BICD 100 Midterm II Grossman

Recessively Inherited Traits (Pedigree)

Typically skips generation, parent may be carriers.

Dominant Autosomal Trait (Pedigree)

Dominant traits appear in every generation, affected individuals will have an affected parent

Incomplete dominance

Incompletely dominant traits are blended. In flowers being crossed CrCr (red) and CwCw (white), F1 generation will generate all pink flowers

Codominance

Influence of both alleles equally, no blend. In flower example, CrCr x CwCw will give all flowers with splotches of white and red.

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Alternative example : blood types. A, B, O (absent) expressed equally

Lethal Recessive Allele (Agouti Mouse Example)

In a heterozygous cross between AyA mice, AyAy is lethal. Special ratio of 1/3 yellow, 2/3 Agouti

Epistasis (general)

occurs when expression of one gene pair masks or modifies expression of another gene/gene pair

Recessive Epistasis

In mouse example where B/b is pigment placer gene, B/b is epistatic to the actual pigment gene (A/a). So, bb will always result in albino. aa = black, Aa/AA = agouti.

Dominant Epistasis

occurs when a dominant allele at one genetic locus masks expression of alleles at other locus. In squash example, B/b must be homoz recessive to exhibit yellow phenotype. aabb is only phenotype avail for green.

Complementary Gene Action

Both sets of genes must be active in order to exhibit the trait.

Penetrance

percentage of individuals who show some expression of a mutant phenotype

Expressivity

range of expression of a mutant phenotype

Temp. Sensitive Mutations

mutations whose expression is affected by temperature

Permissive Temp (temp sens mutations)

wildtype phenotype is expressed

Restrictive Temperature (temp sens mutations)

mutant phenotype expressed

Silenced Genes

Gene which is no longer expressed, phenotypic expression is delegated to the non-silenced homolog

Parental Imprinting

Dwarf mouse example. Even if dominant (normal allele) is present on mother, all progeny dwarf. Normal father crossed with dwarf mother, all progeny normal sized. Maternally silenced.

Human Silencing

Prader-Willi, Angelman caused by the same deletion on the q arm of chrom 15. PWS is paternal segment deletion, AS is maternal segment deleted

Maternal Effect

Offspring’s phenotype for a particular trait is under control from mother’s nuclear gene products. In case where mother’s phenotype does not express for proteins or RNAs crucial for development, embryo dies

X-linkage

traits linked to x chromosome. XY individuals may not be homozygous or heterozygous, hemizygous instead for these traits

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pattern of inheritance is “Criss cross”, phenotypic traits controlled by recessive X linked genes are passed from homozygous mothers to sons

Heteromorphic, Homomorphic

XY, XX chromosome pairings determining sex in humans.

Sex Limited Inheritance

expression of phenotype limited to a **SINGLE SEX** (must be male/female to exhibit trait)

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ex: cock feathered vs hen feathered (only male/female may exhibit each)

Sex Influenced Inheritance

sex of an individual **influences** expression of a phenotype which **isn’t limited to one sex or the other**

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ex : male pattern baldness (both sexes may experience, influenced by testosterone presence)

Nondisjunction event

chromosomes do not properly separate during cell division (in meiosis I or II) leading to aneuploidy

Aneuploidy

change in number of sets of chromosomes, no longer a set

nondisjunction in meiosis I (failure to separate from tetrads) leads to gametes of set number :

n+1, n+1, n-1, n-1

nondisjunction in meiosis II (failure to separate from sister chromatids) leads to gametes of set number :

n+1, n-1, n, n

Cause of Mosaic Turner

if nondisjunction occurs in early development, mosaicism may occur since two different genetic cell lines are resultant from early mitotic error

Bipotential Gonads

during early human development in embryo, humans have bipotential, sexually indifferent gonads, influenced by testosterone or estrogen to follow tract for ovaries or testes

Wolffian ducts

testes containing, influenced by testosterone

Mullerian Ducts

differentiate into ovaries with reproductive tract

PAR

Pseudoautosomal region on y chromosome. Allows synapsis with X

MSY

section of Y chromosome which contains male-specific genes

TDF

testis determining factor : causes undifferentiated gonadal tissue to form into testes

Dosage compensation

process which equalizes expression of X linked genes in XY, XX individuals

Barr Body

inactivated X chromosome, highly condensed structure inaccessible for gene expression

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barr body number can be found by subtracting the one from X chromosome contained (ex, XY has zero barr, XX = 1 barr, XXX = 2 barr)

Lyon Hypothesis

inactivation of X chromsomes randomly occurs in somatic cells during the blastocyst stage, once all inactivation has occurred, all descendant cells have same X chromosome inactivated

Inactivation mechanism

X inactivation center is major control unit, expression only occurs on X chromosome.

X-inactive specific transcript

critical for X inactivation, RNA from XIST doesnt get translated but instead coats X chromosome that produced it

Euploid

complete haplod set of chromosome

Aneuploidy

loss or gain of one or more chromosome, not a complete set

Polyploidy

more than two sets present

Chromosome Aberration

rearrangements include inversion, exchange with non homolog chromosome, transfer to another chromosome

Deletion

removal of one or multiple sections of chromosome.

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Deletion loop forms (on non deleted chromosome) to conform to other chromosome during meiosis

Duplication

repeated chromosome segment

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compensation loop forms similar to deletion. in case of unequal crossing over, duplication and deletion are produced

Gene Redundancy

multiple copies in a genome perform the same function. Sometimes necessary for proper function, 7 RNA creating genes on e. coli

Gene family

Set of similarly functioning genes, formed via duplication of original genes

Copy number variant

number of copies of a particlar gene varies from one individual to the next

Inversion

type of chromosomal aberration in which chromosomal segment is turned around 180deg

Paracentric Inversion

away from center inversion, not centromerically involved

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normal synapsis not possible, dicentric bridges form leading to chromosome breakage.

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2 normal and 2 inverted chromatids (dicentric, acentric) involved in gametes

Pericentric Inversion

includes centromere inversion

Translocations

Translocations alter location of chromosomal segments in genome

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consequences similar to inversion. No genetic material is lost, just rearranged in incorrect order

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semi-sterility observed in gamete creation, along with balanced and unbalanced gametes being produced. 50% of gametes made are abnormal and unable to produce offspring

Reciprocal Translocation

exchange of segments between two non homologous chromosomes

Nonreciprocal Translation

one way exchange of segments between two non homologous chromosomes

Robersonian Translocation

breaks at end of acrocentric chromosome which lead to the fusion of a new larger metacentric chromosome

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ex : familial down syndrome, fusion betwen 14 and 21

diploid number of 45, still contain same amount of genetic material

Fragile X sites

fragile sites fail to stain, look like gap in chromosome. Some sites are commonly found, cause of fragility is unknown

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in fragile X syndrome gene FMR1 is known to be cause of the syndrome

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trinucleotide repeat in wildtype goes from 6-54

carrier 55-230

syndrome form 230+ repeats on chromosome

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only maternally transmitted (x linkage)

Chromosomal Translocation

fuses two genes together to
produce a hybrid gene encoding a protein whose activity is
constitutive

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brings a growth regulatory gene undercontrol of a different promoter which causes inappropriate expression of the gene

Genetic Linkage

two genes on a single pair of homologs, exchange occurs between two nonsister chromatids

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100% linkage yields a 1:2:1 ratio in F2.

2 phenotypes as a result from test cross indicates..

linkage. oterwise, 4 genotypes shown is indicative of