Sheet 9--Test 3 Flashcards
What is the exception to the third postulate of the cell theory: all cells arise by division?
1) Increases Genetic diversity
2) food for evoultion
3) helps eukaryotes evolve rapidly
Why is sexual reproduction so important for the evolutionary success of eukaryotes?
Results in more genetic variability
Why is meiosis necessary?
Reduces chromosome number in gametes
- germ line cell 2n undergoes meiosis to get 4 1n cells
- -gametes are 1n= 23 chromosomes and they have 1 copy of each chromosome and 1 chromatid each
What are germ-line cells?
2n cells that will undergo meiosis to produce gametes
What are somatic Cells?
body cells (non-reproductive cells)
What is synapsis?
- occurs Prophase 1
- Homologous chromosomes pair to form a tetrad
- biggest difference–this does not occur in Mitosis
what is crossing over?
inner chromatids “cross over” and exchange genetic information
what is genetic recombination?
inner chromatids now have genetic information they did not have before
what are chiasmata?
areas where homologous chromosomes join during crossing over– this site remains until anaphase 1
what holds the tetrads together during metaphase 1?
Chiasmata
why does independent assortment occur?
Metaphase 1
homologous chromosomes line up randomly on metaphase plate. Daughter cells get a random mix of chromosomes from each parent.
how is the chromosome number halved during meiosis?
Metaphase 1
tetrads line up on metaphase plate and microtubules attached only to outside kinetochores
- homology with 2 chormatids pulled to each pole during anaphase 1
What is the stage between division 1 and division 2 of meiosis?
Interkinesis
* DNA does not replicate
why is division 2 necessary?
Division (Meiosis) 2 is necessary to separate sister chromatids
- second Meiotic Division resembles Mitosis
- -results in 4 haploid daughter cells.
what are the four main differences between meiosis and mitosis?
Unique Features of Meiosis:
- synapsis and crossing over during prophase 1
- tetrads of chromatids composed of homologous pairs joined by chiasmata on metaphase 1 plate.
- Separation of homologs rather than chromatids at anaphase 1
- Interkinesis: no “S” between meiosis 1 and meiosis 2
How is genetic variation introduced during Meiosis?
1) crossing over (Prophase 1)
2) independent assortment (Metaphase 1)
Which stages of meiosis introduce genetic variation?
Crossing over– Prophase 1
Independent assortment– Metaphase 1
Separation of Homologs– Anaphase 1
How is genetic variation introduced by sexual reproduction?
- random fertilization
- genetic information reshuffled by genetic recombination and independent assortment (meiosis)
- -sperm + egg –> zygote
What is parthenogenesis?
unfertilized eggs grow into an individual
–ex. Male bees are 1N (haploid)
In domestic turkeys viable offspring are sometimes produced from unfertilized eggs. These off spring are diploid, like there mother.
offspring from unfertilized eggs are diploid because homologes fail to separate at Meiosis 1
- -aneuploidy– incorrect # of chromosoems in gametes
- -vertebrates that develope from unfertilized eggs are female
Down syndrome in human is caused by having 3 copies of chromosome 21. What defect in meiosis could cause down syndrome?
Downsyndrome caused by failure of chromosomes #21 to separate correctly during meiosis 1 or meiosis 2
- -sygote gets 3 copies of #21 instead of 2 copies
- -pair didnt seperate or chromatids didnt seperate
- -occurs in anaphase 1 or anaphase 2(chromatids)
What are the current hypothesis for the origin of sex?
Enormous amount of genetic variation permits rapid adaption
1) certain kinds of DNA damage can only repaired using homologous chromosomes as template
- —only way for a haploid to get homologue is to fuse with another haploid
2) contagion– viral infection; can rapidly spread if fuses with related cell and cross over
3) get rid of parasites
What are the current hypothesis for the advantage of being diploid?
1) have a spare good copy of each gene and a bad copy of each gene
- –“red Queen” hypothesis: store bad genes until they are useful to keep up with enviromental change
- —–example- sickle cell anemia–recessive disorder–Aa
2) millers ratchet:
- —diploids can lose bad genes more easily than haploids
What was the major difference between Mendel’s model and earlier notion of inheritance?
used math model to determine genetics
what is a model?
a model is a comparison standard.
–ex. Mendel’s model of inheritance
what is a model organism?
Model organisms are used to infer things about all organisms
what is a hybrid?
hybrid results from the mating of dissimilar parents; offspring are different from parents
- -parents must be pure bread
- – AA x aa = Aa
what are the 5 assumptions of Mendel’s model of inheritance?
1) parents transmit genes that provide information about characteristics
2) neach indiviudal contains 2 genes for each character= dominant and recessive
3) not all copies of a gene are identical
4) alleles from each parent segregate during gamete production
5) presence of a gene doesnt assuure that youll see its expression
Aa–> shows dominant trait.
What are alleles?
different forms of the same gene
A– dominant allele
a– recessive allele
What is the difference between dominant and recessive alleles?
In mendelian genetics each character is determined by 2 alleles:
dominant– A
Recessive– a
What does homozygous mean?
2 haploid gametes containing the same allele fuse during fertilization
what does heterozygous mean?
2 haploid gametes that contain different alleles.
what is a genotype?
total set of alleles that an individual has
–genetic make up
what is a phenotype?
physical appearance or other observable characteristics which result of alleles expression
==physical expression of gene
Why do you see 3:1 segregation of phenotype when you self-cross the F1 generation of monohybrid cross involving a dominant and recessive allele?
F1 generation of a monohybrid cross:
P—AA x aa
Gametes–A—A—a—a
==gametes will have only 1 allele each
F1 generation will have Aa, Aa, Aa, Aa
self cross F1 so we cross Aa and Aa (2 heterozygotes)
F1 gametes–A–a–A–a
==law of segreation= 1 allele per gamete
pundit square= AA, Aa, Aa, aa (3:1) ratio dominant recessive
Why do you see 1:1 segregation of phenotypes when you testcross the F1 generation on a monohybrid cross involving a dominant and a recessive allele?
..
What is the addition rule of probabilities?
Probability of 2 mutually exclusive events is sum of their individual probabilityes.
- -see the word OR use this
- -probability of rolling a 6 OR a 5
What is the multiplication rule of probabilities?
probabilty of 2 independent events occuring simultaneously is equal to the product of each of their probabilities
–see the word AND
what are mendel’s laws of inheritance
…
How does meiosis explain mendel’s laws of segregation
Metaphase 1– random orientation of tetrads on metaphase plate
Anaphase 1– homologs separate
Anaphase 2– chromatids separate
What is the exception to the third postulate of the cell theory: all cells arise by division?
Fertilization requires the union of 2 cells to make one
–sperm + egg –> zygote
which of the following produces identical cells?
mitosis
if you roll a pair of dice, are you more likely to roll a six or a nine?d
..
At the end of telophase 2 of meiosis, each of the four resulting cells contains?
One full set of chromosomes, each a single chromatid
If true breeding dominant yellow seeded plants are crossed with recessive green seeded plants, what will the F2 generation look like?
3 yellow: 1 green
which state of the cell cycle explains mendel’s law of segregation?
Meiotic anaphase 1
The usual reason genes assort independently of one another is that
they are on different chromosomes
Yellow and green are two alleles for seed coat color in peas. Yellow seeded plants might be homozygous or heterozygous. The simplest way to find out is by?
crossing with any green seeded plant
Let P=purple flowers and p= white where purple is dominant , and T=tall plants and t= dwarf where tall is dominant. of the possible offspring in the dihybrid cross, how many would be white and tall?
3/16
what type of blood can you give to a person who is type AB?
all of these
You cross an individual who is wwDd with an individual who is WwDd. what fraction of the offspring will be wwdd?
1/8
What is law of independent assortment
genes located on different chromosomes assort independently of one another during meiosis
–metaphase 1
What are the 7 complications which make it difficult to figure out patters of inheritance?
1) most genes have more than 2 alleles and those alleles interact in complicated ways
2) incomplete dominance (3 phenotypes)
- —red X white –> pink
3) gene interactions (epistasis)
- -ex. lab retriever color
4) continuous variation (polygenese)
- —ex. human height
5) Pleiotropy- one gene many phenotypes
- –ex.sickle cell anemia
6) enviromental effects
- –ex. siamese cat
7) sex linkage– gene is on the X chromosome. label sex chromosome
- -ex. color blindness
Why are there 4 blood types given that there are 3 alleles of the I gene?
alleles–I^A, I^B, i
each person inherits 2 of them
Why do people of O blood type give blood to anyone, but only receive O
O blood type (universal donor) has no A or B antigen on RBS–> can be given to anyone
–produce both Anti A and Anti B–can only give this person O
AB is universal receipeant because of no antibodies.
Why do some women who are Rh- need to worry about their husbands blood type?
baby may be Rh+
- moms immune system will produce Rh antibodies against baby’s red blood cells.
- -condition known as erythroblastosis fetalis
Why do some genes show epistasis?
many genes interact sequentially because their products work in pathways
A–enzyme 1—> B –Enzyme 2—-> C
ex. labrador coat color.
-one gene for pigment
-one gene for color deposition
-two genes on 2 different chromosomes, if working normally ratio would be 9:3:3:1 but they are reall 3/4,3/16,1/16
What is the difference between incomplete dominance and codominance?
Codominance– both alleles of a pair expressed equally
- -ex. AB type blood
- -ex. cross black horse with white horse offspring has black hair AND white hair
Incomplete dominance– heterozygote has intermediate phenotype as alleles dilute effect of each other
- -ex. red (RR) X white (ww) = pink (RW)
- -ex. black bunny X white bunny= grey bunny
Qualitative vs quanitiative
Qualitative–cannot be expressed in numbers
quanititace– can be expressed in number, quanitiative shows continuous variation
–ex. height
why do siamese cats have darker fur on the tips of their ears and end of their tail?
pigment enzyme is heat sensitive; warmer area of body, enzyme is denatured and white fur resules
–cooler areas, enzyme active= black fur.
what does pleiotropy mean?
gene has many phenotypes
ex. sickle cell anemia has many complicated all caused by 1 gene
what were the 3 possible crossover types in the gene mapping exercise?
between a and b, b and c, or a and c
–computer moving the a to b to c thing around
how many possible phenotypes were there, and which ones were recombinant?
8 phenotypes, 6 recombinant
- non- recombinant: +++ and y w min
- -you can have crossing over +wmin or y++ these are recomb
non recom are what you start with
When does synapsis occur?
prophase 1
does synapsis occur in mitosis, meiosis, or both?
Meiosis and NOT mitosis
what phase does the chiasmata last until
anaphase
what forms during synapsis
tetrad
when does independent assortment occur
metaphase 1
Does DNA replicate in interkinesis
no
when are sister chromatids separated?
meiosis 2–results in 4 haploid cells
what is meiosis 2 similar too?
mitosis
when does synapsis and crossing over occur?
prophase 1
when does independent assortment occur?
metaphase 1
when does the separation of homologs occur?
anaphase 1
what sex are vertebrates that develop from unfertilized eggs
female and diplod
why are offspring from unfertilized eggs diploid?
homologs fail to separate
what is down syndroe caused by?
failure of chromosome 21 to separate during meiosis 1 or 2 during anaphase 1 or 2
if a gene is present will you see its expression?
no, only see dominant
when do homologs separate
anaphase 1
when do chromatids separate
anaphase 2
