Genetics and Evolution Flashcards
Are gene products always proteins?
no, tRNA and rRNA genes and other small nuclear RNA genes do not encode polypeptides
Locus?
specific location where a gene is located on a specific chromosome
Can all physical traits be mapped on a single locus?
no, some complex traits can be controlled by many different genes and can map on many loci
Is it possible for there to be more than two different alleles of a specific gene?
yes
What is true of an individual that has two different alleles at a given locus?
there is a different allele on each of the two members of a homologous pair
Can a haploid organism like an adult fungus have recessive alleles?
no because there is only one copy of the gene
Classical Dominance?
there are three genotypes (CC, Cc, cc) but only two phenotypes are expressed because whenever the dominant is present it will be expressed
Incomplete Dominance?
phenotype is a blended mix of the alleles (red and white make pink flowers)
How many phenotypes are possible if red and white flowers display incomplete dominance?
3 (red, white, pink)
Codominance?
two alleles are both expressed but not blended (ABO blood)
What is the phenotype of an individual heterozygous for blood type A and B alleles?
AB
What is the phenotype of an individual heterozygous for blood type B and i alleles?
B
If a woman heterozygous for type A blood marries a man who is heterozygous for type B blood, what are the possible genotypes of their children?
A (A,i)
B (B,i)
AB (A,B)
O (i,i)
The Rhesus factor (Rh) follows a _____ _____ pattern.
classically dominant
Rh positive = RR, Rr
Rh negative = rr
Pleiotropism?
altering of many different, seemingly unrelated aspects of the organism’s phenotype
Polygenism?
complex traits that are influenced by many different genes (ex. height)
Penetrance?
likelihood that a person with a given genotype will express the expected phenotype
Epistasis?
expression of alleles for one gene is dependent on a different gene
100 people are homozygous for an allele that is implicated in cancer, but only 20 develop cancer. What are potential explanations for why only some people express a gene if they have the same genotype?
- the trait for cancer is probably polygenic
- cancer development is also influenced by the environment, such as exposure to carcinogens, which complicates the penetrance of the gene
What pattern of expression will a recessive allele on the X chromosome display in males?
it will always be expressed because men only have one X chromosome
Sex linked traits?
traits determined by genes on the X or Y chromosome
What type of cell division produces haploid cells from diploid cells by reducing the number of copies of each chromosome for two to one?
meiosis
Where does meiosis occur in males? females?
What is the end result for both?
males- testes, haploid spermatozoa
females- ovaries, ova
What are the specialized cells in males that undergo meiosis? females?
males- spermatogonia
females- oogonia
What makes meiosis different than mitosis?
meiosis has two rounds of cell division
recombination occurs between homologous chromosomes
What happens in prophase 1 of meiosis? (longest phase)
- chromosomes condense
- nuclear envelope breaks down
- synapsis- homologous chromosomes pair with each other, bring two copies of each gene on two different chromosomes close together (paired chromosomes are called bivalent or tetrad)
- Crossing over or recombination- genes are cut and then re ligated with genes swapped (genetic variation)
Does crossing over change the number of genes on a chromosome?
no if done error free, it is a one for one swap
Does recombination create combinations of alleles on a chromosome that are not found in the parent?
yes, it contains the same genes, but the alleles could be different and mixed up
What happens in Metaphase 1?
- alignment along the metaphase plate occurs
- tetrads are aligned at the center (mitosis- sister chromatids are aligned at the center)
What happens in Anaphase 1?
homologous chromosomes separate and sister chromatids remain together
What happens in Telophase 1?
- divides into two cells
- at this point, the cells are haploid (pair of sister chromatids)
What is the purpose of the second set of meiosis?
to separate the sister chromatids so that each cell has a single set of unreplicated chromosomes
What is the difference between meiosis 2 and mitosis?
in meiosis 2 there is a haploid number of chromosomes
mitosis there is a diploid number
What is the result after Telophase 2?
4 haploid cells have been produced from a single diploid parent cell
When homologous chromosomes separate, do all paternal and maternal chromosomes stay together in the daughter cells?
no, they separate randomly to increase genetic variation
Are the sister chromatids that separate during meiotic anaphase 2 identical in their DNA sequence?
no, they would be though if recombination had not occurred during prophase 1
Which of the following occur in meiosis, but not mitosis?
- separation of sister chromatids on microtubules
- pairing of homologous chromosomes
- recombination between sister chromatids
just 2
- happens in both
- recombination occurs between homologous chromosomes, not sister chromatids
If cells are blocked in meiotic metaphase 2 and prevented from moving on in meiosis, which one of the following will be prevented?
A. crossing over
B. separation of homologous chromosomes
C. separation of sister chromatids
D. breakdown of nuclear envelope
C
A. happens during prophase 1
B. occurs during anaphase 1
C. occurs in anaphase 2
D. occurs in prophase 1 or 2
Nondisjunction?
failure of homologous chromosomes to separate during meiosis 1 and sister chromatids during meiosis 2
A gamete normally has how many copies of each chromosome?
one (haploid)
Gametes resulting from nondisjunction will have how many copies of a given chromosome?
either 2 or none
How many copies of the chromosome will the zygote have if a nondisjunction gamete fuses with a normal gamete?
either 3 (trisomy) or 1 (monosomy)
Turner Syndrome?
only one X chromosome and no Y, female features but underdeveloped ovaries
In an individual with down syndrome, are the defects in development caused by an absence of genetic info?
no, there is too much
Mendel’s Law of Segregation?
- the two alleles of an individual are separated and passed on to the next generation singly
- ex. if a pea is heterozygous, Gg, its gametes will contain either G or g but never both
At what stage of meiosis are different alleles of a gene separated?
meiosis 1 when homologous chromosomes separate
Mendel’s Law of independent assortment?
- alleles of one gene will separate into gametes independently of alleles for another gene
- ex. shape gene and color genes do not influence each other
F1 generation?
progeny of a testcross
If the color gene and the shape gene are right next to each other on a chromosome, will they display independent assortment?
no, linkage
Rule of multiplication?
the probability of both of two independent events happening can be found by multiplying the odds of either event alone
Rule of addition?
the chance of either of two events happening (either A or B happens, not both)
A man is homozygous for eye color, bb, is married to a woman who is heterozygous at the same gene: Bb. What re the chances that a child will have Bb genotype and be a boy?
50% chance of Bb
50% chance of boy
.5 * .5 = 25%
If the color gene and the height gene display linkage, is it possible to predict the possible gametes of a TTgg individual? of a TtGg?
yes because it can only make Tg gametes
no, it is necessary to know which gametes assort together
When genes are located on the same chromosome, they will display ____ and not _____ _____.
linkage
assort independently
What is the exception to linkage?
meiotic recombination- can separate alleles that were located on the same chromosome
If it is known that two genes are located on the same chromosome but during a cross they assort completely randomly, how can this be?
they can be on the same chromosome but far apart so recombination would occur
The frequency of recombination between two genes on a chromosome is proportional to what?
the physical distance between the genes along the linear length of the DNA, the farther apart they are the more frequent they go through recombination
Frequency of recombination formula?
number of recombinant phenotypes divided by total number of offspring
If the recomb frequencies are 16% between height and color genes, 10% between height and flower size genes, and 26% between flower and color genes, what is the order of genes on the chromosome?
flower
height
color
Hemizygous Genes?
individual has only one copy of the chromosome (ex. X linked traits in males)
Mitochondrial traits are only inherited through the _____.
mother
Mitochondrial traits are only inherited through the _____.Why?
mother
because males only contribute nuclear genes and females contribute nuclear genes and whatever else is in the cell
Hemizygous Genes?
individual has only one copy of the chromosome in a diploid organism (ex. X linked traits in males)
Genes encoded by the mitochondrial genome are usually given the prefix ____.
mt
Sex linked traits?
traits determined by genes located on the X or Y chromosome
Would it be possible for a father to pass a Y linked trait to a daughter?
no because females do not have a Y chromosome
Can males be carriers of recessive Y linked traits without expressing them?
no because there is only one Y chromosome so if they carry it, they also express it
When will a female express a X linked recessive trait?
only when she is homozygous with the gene on both of her X chromosomes
Example of an X linked recessive trait?
hemophilia
From what parent do males receive X linked recessive traits?
from their mother (males are more affected than females)
Is the colorblindness allele recessive or dominant?
recessive, an allele that encodes an inactive protein is generally recessive, in colorblindness the pigment gene does not produce a functional protein
X linked dominant traits, when will females display it? males?
females- needs one or two copies of the allele
males- if he inherited the affected allele from his mother
Autosomal traits? dominant? recessive?
- both males and females are affected the same
- on the other 22 chromosomes, not sex related
- dominant- need a single copy
- recessive- need both copies
Example of an X linked recessive trait?
hemophilia
can skip generations, affects males more
X linked dominant traits, when will females display it? males?
females- needs one or two copies of the allele
males- if he inherited the affected allele from his mother
can not skip generations, affects males more, affected fathers have all affected daughters
Autosomal traits? dominant? recessive?
- both males and females are affected the same
- on the other 22 chromosomes, not sex related
- dominant- need a single copy, does not skip generations, affected parent passes all or half of offspring
- recessive- need both copies, can skip generations
Is recombination possible in males between X and Y chromosomes?
no
Population genetics?
inheritance of traits in populations over time
population- members of a species that mate and reproduce with each other
If a group of sea turtles lives most of the year dispersed over a large area of ocean without contact but congregate once a year to reproduce, is this group a population?
yes, they only need to reproduce to be considered a group
Gene pool?
sum total of all genetic info in a population
If there are 5,000 hippos in a population, out of which there are 100 homozygotes of an autosomal allele h and 400 heterozygotes, what is the frequency of the allele in the population?
5,000 hippos * 2 copies of the gene each = 10,000 copies
100 homozygotes * 2 copies each = 200 copies
400 heterozygotes * 1 copy each = 400 copies
200 + 400 = 600 copies
600/10,000 = .06
If 20% of the population is heterozygous for an allele Q and 10% homozygous, what is the frequency of the allele?
50% of the gene * 20% heterozygotes = 10%
10% alleles + 10% homozygous = 20%
Hardy Weinberg Law? conditions?
frequencies of alleles in the gene pool of a population will not change over time if these assumptions are true:
no mutation no migration no natural selection random mating population is large to prevent drift
Hardy Weinberg equation?
p + q = 1
p = frequency of dominant allele q = frequency of recessive allele
Hardy Weinberg equation (proportion of genotypes)?
p^2 + 2pq + q^2 = 1
p^2 = frequency of GG 2pq = frequency of Gg q^2 = frequency of gg
If the frequency of the G allele is .25 in a population of 1,000 mice, determine the number individuals who are Gg heterozygotes?
.25 + q = 1
q = .75
2pq = 2(.25)(.75) = .375
.375 * 1000 = 375
Hardy Weinberg equilibrium?
- population reaches equilibrium after one generation
- parent and F1 generation will not have the same frequncies
- F1 and F2 generations will be the same
Fitness in evolution?
how successful an animal is in passing on its alleles to future generations
Fitness in evolution?
how successful an animal is in passing on its alleles to future generations, the more offspring, the more fitness
If an allele of a gene causes in elderly polar bears after their reproductive years have passed, how will it affect the fitness of the bears carrying the allele?
it will not affect fitness because it does not affect their ability to pass on the alleles
If a recessive allele causes sterility in homozygotes, how will it affect the fitness of heterozygotes?
it will not affect the fitness
If a population of sea otters contains only one allele of a gene that protects against cold, can natural selection drive evolution of this trait? Can natural selection cause new alleles to appear in the population?
if there is only one allele, there is no variability that natural selection can act on, so allele frequencies cannot change
natural selection can only alter existing alleles, not create new ones
What are the two sources of genetic variation in a population?
new alleles (mutations) new combinations of existing alleles (recombination)
Do new alleles in a population generally confer greater or lesser fitness on an individual carrying them?
most changes are harmful
If a mutation occurs in a muscle cell of an individual who then has many progeny, does this mutation increase genetic variation in the population?
no, mutation must occur in the germ line to introduce a new allele into the population, mutations in somatic cells cannot be passed to the new generation
Does mitosis contribute to the genetic variation in a population?
no, mitosis can only copy an identical cell, it is not involved in creation of new combinations of alleles
If a population of flowers loses the ability to reproduce sexually and reproduces only asexually, how will this affect natural selection in the population?
if they can only reproduce asexually, then they have lost the ability of meiosis to generate new combinations of alleles for natural selection to act on
Plants that are pollinated by insects sometimes have physical features of the flower that prevent self pollination, what is the advantage of preventing self pollination?
self pollination reduces genetic diversity
What is the only thing that can create new alleles?
mutations of the genome
What are the 6 modes of natural selection?
- directional selection- remove one of the extremes and the average moves the other way, giraffes get taller as all short giraffes die for lack of food
- divergent selection- remove the average splitting the species in two, small deer survive because they can hide, big deer survive because they can fight, medium deer cannot do either and die
- stabilizing selection- both extremes die and the population moves toward the average, birds too large or too small cannot mate and die
- artificial selection- humans intervene controlling mating, pets and crops
- sexual selection- some animals attract more mates, some birds have bright plumage to mate
- kin selection- animals that live socially sacrifice themselves for someone else, female lion sacrifices herself to save her sister’s children
What is the difference between a population and a species?
members of a species can mate and produce offspring, members of a population do
population is a subset of species
Reproductive isolation two types?
keeping existing species separate
prezygotic
postzygotic
Prezygotic?
barriers prevent formation of hybrid zygote such as:
ecological- river separating species
temporal- individuals mate at different times of the year
mechanical- chihuahuas cannot mate with great danes
behavioral- mating rituals
gametic- incompatible sperm-egg, dog and cat
Postzygotic?
barriers prevent development of hybrid, horse and donkey (sterile)
Speciation?
creation of a new species
Cladogenesis?
one species diversifies and becomes one or two more species
Anagenesis?
one species changes so much that if it were to go back in time it would not be able to reproduce with its ancestors
Allopatric isolation?
type of cladogenesis, geographic isolation leads to reproductive isolation
Sympatric speciation?
a species gives rise to a new species in the same geographical area, divergent selection
Homologous structures?
physical features shared by two different species as a result of a common ancestor
Analogous structures?
serve the same function in two different species, but not due to a common ancestor (ex. bacterial flagella and human sperm)
Convergent evolution?
two different species come to possess many analogous structures due to similar selective pressures
Divergent evolution?
divergent selection causes cladogenesis
Parallel evolution?
two species go through similar evolutionary changes due to similar selective pressures
What was different about the atmosphere of young Earth as opposed to now?
lacked O2
it was a reducing environment- electron donors were prevalent, O2 is an electron acceptor and breaks organic bonds
binomial classification?
each organism is given two names: genus and species
Homo sapiens? genus, species?
genus- Homo
species- sapiens
8 categories of taxonomy?
Domain Dumb Kingdom King Phylum Phillip Class Came Order Over Family From Genus Greece Species Sunday
Protobionts?
microspheres
liposomes
coacervate
All life evolved from _____.
Prokaryotes
What was different about the atmosphere of young Earth as opposed to now?
lacked O2
In the early world, simple organics, monomers could form _____.
spontaneously, with metal ions on rock acted as catalysts
(abiotic synthesis)
(polypeptides made this way- proteinoids)
Microspheres?
proteinoids in water spontaneously form droplets
when lipids are added liposomes form
Coacervate?
complex particle including polypeptides, nucleic acids, polysaccharides
Protobionts?
microspheres
liposomes
coaceravate
In primitive Euk, introns were spliced out by ____.
ribozymes
A mechanism of heredity was first provided by ____. Why?
RNA
because of its self replicating catalyzing abilities
What were protobionts lacking?
organized form of heredity
What was the last step in the evolution of the earliest cells?
switch from RNA to DNA because it is more stable
9:3:3:1 ratio indicates what?
independent assortment
If a white bull and a red bull mate and they have offspring with a roan coat (there are individual red and white hairs that do not blend) what is this displaying?
codominance
