Questions #9 Flashcards
October 24 - October 31
What is the exception to the third postulate of cell theory: all cells arise by division?
Fertilization requires the union of 2 cells to make one.
Why is sexual reproduction so important for the evolutionary success of eukaryotes?
It increases the genetic diversity.
Why is meiosis necessary?
Reduces chromosome number in gametes.
What are gem-line cells, and what are somatic cells?
gem-line cells=2n cells that will undergo meiosis to produce gametes somatic=non reproductive cells.
What is synapsis, and what is crossing over?
- synapse happens at prophase of meiosis I. It refers to the homologous chromosomes coming close together.
- crossing over trades DNA between homologous and the result is genetic recombination and variation.
What is genetic recombination
the production of offspring with combinations of traits differing from either parent
What are chiasmata?
Sites where crossing over has occurred.
What holds the tetrads together during metaphase I?
chiasmata
Why does independent assortment occur?
One homologue comes from the mother and one from the father. When homologous chromosomes separate in meiosis I chance determines which direction the mother or father homologue go.
How is the chromosome number halved during meiosis?
tetrads line up at metaphase 1 and the microtubules attach to the kinetochores on the outside and pull them apart
What is the stage between divisions 1 and 2 of meiosis?
interkinesis
Why is division 2 necessary?
to separate sister chromatids
What are the four main differences between meiosis and mitosis?
- synapsis and crossing over in prophase 1
- tetrads of chromatids compared of homologous pairs joined by chiasmata on metaphase 1 plate
- separations of homologs rather than chromatids at anaphase 1
- interkinesis: no S between meiosis 1 and meiosis 2
How is genetic variation introduced by sexual reproduction?
- random fertilization
- crossing over
- independent assortment
What is parthenogenesis?
unfertilized eggs grow into an individual
ex. male bees in 1N (haploid)
in domestic turkeys viable offspring are sometimes produced from unfertilized eggs. these offspring are diploid, like their mother, what defect in meiosis could give rise to diploid eggs
offspring from unfertilized eggs are diploid because homologues fail to separate at Meiosis 1 (nondisjunction)
Down syndrome in humans is caused by having 3 copies of chromosome 21. What defect in meiosis could cause Down’s syndrome?
caused by inheritance of third number 21 chromosome, failed to separate
What are the current hypotheses for origin of sex?
(enormous amount of genetic variation permits rapid adaptation)
- certain kinds of DNA damage can only be repaired using homologous chromosome as template (only way for a haploid to get a homologue is to fuse with another haploid)
- contagion-viral infection; can rapidly spread if fuses with related cell and cross over
- get ride of parasites
What are the current hypotheses for the advantage of being diploid?
1.have a spare good copy of each gene and a spare bad copy of each gene
“red queen”- good to store bad genes until environment changes to where they are useful
2. Miller’s ratchet: diploids can lose bad genes more easily than haploids can
What
What was the major difference between Mendel’s model and earlier notions of inheritance?
first quantitative study
What is a model and what is a model organism?
model=comparison standard
model organism=used to infer things about all organisms
What is a hybrid?
results from the mating of dissimilar parents, offspring are different from the parents
What are the five assumptions of Mendel’s model of inheritance?
- parents transmit genes that provide information about characters
- each individual contains 2 alleles for each character
- not all copies of a gene are identical
- alleles from each parent segregate during gamete production
- presence of a gene doesn’t assure that you’ll see its expression
What are alleles?
Different forms of a genes
What is the difference between dominant and recessive alleles?
dominant is displayed over the recessive
What do homozygous and heterozygous mean?
homozygous = 2 of the same letters (BB or bb) heterozygous = 2 different letters (Bb)
What is the difference between genotypes and phenotypes?
genotype is the alleles they have and phenotype is the trait that is displayed
Why do you see 3:1 segregation of phenotypes when you self-cross the F1 generation of a monohybrid cross involving a dominant and a recessive allele?
three of them will have a dominant allele
Why do you see 1:1 segregation of phenotypes when you test cross the F1 generation of a monohybrid cross involving a dominant and recessive allele?
If it has a recessive allele and is crossed with a homozygous recessive, the offspring will express the recessive trait
What is the addition rule of probabilities?
probability of 2 mutually exclusive events in sum of their individual probabilities (or = +)
What is the multiplication rule of probabilities
probability of 2 independent events occurring simultaneously is equal to the product of each of their probabilities (and = x)
If you roll a pair of dice, are you more likely to roll a six or a nine?
six
What are Mendel’s Laws of Inheritance?
law of segregation=alternate forms of a trait are encoded by discreet alleles, one from dad. They will segregate during gamete formation, each gamete has equal probability of getting either allele law of independent assortment=genes located on different chromosomes assort independently of one another during meiosis
How does meiosis explain Mendel’s laws of segregation and independent assortment?
metaphase 1: random orientation of tetrads on metaphase plate
anaphase 1: homologs separate
anaphase 2: chromatids separate
in cats hair length and hair color are specified by unlinked genes. Short hair is dominate over long, and black is dominant over brown. What would the F1 progeny of a cross between a true-breed black cat with short hair and a brown cat with long hair look like? what ratio of phenotypes would you observe in the F2 generation
9:3:3:1
What are seven complications which make it difficult to figure out patterns of inheritance?
- most genes have more than 2 alleles and those alleles interact in complicated ways
- incomplete dominance
- gene interactions (epistasis)
- continuous variation
- pleiotropy
- environmental effects
- sex linkage
Why are there 4 blood types given there are 3 alleles for the I gene?
the A and B can be co dominant
Why can people of O blood type give blood to anyone, but only receive O type blood?
they don’t have any of the proteins so the antibodies don’t attack it but their antibodies will attack the proteins from the others
Why do women who are Rh- need to worry about their husbands blood type?
baby may be Rh+, mom is Rh- the mom’s immune system will produce Rh antibodies will produce Rh antibodies against baby’s red blood cells
Why do some genes show epistasis?
many genes interact sequentially because their products work in pathways
ex. labrador coat color
one gene for pigment
one gene for color deposition
3/4 (12/16), 3/16, 1/16- missing a 3/16
What is the difference between incomplete dominance and codominance
codominance is when both alleles of a pair are expressed equally (AB type)
incomplete dominance is when there’s an intermediate phenotype (redxwhite=pink)
What is the difference between quantitative and qualitative characters?
qualitative cannot be expressed in numbers
why do Siamese cats have darker fur on the tips of their ears and the end of their tails
pigment enzyme is heat sensitive, in warmer areas of the body enzyme is denatured and white fur results
What does pleiotropy mean?
What does pleiotropy mean?
In the pedigree analysis, what does a circle with a dot in it mean?
female that is a carrier
What did the three patients in the karyotyping analysis have in common
they were all trisomic
What did you do in the princess and the pea exercise
figured out how to breed 25 wrinkled peas before you run out of money
