Definitions

Quantitative trait

a trait that is a measurable phenotype (of continuous variation), controlled by multiple genes acting cumulatively

Continuous variation

traits vary across a spectrum
• Human height

Discrete variation

easily distinguishable categories
• such as Mendel’s observations of pea traits (yellow/green or round/wrinkled seeds)

Quantitative trait loci

the genes that cumulatively control a trait that is a measurable phenotype
• e.g., global variation of skin pigmentation

Epistasis

interaction between genes at different loci

Epistatic

describes the gene that is “masking” or “overpowering”

Hypostatic

describes the gene that is being “hidden” or “masked”

Sex

a set of biological attributes in humans and animals. It is primarily associated with physical and physiological features including chromosomes, gene expression, hormone levels and function, and reproductive/sexual anatomy. Sex is usually categorized as female or male but there is variation in the biological attributes that comprise sex and how those attributes are expressed.

Gender

Socially and culturally constructed roles, behaviours, expression, and identities of girls, women, boys, men, and gender diverse people. Gender identity is not confined to a binary (girl/woman, boy/man) nor is it static - it exists along a continuum and can change over time.

Chromosomal sex

XX, XY + aneuploidy (XO, XXY, XYY, XXX)

Anatomical sex

determined by identifying genitalia in ultrasounds or at birth. What happens in the hospital when a baby is born, typically determined by looking at external entail which is not all-inclusive or one or the other.

Hormonal sex

levels of androgens and estrogens. Typically higher androgen (e.g., testosterone) levels in males. Typically higher estrogen levels in females

AMAB/AFAB

assigned male/female at birth

Cisgender

gender identity aligns with assignment at birth

Pronouns

(ex: she/her, he/him, they/them)

Transgender

gender identity aligns with assignment at birth
- Trans woman = woman
- Trans man = man

Nonbinary

umbrella term. ex: Agender, genderfluid, two-spirit

Sex-determination genes

responsible for the development of sex-associated structures in the developing embryo (ex. SrY, Sox9).

Sex-influenced genes

sex-determination genes located on autosomes (ex: Sox9)

Sex-linked genes

sex-determination genes located on sex chromosomes (ex: SRY)

• Y-linked

• X-linked

Dosage compensation

how the gene expression of sex chromosomes is adjusted so that there is no difference in protein produced by males and females. In humans, this happens through the “inactivation” of additional X copies.

Xa

“active” X chromosome where transcription occurs

Xi

“inactive” X chromosome where transcription does not occur, as the tightly packed heterochromatin makes DNA inaccessible to the transcription machinery

Bi-potential genetical ridge

embryonic tissue with potential to become ovaries or testes depending on the presence of SRY and the Y chromosome.

SRY present

male developmental pathway activated

SRY absent

male developmental pathway is not activated, proceeds with female developmental pathway instead

True-breeding strains

all offspring look like their parents (in terms of one of the above traits

P generation

Parental generation

Fn generation

Filial (offspring) generation. F1, F2, F3, …

Dominant trait

allele whose expression overrides the other allele

Recessive trait

allele whose expression is masked, unless the individual is homozygous for this allele

Phenotype

measurable traits that can be easily visible (physical attributes) or otherwise measurable

Genotypes

an individual’s combination of alleles

Allele

specific version of a gene

Homozygous

an organism that has two of the same alleles for a given gene, which can be dominant (AA) or recessive (aa) (also called true-breeding)

Heterozygous

an organism that has two different alleles for a given gene (Aa)

The Law of Equal Segregation

During the production of gametes(meiosis), the two alleles of a gene are divided (segregated) among gametes, so that each gamete receives only one allele. This results in equal numbers of gametes with each allele.

The Law of Independent Assortment

The distribution of alleles from one gene to offspring is not dependent on the distribution of alleles from another gene. Exception: linked (such as Y- or X-linked) genes

Monohybrid

cross between two individuals heterozygous for one gene. Aa x Aa

Dihybrid

cross between two individuals heterozygous for two genes. AaBb x AaBb

Trihybrid

cross between two individuals heterozygous for three genes AaBbCc x AaBbCc

Wildtype

one phenotype that is far more predominant in a population

Mutant

phenotypic differences in relation to the wildtype of the population

Incomplete dominance

the phenotype is one for which the heterozygote has a phenotype that is an intermediate between the two homozygous phenotypes. Example: true-breeding white and red snapdragons creates pink offspring.

Codominance

Both the dominant and recessive phenotypes are displayed in the heterozygote.

Penetrance

the allele always correlates with the phenotype. all carriers express the trait

Incomplete penetrance

An allele controls a phenotype, but that phenotype is not always expressed or is only expressed to a certain degree. only some carriers express the trait

Variable expressivity

the degree to which a phenotype is expressed
o E.g., Polydactyly

Pleiotropy

one allele causes several (seemingly unrelated) phenotypes E.g., sickle cells and their different shape from regular red blood cells

Lethal alleles

mutations in essential genes that lead to the death of the organism that carries them (often in embryonic development)

Recessive lethal alleles

the lethal allele is only fatal when present in both allele copies

Dominant lethal alleles

allele only needs to be present in one copy to be fatal (uncommon)

Null hypothesis (H0)

states that there is no difference between groups or no relationship between variables. a presumption of no change

Alternative hypothesis (Ha)

states that a difference occurs between groups/variables

Epistasis

interaction between genes at different loci

Epistatic

describes the gene that is “masking” or “overpowering”

Hypostatic

describes the gene that is being “hidden” or “masked”

Quantitative trait

a trait that is a measurable phenotype (of continuous variation), controlled by multiple genes acting cumulatively

Continuous variation

traits vary across a spectrum

Discrete variation

easily distinguishable categories
• such as Mendel’s observations of pea traits (yellow/green or round/wrinkled seeds)

Quantitative trait loci

the genes that cumulatively control a trait that is a measurable phenotype
• e.g., global variation of skin pigmentation

Turner syndrome

XO. Anatomically female.

Klinefelter syndrome

XXY. Presence of SRY and pair of female sex chromosomes. Anatomically male. May have a delayed puberty

Triple X Syndrome

XXX. Anatomically female. Extra X. May deal with infertility.

XYY Syndrome

XYY. Anatomical males. Normal fertility and sexual development.

Translocation of SRY

XX. Anatomically male. Male internal and external genitalia.

5-alpha-reductase deficiency

XY. Anatomically female/ambiguous until puberty. Testosterone cannot be converted to DHT. Puberty hits and then anatomically male.

Complete androgen insensitivity (CAIS)

XY. Phenotypically female. Undescended testes and vagina. No uterus. Need hormone help to have puberty.

Swiyer Syndrome

XY. Inactivation of SRY. Anatomically female. Vagina, uterus, fallopian tubes, but no ovaries. Need hormone help to undergo puberty.

Complete adrenal hyperplasia (CAH)

XX. Buildup of testosterone. Anatomically female. May have ambiguous or male external genitalia.

haploinsufficient

a model of dominant gene action in diploid organisms, in which a single copy of the wild-type allele at a locus in heterozygous combination with a variant allele is insufficient to produce the wild-type phenotype.

DNA

an organism’s molecule that carries genetic information

Gene

a unit of heredity; a section of DNA that contributes to certain traits

Allele

alternate versions of a gene

Population

organisms of the same species living in the same place at the same time, that can feasibly mate with each other and produce fertile offspring

Gene pool

a collection of genes (including alleles) present in a population

Genetic diversity

the genetic differences between individuals of a species

Genetic variation

variation between or among populations

Clines

Describe traits that exist on a spectrum across a species’ geographical range

Sister Chromatids

the two DNA molecules that form halves of a single, replicated chromosome

Homologous Chromosomes

One pair of chromosomes from each parent that contain different DNA.

Genome

A cell’s entire genetic content

Ploidy

describes the number of copies of each chromosome an organism’s genome typically has

Nucleotide

The monomers of DNA and RNA. Three components comprise each: a nitrogenous base, a pentose (five-carbon) sugar, and one or more phosphate group. Linked together one after another to form DNA or RNA

Chromosome

A long wrapped up strand of DNA. Can be all or just a part of an organism’s entire genome. Only one strand, unless it's been replicated

Chromatin

strands of nucleosomes (protein) and DNA

Chromatid

After replication, each chromosome is comprised of two DNA molecules. Each individual DNA molecule is attached at the middle with a centromere

Nucleosomes

The structure that is created when DNA is coiled twice around clusters of histones

Histone

proteins that act as a spool for DNA. H2A, H2B, H3, and H4

Haploid

a genome that consists of one copy of each chromosome. This type of organism likewise only has one copy of each chromosome

Diploid

an organism in which each chromosome is represented in two copies

Mutation

A change in DNA sequence from a reference organism (or most common phenotype)

Germline mutation

A mutation that is inherited in embryonic stage that affects all the tissues of an individual and will be passed on through half of their gametes

Somatic mutation

Mutation appears in bodily tissues and continues only in the bodily tissue of the individual and is not carried in their gametes

Strand Slippage

during replication, something happens with the strand and errors happen in base pairing

Base substitution

A nucleotide is swapped out in a strand of DNA or RNA. Caused by oxidative stress and tautomeric shifts

Insertion

An extra nucleotide is added to a DNA strand. Caused by strand slippage

Deletion

A nucleotide is removed from a DNA strand. Caused by strand slippage

Tautomeric shifts — A spontaneous rearrangement of hydrogens within the nucleotide structure, allowing for new base pairings. Occurs when there is a mutation resulting in a new base pairing (that shouldn’t be there) when or before a DNA region is able to be repaired.

Deletion

A chunk of the chromosome is removed, deleted, or not transcribed.