Genetics

Question 1

What is double stranded DNA? What does it look like?

Answer 1

Is DNA that forms a double helix, it also has equal amount of thymine to adenine as well as equal amounts of cytosine to guanine.

Question 2

DNA molecule?

Answer 2

The molecule inside cells that contains the genetic information responsible for the development and function of an organism. DNA molecules allow this information to be passed from one generation to the next.

Question 3

What is chromatin (DNA + histone proteins)

Answer 3

Chromatin refers to a mixture of DNA and proteins that form the chromosomes found in the cells of humans and other higher organisms. Many of the proteins — namely, histones — package the massive amount of DNA in a genome into a highly compact form that can fit in the cell nucleus. A histone which is part of what chromatin is made of is a protein that provides structural support for a chromosome. Each chromosome contains a long molecule of DNA, which must fit into the cell nucleus. To do that, the DNA wraps around complexes of histone proteins, giving the chromosome a more compact shape.

Question 4

What are chromosomes and autosomes?

Answer 4

A structure found inside the nucleus of a cell. A chromosome is made up of proteins and DNA organized into genes. Each cell in the human body contains 23 pars of chromosomes. An autosome is any chromosome that is not a sex chromosome, autosomes are diploid cells in your body.

Question 5

What are sex chromosomes ( X and Y)

Answer 5

These chromosomes are the only none autosomal chromosomes in your body they determine your genetic sex. XX for female and XY for male

Question 6

Definition of somatic cell (versus germ line cell)

Answer 6

A somatic cell is any cell in a living organism other than a reproductive cell. Somatic cells are involved in building the body of multicellular animals. Germ cells are involved in producing haploid gametes, which participate in sexual reproduction.

Question 7

Whats the difference between a replicated and unreplicated chromosome?

Answer 7

A replicated chromosome has gone through mitosis, it has duplicated itself so that there is an identical copy of itself. An unreplicated chromosome has 46 chromosomes in a cell instead of the 92 that are present in the middle of replication during mitosis.

Question 8

Whats the difference between chromatid (sister and non-sister) ?

Answer 8

Sister chromatids are the duplicated chromosome itself, they contain the exact same alleles. Non-sister chromatids are the chromatids of the homologous chromosome, they may contain different alleles.

Question 9

What does the term locus mean?

Answer 9

The physical site or location of a specific gene on a chromosome.

Question 10

What is a centromere and what is an arm in terms of genetics?

Answer 10

The centromere appears as a constricted region of a chromosome and plays a key role in helping the cell divide up its DNA during division (mitosis and meiosis). Specifically, it is the region where the cell’s spindle fibers attach.

A chromosome arm either of the two segments of the chromosome that is separated by the centromere.

Hint* when you count the number of centromeres in a diagram you are counting the number of chromosomes.

Question 11

Definition of homolog/homologous chromosome

Answer 11

Homologous chromosomes are made up of chromosome pairs of approximately the same length, centromere position, and staining pattern, for genes with the same corresponding loci. One homologous chromosome is inherited from the organism’s mother; the other is inherited from the organism’s father. However, the two chromosomes do have some variation as they have different alleles.

Question 12

Gene VS Allele

Answer 12

A gene is a stretch of DNA or RNA that determines a certain trait. Genes mutate and can take two or more alternative forms; an allele is one of these forms of a gene. For example, a gene is a chromosome unit that determines a person’s eye color, the gene for eye color has several variations (alleles) such as an allele for blue eye color or an allele for brown eyes.

Question 13

Mutations

Answer 13

Mutations can be caused by any number of things and can result in many different circumstances. For example down syndrome is caused by a mutation on chromosome 21 resulting in three chromosomes instead of a pair.

Question 14

Homozygous vs Heterozygous genotype

Answer 14

We all have two alleles, or versions, of each gene. Being homozygous for a particular gene means you inherited two identical versions. It’s the opposite of a heterozygous genotype, where the alleles are different. People who have recessive traits, like blue eyes or red hair, are always homozygous for that gene.

Question 15

What is gynotype notation? Examples

Answer 15

If something is Homozygous dominant it could be BB
Heterozygous would be Bb
Homozygous recessive would be bb

Question 16

Haploid, Diploid and Polyploid

Answer 16

Haploid (n) means 1 set - human gamete cells are haploid
Diploid (2n) means 2 sets - human somatic cells are diploid
Polyploid (Xn) for example pinaples have 4 sets

For somatice cells 2n=46
the 2 stands for the ploidy
the n refrences the haploid number
the 46 is the total number of chromosomes in a cell

Question 17

What are the G1 , S and G2 phases?

Answer 17

Initially in G1 phase, the cell grows physically and increases the volume of both protein and organelles. In S phase, the cell copies its DNA to produce two sister chromatids and replicates its nucleosomes. Finally, G2 phase involves further cell growth and organisation of cellular contents.

Question 18

What are Prophase, metaphase, ananphase, and telophase?

Answer 18

Prophase – The chromosomes shorten and thicken. Metaphase – Chromosomes line up in the middle of the cell. Anaphase – Chromatids break apart at the centromere and move to opposite poles. Telophase – Two nuclei formed after nuclear envelopes reform around each group of chromosomes.

Question 19

What is the metaphase plate?

Answer 19

The metaphase plate is an imaginary plane perpendicular to the spindle fibres in the midline region of dividing cells. It is the area in which chromosomes attach in metaphase prior to the anaphase stage of mitosis

Question 20

What are spindle fibers?

Answer 20

Prophase: Spindle fibers form at opposite poles of the cell. In animal cells, a mitotic spindle appears as asters that surround each centriole pair. The cell becomes elongated as spindle fibers stretch from each pole. Sister chromatids attach to spindle fibers at their kinetochores.

Question 21

What are daughter cells or progeny cells?

Answer 21

Daughter cells in mitosis and exact dna clones of the original mother cell. They are formed during mitosis and are genetically identical. however during meiosis they are not genetically identical and are distinct from their mother cell because they are haploid.

Question 22

What occurs during Meiosis I?

Answer 22

Metaphase
DNA replication precedes the start of meiosis I. During prophase I, homologous chromosomes pair and form synapses, a step unique to meiosis. The paired chromosomes are called bivalents, and the formation of chiasmata caused by genetic recombination becomes apparent. Chromosomal condensation allows these to be viewed in the microscope. Note that the bivalent has two chromosomes and four chromatids, with one chromosome coming from each parent.

Prometaphase I

The nuclear membrane disappears. One kinetochore forms per chromosome rather than one per chromatid, and the chromosomes attached to spindle fibers begin to move.

Metaphase I

Bivalents, each composed of two chromosomes (four chromatids) align at the metaphase plate. The orientation is random, with either parental homologue on a side. This means that there is a 50-50 chance for the daughter cells to get either the mother’s or father’s homologue for each chromosome.

Anaphase I

Chiasmata separate. Chromosomes, each with two chromatids, move to separate poles. Each of the daughter cells is now haploid (23 chromosomes), but each chromosome has two chromatids.

Telophase I

Nuclear envelopes may reform, or the cell may quickly start meiosis II.

Question 23

What occurs during Meiosis II?

Answer 23

During meiosis II, the sister chromatids within the two daughter cells separate, forming four new haploid gametes. The mechanics of meiosis II is similar to mitosis, except that each dividing cell has only one set of homologous chromosomes.

Question 24

Crossing over (process) and Recombination (outcome) - when does it occur?

Answer 24

During prophase I homologous chromosomes will line up with one another, forming tetrads. During this lining up, DNA sequences can be exchanged between the homologous chromosomes. This type of genetic recombination is called crossing over, and allows the daughter cells of meiosis to be genetically unique from one another.

Crossing over can only occur between homologous chromosomes. Cells become haploid after meiosis I, and can no longer perform crossing over.

Question 25

Independent assortment (what is it and when does it occur; you should be able to diagram this process)

Answer 25

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.

Question 26

What are homologous chromosomes and how do you identify them?

Answer 26

Homologous chromosomes are chromosomes which contain the same genes in the same order along their chromosomal arms. There are two main properties of homologous chromosomes: 1) the length of chromosomal arms and 2) the placement of the centromere.

Question 27

What is linkage (physical linkage) ?

Answer 27

Linkage, as related to genetics and genomics, refers to the closeness of genes or other DNA sequences to one another on the same chromosome. The closer two genes or sequences are to each other on a chromosome, the greater the probability that they will be inherited together.

Question 28

Describe the outcomes of random fusions of gametes during fertilization?

Answer 28

The fusion of two haploid gametes results in the formation of a diploid zygote. This zygote can then divide by mitosis and differentiate to form a developing embryo.