Genetics and Evolution Flashcards
every gene can be pinpointed to a specific location called the _____
locus (plural = loci)
Can all physical traits of an organism be mapped to a single locus?
No. Not all traits are controlled by one locus. Every gene is located at a specific locus, but physical traits, particularly complex traits, like weight or height, can be controlled by many different genes and therefore do not map to a single locus, but many.
Distinguish between allosomes and autosomes
autosomes are non-sex chromosomes allosomes are sex chromosomes
Different versions of a gene are called _____
alleles
A person carrying 2 different alleles at a given locus is called a ___1____, whereas a person that is carrying 2 identical alleles at a given locus is called a ___2___
1) heterozygote 2) homozygote
What is classical dominance regarding alleles?
refers to 2 alleles, one dominant allele and one recessive allele. In a heterozygous individual, the dominant allele will always be expressed of the phenotype of that individual. The only way an individual will express the recessive allele is if the individual is homozygous recessive
Mitosis produced two identical daughter cells, whereas meiosis produces 4 ____ gametes
haploid
What are the 3 (or 4) phases of mitosis?
G1 phase, S phase, G2 phase G
Go phase is a cell that is an arrest phase, where it does not replicate its DNA
What is interphase?
the process by which the nucleus turns into 2 nuclei; also during this phase the cell continues to grow, make proteins, and etc.
this is the where a cell will spend most of its life
Distinguish between G1, S, and G2 phase
G1: this is the phase where the cell is just growing in size
S phase: this is the phase where DNA replicates (the number of chromosomes in the cell is still the same because the 2 sister chromatids (connected via their centromere) is still considered one chromosome); the centrosomes also duplicate during this phase
G2: this is the second growth phase of the cell; at the end of this phase, the cell will enter into mitosis
Where are the 2 checkpoints during interphase and what does each checkpoint check for
First checkpoint is between G1 and the S phase
Second checkpoint is between G2 and mitosis
cyclin dependent kinases are activated by cyclins, and when this occurs it activates DNA replication at the first checkpoint, and activates mitosis at the second checkpoint.
p53 (recognized as the guardian of the genome) and other similar proteins (i.e. tumor suppressor genes) bind to DNA directly to block the progression of the cell cycle
Briefly describe meiosis 1
DNA replication occurs during interphase (technically not a part of Meiosis I)
Prophase I: recombination occurs between the homologous chromosomes
Metaphase I: The homologous chromosomes align as a pair along the metaphase plate. Centrosomes attach to centromeres via kinetochores
Anaphase I: Homologous chromosome pairs (not the sister chromatids) are separated and pulled to opposite sides of the cell
Telophase I: cytokinesis starts and revers of prophase (chromosomes unravel and nuclear membrane reforms and microtubules dissolve)
The diploid cell splits into 2 haploid cells (note that each chromosome is still connected to its sister chromatid)
Briefly describes Meiosis II
Prophase II: chromosomes condense, centrioles migrate to opposite ends of the cell, nuclear membrane dissolves
Metaphase II: Each chromosome (aka the 2 sister chromatids connected via a centrosome) line along the metaphase plate
Anaphase II: the sister chromatids are separated and pulled to opposite ends of the cell
Telophase II: cytokinesis and reverse of prophase II
2 haploid cells become 4 haploid gametes
After DNA replication, in a human there are ____ chromosomes and ____ chromatids
46 chromosomes and 92 chromatids
When does crossing over/recombination occur during meiosis?
during prophase I
What is the synaptonemal complex?
the complex made of various proteins that helps to precisely align homologous chromosome pairs so that they can undergo recombination
What is a tetrad?
refers to the pair of duplicated homologous chromosomes (aka 4 sister chromatids) that are aligned/paired up with each other
In mitosis, sister chromatids are aligned at the metaphase plate during metaphse; however, in meiosis I, _____ are aligned at the metaphase plate during metaphase
tetrads
What’s the primary difference between meiosis II and mitosis
In meiosis II there are a haploid number of chromosomes
in mitosis, there are a diploid number of chromosomes
When homologous chromosomes separate, do all paternal and maternal chromosomes stay together in the daughter cells?
No. Homologous chromosomes separate (segregate) randomly. This allows for genetic variation
Does meiotic recombination occur between homologous chromosoes, sister chromatids, or both
recombination occurs only between homologous chromosomes. it does not occur between sister chromatids
Failure of chromosomes to separate correctly during meiosis is called ______
nondisjunction
this can refer to the homologous chromosomes not separating properly during metaphase I, or the sister chromatids not separating properly during metaphase II
If 2 homologous chromosomes of chromosome #12 fail to separate during meiosis I, how many copies of chromosome #12 will the resulting gametes have?
After meiosis I, one daughter cell will have 4 copies of chromosome #12, while the other daughter cell will have no copies of chromosome #12. Thus, after meiosis II, 2 daughter cells will each have 2 copies of chromosome #12 (when they’re only supposed to have 1 copy each), and the other 2 daughter cells will each have no copies of chromosome #12
In nondisjunction, 2 daughter cells will each contain 2 copies of a chromosome while the other 2 daughter cells will contain no copies of a chromosome. Such a gamete can fuse with a normal gamete to create a zygote with either 3 copies of a chromsome called ___1__ or one copy of a chromosome called __2____
1) trisomy
2) monosomy
Does an individual with Down Syndrome have trisomy or monosomy?
Trisomy
Does an individual with trisomy have a defect in development due to an absence of genetic information?
No. There are 3 chromosomes when there are supposed to be 2. Thus, there is not an absence of genetic information. Rather, there is too much genetic information, which results in too many genes being expressed and too many gene products being formed. Gene dosage is important, and too much or too little gene dosage can have dramatic consequences
At what stage during meiosis are the different alleles of a gene separated?
During metaphase I, when the homologous chromosomes are separated
The progeny of a testcross are called the ___ generation
F1
When do you use the rule of multiplation (rule of probability)?
when you want to determine the probability of 2 independent events happening at the same time
P(A + B) = P(A) x P(B)
When do you want to use the rule of addition (rule of probability)?
When you want to find out the chances of either event occuring
P(A or B) = P(A) + P(B) - P(A + B)
If the phenotype of a heterozygote is a blended mix of both alleles, this is called _____ dominance
incomplete
______ is when 2 alleles are expressed but not blended
Codominance
Example is ABO blood typing. Type A and type B express codominance, while type O is recessive to both of the other alleles, which is why a person with an A allele and B allele has AB blood. (A person with A allele and O allele, the person will have type A blood; note this is not codominance)
What is pleiotropism?
refers to one gene controlling many different, seeming unrelated aspects of an organism’s total phenotype i.e. a mutation in a pleiotropism gene may cause altered development of heart, bone, and inner ears
What is polygenism?
refers to complex traits that are influenced by many genes
i.e. height is influenced by genes for growth factors, receptors, hormones, bone deposition, muscle development, energy utilization, etc.
What is penetrance?
it describes the likelihood that a person with a given genotype will express the expected phenotype. An allele or mutation can have a high, incomplete, or low penetrance. This penetrace/likelihood can be affected by environment and lifestyle factors.
i.e. a woman that carries a certain mutation that increases their risk of breast cancer display variabl rates of breast cancer depending on their diet, if they ave had children and breast fed them, and other lifestyle/environment factors
What is epistasis?
refers to an expression of an allele for one gene being dependent on a different gene
i.e. a gene for curly hair cannot be expressed if a different gene causes baldness
Failure of genes to display independent assortment is called _____.
linkage
When does linkage occur?
Occurs when genes are located on the same chromosome and therefore do not display independent assortmen
What is the Mendelian ratio observed when heterozygotes of 2 alleles are crossed?
9:3:3:1
9 are phenotypic dominant
1 are phenotypic recessive
Is recombination between 2 genes more likely if the 2 genes are near each other on a chromosome or farther apart?
farther apart
What does a high value of recombination frequency mean? What does a low mean?
recombination frequency is proportional to how far 2 genes are spread a part on a chromosome
A high value of recombination frequency means that the genes are spread a part farther, and have a higher chance of recombination during crossover of chromosomes
A low value of recombination frequency means that the genes are close to one another, and have a lower chance of recombination during crossover
What is the total distance of a chromosome in map units?
50 units long
The recombination between Gene A and Gene B is examined and found to be 10 recombinant plants out of 100 progeny. The frequency of recombination between Gene B and Gene C is examined and found to be 20 recombinant plants out of 100 progency. Is gene expected to be closer on the chromosome to Gene A or Gene C
Gene B will be found closer to Gene A, as there is a smaller recombination frequency ratio
What does autosomal dominant and autosomal recessive mean
autosomal dominant: refers to the type of mutant gene where you only need one copy of the mutant gene on one of your chromosomes to express that mutation
autosomal recessive: refers to the type of mutant gene where you need both copies (one on each chromosome) of the mutant gene in order to express that mutation
