Unit II Exam: Complex Patterns of Inheritance, Advanced Pedigree Analysis, and Cytogenetics

Vocabulary flashcards generated from lecture notes covering complex patterns of inheritance, pedigree analysis, cytogenetics, and chromosomal disorders.

Incomplete Dominance

A genetic situation where a gene exists in two alleles, neither of which is dominant over the other, resulting in a heterozygous phenotype that is intermediate to that of either homozygous genotype.

Snapdragon Flower Color Example

An illustration of incomplete dominance where genotype $R_1 R_1$ yields red flowers, $R_2 R_2$ yields white flowers, and heterozygous $R_1 R_2$ yields pink flowers.

Multiple Alleles

A phenomenon in which a gene exists in three or more different alleles within a population.

Codominance

A situation where a gene exists in two alleles and neither suppresses the expression of the other, leading to a heterozygous individual fully expressing both alleles in the phenotype, usually in a mosaic pattern.

Pleiotropy

A genetic condition in which a single gene affects multiple, distinct aspects of an individual's phenotype.

Fibrillin Gene Mutation

A pleiotropic gene mutation causing Marfan syndrome, which leads to abnormalities in joints, flat feet, near-sightedness, and enlargement of the aorta.

Polygenic Traits

Traits under the influence of multiple gene pairs at multiple loci, resulting in a continuous wide spectrum of phenotypes in the population.

Multifactorial Trait

A trait that is influenced by both genetic factors and environmental exposure.

Epistasis

A phenomenon in which one gene pair completely overrides or masks the expression of another gene pair.

Albinism in Humans

An example of epistasis where inheriting two mutated alleles for the tyrosinase gene causes this condition regardless of other skin color genes inherited.

X-Linked Trait

A trait influenced by a gene located on the X chromosome but not on the Y chromosome.

Pheomelanin Red Hair Co-inheritance

An example of pleiotropy where an allele for pheomelanin causes red hair and simultaneously tends to produce freckles, red eyebrows, and reddish eyelashes.

Type 1 Diabetes Susceptibility

A multifactorial trait where genetic predisposition combined with environmental factors like viral exposure determines if a child develops the disorder.

Wavy Hair Inheritance

An example of incomplete dominance where inheriting one straight hair allele and one curly hair allele results in a wavy hair phenotype.

Hair Texture Multigene Influence

An example of a polygenic trait where several different gene pairs on multiple chromosomes influence a person's hair texture.

Labrador Retriever Coat Color Epistasis

An epistatic pattern where inheriting two recessive alleles for the deposit gene causes pale tan fur regardless of brown or black fur genes.

Spotted Gloog Offspring

An example of codominance resulting from mating a black-furred gloog with a white-furred gloog to produce black and white spotted babies.

Grey Gloog Offspring

An example of incomplete dominance resulting from mating a black-furred gloog with a white-furred gloog to produce grey-furred babies.

$I^A$ Allele

The allele symbol for the A antigen in the ABO blood group system.

$I^B$ Allele

The allele symbol for the B antigen in the ABO blood group system.

$i$ Allele

The allele symbol for the absence of antigen in the ABO blood group system.

Type A Blood Genotypes

The genotypes $I^A I^A$ and $I^A i$ that result in the Type A blood phenotype.

Type B Blood Genotypes

The genotypes $I^B I^B$ and $I^B i$ that result in the Type B blood phenotype.

Type AB Blood Genotype

The heterozygous genotype $I^A I^B$ that results in the co-expression of both Type A and Type B glycoproteins.

Type O Blood Genotype

The homozygous recessive genotype $ii$ that yields Type O blood.

Female Sex Chromosome Composition

The chromosomal makeup of human females consisting of two X chromosomes.

Male Sex Chromosome Composition

The chromosomal makeup of human males consisting of one X chromosome and one Y chromosome.

Hemophilia Cause

An X-linked recessive disorder characterized by the inability of the blood to clot properly, caused by a recessive allele on the X chromosome.

X-Linked Recessive Pedigree Clues

Unaffected parents having affected children, an overwhelmingly higher ratio of affected males, and affected males inheriting the trait through carrier mothers from affected maternal grandfathers.

Autosomal Dominant Pedigree Clues

Affected parents having unaffected children, equal male and female occurrence, and affected fathers passing the trait to sons.

X-Linked Dominant Pedigree Clues

Affected males with unaffected wives passing the trait to all of their daughters and none of their sons.

Autosomal Recessive Pedigree Clues

Unaffected parents having affected children, including affected females born to unaffected fathers.

Y-Linked Trait

A genetic trait determined by a gene carried strictly on the Y chromosome.

Y-Linked Inheritance Pattern

A pattern where a trait is exclusively passed from affected fathers to all of their sons and never to daughters.

Mitochondrial Function

Organelles responsible for converting food energy into cellular energy in the form of ATP.

Mitochondrial Genome

Small loops of DNA contained within each mitochondrion containing roughly a few dozen genes.

Mitochondrial Inheritance

The transmission of mitochondrial genes exclusively from the mother to all of her offspring (sons and daughters), and never from the father.

Mitochondrial Disorder Target Tissues

Cells requiring large numbers of mitochondria and high ATP demand, such as muscle, nerve, and kidney cells.

Mitochondrial Disorder Symptoms

Clinical manifestations resulting from deficient ATP production, including fatigue, muscle weakness, visual problems, and kidney malfunction.

Penetrance

The percentage of individuals with a specific genotype who actually display the corresponding phenotypic trait.

Complete Penetrance

A condition where $100\%$ of individuals carrying a specific genotype exhibit the corresponding phenotype.

Incomplete Penetrance

A condition where less than $100\%$ of individuals carrying a specific genotype express the associated phenotype.

86% Penetrance Interpretation

Directly implies that $86\%$ of people who inherit a particular genotype will display the phenotypic disease or trait.

Huntington's Disease Penetrance Example

An autosomal dominant condition demonstrating complete penetrance with genotype $Hh$, where every carrier eventually develops the disease.

Breast Cancer $Bb$ Penetrance Example

An autosomal dominant genotype demonstrating incomplete penetrance, where only a subset of individuals inheriting the allele develop breast cancer.

Expressivity

The degree or intensity to which a given genotype is expressed phenotypically in an individual.

Variable Expressivity

A situation where individuals carrying the exact same genotype show varying severity or presentation of the phenotype.

Free Earlobes Variable Expressivity

Variations in how sharply or prominently free earlobes are pronounced among individuals with genotype $Ee$.

Widow's Peak Variable Expressivity

Differences in how sharply pointed the V-shaped hairline is among individuals sharing genotype $Ww$.

Cystic Fibrosis Variable Expressivity

Variations in the severity of respiratory symptoms among individuals with genotype $cc$ due to environmental factors and modifier genes.

Polydactyly Variable Expressivity

Variations in symptom manifestation in $Pp$ individuals, ranging from an extra fingertip on one hand to fully formed extra digits on hands or feet.

Cytogenetics

The branch of genetics focused on the study of chromosome structure, function, and abnormalities.

Karyotype

An organized visual display or profile of an individual's complete set of chromosomes arranged by size and shape.

Diagnostic Uses of Karyotyping

Detecting chromosomal abnormalities in unborn fetuses, screening children or adults for genetic disorders, and classifying cancer cell types to select treatments.

Centromere

The primary constriction region on a chromosome that joins sister chromatids and separates the chromosome into p and q arms.

Telomeres

The protective caps at the ends of chromosomes that prevent degradation and maintain chromosomal stability during cell division.

p Arm

The shorter arm of a chromosome relative to the centromere.

q Arm

The longer arm of a chromosome relative to the centromere.

Metacentric Chromosome

A chromosome whose centromere is positioned centrally, dividing it into p and q arms of approximately equal length.

Submetacentric Chromosome

A chromosome whose centromere is located off-center, producing a distinctly shorter p arm and a longer q arm.

Acrocentric Chromosome

A chromosome with its centromere located near one end, producing a extremely small p arm and a long q arm.

G-Banding

A staining technique using Giemsa stain that creates unique light and dark bands along chromosomes for identification and structural analysis.

Purposes of G-Banding

Distinguishing similar-looking chromosomes, identifying structural chromosomal abnormalities, and mapping genes to specific physical loci.

Gene Locus

The specific physical position or location of a gene on a chromosome.

Locus Code 12q7.3 Interpretation

Indicates a gene location on Chromosome 12, long arm (q), region 7, band 3.

Locus Code 1p3.4 Interpretation

Indicates a gene location on Chromosome 1, short arm (p), region 3, band 4.

Amniocentesis Timing

A prenatal diagnostic test performed around the 16th week of pregnancy.

Amniocentesis Technique

Withdrawal of a small amount of amniotic fluid (containing fetal urine and shed skin cells) using a fine needle and syringe.

Amniocentesis Diagnostic Testing

Biochemical testing on fluid (e.g., for Tay-Sachs) and fetal cell culturing for karyotyping and allele analysis.

Amniocentesis Turnaround Time

Requires culturing fetal cells for at least 7 to 10 days before a karyotype can be completed.

Amniocentesis Risks

An increased risk of spontaneous abortion (miscarriage) by about $0.3\%$ and a minor risk of maternal infection.

Amniocentesis Advantages

Lower added miscarriage risk than CVS, avoids risk of finger/toe deformities, and provides somewhat more reliable results than CVS.

Amniocentesis Disadvantages

Requires waiting until the second trimester of pregnancy and involves a long cell culture wait time for results.

Chorionic Villi Sampling Timing

A prenatal genetic test performed 8 to 10 weeks into pregnancy.

Chorionic Villi Sampling Technique

Guiding a hollow catheter tube into the chorionic villi of the placenta and removing tissue cells by suction.

Chorionic Villi Sampling Turnaround Time

Karyotyping and analysis can be performed on the same day the procedure is conducted.

Chorionic Villi Sampling Risks

Increased miscarriage risk of about $0.8\%$ risk of maternal infection, and a $0.1\%$ to $0.03\%$ risk of finger and toe malformations.

Chorionic Villi Sampling Advantages

Can be performed earlier in pregnancy than amniocentesis (allowing safer early termination if necessary) and provides rapid karyotype results.

Chorionic Villi Sampling Disadvantages

Higher miscarriage risk than amniocentesis, small risk of fetal limb deformities, and slightly lower accuracy due to placental mosaicism.

Preimplantation Genetic Diagnosis Timing

Performed on an early in vitro embryo before it is implanted into the mother's uterus.

Preimplantation Genetic Diagnosis Technique

In vitro fertilization creates a zygote grown to an 8-celled embryo in two days; a single cell is removed and screened for genetic disorders.

Preimplantation Genetic Diagnosis Advantage

Allows selection of healthy embryos prior to uterine implantation, avoiding pregnancy termination choices.

Preimplantation Genetic Diagnosis Risks

Genetic test results are not 100% accurate, and the transplanted embryo may fail to implant properly in the uterus.

Polyploidy

A chromosomal condition in which an organism possesses whole extra sets of chromosomes.

Aneuploidy

A condition in which an individual has an abnormal chromosome number that is not an exact multiple of the haploid set (e.g., missing or having one extra chromosome).

Monosomy

A form of aneuploidy characterized by the absence of a single chromosome from a homologous pair (45 total chromosomes in humans).

Trisomy

A form of aneuploidy characterized by having three copies of a specific chromosome instead of two (47 total chromosomes in humans).

Triploidy Chromosomal Profile

A polyploid state characterized by three full sets of chromosomes, totaling 69 chromosomes in humans.

Tetraploidy Chromosomal Profile

A polyploid state characterized by four full sets of chromosomes, totaling 92 chromosomes in humans.

Fate of Triploid and Tetraploid Conceptions

Almost always results in spontaneous abortion (miscarriage); rare live births exhibit severe multiorgan defects and die shortly after birth.

Dispermy

The fertilization of a single ovum by two distinct sperm cells, serving as the most common cause of triploidy.

Failed Cytokinesis

A cleavage error during early embryonic mitosis that serves as a primary cause of tetraploidy.

Primary Risk Factor for Trisomy

Advanced maternal age, with risk increasing significantly each year once a woman reaches age 35.

Maternal Age Meiotic Delay Hypothesis

Hypothesis stating that older primary oocytes spend more time suspended in meiotic arrest, increasing the rate of nondisjunction errors during division.

Uterine Selection Relaxation Hypothesis

Hypothesis proposing that an older mother's uterus is less sensitive to biochemical abnormalities, making it less likely to abort abnormal embryos spontaneously.

Typical Fate of Numerical Chromosome Abnormalities

Spontaneous abortion (miscarriage) during early pregnancy.

Patau Syndrome Karyotype

Trisomy 13, characterized by three copies of chromosome 13.

Patau Syndrome External Symptoms

Cleft lip and palate, eye defects, polydactyly (extra fingers/toes), and feet with protruding heels.

Patau Syndrome Internal Symptoms

Severe brain and nervous system malformations, along with defects in the heart, kidneys, liver, pancreas, and intestines.

Patau Syndrome Prognosis

Considered a lethal condition, with an average survival duration of six months following birth.