Genetics and Evolution

Question 1

every gene can be pinpointed to a specific location called the _____

Answer 1

locus (plural = loci)

Question 2

Can all physical traits of an organism be mapped to a single locus?

Answer 2

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.

Question 3

Distinguish between allosomes and autosomes

Answer 3

autosomes are non-sex chromosomes allosomes are sex chromosomes

Question 4

Different versions of a gene are called _____

Answer 4

alleles

Question 5

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___

Answer 5

1) heterozygote 2) homozygote

Question 6

What is classical dominance regarding alleles?

Answer 6

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

Question 7

Mitosis produced two identical daughter cells, whereas meiosis produces 4 ____ gametes

Answer 7

haploid

Question 8

What are the 3 (or 4) phases of mitosis?

Answer 8

G1 phase, S phase, G2 phase G

G_o phase is a cell that is an arrest phase, where it does not replicate its DNA

Question 9

What is interphase?

Answer 9

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

Question 10

Distinguish between G1, S, and G2 phase

Answer 10

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

Question 11

Where are the 2 checkpoints during interphase and what does each checkpoint check for

Answer 11

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

Question 12

Briefly describe meiosis 1

Answer 12

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)

Question 13

Briefly describes Meiosis II

Answer 13

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

Question 14

After DNA replication, in a human there are ____ chromosomes and ____ chromatids

Answer 14

46 chromosomes and 92 chromatids

Question 15

When does crossing over/recombination occur during meiosis?

Answer 15

during prophase I

Question 16

What is the synaptonemal complex?

Answer 16

the complex made of various proteins that helps to precisely align homologous chromosome pairs so that they can undergo recombination

Question 17

What is a tetrad?

Answer 17

refers to the pair of duplicated homologous chromosomes (aka 4 sister chromatids) that are aligned/paired up with each other

Question 18

In mitosis, sister chromatids are aligned at the metaphase plate during metaphse; however, in meiosis I, _____ are aligned at the metaphase plate during metaphase

Answer 18

tetrads

Question 19

What’s the primary difference between meiosis II and mitosis

Answer 19

In meiosis II there are a haploid number of chromosomes

in mitosis, there are a diploid number of chromosomes

Question 20

When homologous chromosomes separate, do all paternal and maternal chromosomes stay together in the daughter cells?

Answer 20

No. Homologous chromosomes separate (segregate) randomly. This allows for genetic variation

Question 21

Does meiotic recombination occur between homologous chromosoes, sister chromatids, or both

Answer 21

recombination occurs only between homologous chromosomes. it does not occur between sister chromatids

Question 22

Failure of chromosomes to separate correctly during meiosis is called ______

Answer 22

nondisjunction

this can refer to the homologous chromosomes not separating properly during metaphase I, or the sister chromatids not separating properly during metaphase II

Question 23

If 2 homologous chromosomes of chromosome #12 fail to separate during meiosis I, how many copies of chromosome #12 will the resulting gametes have?

Answer 23

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

Question 24

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____

Answer 24

1) trisomy
2) monosomy

Question 25

Does an individual with Down Syndrome have trisomy or monosomy?

Answer 25

Trisomy

Question 26

Does an individual with trisomy have a defect in development due to an absence of genetic information?

Answer 26

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

Question 27

At what stage during meiosis are the different alleles of a gene separated?

Answer 27

During metaphase I, when the homologous chromosomes are separated

Question 28

The progeny of a testcross are called the ___ generation

Answer 28

F₁

Question 29

When do you use the rule of multiplation (rule of probability)?

Answer 29

when you want to determine the probability of 2 independent events happening at the same time

P(A + B) = P(A) x P(B)

Question 30

When do you want to use the rule of addition (rule of probability)?

Answer 30

When you want to find out the chances of either event occuring

P(A or B) = P(A) + P(B) - P(A + B)

Question 31

If the phenotype of a heterozygote is a blended mix of both alleles, this is called _____ dominance

Answer 31

incomplete

Question 32

______ is when 2 alleles are expressed but not blended

Answer 32

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)

Question 33

What is pleiotropism?

Answer 33

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

Question 34

What is polygenism?

Answer 34

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.

Question 35

What is penetrance?

Answer 35

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

Question 36

What is epistasis?

Answer 36

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

Question 37

Failure of genes to display independent assortment is called _____.

Answer 37

linkage

Question 38

When does linkage occur?

Answer 38

Occurs when genes are located on the same chromosome and therefore do not display independent assortmen

Question 39

What is the Mendelian ratio observed when heterozygotes of 2 alleles are crossed?

Answer 39

9:3:3:1

9 are phenotypic dominant

1 are phenotypic recessive

Question 40

Is recombination between 2 genes more likely if the 2 genes are near each other on a chromosome or farther apart?

Answer 40

farther apart

Question 41

What does a high value of recombination frequency mean? What does a low mean?

Answer 41

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

Question 42

What is the total distance of a chromosome in map units?

Answer 42

50 units long

Question 43

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

Answer 43

Gene B will be found closer to Gene A, as there is a smaller recombination frequency ratio

Question 44

What does autosomal dominant and autosomal recessive mean

Answer 44

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