Exam 2 Flashcards
Allele
- one or two alternative forms of a gene that arise by mutation and are found at the same place in a chromosome
- wild type allele: normal allele (most common one in the population)
Loss of function mutation
-reduced productivity of gene product
Null Alelle
- no productivity of gene function at all
Gain of function mutation
- increased or extra productivity
- or does a new function
Neutral mutation
- change to distinguish one allele from another
- no phenotypic change
Incomplete dominance
- dominant allele is not fully expressed when recessive allele is present (blend of 2 colors)
Ex: pink flower offspring from red and white P gen
P generation-> 1 RR=red x 1 rr=white F1 generation-> 4 Rr-> PINK F2 generation-> 1 RR:2Rr:1rr
Codominance
- alleles work together, both are expressed or seen
Ex: white chicken with black speckles
- MN blood types antigens on RBC
- two alleles L^M and L^N
- phenotypes:
LMLM=M antigen x LNLN= N antigen
LMLN= both antigens present, NOT BLENDEDi
Pleitropy
- one gene that impacts several aspects of the overall phenotype
Epistasis
- recessive epistasis
- one gene is very dependent on another gene to allow the other gene to be expressed
- 16 square Punnett
Ex: cross BbCc x BbCc
BB=black bb= brown cc=epistasis recessive
If has __cc ex: Bbcc it will be ALBINO
- Bb is the hypostatic, or hidden gene
- 9:3:4 ratio
Penetrance
- percent of individuals with a specific allele or genotype that we would expect
- answers: yes OR no if you have the allele will you express the phenotype
Ex: if 45/50 people exhibit trait:
90% penetrance
Incomplete penetrance
- genotype/allele does not always produce the expected phenotype
Expressivity
- the degree of HOW MUCH of the phenotype you will display, how severe?
- assume 100% penetrance (you will def express it)
Temperature effect
- causes variability or expressivity
- temperature sensitive allele
Ex: rabbits in the Himalayas produces dark fur at extremities less than 25 Celsius or less
Norm of reaction: range of phenotypes produced by a genotype in diff environment **
Thomas Hunt Morgan
- first explained sex linked inheritance
- found some traits were specific to sex
- suggested that genes on the same chromosome segregated together and those closely linked were rarely subject to recombination
Ex: fruit flies in a male only have the X chromosome and it is dependent on whether or not they have white eyes
Sex chromosomes and pedigree analysis of them
- genes are expressed by the X chromosome
- females have 2 X chromosomes and males only have one an XY
- males can not be carriers of the recessive allele can only be affected if have it and are more commonly affected than females
- if father has the recessive allele any daughter will be at least a carrier Bc they receive one X from mom and one X from dad
- if the daughters son is affected must have the recessive allele because only has ONE X the affected one
- mom affects all sons with recessive allele and dad affects all daughters with recessive allele
- although phenotypes appear to skip generations, they NEVER do
Autosomes
- any chromosomes that are not sex chromosomes
3 types of sex inheritance
1) sex linked inheritance
- only on the X or Y chromosome
- Y-linked will affect ALL male offspring
2) sex limited inheritance
- in Autosomes both male and females have it
- “on” or “off” scenario, ONLY ONE SEX will express it (zero penetrance in other sex)
Ex: only female hormones will trigger lactating breasts, males will never trigger
3) sex influenced inheritance
- on Autosomes both males and females
- variation in how males and females will express the same gene
Ex: all people have body hair but males have much more
Genomic imprinting (Prader Willi/angelman syndrome)
- occurs with autosomal genes
- one copy of the gene from either mom or dad is silenced by cytosine methylation and the over gene is turned “on” or activated
Angelman Syndrome-> the mutated allele from mom is inherited (then turned off) and the father gene is already silenced through methylation causes excessive laughter
Prader Willi-> the mutated allele from father is inherited(then turned off) and the mom is already silenced through methylation causes excessive eating
Epigenetics
- genome modification that doesn’t affect the DNA sequence but will affect the function
Cytoplasmic Inheritance
- genes are located in the cytoplasm (chloroplasts and mitochondria)
- zygote will inherit nuclear genes from both parents, but all (most) cytoplasmic genes come from the mother
- affected females will pass it on to all children (male/female)
- males do not pass trait on to children
Genetic maternal effect
- genes/allele are passed on by both parent but phenotype is determined by the genotype of the mother
Chromosomal sex determination
- chromosome theory of inheritance->
chromosome theory of inheritance
- genes are located on chromosomes and chromosomes are substrate for gene segregation
Henking
- male insects had strange body in nuclei = X body
McClung
- male grasshoppers have a heterochromosome, female grasshopper cells had one more chromosome than males
X body=chromosome
Heteromorphic chromosomes-> distinction btw X and Y chromosomes
Stevens
- female mealworms have 20 large chromosomes
- males have 19 large and 1 smaller one a Y
- X and Y separate into different sperm cells, while all egg cells get single X
Wilson
- female butterflies have 2 X chromosomes
- males have one X chromosome
Alfred H Sturtevant
- Thomas Morgan’s student
- generated the first map of chromosome based on the frequency of recombination
- postulated that frequency can determine the physical distance separating the two genes on a chromosome
frequency of recombination rules (high, low, etc)
- if it is high genes are further spread, can undergo double crossovers if very far (appears the crossover never occurred)
- if it is low genes are closer together, Thomas hunt Morgan said the closer together they are the less of a chance of recombination there is
- frequency can not be >50% or =50% , if they are they are on different chromosomes
Recombination frequency formula
= # of recombination progency / total # of progency x100
Genetic maps
- use recombination frequencies to make chromosome maps
- distances are in terms of map units (=1% recombination frequency) aka centimorgans (cM)
Physical maps
- chromosome maps based on physical distances (base pairs)
Define Interference(pos, neg, complete) and formula to find it
- when the crossover in one region affects the probability of a crossover in a nearby region
- the closer the genes are together, the more interference there is (positive interference)
- the further the genes are, the less interference there is (negative interference)
- if interference is 1 you will have zero crossovers
1- coefficient of coincidence
Coefficient of coincidence
COC= # of observed cross overs/# of expected cross overs x 100
- get expected from data table
- get observed by calculating probability of BOTHS DCO multiply those together then multiplying by total number of progeny
Two types of Linkage
1) complete linkage
- occurs between the genes on a single pair of homologous chromosome, close together so crossing over(recombination) is very rare
- produces two genetically different parental gametes
- will not seperate according to THM (fruit fly body and wing shaped are linked genes 1:2:1 ratio instead of 9:3:3:1)
2) incomplete linkage
- occurs between two pairs of homologous genes that have 2 genes that are on same chromosome, but some distance apart so allows crossing over (recombination) btw nonsister chromatids
- produces two recombinant or crossover gametes and 2 parental gametes
- 4 sets 9:3:3:1
Linkage groups
- number of chromosomes in 1 set(n)
- ALL THE GENES LOCATED ON THE SAME CHROMOSOME
- significance of linked genes is that they are used as distant markers (determine linkage group and genetic map in humans)
- distant markers can be tied together by intermediate markers to span further than 50cM
Ex: humans have 2n (2 sets of chromosomes)
N=23 so linkage groups = 23
Ex 2: drosophila fruit fly have 2n=4 pairs of chromosomes. N=4
Linkage groups=4
Turner Syndrome
- sex chromosome abnormality due to nondisjunction
- females have only one copy of sex chromosome (XO)
- 45 total chromosomes, X no Y
- develop female because presence of X
- do not undergo puberty
Klinefelter Syndrome
- sex chromosome abnormality due to nondisjunction
- have XXY chromosomes, more than one X only one X is functional other is inactivated and becomes a Barr body
- develops male because Y chromosome, but will have secondary female sex characteristics
- enlarged breasts, small testes, reduced facial hair
- often STERILE
Poly X females
- sex chromosome abnormality due to nondisjunction
- 3 X chromosomes no Y (XXX)
- 47 total chromosomes
- only 1 sex chromosome is functional, other 2 are Barr bodies
- tall, thin, sometimes normal fertility, normal intelligence
If have more X more severe ex: XXXX OR XXXXX will have cognitive impairment with normal female anatomy
Aneupolyploidy
- changes deletion or addition of single chromosomes not based on pair
- common in humans
3 reasons occurs:
1) loss of chromosome Bc loss of centromere
2) robertsonian translocation
3) nondisjunction
Types
1) nullisomy- loss of both members of homologous pairs (2n-2), lethal
2) monsomy(Turners)- loss of single chromosome (2n-1), if lose single Autosomes lethal
3) trisomy(klinefelters)- gain of a single chromosome (2n+1), lethal
4) tetrasomy- gain of two homologous chromosomes (2n+2)
- two additional chromosomes of same set
Polyploidy
- # chromosomes in an entire set change 2n is normal
- 3n means one chromosome was added to each set, common in plants
Causes:
1) errors in meiosis
2) events at fertilization- dispermy (fertilization of egg with two sperm)
3) errors in mitosis following fertilization
Types:
1) autoploidy- all chromosomes sets (polyploidys) originate from the organisms body itself SAME SPECIES
- due to nondisjunction, no cell division
2) allopolyploidy- polyploidy originated due to hybridization among 2 different organisms
- DIFFERENT SPECIES
Principle of segregation vs independent assortment
Segregation
- during the formation of gametes there is a 50/50 chance of getting one of the traits, but can not get both Bc for example it is color can only be one color
- one trait/characteristic
Independent Assortment
- during formation of gametes TWO alleles with different traits do not influence eachother AT ALL when distributing
- two or more different traits with 50/50 chance of getting either one they DO NOT influence eachother
Ex: height (tall vs short) or color (yellow vs white)
50/50 chance of being tall or short
50/50 chance of being yellow or white
Inversion
- chromosome segment breaks off and flips then adds back to the same chromosome
types
1) paracentric inversion- do not include the centromere
- most NONVIABLE (heterozygous)
2) pericentric inversion- include the centromere
- about half of gametes are viable
3) POSITION EFFECT- regulation of genes is sometimes context dependent (can change how it’s going to work, used incorrectly, or unable to see what’s on or off)
Ex: if break in the middle of a gene, gene is null(lost)
Deletion
- breaks off part of chromosome and does not reattach
- if break off centromere lose chromosome completely
- lethal for homozygous deletions
Heterozygous deletions
1) psuedodominance- loose wild type allele see recessive
- allows recessive alleles on undeleted chromosome to be expressed
2) haploinsufficient- left with wild type allele but not enough to get you wild type phenotype
- some genes have to be present in 2 copies to produce enough gene produce
Translocation
- segment of chromosome breaks off and goes onto nonhomologous chromosome
- nonreciprocal exchange (moves from one to the other without equal exchange)
robertsonian translocation
- translocation + deletion
- causes some forms of Down syndrome
Reciprocal translocation
- stitches two random broken chromosomes together Can be in WRONG ORDER
