Marks' Chapter 18 (Introduction to Human Genetics)

Human genetics

The study of heredity and the variation in inherited characteristics in humans.

Autosomal chromosomes

The numbered chromosomes (1-22) that are not involved in determining the sex of an individual.

Sex chromosomes

The X and Y chromosomes that determine the sex of an individual.

Diploid

Having two sets of chromosomes, one from each parent.

Mitosis

The process of cell division that results in two daughter cells with the same number and kind of chromosomes as the parent cell.

Meiosis

The process of cell division that produces four daughter cells with a haploid number of chromosomes.

Mendelian inheritance patterns

Patterns of inheritance described by Gregor Mendel, including autosomal dominant, autosomal recessive, X-linked dominant, and X-linked recessive.

Autosomal dominant

A type of inheritance where a mutation in one copy of a gene is sufficient to cause the trait or disorder.

Autosomal recessive

A type of inheritance where a mutation in both copies of a gene is necessary to cause the trait or disorder.

X-linked dominant

A type of inheritance where a mutation in one copy of a gene on the X chromosome is sufficient to cause the trait or disorder.

X-linked recessive

A type of inheritance where a mutation in the only copy of a gene on the X chromosome causes the trait or disorder.

Nondisjunction

Failure of chromosomes to separate properly during meiosis, leading to an abnormal number of chromosomes in the resulting cells.

Aneuploidy

The presence of an abnormal number of chromosomes in a cell.

Epigenetics

The study of heritable changes in gene expression that do not involve changes to the DNA sequence.

Epigenetics

Mechanisms whereby genes can be expressed, or not expressed, in a heritable manner, without altering the DNA base sequence.

Imprinting

The process of altering the expression of an allele without altering the nucleotide sequence of the allele, and is reset when gametes are produced.

Hardy-Weinberg equilibrium

Allows one to determine estimates of allele frequencies in a general population, which can generate the frequency of heterozygotes, as well as the frequency of those affected by a disease.

Multifactorial diseases

Diseases that are caused by a combination of genetic and environmental factors.

DNA structural abnormalities

Abnormalities in the structure of DNA, such as triplet nucleotide repeat expansions, that can lead to disease.

Anticipation

The phenomenon where a genetic disorder or a disease becomes more severe and has an earlier onset in successive generations.

Tumor suppressor genes

Genes that normally prevent uncontrolled cell proliferation, and often display an autosomal dominant pattern of inheritance, yet the molecular mechanism is recessive.

Loss of heterozygosity

The loss of a functional allele

Sickle-cell trait

A condition where an individual carries one normal β-globin gene and one sickle β-globin gene

Mitochondrial diseases

Diseases caused by mutations in the mitochondrial genome, which are inherited maternally.

Heteroplasmy

The presence of a mixture of normal and mutated mitochondrial DNA within an individual.

Ploidy

The copy number of the chromosome complement in multiples of 23 chromosomes in human cells.

Monoploid

A cell with only one copy of each chromosome.

Diploid

A cell with two copies of each chromosome.

Triploid

A cell with three copies of each chromosome.

Aneuploidy

An abnormal number of individual chromosomes.

Karyotype

The complete set of chromosomes in a cell, arranged in a specific order.

Translocation

The movement of a piece of one chromosome to another chromosome.

Philadelphia chromosome

A specific translocation between chromosomes 9 and 22, associated with Chronic Myelogenous Leukemia (CML).

Independent assortment

The random sorting of chromosomes into daughter cells during meiosis.

Sister chromatids

Two identical copies of a chromosome that are held together by a centromere.

Crossing over

The exchange of genetic information between homologous chromosomes during meiosis.

Genetic diversity

The variety of genetic traits within a population or species.

Karyotype analysis

The examination of an individual's chromosomes to detect abnormalities or genetic disorders.

Loci/Locus

The specific locations where genes reside on a chromosome.

Allele

The form of a gene at a given locus.

Homozygous

The state in which the two alleles at a locus are identical.

Heterozygous

The state in which the two alleles at a locus have different nucleotide sequences.

Phenotype

The observable traits of an individual, produced by the interaction of genes and the environment.

Genotype

The genetic composition of an individual.

Heritability

The ability to inherit a trait from a parent, determined by genetic and environmental components.

Autosomal alleles

Alleles that are present as pairs within cells.

Dominant trait

A trait that manifests itself even when an allele is in a heterozygous state.

Recessive trait

A trait that manifests only when the gene is in a homozygous state.

Codominant traits

Traits in which both alleles in a heterozygous pair are expressed.

Recessive X-linked traits

Traits that occur when a mutant allele is located on the X chromosome and are expressed in males but not usually in females.

BRCA1 and BRCA2 genes

Genes associated with breast cancer.

Penetrance

The probability that an individual will express a phenotype when inheriting a particular mutant allele.

Variable expressivity

The severity of the expressed phenotype caused by a mutant allele.

Mutations

Alterations in a DNA sequence of an allele that can give rise to a nonfunctional or unregulated gene product.

Point mutations

A type of mutation where there is a change in one base of the DNA

Sickle-cell disease

An example of a disease caused by point mutation

Deletions

A type of mutation where there is a loss of bases in the DNA

Cystic fibrosis

An example of a disease caused by deletion mutation

Insertions

A type of mutation where there is a new DNA sequence added into the existing DNA

Menkes disease

A disorder of copper metabolism which is an example of a disease caused by insertion mutation

Loss of a chromosome

A type of mutation where it creates an aneuploid state

Turner syndrome

An example of a disease caused by the loss of a chromosome mutation

Extra copy of a chromosome

A type of mutation where trisomy for an autosomal chromosome leads to disease

Down syndrome

An example of a disease caused by an extra copy of a chromosome mutation

Trinucleotide repeats

A type of mutation where expansion of specific trinucleotide sequences in a gene can give rise to a disease

Huntington disease

An example of a disease caused by trinucleotide repeats mutation

Epigenetic

A type of mutation where there are no alterations in base sequence but chemical modifications to the DNA and histones do occur

Angelman and Prader–Willi syndromes

Examples of diseases caused by epigenetic mutations

Autosomal Dominant Inheritance

Inheritance pattern where an affected individual most often has an affected parent, and are heterozygotes

50%

The chance an affected heterozygous parent in an autosomal dominant inheritance can pass the affected allele to their offspring

Autosomal recessive Inheritance

Inheritance pattern where both parents must transmit the mutant alleles and generations may be skipped in the expression of the disease

25%

The chance in four children will be affected by the disease in an autosomal recessive inheritance

50%

The chance in four children will be a carrier of the disease in an autosomal recessive inheritance

Carrier

An individual who carries a recessive allele for a genetic disorder but does not express the disease themselves

Pedigree

A diagram that shows the genetic relationships within a family and the presence or absence of a particular trait or disease.

Punnett square

A diagram used to predict the possible genotypes and phenotypes of offspring based on the genotypes of the parents.

X-linked inheritance

Inheritance of mutant alleles on the X chromosome, resulting in different patterns of inheritance between males and females.

Hemizygous

Having only one copy of a gene or chromosome, as males have only one copy of the X chromosome.

X-linked recessive disorders

Genetic disorders where there is no male-to-male transmission in a pedigree, and females are usually asymptomatic

Lyon hypothesis

The hypothesis that in females, one of the X chromosomes is randomly inactivated in each cell to compensate for the difference in gene dosage between males and females.

Gene dosage

The number of copies of a gene present in a cell or organism.

Barr bodies

Dense, inactive X chromosomes that are formed during X chromosome inactivation in females.

X-linked dominant disorder

Women carrying ______ will express symptoms of the disease.

Mitochondrial inheritance

The inheritance of genetic traits through the mitochondrial genome, which is passed down from the mother to her offspring.

16,569 bp

Human mitochondria have a genome of ______.

Heteroplasmy

The presence of both normal and mutated mitochondrial genomes within the same cell.

Homoplasmy

The presence of either all normal or all mutated mitochondrial genomes within a cell.

Disease allele

An alternative form of a gene that is associated with a particular disease or disorder.

Cytogenetics

The branch of genetics that studies the structure and function of chromosomes, particularly in relation to genetic disorders.

Centromere

DNA segment where homologous chromosomes are attached during cell division.

Metacentric

When the centromere is positioned in the middle of the chromosomes

Submetacentric

When the chromosomes have the centromeres positioned between the middle of the chromosome and the tip of the chromosome

Acrocentric

When the chromosomes have their centromeres located at the tips of the chromosomes

Telomeres

The ends of chromosomes.

Chromosome Nomenclature

The system of naming and designating different parts and variations of chromosomes, including deletions, duplications, inversions, and translocations.

p arm

Karyotype nomenclature for the short arm of the chromosome

q arm

Karyotype nomenclature for the long arm of the chromosome

del

Karyotype nomenclature for the deletion of chromosomal material

der

Karyotype nomenclature for the derivative, usually a structurally arranged chromosome

dup

Karyotype nomenclature for the duplication of a part of a chromosome