Exam 1

Question 1

Definition of DNA

Answer 1

DNA is a double-stranded helical
nucleic acid polymer
•Two strands of nucleotides are held together by hydrogen bonds
•Nitrogenous base pairs:
A-T
G- C

Question 2

Definition Of RNA

Answer 2

Ribonucleic acid (abbreviated RNA) is a nucleic acid present in all living cells that has structural similarities to DNA. Unlike DNA, however, RNA is most often single-stranded. An RNA molecule has a backbone made of alternating phosphate groups and the sugar ribose, rather than the deoxyribose found in DNA.

Question 3

Definition of Gene

Answer 3

• A discrete unit of inheritance
• A specific DNA region located on a chromosome
• A sequence of nucleotides that encodes information for a functional product, which may be RNA or protein
- ex: the plant gene amylase that encodes instructions to make a protein that functions as an enzyme that breaks down the starch amylose.

Question 4

Definition of locus

Answer 4

Each gene has a specific location (locus) on a chromosome.
• Number of genes on chromosomes varies from a few hundred to thousands and is dependent on the species

Question 5

Definition of allele

Answer 5

• One of multiple different forms of a gene found at a locus A or a
+ or a+
ex: A gene that codes for a protein that gives a fruit fly its eye color can come in a version (allele) for red eyes or an allele for white eyes.
• Individuals possess 2 alleles for each gene, receiving one allele from each parent.

Question 6

Definition of homozygous

Answer 6

Homozygote
- an individual carrying identical alleles of one gene
ex: AA or aa or + + or a+ a+

Question 7

Definition of heterozygous

Answer 7

Heterozygote
- an individual carrying two different alleles of one gene ex: Aa or + a or a+ a

Question 8

Definition of dominant

Answer 8

Dominant allele - the allele expressed in a heterozygote
The A allele is expressed in individuals of genotype Aa The + allele is expressed in individuals of genotype + a The a+ allele is expressed in individuals of genotype a+ a

Question 9

Definition of recessive

Answer 9

Recessive allele - the allele not expressed in a heterozygote
The a allele is not expressed in individuals of genotype Aa or + a or a+ a
The a allele is expressed in aa homozygotes

Question 10

Definition of wild type

Answer 10

Wild-type
- the most commonly-observed phenotype or genotype
- designated as the norm or standard
- often (but not always) the dominant allele and presumed to be the most fit in a Darwinian sense (re: reproductive success)
􏰀 the A allele is wild-type in the genotype Aa (phenotype A)

Question 11

Definition of mutation

Answer 11

Mutation
- the process that produces an alteration in DNA that leads to
a change in a gene product or the regulation of a gene
- mutation is the source of new alleles in a population
- a new mutation is often deleterious to an organism
- most mutations are recessive

Question 12

Know the difference between Transmission, Molecular, and Population Genetics

Answer 12

Transmission (Classical) Genetics:
⚫ Mechanism of transmission of genes from generation to generation
⚫ Focuses on the organism
Molecular Genetics:
⚫ Molecular/chemical mechanisms underlying storage, replication, and expression of genetic material
⚫ Focuses on the gene – structure, organization and function Population Genetics:
⚫ Explores genetics of groups of individuals of same species and how gene pools can change over time (evolution)
⚫ Focuses on a population

Question 13

Understand Difference between Genotype and Phenotype

Answer 13

Genotype: the specific alleles an individual possesses at a genetic locus
Phenotype: the individual’s observable appearance = how its genotype is expressed or visualized (trait)
ex: A red-eyed fruit fly has two copies of the wild-type (normal) allele (+) for eye color.
This fly’s genotype is ++ and its phenotype is “red-eyed.”

Question 14

Definition of prokaryotes

Answer 14

a microscopic single-celled organism that has neither a distinct nucleus with a membrane nor other specialized organelles. Prokaryotes include the bacteria and cyanobacteria.

Question 15

Definition of eukaryotes

Answer 15

Eukaryotes are organisms whose cells contain a nucleus and other membrane-bound organelles. There is a wide range of eukaryotic organisms, including all animals, plants, fungi, and protists, as well as most algae. Eukaryotes may be either single-celled or multicellular.

Question 16

Definition of the cell cycle

Answer 16

The stages in the life of a cell = cell cycle
- begins with a newly divided daughter cell, then
- passage through the growth and DNA synthesis stages of
interphase, and then
- the processes of nuclear division and cytokinesis of M
(mitotic) phase.
- Checkpoints regulate progression of the cell through each stage of the cell cycle.

Question 17

Definition of mitosis

Answer 17

mitosis is a part of the cell cycle in which replicated chromosomes are separated into two new nuclei. Cell division by mitosis gives rise to genetically identical cells in which the total number of chromosomes is maintained. Therefore, mitosis is also known as equational division.

Mitosis = asexual reproduction
• produces genetically identical daughter cells.
Sexual reproduction combines genetic material from 2 parents using mechanisms to produce genetically variable offspring.
􏰀 Two stages of sexual reproduction
1) Meiosis: Produces haploid gametes
2) Fertilization: Fuses haploid gametes to create diploid
offspring

Question 18

Definition of meiosis

Answer 18

Meiosis is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately result in four cells with only one copy of each chromosome

Preceded by Interphase during which DNA is replicated.
• Meiosis I
Prophase I
Metaphase I
Anaphase I
Telophase I/Cytokinesis I
􏰀 Interkinesis: Between Meiosis I and II
• Meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II/Cytokinesis II

Question 19

Definition of gametogenesis

Answer 19

Gametogenesis is the production of gametes from haploid precursor cells. In animals and higher plants, two morphologically distinct types of gametes are produced (male and female) via distinct differentiation programs. Animals produce a tissue that is dedicated to forming gametes, called the germ line.

Question 20

How histones and chromatin impact gene expression

Answer 20

Chromatin serves as a platform for numerous cellular signals to influence gene expression. Both DNA and histone proteins are prone to methylation, while acetylation is associated only with histones. These two modifications frequently govern the gene expression pattern in a cell by altering between transcriptional activation and repression.

Question 21

Understand the difference between chromosomes and Chromatids and be able to track each through mitosis and meiosis

Answer 21

Chromosomes have the genetic material DNA whereas chromatids help the cells in cell division and their duplication. The chromosomes are present throughout the whole cell life cycle but chromatids are formed when the cell has to undergo cell divisions. Chromosomes are the separate pieces of DNA in a cell. And Chromatids are identical pieces of DNA held together by a centromere. In Mitosis the DNA content per chromosome doubles during S phase (each chromosome starts as one chromatid, then becomes a pair of identical sister chromatids during S phase), but the chromosome number stays the same. A chromatid, then, is a single chromosomal DNA molecule. In meiosis Each daughter cell will have half of the original 46 chromosomes, or 23 chromosomes. Each chromosome consists of 2 sister chromatids. The daughter cells now move in to the third and final phase of meiosis: meiosis II. At the end of meiosis I there are two haploid cells.

Question 22

Be able to recognize descriptions and diagrams of all stages of mitosis and meiosis

Answer 22

Mitosis: Interphase, Prophase, Metaphase, Anaphase, Telophase, Cytokinesis

Interphase
cell makes enough for two cells, doubles in size, centrioles form, chromosomes duplicate
Prophase
nuclear membrane breaks, chromatids pair up in the middle, centrioles move to opposite sides, spindle fibers form
Metaphase
chromatid pairs line up in the center attached to spindle fibers
Anaphase
chromatids are pulled apart, now cell has two identical chromosomes
Telophase
two nuclear membranes form around the chromosomes = two nuclei, cell wall starts to form two new cells
Cytokinesis
cell membrane pinches off to form two new identical cells

Meiosis: Prophase I
The chromosomes condense, and the nuclear envelope breaks down. crossing-over occurs.

Metaphase I
Pairs of homologous chromosomes move to the equator of the cell.
Image: Metaphase I

Anaphase I
Homologous chrmosomes move to the oppisite poles of the cell.
Image: Anaphase I

Telophase I and Cytokinesis
Chromosomes gather at the poles of the cells. the cytoplasm divides.
Image: Telophase I and Cytokinesis

Prophase II
A new spidle forms around the chromosomes.
Image: Prophase II

Metaphase II
Chromosomes line up at the equator.
Image: Metaphase II

Anaphase II
Centromeres divides. chromatids move to the opposite poles of the cells.
Image: Anaphase II

Telophase II And Cytokineses
A nuclear envelope forms around each set of chromosomes. the cytoplasm divides.

Telophase ll
the two cells produced by meiosis I divide to form four haploid daughter cells,
Image: Telophase ll

Interphase
Interphase is the phase of the cell cycle in which a typical cell spends most of its life. During this phase, the cell copies its DNA in preparation for mitosis.
Image: Interphase Prophase I
The chromosomes condense, and the nuclear envelope breaks down. crossing-over occurs.
Image: Prophase I

Metaphase I
Pairs of homologous chromosomes move to the equator of the cell.
Image: Metaphase I

Anaphase I
Homologous chrmosomes move to the oppisite poles of the cell.
Image: Anaphase I

Telophase I and Cytokinesis
Chromosomes gather at the poles of the cells. the cytoplasm divides.
Image: Telophase I and Cytokinesis

Prophase II
A new spidle forms around the chromosomes.
Image: Prophase II

Metaphase II
Chromosomes line up at the equator.
Image: Metaphase II

Anaphase II
Centromeres divides. chromatids move to the opposite poles of the cells.
Image: Anaphase II

Telophase II And Cytokineses
A nuclear envelope forms around each set of chromosomes. the cytoplasm divides.

Telophase ll
the two cells produced by meiosis I divide to form four haploid daughter cells,
Image: Telophase ll

Interphase
Interphase is the phase of the cell cycle in which a typical cell spends most of its life. During this phase, the cell copies its DNA in preparation for mitosis.
Image: Interphase

Question 23

Understand what crossing over is, when it occurs and what it accomplishes

Answer 23

Crossing over is a cellular process that happens during meiosis when chromosomes of the same type are lined up. When two chromosomes — one from the mother and one from the father — line up, parts of the chromosome can be switched. The two chromosomes contain the same genes, but may have different forms of the genes. Crossing over is a process that happens between homologous chromosomes in order to increase genetic diversity. During crossing over, part of one chromosome is exchanged with another. The result is a hybrid chromosome with a unique pattern of genetic material.

Question 24

Be able to compare/contrast mitosis and meiosis

Answer 24

mitosis only
daughter cells identical, asexual, diploid and ends with diploid, 2 daughter cells, # of chromosomes stay the same, produces most cells in body

meiosis only
don’t make identical copies, sexual reproduction, diploid ends with haploid, 4 daughter cells, # chromosomes splits in half, produces gametes, daughter cells unique

both mitosis and meiosis
forms of cellular reproduction, involve chromosomes from both parents

Question 25

The generations of a monohybrid cross and the expected ratios of each

Answer 25

Monohybrid = follows 1 character • Characters are “either/or” (have just 2 possible traits) • Parents (P) are “true breeders” = homozygous for 1 of the traits • F1 offspring express only 1 of the P generation phenotypes • F2 offspring express both P generation phenotypes 􏰀 in a 3:1 ratio Also conducted reciprocal crosses = switching which trait is carried in the male gamete: 􏰀 same results • Tested 7 different characters: 􏰀 Still same 3:1 phenotype ratio in the F2 generation for all characters

Question 26

Understand Mendel’s law of segregation and what it predicts

Answer 26

The law of segregation, only one of the two gene copies present in an organism is distributed to each gamete (egg or sperm cell) that it makes, and the allocation of the gene copies is random. The 2 alleles separate when gametes form, and 1 allele goes into each gamete (Law of Segregation) A single random allele from each pair of parent alleles will be passed on to the gamete.

Question 27

Understand Mendel’s law of independent assortment and what it predicts

Answer 27

Mendel's law of independent assortment states that the alleles of two (or more) different genes get sorted into gametes independently of one another. In other words, the allele a gamete receives for one gene does not influence the allele received for another gene. The Law of Independent Assortment states that different genes and their alleles are inherited independently within sexually reproducing organisms. During meiosis, chromosomes are separated into multiple gametes. Genes linked on a chromosome can rearrange themselves through the process of crossing-over.

Question 28

Be able to perform a dihybrid cross and know the expected genotypic and phenotypic ratios

Question 29

Incomplete dominance and codominance and how to distinguish between the two

Answer 29

Codominance signifies that no allele can block or mask the expression of the other allele. Incomplete dominance signifies the condition in which a dominant allele does not completely mask the effects of a recessive allele. Incomplete dominance is when there is a blending of the two alleles that results in a third phenotype that doesn’t look like either of the parents. The classic example is when a white flower and red flower are crossed. With incomplete dominance, all their offspring would be solid pink flowers, a completely new phenotype. You don’t see either of the parent phenotypes (i.e. white or red) in the offspring. In codominance , both alleles are expressed together in the offspring. If we cross a red flower and white flower that have a codominance inheritance pattern, the offspring would be flowers with red and white patches on them. Unlike incomplete dominance, where the two parent phenotypes are blended together into a new phenotype, in codominance, both parent phenotypes show up together on the offspring.

Question 30

Lethal alleles and how they affect phenotypic ratio

Answer 30

Lethals or lethal genes or lethal alleles are alleles causing the end of an entity which carries it. Basically, lethal genes are lethal to the organism carrying it, lethal meaning (here) death. Typically it is the consequence of gene-mutation that is required to grow and develop. Lethal alleles, though unexpressed in the general population because of the mortal outcome of having two sets of them, can have a visible effects in phenotipic ratios when linked to other genes.

Question 31

Know what epistasis is, the expected phenotypic ratio, and how to distinguish epistatic and hypostatic genes

Answer 31

Epistasis is a circumstance where the expression of one gene is affected by the expression of one or more independently inherited genes. The phenotypic ratio is therefore 13:3. This type of epistasis is sometimes called dominant suppression, because the deviation from 9:3:3:1 is caused by a single allele that produces a dominant phenotype, and the action of this allele is to suppress the expression of some other gene. expected 9:3:3:1 becomes a 9:7 ratio. Genes whose expression interferes with or masks the effects of other genes are said to be epistatic to the effected genes. Genes whose expression is affected (blocked or masked) are hypostatic to the interfering genes.

Question 32

Understand the basic concepts of sex-linked traits and cytoplasmic inheritance

Answer 32

Sex-linked traits are characteristics that are determined by genes located on the sex chromosomes. Inheritance patterns for these traits can differ for males and females, since the X and Y chromosomes differ. One example of a sex-linked trait is color blindness, which is primarily seen in males. Cytoplasmic DNA is found in certain cell organelles and can be passed onto offspring strictly from the female, male, or a mixture of both parents. Cytoplasmic inheritance examples are Iojap in maize, pokiness in Neurospora, Oenothera, etc.

Question 33

Definition of Mendelian independent assortment vs. linkage

Answer 33

hromosomes contain hundreds to multiple thousands of genes. Genes that are on separate chromosomes are inherited independently of one another and are said to follow the principle of independent assortment (discussed in another section and illustrated by the second part of this animation). Remember that this principle states that an RrYy individual is expected to make equal numbers of RY, Ry, rY and ry gametes. Genes that are located on the same chromosome are not free to participate in independent assortment and are referred to as linked genes. These genes tend to be inherited together as a unit, as you can see in the first part of this animation. In this case, the RrYy individual makes only RY and ry gametes because these alleles are present together on the parental homologs (shown in blue and pink) and are not separated during gamete formation. When two genes are always inherited together in this manner, it is referred to as complete linkage. Complete linkage creates only parental gametes, meaning that the gametes that are produced are chromosome copies of the parent they came from. If all genes demonstrated complete linkage during gamete formation, then the result would be that each individual chromosome in a gamete would be either a maternal or paternal replica and the offspring would show little genetic variation from their parents. For this reason, complete linkage rarely occurs in nature and other modes of inheritance, such as crossing over, have evolved.

Question 34

Definition of •crossing over and recombination

Answer 34

Crossing over allows alleles on DNA molecules to change positions from one homologous chromosome segment to another. Genetic recombination is responsible for genetic diversity in a species or population. Genetic recombination is the exchange of genetic material between different organisms which leads to production of offspring with combinations of traits that differ from those found in either parent.

Question 35

Definition of •testcrosses with linked loci two-point mapping three-point mapping

Answer 35

The test cross is another fundamental tool devised by Gregor Mendel. In its simplest form, a test cross is an experimental cross of an individual organism of dominant phenotype but unknown genotype and an organism with a homozygous recessive genotype (and phenotype). Two-point mapping, wherein a mutation in the gene of interest is mapped against a marker mutation, is primarily used to assign mutations to individual chromosomes. It can also give at least a rough indication of distance between the mutation and the markers used. By solving a three point cross you can determine two important things: order of the genes on a chromosome. determine the distance (in map units) between each pair of genes. The genotype of the organism must be heterozygous at all loci that will be used for the cross.

Question 36

How to distinguish recombinant and non-recombinant phenotypes

Answer 36

Recombination: 1. The DNA is obtained by connecting at least two distinct strands. 2.The plasmid vector is inserted with foreign DNA. 3. They differ from parental DNA. 4. They exhibit genetic variety and hence contribute to evolution. Non-Recombination: 1. There is no genetic recombination in this DNA. 2. There is no insertion of foreign DNA. 3. They are analogous to parental DNA. 4. They exhibit little genetic variation and so have no impact on evolution.

Question 37

Understand that percentage of recombinant phenotypes goes down the more closely genes are linked/located.

Answer 37

If the genes are far apart on a chromosome, or on different chromosomes, the recombination frequency is 50%. In this case, inheritance of alleles at the two loci are independent. If the recombination frequency is less than 50% we say the two loci are linked.

Question 38

Understand when you would use a 2 point testcross vs when you would use a three point testcross and why

Answer 38

A two-point test cross is done to calculate the recombination frequency of two linked genes. It is useful for determining the frequency of gametes produced. three-point testcross is used to determine the order of three linked genes. A three-point testcross is used to determine the order of three linked genes.