Unit 1 - Definitions Flashcards
DNA
hereditary material in humans & most living organisms
chromatin
complex of DNA and protein in eukaryotic cells
eukaryotic chromosome
linear molecule of DNA associated with histone proteins and packaged into higher order structures
telomere
stable ends of a linear chromosome
centromere
constricted region of chromosome where kinetochore forms and spindle microtubules attach during the cell division (sister chromatids held together by these too)
locus
position of a gene on a chromosome
haploid (n)
one set of Chromosomes
diploid (2n)
two sets of Chromosomes
non-homologous chromosomes
like XY sex chromosomes, have alleles on different genes.
autosomes vs sex chromosomes
chromosomes that are the same in M/F
vs
a pair of chromsomes that differ in M/F
homologous chromosomes
chromosome pairs of approximately the same length, centromere position, and staining pattern, for genes with the same corresponding loci
- may show allelic variation at a locus
kinetochore
complex of proteins that assembles at the centromere and serves as site of mircotubule attachment during cell division
spindle microtubules
filaments responsible for moving chromosomes during cell division
sister chromatids
2 linear chromatids that are connected by a centromere, they will be genetically identical
meiosis vs fertilization
production of haploid gametes (n)
vs
restoration of the diploid state (2n) in the next generation
genotype
the complete genetic makeup of an individual organism.
- determines phenotype
phenotype
a measurable trait of an organism that is controlled by one or more genes but can be influenced by environmental effects.
dominant allele
an allele whose trait is expressed in heterozygous individuals (ex: RR, R_)
recessive allele
an allele whose trait is NOT expressed in heterozygous individuals (ex: rr)
monohybrid cross
a cross between parents that differ by a single trait (RR x rr)
dihybrid cross
a cross between parents that differ by two traits (RR YY x rr yy)
Probability
No. of times a particular event is expected to occur out of the total number of possible outcomes
product v sum rule
product rule
- joint events, multiply together probabilities
sum rule
- disjoint events, add together probabilities
wild type gene
the allele most often found in natural populations.
Often symbolized by one or more letters and a plus sign (+).
Allelic series
the set of >2 alleles that occur within a given natural
population.
Complete dominance
The phenotype of the heterozygote is the same as the phenotype of one of the homozygotes.
Biochemical basis of dominance
In a biochemical pathway, half the amount of “normal” protein is produced by the heterozygote compared to the dominant homozygote. When half the amount of the
“normal” protein is sufficient to obtain a given phenotype, the heterozygote is deemed haplosufficient (half # of copies is enough to give full phenotype)
Incomplete (partial) dominance
The phenotype of the heterozygote is intermediate between phenotypes of the two homozygotes. The heterozygote phenotype may fall at any point within the range of the homozygotes.
haploinsufficient vs haplosufficient
dominant phenotype in diploid organisms that are heterozygous for a loss-of-function allele
vs
a single copy of a functional gene is enough to maintain normal function.
Codominance
The phenotype of the heterozygote simultaneously expresses the phenotype of both homozygotes. The phenotype of the heterozygote does NOT fall within the range of homozygous phenotypes.
Dominance
an allele at one locus interferes with or prevents (hides) the expression of a gene at the same locus.
Epistasis
an allele at one locus interferes with or prevents (hides) the expression of a gene at a different locus.
Epistatic genes
can mask other loci and, at the same time, be dominant or recessive to alleles at their locus.
Complementation
The expression of a wild type phenotype in an individual carrying two mutant alleles. This is an indication that the alleles are on different loci.
event vs total group size
event
- “thing” we can see and count
- usually phenotypes sometimes genotypes
total group size
- total number of counts observed for all events
P = n! / (x!) (y!) x (p^x) (q^y)
n = total group size (observations in all events = x+y)
x = number of times we observe event 1
y = number of times we observe event 2
p = probability of event 1
q = probability of event 2
P = n! / (x!) (y!) (z!) (etc!) x (p^x) (q^y) (r^z) (etc)
n = total group size (x+y+z)
x = number of times we observe event 1
y = number of times we observe event 2
z = number of times we observe event 3
p = probability of event 1
q = probability of event 2
r = probability of event 3
Sexual reproduction
- alternation between haploid and diploid cell types (most eukaryotes)
- process of organism reproduction that results in offspring that are genetically distinct from their parents
Sex
the phenotype of sex; a classification system based on biological differences between males and females rooted in anatomy or physiology.
Monoecious
the condition of having both male and female reproductive structures in the same organism
Dioecious
species of organisms that have either male or female reproductive structures.
Gender
a classification based on the social construction (and maintenance) of cultural distinctions between males and females. Gender refers to “a social construct regarding culture-bound conventions, roles, and behaviors for, as well as relations between and among, women and men, boys and girls” (Krieger, 2003).
Genetic sex determination
sexual phenotype is determined by genes at one or more loci carried on autosomes. There are no sex chromosomes in this system
Environmental sex determination
sexual phenotype is determined in part, or in full, by environmental factors
primary sex characteristics
- type of gamete that is made.
- In humans, this is sperm vs. egg.
secondary sex characteristics
- traits that tend to differ between the sexes of a species, but which are not directly part of the reproductive system.
- In humans, examples include height, bone density & structure, muscle mass, fat distribution, facial hair, voice, & some aspects of social behaviour
dosage compensation and ex
mechanism that equalizes the amount of protein produced by X-linked genes between heterogametic and homogametic sexes.
ex:
males (XY): 1× gene products
females (XX): 2× gene products (double “dose” of X-linked genes)
Bar body
a mostly inactivated X chromosome in females.
Anhidrotic ectodermal dysplasia
- Human X-linked trait characterized by several conditions including skin having no hair and no sweat glands.
- Heterozygous women have irregular “patches” of affected skin.
Linkage group
a collection of genes that do not assort independently into gametes because they are located on the same chromosome.
Meiocyte
a diploid cell in which meiosis can take place
Recombination
assortment of alleles into novel (non-parental) combinations
Inter-chromosomal recombination & mechanism
- assortment of alleles for genes on different chromosomes into novel combinations.
- mechanism: random alignment of chromosome pairs (metaphase I) and segregation (anaphase I) in meiosis
Intra-chromosomal recombination & mechanism
- assortment of alleles for genes located on the same chromosome into novel combinations.
- mechanism: exchange of DNA by crossing over (prophase I) in meiosis
Genetic map
map of gene location on chromosomes obtained by using genetic recombination data
Discontinuous (or qualitative) trait
a trait having only a few, distinct, phenotypes; often with a simple relationship to genotype (but not always).
Polygenic trait
a trait determined by the affects of alleles at many different loci.
ex:
1. quantitative traits (continuous)
2. threshold traits (present or absent)
3. meristic traits (countable)
mendelian vs quantitative traits
Arise from genes that have an effect large
enough for a recognizable discontinuity in
the presence of segregation at other loci
and non-genetic variation
vs
Arise from many genes with small effects
relative to segregation at other loci and
non-genetic variation
Quantitative Genetics
the branch of genetics that uses statistical and analytical
procedures to understand how genes and environment influence continuous traits in groups of individuals, and study the inheritance of such traits.
Quantitative Trait Loci (QTL)
a chromosome segment containing gene(s) (polygene)
that control a polygenic trait