Chapter 6: Heredity Flashcards
multiplication rule
to determine the probability of two or more independent events occurring together multiply the probabilities of each separate event
gene
genetic material on a chromosome for a trait
allele
variance of genes such as different color
locus
location on chromosome where gene is located
homologous chromosome
- a pair of chromosomes that contains same genetic material (gene for gene)
- each parent contributed 1 of the chromosomes in the pair and this different alleles may exist for a gene (dominant and recessive or incomplete dominance (color blending)/ co-dominant such as blood type)
law of segregation
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 allele)
— occurs in anaphase 1
law of independent assortment
migration of homologues within one pair of homologous chromosomes does not influence the migration of homologues of other homologous pairs (independent assortment of alleles)
test crosses
- monohybrid crosses test one gene
- dihybrid test two (on different chromosomes)
- crosses have P, F1, F2, etc generations
- You can cross (unknown dominant genotype) X (homozygous recessive) to determine if hetero or homo dominant
- to determine probabilities in dihyrbrid, usually easier to calculate probability of each gene separately then multiply
incomplete dominance
blending of expressions of alleles (R= red, R’=white, RR’=pink
codominance
- both inherited alleles are completely expressed
2. Blood types A and B or both can show up as AB if expressed
multiple alleles
- Blood groups have 3 possible alleles
- the codominant A and B and the O, leading to 4 possible phenotypes (6 possible genotypes)
- AO/AA (A type)
- BO/BB (B type)
- AB (AB type)
- OO (O type)
epistasis
- one gene affects phenotypic expression of 2nd 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 ccxx=no pigment
pleiotropy
- single gene has more than 1 phenotypic expression
- gene in pea plants that expessed seed texture also influences phenotype of starch metabolism and water uptake; sickle cell anemia leads to different health conditions
polygenic inheritance
the interaction of many genes to shape a single phenotype w/ continuous variation (height, skin color in humans)
linked genes
- two or more genes that reside on the same chromosomes and this cannot separate independently because they are physically connected (inherited together)
- linked genes exhibit recombination about 18% of the time?
- In a cross of BbVv x bbvv (says that BV and bv are linked and is in a homologue)
- we can only get BV and bv and no Bv or bV
- however, if there is recombination, we may get 18% Bv and bV
- the greater the recombination frequencies (18% above) means farther distance apart on the same chromosome.
linkage map
B-V is 18%, A-V is 12%, B-A is 6%=>
B——A————V
sex-linked
- refers to single gene resides on X chromosome
- when male (XY) receives an X from mother, whether it is dominant of recessive will be expressed because there is no copy on the Y chromosome
sex-influenced
can be influenced by sex of individual carrying trait (Bb female not bald, Bb male is)
penetrance
probability an organism with a specific genotype will express a particular phenotype
expressivity
term describing the variation of phenotype for a specific genotype
X-inactivation
- during embryonic development in female mammals, one o two X chromosomes does not uncoil into chromatin=> dark and coiled compact body chromosome (Barr body)=> cannot be expressed
- Thus, only the genes on the other X chromosomes will be expressed.
- either one can be inactivated=> genes in the female will not be expressed similarly, so all cells in a female mammal not necessarily functionally identical (calico cats)
hemophilia
cannot form blood clot. XHXh is normal carrier. But if XH is inactivated=> Xh is expressed
nondisjunction
- failure of one/more chromosomes pairs or chromatids to separate during mitosis
- failure of two chromatids of a single chromosome during anaphase or meiosis ( homologous chromosomes to separate during meiosis 1 or sister chromatids to separate during meisosi 2; result in trisomy or monosomy; ex down syndrome ** note specifically during anaphase
mosaicism
in cells that undergo nondisjunction in mitosis during embryonic development; fraction of body cells have extra or missing chromosome
polyploidy
all chromosomes undergo meiotic nondisjunction and produce gametes with twice the number of chromosomes. Common in plants.
point mutation
- single nucleotide changes causing substitution, insertion, deletion (latter 2 could use frameshift)
- transition mutation: purine to purine or pyrimidine to pyrimidine
- transverse mutation: purine to pyridine or vice versa
aneuploidy
genome with extra/missing chromosome<= often caused by nondisjunction (down syndrome =trisomy 21)
turner syndrome
- nondisjunction in sex chromosome
- gametes (single, frome one parent) can be XX/XY or O (no chromosome)=> XO sterile, physically abnormal
- klinefelter (XXY); down syndrome (trisomy 21)
chromosomal abberations
chromosome segments are changed
duplications
chromosome segment is repeated on same chromo
inversions
chromosome segments are rearranged in reverse orientation
translocation
segment is moved to another chromosome. Can be reciprocal (two non-homolgous chromosomes swap chuncks or Robertsonian (one chromo from a pair becomes attached to another from a pair
e.g. an extra chromo 21 attached to 14 can cause down syndrome as well
