Clinical Genetics Exam 1

Allele

An alternative form of a gene.

Partial dominance

A form of dominance in which the expression of the heterozygote is intermediate to the expressions of the homozygous genotypes and more closely resembles the expression of the homozygous dominant genotype

Co-dominant alleles

Pairs of alleles that both affect the phenotype when present in a heterozygote. Ex. AB blood type.

Wild type

The phenotype for a character most commonly observed in natural populations

Mutant

An organism or a new genetic character arising or resulting from an instance of mutation, which is generally an alteration of the DNA sequence of the genome or chromosome of an organism. It is a characteristic that would not be observed naturally in a specimen.

Mutation

A random error in gene replication that leads to a change

Null gene

Nonfunctional gene caused by a mutation, may not produce proteins

Amorphic

Complete loss of gene function

Hypomorphic

Refers to a mutation that reduces but does not eliminate the activity of a particular gene product (partial loss of function)

Sterile mutation

Mutation that causes sterility. Ex. kl-3 gene: sperm tails do not form.

Lethal mutation

A gene or chromosomal mutation that influences the development of an organism in such a way that the organism cannot survive

Loss of function mutation

Causes a complete or partial loss of function

Dominant negative mutation

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

Gain of function mutation

Causes the appearance of a new trait or function or causes the appearance of a trait in inappropriate tissue or at an inappropriate time

Complementation test

A test for determining whether two mutations are in different genes (they complement) or the same gene (they do not complement)

Penetrance

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

Expressivity

The degree to which a trait is expressed (can cause same gene to look different in different people)

Epistasis

A type of gene interaction in which one gene alters the phenotypic effects of another gene that is independently inherited.

Pleiotropy

The production by a single gene of two or more apparently unrelated effects.

Consanguineous mating

Mating between biological relatives

Inbreeding depression

When individuals with similar genotypes - typically relatives - breed with each other and produce offspring that have an impaired ability to survive and reproduce

Hybrid vigor

A phenomenon in which the hybrid state is selected because it has greater survival and reproductive success; also known as heterosis

Classical genetics

The study of the patterns and mechanisms of the transmission of inherited traits from one generation to another

Molecular genetics

The study and manipulation of DNA on a molecular level

Population genetics

Study of allele frequency distribution and change under the influence of evolutionary processes.

Name the 2 locations of DNA in eukaryotic cells

Mitochondria and nucleus

Name the 2 locations of DNA in prokaryotic cells

Plasmids and nucleolus

Ploidy

Number of sets of chromosomes in a cell

Diploid

(genetics) an organism or cell having two sets of chromosomes or twice the haploid number

Haploid

An organism or cell having only one complete set of chromosomes.

Somatic cells

Any cells in the body other than reproductive cells

Gametes

Sex cells

Germ line

The lineage of reproductive cells that contributes to the formation of a new generation of organisms, as distinct from somatic cells, which form the body and leave no descendants in the next generation.

Mitosis

Part of eukaryotic cell division during which the cell nucleus divides and forms two daughter cells. These cells are identical diploid cells.

Meiosis

Cell division that produces reproductive cells in sexually reproducing organisms. There are two steps: meiosis 1 and meiosis 2. At the end of meiosis 1 there are 2 diploid cells. Then these cells further divide into 4 haploid cells. These are not identical to the mother cell.

Clone

An organism that is genetically identical to the organism from which it was produced

Fission (cell)

Division of a parent cell into two or more daughter cells

Centriole

Structure in an animal cell that helps to organize cell division

Spindle

Fanlike microtubule structure that helps separate the chromosomes during mitosis

Quiescent

Inactive; at rest

Kinetochore

A specialized region on the centromere that links each sister chromatid to the mitotic spindle.

Cell cycle

Interphase (G1, S,G2, M), Mitosis (Prophase, Metaphase, Anaphase, Telephase), and Cytokinesis

Interphase

Cell grows, performs its normal functions, and prepares for division; consists of G1, S, and G2 phases. During G1 phase there is growth and metabolism. During S phase there is DNA synthesis and chromosome duplication. During G2 phase the cell prepares for mitosis.

Prophase

First and longest phase of mitosis, during which the chromosomes become visible and condense. The centrioles separate and take up positions on the opposite sides of the nucleus

Metaphase

Second phase of mitosis, during which the chromosomes line up across the center of the cell. The nuclear membrane breaks apart.

Anaphase

Phase of mitosis in which the chromosomes separate and the sister chromatids move to opposite ends of the cell

Telephase/Cytokinesis

Nuclear membranes form around each of the two sets of chromosomes the chromosomes begin to spread out (decondense) and the spindle starts to break down. Nuclear membrane forms.

The cell splits into two daughter cells, each with the same number of chromosomes as the parent. In humans such cells have two copies of 23 chromosome and are called diploid.

Prophase 1

Chromosomes become visible; nuclear envelope breaks down; crossing-over occurs. There are 5 stages: leptonema, zygonema, pachynema, diplonema, diakinesis.

Leptonema

chromosomes condense and become visible. Each chromosome has two sister chromatids.

Zygonema

Homologous chromosomes begin to pair (synapse) with Synaptonemal complex

Pachynema

The chromosomes are fully condensed and paired. Each bivalent becomes shorter, thicker, and splits into two sister chromatids called tetrads. Crossing over occurs at this point.

Diplonema

Within tetrads, sister chromatids separate but are still in contact at the Chiasma.

Diakinesis

Paired chromosomes condense further and become attached to spindle fibers. The spindle fibers attach to kinetochores and the chromosomes move to the central plane in pairs.

Metaphase 1

Paired chromosomes align on the equatorial plane in the cell. The chromosomes are oriented towards the opposite poles and the chisamata move towards the teleomers.

Anaphase 1

Homologous chromosomes disjoin and move to opposite poles of the cell.

Telephase 1

Chromosome movement is complete and new nuclei form. The spindle appartates is dissable. At this point just a membrane separates the daughter cells. The chromosomes still have two sister chromatids.

Prophase II

Chromosomes each condisiting of two chromatids condense and become attached to spindle fibers (a new spindle apparatus).

Metaphase II and anaphase II

The chromosomes align on the equitorial plane in each cell and then the sister chromatids disjoin and move to opposite poles in each cell.

Telophase II and cytokinesis

Chromosomes decondense and new nuclei begin to form. The separated chromatids gather at poles so the daughter nuclei will form. The chromatids are now considered chromosomes. Each daughter cell formed contains a haploid set of chromosomes. The haploid cells are separated by cytoplasmic membranes.

The principle of Dominance

In a heterozygote, one allele may conceal the presence of another.

The Principle of Segregation

In a heterozygote, two different alleles segregate from each other during the formation of gametes.

The principle of Independent Assortment

The alleles of different genes assort independently of each other.

ABO system

A system of four types (A, AB, B, and O) which human blood is classified into, based on the presence or absence of certain antigens. IA and IB are dominant and IO is recessive (chromosome 9).

Rh type

The D gene determines the Rh type. D (Rh positive) is dominant. d (Rh negative) is recessive (chromosome 1).

5 antigens of the Rh system

D, C, c, E, and e. C/c and E/e are codominant

Haplotype

A group of alleles of different genes on a single chromosome that are closely enough linked to be inherited usually as a unit.

Phenotypic ratio with two heterozygotes in a dihybrid cross

9:3:3:!

Formed line method

The first trait gets forked into the 3 dominant and 1 recessive trait. Then each trait gets forked into the 3 dominant and 1 recessive second trait. Follow the fork to determine the number associated with each phenotype. Ex. 3 A and 3 D means 9 A D.

Probability method

Look at the probability of the separate components and then muliple all them together. Ex. Aa Bb Cc self cross, what is the chance of Aa Bb Cc, would be solved by looking at the separate probability of each, 1/2. Mulitplied would be a 1/6 chance.

Chi-square test

A significance test used to determine if a linear relationship exists between two variables measured on interval or ratio scales. x2=E(observed-expected)^2 / expected. When the value is small, the observed and expected values are similar and the hypothesis is true. There is a critical value of X2 where the value is large enough to reject the hypothesis. This critical value depends on the degrees of freedom. The degrees of freedom is the number of different phenotype - 1.

Sex Determination in humans

-Primarily determined by the presence or absence of a Y chromosome. The Y chromosome has a SRY gene. This has a testis-determining factor that will later produce testosterone. On the X chromosome, there is a tmf gene that is necessary for secondary male sex characteristics.

Ratio system of Drosophilia

There is a ratio of autosomal and sex chromosomes (X:A) that determine the sex. If the ratio is more than 1, then the fly is female. If the ratio is under 0.5 then the fly is male. If the ratio is between 0.5 and 1, then the fly is intersex.

The Haplo-Diplo system

females are diploid, males are haploid

The ZW system

A sex determination system in fish, butterflies, birds where males are ZZ and Females are ZW. The egg determines the sex of the offspring.

Nondisjunction

Error in meiosis in which homologous chromosomes fail to separate. Causes XXY similar chromosomes.

Possible mechanisms to control dosage

X linked genes in males might work twice as hard, one copy of the X linked genes may be inactivated in females, and both X genes work half as hard in females.

Dosage compensation in Drosophilia

Hyperactivation of X-linked genes in male drosophilia

Dosage compensation in mammals

Inactivation of X-linked genes in female mammales. Causes a mosaic.

Frequency of recombination

the proportion of recombinant chromosomes among the total number of chromosomes observed