a primary spermatocyte

Oogenesis

-Early in development, diploid oogonia produce diploid primary oocytes
-The primary oocytes initiate meiosis 1
-The division in meiosis 1 is asymmetric producing two haploid cells of unequal size
A large secondary oocyte
A small polar body

If the secondary oocyte is fertilized

Meiosis 2 is completed
A haploid egg and a second polar body are produced
The haploid egg and sperm nuclei then fuse to create the diploid nucleus of a new individual

The chromosome theory of inheritance describes

how the transmission of chromosomes account for Mendelian patterns of inheritance
Established how chromosomes carry and transmit genetic determinants of traits

The chromosome theory of inheritance allows us to see

the relationship between Mendel's laws and chromosome transmission

Mendel's law of segregation can be explained by

the homologous pairing and segregation of chromosomes during meiosis

Mendel's law of independent assortment can be explained by

the relative behavior of different (nonhomologous) chromosomes during meiosis

heterogametic

Males contain one X and one Y chromosome

homogametic

Females have two X chromosomes

The sex chromosomes are designated

Males contain two Z chromosomes
Hence, they are homogametic
Females have one Z and one W chromosome
Hence, they are heterogametic

Genes that are physically located on the X chromosome are called

X-linked genes or X-linked alleles

Mendelian inheritance describes inheritance patterns that obey two laws

Law of segregation
Law of independent assortment

Simple Mendelian inheritance involves

A single gene with two different alleles
Alleles display a simple dominant/recessive relationship

Simple Mendelian

This term is commonly applied to the inheritance of alleles that obey Mendel's laws and follow a strict dominant/recessive relationship. In this chapter, we will see that some genes are found in three or more alleles, making the relationship more complex.

Incomplete
penetrance

In the case of dominant traits, this pattern occurs when a dominant phenotype is not expressed even though an individual carries a dominant allele. An example is an individual who carries the polydactyly allele but has a normal number of fingers and toes.

Incomplete
Dominance

This pattern occurs when the heterozygote has a phenotype that is intermediate between either corresponding homozygote. For example, a cross between homozygous red-flowered and homozygous white-flowered parents will produce heterozygous offspring with pink flowers.

Overdominance

This pattern occurs when the heterozygote has a trait that is more beneficial than either homozygote.

Codominance

This pattern occurs when the heterozygote expresses both alleles simultaneously without forming an intermediate phenotype. For example, in blood typing, an individual carrying the A and B alleles will have an AB blood type

X-linked

This pattern involves the inheritance of genes that are located on the X chromosome. In mammals and fruit flies, males have one copy of X-linked genes, whereas females have two copies

Sex-influenced inheritance

This pattern refers to the effect of sex on the phenotype of the individual. Some alleles are recessive in one sex and dominant in the opposite sex.

Sex-limited
inheritance

This pattern refers to traits that occur in only one of the two sexes. An example is breast development in mammals

Lethal alleles

An allele that has the potential of causing the death of an organism.

Prevalent alleles in a population are termed

wild-type alleles

Alleles that have been altered by mutation are termed

mutant alleles
-They are often defective in their ability to express a functional protein
-often inherited in a recessive fashion

Genetic diseases are usually caused by

mutant alleles
-the recessive allele contains a mutation

Dominant Mutants are much less common than recessive.
Three explanations for most dominants

-Gain-of-function
-Dominant-negative
-Haploinsufficiency

Incomplete Penetrance

dominant allele does not influence the outcome of a trait in a heterozygote individual
Example = Polydactyly

there are three possible explanations for overdominance at the molecular/cellular level

Disease resistance
Homodimer formation:Composed of two different subunits, encoded by the same gene
Variation in functional activity

Sex Chromosomes and Traits: X-linked

Hemizygous in males
Only one copy
Males are more likely to be affected

Sex Chromosomes and Traits: Y-linked

Relatively few genes in humans
Referred to as holandric genes
Transmitted only from father to son

Pseudoautosomal inheritance

inheritance refers to the very few genes found on both X and Y chromosomes

pleiotropy

Multiple effects of a single gene on the phenotype of an organism is called

Epistasis

An inheritance pattern in which the alleles of one gene mask the phenotypic effects of the alleles of a different gene
-Epistatic interactions often arise because two (or more) different proteins participate in a common cellular function

Complementation

A phenomenon in which two parents that express the same or similar recessive phenotypes produce offspring with a wild-type phenotype
-Complementation shows that the two mutant lines had the same phenotype caused by mutations in different genes

Gene modifier effect

A phenomenon in which an allele of one gene modifies the phenotypic outcome of the alleles of a different gene.

Gene redundancy

A pattern in which the loss of function in a single gene has no phenotypic effect, but the loss of function of two genes has an effect. Functionality of only one of the two genes is necessary for a normal phenotype; the genes are functionally redundant.

Paralogs

A species may have two or more copies of similar genes
These copies are not identical due to the accumulation of random changes during evolution

continuous traits

Quantitative traits such as height or weight

Diseases are often threshold traits—

traits that are inherited due to the contributions of many genes

Mean

_𝑋_ = ( Σ X ) / N

Variance

Vx = ( Σfi (Xi − _𝑋_)2 ) / N - 1

Standard Deviation

SD = __𝑉𝑥_

covariance

CoV(X,Y) = Σfi [(Xi − _𝑋_) (Yi − _𝑌_ )]
N - 1