Medical Genetics

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Genes

A sequence of nucleotides that codes for a basic unit of biological information.

Genetics

The science of hereditary.
It seeks a precise explanationof the biological structures and mechanisms that determine what is inherited and how it is inherited.

Artificial Selection

The purposeful control over mating by choice of parents for the next generation.

Self-Fertilization

The process whereby both egg and pollencome from the same plant.

Law of Segregation

A Mendelian law that states that the pairs of homologous chromosomes separate in meiosis so that only one chromosome from each pair is present in each gamete

Carl Correns
Hugo De Vries
Erich Von Tschermak

All were involved in the rediscovery of Mendel's research

Pure-Breeding

Lines that produce offspring carrying specific parental traits that remain constant from generation to generation

Second Filial
F2 Generation

The progeny of the first filial or F1 generation

Un-Affected

Square or circle that is not shaded

Recessive

Inherited trait expressed only when the controlling gene is homozygous, only expressed in the homozygous condition

Un-Affected mating

Circle and square not shaded connected with line

Affected

Square or Circle Shaded

Alleles

The alternative form of a single gene

Reciprocal Cross

A cross in which the traits carried by the male parent and the female parent are reversed

Hybrid

The mating of parents with antagonistic traits

Di-Hybrid Crosses

Helped reveal the Law of Independent Assortment

Punnett Square

Introduced in 1906 by Reginald Punnett
Provides a simple and convenient method of tracking possible combinations of gametes that might be produced in a given cross.

Product Rule

The probability of two independent events occurring simultaneously is the product of the individual probabilities.

Sum Rule

Probability that one of two or more mutually eclusive events will occur is equal to the sum of the individual probabilities of the events

Test Cross

A genetic cross in which a test organism showing the dominant trait is crossed with one showing the recessive trait; used to determine whether the test organism is homozygous dominant or heterozygous.

Gamete Formation

Different pairs of alleles on different chromosomes segregate independently of each other

Pedigree

A family history of a specific trait shown for a minimum of three generations

Consanguineous Mating

Designated by the symbol = (double line between on pedigree), Mating of related individuals, More prone to disorders

First Filial
F1 Generation

The first generation of hybrid offspring resulting in a genetic cross

Zygote

Fertilized egg, the cell resulting from the union of an ovum and a spermatozoon (including the organism that develops from that cell)

Heterogeneous Trait
Heterozygous Trait

Yy genotype
A mutation in any one of a number of genes that can give rise to the same phenotype

Homozygous Trait

YY or yy genotype, an identical pair of alleles on homologous chromosomes for any given trait

Allele Frequency

The proportion of all copies of a gene in a population that are of a given allele type, the number of times an allele occurs in a gene pool, compared to the total number of alleles in that pool for the same gene

Wild-Type Allele

Designated by a Superscript +, The non-mutant form of a gene, encoding the normal genetic function. Generally, but not always a dominant allele.

Monomorphic

A gene with only one wild-type allele

Phenocopy

A non-inherited change in phenotype arising from environmental effects that mimic the effect of a mutation in a gene

Multi-Factorial

Refers to traits determined by two or more factors, including multiple genes interacting with each other or more genes interacting with the environment

Modifier Gene

Produces a sutle, secondary effect on phenotype by altering the effect of the alleles of other genes

Quantitative Trait
Continuous Trait

An inherited trait that exhibits many intermediate forms; determined by segregating alleles of many different genes whose interaction with each other and the environment produces the phenotype

Permissive Conditions

The range of conditions under which an organism possessing a conditional lethal allele can remain viable. (Survive)

Pleiotropy

A phenomenon in which a single gene determines a number of distinct and seemingly unrelated charcteristics, A gene that has more than one effect

Expressivity

The degree or intensity with which a particular genotype is expresses in a phenotype

Complete Penetrance

All individuals carrying a dominant mutant gene show the mutant phenotype, if you have the gene it will be expressed.

Codominance

Equal Expression, Blood type "AB" or "IAIB", The situation in which the phenotypes of both alleles are exhibited in the heterozygote because both alleles affect the phenotype in separate, distinguishable ways.

Incomplete Dominance

Partial expression, Neither gene is fully expressed, The situation in which the phenotype of heterozygotes is intermediate between the phenotypes of individuals homozygous for either allele because the dominant gene is unable to completely mask the recessive gene.

Complete Dominance

Expressed in the heterozygous or homozygous conditions, whenever the allele is present it is expressed, The situation in which the phenotypes of the heterozygote and dominant homozygote are indistinguishable. TT and Tt produce the same phenotype

Epistasis

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

Mutations

The source of new genes, has a rare occurrence in the population

Polymorphic

Genes with more than one wild-type allele

Mouse Agouti Gene

One wild-type and several mutant alleles

Complementary Gene Action

Dominant alleles of two or more genes are required to generate a particular trait

Chromosomes

Long thread-like bodies found in the nucleus whose name means "colored bodies"

Meiosis

The process of two consecutive cell divisions in the dipliod progenitors of gametes

Haploid

Describes a single set of chromosomes

Submetacentric Chromosomes

A chromosome whose centromere lies between its middle and its end but closer to the middle.

Homologs

Chromosomes that match in size, shape, and banding pattern

Metacentric Chromosomes

Centrally placed centromere that divides chromosome into two arms having approximately equal length

Acrocentric Chromosomes

Centromere is very near one end, forms chromosome with long and short arms of distinctly different lengths - short arm is often composed of highly repetitive (satellite) DNA

Karyotype

An image of all the chromosomes of an organism arranged into pairs based of stainig pattern and , by convention, in decreasing size, with sex chromosomes last.

Non-Disjunction

Occurs when chromosomes fail to separate properly during meiosis

Polar Body

The smaller diploid sister cell that results during meiosis I in females

Synapsis

The process of matching chromosomes becoming zipped together during the zygotene stage of prophase I

Anaphase

The stage of meiosis or mitosis when chromosomes move toward opposite ends of the nuclear spindle

Prometaphase

The second stage of mitosis, in which discrete chromosomes consisting of identical sister chromatids appear, the nuclear envelope fragments, and the spindle microtubules attach to the kinetochores of the chromosomes.

Telophase

The final stage of mitosis or meiosis, during which a nuclear membrane forms around each set of new chromosomes

Prophase

The first stage of mitosis or meiosis in eukaryotic cell division, during which the nuclear envelope breaks down and strands of chromatin form into chromosomes

Metaphase

The stage in mitosis or meiosis in which the duplicated chromosomes line up along the equatorial plate of the spindle

Prophase I

The first phase of meiosis I. During prophase I the replicated chromosomes condense, homologous chromsomes pair up, crossing over occurs between homologous chromosomes, the spindle is formed, and the nuclear envelope breaks apart into vesicles. Prophase I is the longest phase of meiosis.

Anaphase I

The third phase of meiosis I. the replicated homologous chromosomes are separated (the tetrad is split) and pulled to opposite sides of the cell.

Anaphase II

The third phase of meiosis II. During anaphase II the sister chromatids are finally spearated at their centromeres and puled to opposite sides of teh cell. Note that anaphase II is identical to mitotic anaphase, excep the number of chromosmes was reduced by half during meiosis I.

Prophase II

The first phase of meiosis II. Prophase II is identical to mitotic prophase, except that the number of chromosomes was reduced by half during meiosis I.

Metaphase I

The second phase of meiosis I. During metaphase I the paired homologous chromsomes (tetrads) align at the center of the cell (the metaphase plate).

Metaphase II

The second phase of meiosis II. Metaphase II is identical to mitotic metaphase where the duplicated chromosomes line up along the equatorial plate of the spindle, except that the number of chromosomes was reduced by half during meiosis I.

Telophase I

The fourth of meiosis I. the number of chromosoms is now reduced by half. After this phase the cell is considered to be haploid. Note however, that the chromosomes are still replicated, and the sister chromatids must still be separated during meiosis II.

Cytokinesis

The final stage of the cell cycle, in which the cell's cytoplasm divides, distributing the organelles into each of the two new cells.

Telophase II

The fourth stage of meiosis II where chromosomes arrive at opposite of cell; nuclear envelopes form around chromosome sets; four haploid cells

Meiosis I

The first division of a two-stage process of cell division in sexually reproducing organisms that results in cells with half the chromosome number of the original cell.

Meiosis II

The second division of a two-stage process of cell division in sexually reproducing organisms that results in cells with half the chromosome number of the original cell.

Mitosis

In eukaryotic cells, a process of cell division that forms two new nuclei, each of which has the same number of chromosomes

Primary Spermatocytes

Germ-line cells in which meiosis I occurs

Secondary Spermatocytes

Germ-line cells in which meiosis II occurs

Spermatids

Immature sperm cell, Four haploid cells that are formed when a diploid reproductive cell divides meiotically

Spermatogonia

Diploid germ cells in the testes

S Phase

The synthesis phase of the cell cycle; the portion of interphase during which DNA is replicated.

G2 Phase

The stage of the cell cycle from the
completion of chromosome replication
until the onset of cell division.

G1 Phase

The stage of the cell cycle from the
birth of a new cell until the onset of
chromosome replication at S phase.

G0

In the cell cycle, a resting form of G1. Cells in G0 normally do not divide.

M Phase

The mitotic phase of the cell cycle, which includes mitosis and cytokinesis.

Number of Chromosomes/Chromatids in Primary Oocytes

Chromosomes - 46
Chromatis - 92

Number of Chromosomes/Chromatids in Scondary Oocytes

Chromosomes - 23
Chromatids - 46

Number of Chromosomes/Chromatids in Oogonia

Chromosomes - 46
Chromatids - 46

Number of Chromosomes/Chromatids in Ova

Chromosomes - 23
Chromatids - 23

Sister Chromatids

Identical chromosomes, duplicated during metaphase and still attached to each other

Autosomes

Non-sex chromosomes

Turner Syndrome

A female with a genotype of XO

Interphase

A period between cell divisions

Kinetochore

The chromosomal structure to which spindle fibers attach during miotic divisions

Genotype

The actual alleles present in an
individual.

Phenotype

A observable characteristic

Hemizygous

Describes the genotype for
genes present in only one copy in an
otherwise diploid organism, such as
X-linked genes in a male.

Mode of Inheritance

1. Dominant
2. Recessive
3. Autosomal
4. X-Linked

Dominant Allele

an allele whose phenotype
is expressed in a heterozygote .
See recessive allele.

Recessive Allele

an allele whose phenotype
is not expressed in a heterozygote.

Autosomal

a chromosome not involved
in sex determination. The diploid
human genome consists of 46 chromosomes,
22 pairs of autosomes, and
1 pair of sex chromosomes (the X and
Y chromosomes).

X-Linked

carried by the X chromosome.

Pedigree Symbols

circle - female
square - male
filled circle - affected female
filled square - affected male
half filled female - carrier female
half filled male - carrier male
Double line connecting circle and square - Consanguineous Mating
line connecting a circle and a square - mated
line coming off of a mated pair - offspring
dashed line through a square or circle - deceased

Tetraploid

describes cells or organisms
with four complete sets of chromosomes.

Triploid

describes cells or organisms
with three complete sets of chromosomes.

Diploid

Zygotes and other cells carrying
two matching sets of chromosomes
are described as diploid.

Crossing Over

During meiosis, the breaking
of one maternal and one paternal
chromosome, resulting in the
exchange of corresponding sections
of DNA and the rejoining of the chromosome.
This process can result in
the exchange of alleles between chromosomes.

Chiasmata

The zipper-like connection between paired homologs in early prophase

Reduction Division

cell division that reduces the number of chromosomes, usually by segregating homologous chromosomes to two daughter cells. Meiosis I is a reductional division.

Meiotic Prophase Stages

Leptotene
Zygotene
Pachytene
Diplotene
Diakinesis

Synaptonemal Complex

structure that helps align homologous chromosomes during prophase of meiosis I.

Linked Genes

Parental combinations outnumber recombinant types

Syntenic Genes

relationship of two or more loci found to be located on the same chromosome.

Recombination

Progeny resulting from a cross that exhibit a reshuffled combination of alleles distinct from that of the parents

Chi Square Test

A probability test that measures "goodness of fit" between observed and predicted results

TH Morgan

came up with the first solid evidence associating a specific gene with a specific chromosome, discovered that genes are chromosmes and discovered sex-linkage through the fly lab, 20th century; developmental biologist; father of population genetics; 1903 Adaptation and Evolution; attacked Darwin; didn't like struggle for existence 1907-1908 Morgan becomes anti-Mendelian 1909 speech American Society of Naturalists: the only way to study evolution is through genetics discussed chromosomes; fruit fly experiments chromosome mapping 1916 used coin toss analogy to show randomness of mutation

Map Units (m.u.)
Centimorgan

One percentage point of recombination, or recombination frequency, is a unit of measure

Dominant Traits (Pedigree)

1. Affected children always have at least one affected parent.
2. As a result, dominant traits show a vertical pattern of inheritance: the trait shows up in every generation.
3. Two affected parents can produce unaffected children, if both
parents are heterozygotes.

Recessive Traits (Pedigree)

1. Affected individuals can be the children of two unaffected carriers, particularly as a result of consanguineous matings.
2. All the children of two affected parents should be affected.
3. Rare recessive traits show a horizontal pattern of inheritance: the trait fi rst appears among several members of one generation and is not seen in earlier generations.
4. Recessive traits may show a vertical pattern of inheritance if the trait is extremely common in the population.

Genetic Linkage

Genes that "travel" together from one generation to the next

Physical Markers

Genes that can serve points of reference on a chromosome are useful as genetic markers while cytologically visible abnormalities that also make it possible to keep track of chromosomes

Terminalization

The movement of chiasmata toward the end of a chromosome

Null Hypothesis

A hypothesis that predicts no linkage brtween genes

Chromosomal Interference

Crossovers do not occur independently and the occurence of one crossover reduces the likelihood of another occuring elsewhere on the chromosome

Tetratype

A tetrad that carries four kinds of haploid cells(two different parental class cells and two different recombinant class cells)

Mosaic

an organism containing tissues of different genotypes .

Crossing over takes place in paired bivalents consisting of _____ chromatids, and involves _____ of the chromatids.

4 and 2

Which of the following is not a phenotypic description of allele interactions affecting the expressions of traits?
A. Incomplete Dominance
B. Co-Dominance
C. Polymorphic
D. Multifactorial
E. Pleiotropic

D. Multifactorial

An interaction between non-allelic genes that result inthe masking of expression of a phenotype is:
A. Epistasis
B. Epigenetics
C. Dominance
D. Co-Dominance
E. Incomplete Dominance

A. Epistasis

Which of the following diseases show pleiotropism?
A. Albinism
B. Muscular Dystrophy
C.Colorblindness
D. Sickle Cell Anemia
E.Male Pattern Baldness

D. Sickle Cell Anemia

A deviationfrom normal Mendelian ratios, which may be resolved by counting and/or controlled crosses, is seen in which of the following terms?
A. Pleiotropy
B. Co-Dominance
C. Incomplete Dominance
D.Complete Dominance
E. Penetrance and Expressivity

E. Penetrance and Expressivity

Which of the following ratios show incomplete dominance?
A. 2:1
B. 3:1
C. 1:2:1
D. 1:1
E. 4:1

C. 1:2:1

Which of the following ratios show co-dominance?
A. 2:1
B. 3:1
C.1:2:1
D. 1:1
E. 4:1

C. 1:2:1

Which of the following ratios indicates a lethal gene?
A. 2:1
B. 3:1
C.1:2:1
D. 1:1
E. 4:1

A. 2:1

A person who has type O blood has:
A. Anti-A antibodies
B. Anti-B antibodies
C. Anti-AB antibodies
D. Both anti-A and anti-B antibodies
E. No surface antigens

D. Both anti-A and anti-B antibodies

If two or more forms of the same gene exist, the different forms are called:
A. Incomplete Dominance
B. Penetrance and Expressivity
C. Pleiotropic
D. Alleles
E. Di-Hybrid

D. Alleles

The blood groups A, B, and O are different types of:
A. Incomplete Dominance
B. Penetrance and Expressivity
C. Pleiotropy
D. Alleles
E. Heterozygotes

D. Alleles

The blood groups A, B, and O show:
A. Complete Dominance
B. Recessiveness
C. Co-Dominance
D. Complete Dominance, Recessiveness, and Co-Dominance
E. None of the choices are correct

D. Complete Dominance, Recessiveness, and Co-Dominance

Which of the following monohybrid ratios can describe incomplete and co-dominance?
A. 2:1
B. 3:1
C. 1:3
D. 1:2:1
E. 4:1

D. 1:2:1

Which of the following ratios demonstrate gene interaction?
A. 2:1
B. 3:1
C. 1:2:1
D. 9:3:4
E. 1:3

D. 9:3:4

A ______ results whenever the nucleotide sequence is changed.
A. Phenotype
B. Genotype
C. Mutation
D. Trait
E. Character

C. Mutation

When the same gene is related to respiratory problems and sterility, it can be described as:
A. Pleiotropy
B. Co-Dominance
C. Incomplete Dominance
D. Complete Dominance
E. Penetrance and Expressivity

A. Pleiotropy

Another name for a normal gene is:
A. Wild-Type
B. Pleiotropy
C.Dominant
D. Co-Dominant
E. Recessive

A. Wild-Type

The phenotypic ratio 1:2:1 may indicate:
A. Complete Dominance
B. Co-Dominance
C. Epistasis
D. Recessive Lethal
E. Co-Dominance and Epistasis Only

B. Co-Dominance

The phenotypic ratio 3:1 may indicate:
A. Complete Dominance
B. Co-Dominance
C. Epistasis
D. Incomplete Dominance
E. Co-Dominance and Epistasis Only

A. Complete Dominance

The phenotypic ratio 2:1 may indicate:
A. Complete Dominance
B. Co-Dominance
C. Epistasis
D. Recessive Lethal
E. Co-Dominance and Epistasis Only

D. Recessive Lethal

The phenotypic ratio 9:7 may indicate:
A. Complete Dominance
B. Co-Dominance
C. Epistasis
D. Recessive Lethal
E. Complementary Gene Action

E. Complementary Gene Action

In Drosophilia Virilis, nuclei of somatic cells contain 12 chromosomes while nuclei of sperm cells contain only 6 chromosomes. What does "n" equal for this species?
A. 3
B. 6
C. 12
D. 24
E. 6 or 12, depending on the cell type

B. 6

The stage of mitosis when chromosomes condense to form rod-shaped structures visible under the microscope is called:
A. Interphase
B. Prophase
C. Metaphase
D. Anaphase
E. Telophase

B. Prophase

The stage of mitosis when sister chromatids separate from each other and migrate to opposite poles of a cell is called:
A. Interphase
B. Prophase
C. Metaphase
D. Anaphase
E. Telophase

D. Anaphase

During which of the following stages of the cell cycle would a chromosome consist of only a single chromatid?
A. G1
B. G2
C. Mitotic Prophase
D. Mitotic Metaphase
E. All the choices are correct

A. G1

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