Biology-Heredity Flashcards
multiplication rule
you use this to determine the probability of two or more independent events occurring together, you multiply the probabilities of each event happening separately
gene
genetic material on a chromosome that contains the instructions for creating a particular trait
allele
one of several varieties of a gene
locus
location on a chromosome where a gene is located. Every gene has a unique locus on a particular chromosome
homologous chromosomes
refer to a pair of chromosomes (a homologous pair) that contains the same genetic info, gene for gene.
Each parent contributed 1 of the chromosome in the pair and thus different alleles may exist for a gene (dominant and recessive or incomplete dominance (color blending)/ co-dominant such as blood type).
dominant
actual trait that is expressed
homozygous dominant
refers to the inheritance of two dominant alleles (PP)
heterozygous
refers to the condition where two inherited alleles are different (Pp)
phenotype
actual expression of a gene
genotype
represents actual alleles
Mendel
credited w/ the discovery of the laws of segregation and independent assortment
law of segregation
refers to the segregation (separation) of alleles (and their chromosomes) to individual gametes
one member of each chromosome pair migrates to an opposite pole so that each gamete is haploid (aka each gamete has only one copy of each chromosome), occurs in anaphase I.
law of independent assortment
refers to the independent assortment of alleles (and chromosomes)
migration of homologues within one pair of homologous chromosomes does not influence the migration of homologues of other homologous pairs (independent assortment of alleles)
Monohybrid cross
An experiment in which only one trait is being investigated
Dihybrid cross
An experiment where two traits are being investigated
Complete (full) dominance
When traits are expressed as if one allele is dominant to a second allele
Test Cross
Mating of an individual whose genotype you are trying to determine with an individual whose genotype is known
unknown dominant genotype x homozygous recessive phenotype to determine if hetero or homo dominant
Incomplete dominance
Blending of the individual expressions of the two alleles
e.g. R red, R’ white, RR’ comes out pink
Codominance
Both inherited alleles are completely expressed
e.g. blood types A and B or both can show up as AB if expressed
Antigens
Foreign substances (immune system)
Antibodies
Attack the antigens
Agglutination
Clumping of the blood that may result in death
Epistasis
Occurs when one gene affects the phenotypic express of a second gene
Pigmentation (one gene controls (turn on/off) the production of pigment, and 2nd gene controls color or amount). IF 1st gene codes for no pigment —> 2nd gene has no effect
CCBx => black fur in mice
ccxx => no pigment
Pleiotropy
Occurs when a single gene has more than one phenotypic expression (gene in pea plants that expressed seed texture also influences phenotype of starch metabolism and water uptake; sickle cell anemia leads to different health conditions).
Sickle cell disease
A human blood disorder that is caused by an allele that incorrectly codes for hemoglobin
Polygenic inheritance
The interaction of many genes to shape a single phenotype, which is the opposite of pleiotropy (one gene influences many phenotypes)
(height, skin color)
linked genes
genes that reside on the same chromosome and thus cannot segregate independently because they are physically connected. Linked genes exhibit recombination about 18% of the time.
In a cross of BbVv X bbvv (says that BV and bv are linked and each is in a homologues). We only get BV or bv and no Bv or bV. However, if there is recombination, we may get 18% of Bv and bV.
In which phase do linked genes cross over?
prophase I
linkage map
portrayal of the gene sequence on a chromosome
cytological map
a map that portrays the true relative positions of the genes, which requires additional experimental analysis
sex chromosomes
the X and Y chromosomes
autosomes
all chromosomes excluding the sex ones
sex-linked (or X-linked) genes
genes that reside on the X, or sex, chromosome; Y-linked are also possible.
when male (XY) receives an X from mother, whether it is dominant or recessive will be expressed because there is no copy on the Y chromosome.
X-inactivation
one of the two X chromosomes in each cell does not uncoil into a chromatin => dark and coiled compact body chromosome (Barr body) => cannot be expressed. All cells in a female mammal are not necessarily functionally identical
Hemophilia: cannot form blood clot. X^H X^h is a normal carrier. But if X^H is inactivated => X^h is expressed
Barr body
one chromosome remains coiled as a dark, compact body
Nondisjunction
failure of one or more chromosome pairs or chromatids of a single chromosome to properly separate during mitosis (failure of two chromatids of a single chromosome during anaphase) or meiosis ( homologous chromosomes to separate during Meiosis I or sister chromatids to separate during Meiosis II; result in trisomy or monosomy; ex. Down Syndrome
specifically during anaphase!
mosaicism
a fraction of the body cells, those descendent of a cell where nondisjunction occurs, have an extra or missing chromosome
Polyploidy
occurs if all of the chromosomes undergo meiotic nondisjunction and produce gametes w/ twice the number of chromosomes. Common in plants
Point Mutations
occur when a single nucleotide in the DNA of a gene is incorrect causing substitution, insertion, or deletion (latter 2 could cause frameshift); most have deleterious effects on gene function
(point mutation) Substitution
occurs when a different nucleotide is substituted for the correct one
(point mutation) Deletion
occurs when a nucleotide base-pair is omitted
(point mutation) Insertion
occurs if an extra base pair is inserted
Aneuploidy
a genome w/ extra or missing chromosomes XO sterile, physically abnormal; Klinefelter (XXY); Down Syndrome (Trisomy 21)
Down syndrome
occurs when an egg or sperm w/ an extra number 21 chromosome fuses w/ a normal gamete. The result is a zygote with 3 copies of chromosome 21 (trisomy).
Turner Syndrome
results when there is nondisjunction of the sex chromosomes. Sperm will have either both sex chromosomes (XY) or no sex chromosomes (O). Similarly, eggs will be either XX or O.
A Turner syndrome zygote (XO) is a female who has one X and no second chromosome
chromosomal aberrations
caused when chromosome segments are changed:
- Duplications
- Inversions
- Translocations
(chromosomal aberrations) Duplications
chromosome segment is repeated on the same chromosome
(chromosomal aberrations) Inversions
chromosome segments are rearranged in reverse orientation on the same chromosome
(chromosomal aberrations) Translocations
segment of a chromosome is moved to another chromosome
(21 on 14 can cause Down’s as well, tripled 21 chunk: 3 copies of a segment from chromosome 21 ( two chromosomes 21 and a chromosome 14 with a segment of chromosome 21)
multiple alleles
blood groups have 3 possible alleles, the codominant A and B and the O, leading to 4 possible phenotypes: AO (A type) BO (B type) AB (codominant AB type), OO (O type)
transition mutation
purine to purine or pyrimidine to pyrimidine
transversion mutation
purine to pyrimidine or vice versa
chromosomal breakage (human genetic defects)
spontaneous or induced (mutagenic agents, Xrays). Deficiency = lost fragment
mutagenic agents
cosmic rays, Xrays, UV rays, radioactivity, chemical compounds include colchicine (inhibits spindle formation causing polyploidy), mustard gas. Mutagenic agents are generally also carcinogenic
-Proto-oncogenes stimulate normal growth; if mutated become oncogenes => cancer
Genetic disorders include:
AR: PKU (inability to produce proper enzyme for phenylalanine breakdown; degradation product phenylpyruvic acid accumulates)
cystic fibrosis (fluid buildup in tracts)
Tay-sachs (lysosome defect, can’t breakdown lipids for normal brain fxn)
sickle-cell (defective hemoglobin due to substitution mutation)
AD: Huntingtons (degenerate nervous system disease
SLR: hemophilia (abnormal blood clotting, color blind, duchenne (muscular dystrophy)
Chromosomal: Downs, Turner (XO), Klinefelter (XXY), Sickle-cell anemia
forward mutation
already mutated organism mutates again even more
backward mutation
mutates back to original
extranuclear inheritance
extranuclear genes are found in mitochondria and chloroplasts. Defects in mito DNA can reduce cell’s ATP production. Mitochondria passed to zygote all come from mother, so all related diseases are mother inherited.
NOTE: mitochrondria have their own 70S ribosomes that make mitochondrial proteins w/in mitochondrial matrix
lethal gene
cross between Aa and Aa, we get AA:2Aa:aa. If “aa” was lethal, we would have AA and Aa as 1:2 ratio
hemizygous
one single copy instead of two
Tips
IF the phenotype “skips” generations be suspicious of an autosomal recessive disorder
IF no skip, most likely an autosomal dominant disorder
Be suspicious for x-linked recessive, if a father doesn’t have the phenotype, none of his daughters display it
Partial Monosomy
When only part of one chromosome is lost
Partial trisomy
Addition of only a portion of another chromosome is seen
Partial Monosomy
When only part of one chromosome is lost
Partial trisomy
Addition of only a portion of another chromosome is seen
