Cell Division & Heredity

Question 1

How does the process of Meiosis support cell theory?

Answer 1

Meiosis supports the idea that life is continuous. Meiosis is the process by which gametes are produced. One cell becomes fertilized and divides to produce 4 gametes.

Question 2

Why are homologous chromosomes called “homologous”?

Answer 2

They came from a common ancestor and they have the same genetic information on them at around the same locations.

Question 3

What is Meiosis?

Answer 3

It is the process by which gametes are produced. It halves the number of chromosomes by placing them into gametic cells. A haploid of one parent is then joined with the haploid of another parent to produce a fertilized zygote. Meiosis involves 2 cell divisions.

Question 4

What is a locus?

Answer 4

The location of a gene on a chromosome.

Question 5

What is a gene?

Answer 5

A section of DNA found on a chromosome that encodes for a polypeptide which eventually causes a trait (phenotype). Genes may also regulate the activity of other genes.

Question 6

What is an allele?

Answer 6

Versions of a gene that occur at the same locus on homologous chromosomes.

Question 7

What is a gene pool?

Answer 7

All of the alleles of All the genes in a population.

Question 8

What is a diploid versus a haploid cell?

Answer 8

A diploid cell contains 2 sets or copies of a chromosome while a haploid cell only contains 1 set or copy of a chromosome. The purpose of meiosis is to create 4 haploid gametes.

Question 9

What does the term “ploidy” mean?

Answer 9

A cell’s “ploidy” refers to the number of chromosomes in a set and the number of sets of chromosomes a cell contains.

Question 10

How is meiosis a source of variation?

Answer 10

The end result of Meiosis is to produce 4 (haploid) genetically different daughter cells. Meiosis provides genetic variation within a population, which will translate into the variation of physical traits and characteristics in the population.

Crossing Over, Independent Assortment, & Random Assortment contribute to the Variation part of Natural Selection.

Question 11

What is the end result of Meiosis I?

Answer 11

At the end of Meiosis I, you have 2 haploid daughter cells.

Question 12

What is the end result of Meiosis II?

Answer 12

At the end of Meiosis II, you have 4 genetically different, haploid, & gametic cells.

Question 13

Could crossover happen between sister chromatids?

Answer 13

Yes, crossover could occur between sister chromatids. However, there wouldn’t be any way of truly knowing if that crossover happened, nor is it very important because the sister chromatids are genetically identical to each other.

Question 14

How are mutations a source of variation?

Answer 14

Mutations can change DNA sequences, causing genetic variation in the population. These genetic changes can contribute to differential survival and reproduction in a population. (Mutations can harm the individual and cause the individual to be selected against in an environment.)

Question 15

What is nondisjunction and how does it contribute to the variation of a population?

Answer 15

Nondisjunction is the failure of chromosomes to separate during cell division, thus leaving daughter cells with an abnormal amount of chromosomes. The abnormal amount of chromosomes creates a genetic difference in the population.

Question 16

What is a genome?

Answer 16

All of the hereditary information in an individual, which includes all non-gene sequences of DNA.

Question 17

What is unequal crossover and how is it a source of variation in a population?

Answer 17

Unequal crossover is when the arm of one chromatid is longer than the arm of its sister chromatid. After unequal crossing-over occurs, one chromatid will end up with a tandem repeat of a nucleotide sequence while the other chromatid will end up with a deletion of one nucleotide sequence. This creates genetic variation.

Question 18

Where does variation come from in species that reproduce asexually?

Answer 18

1. Transformation
2. Transduction
3. Conjugation
4. Mutations

Question 19

What is Transformation?

Answer 19

Bacterial cells take up DNA fragments from other cells and may either incorporate that DNA fragment into its own DNA or may be left as a separate plasmid that will replicate independent from the parent cell.

Question 20

What is Transduction?

Answer 20

When viral capsids attach to bacteria cells and inject their viral DNA into the cell which fragments the host cell’s DNA. The killing of the host cell releases DNA fragments of both the bacterial cell and the viral capsid into the surrounding environment. Those DNA fragments will then come into contact with other bacterial cells and interact with them, resulting in variation among the bacteria.

Question 21

What is Conjugation?

Answer 21

A tube is created and extended from one bacterial cell with a certain plasmid, to one without a plasmid, and the plasmid, or even just a fragment of the plasmid, is transferred over. This increases variation in the species.

Question 22

What is the difference between phenotypes and genotypes?

Answer 22

Phenotypes are measurable (or observable) traits in a population that are caused by the genotypes, which are the genes that code for the measurable traits.

Question 23

What happens during crossing-over in meiosis I?

Answer 23

Crossing-over occurs when two homologous chromosomes come together and cross-over, exchanging segments of DNA with each other. This is one way variation is created through meiosis.

Question 24

What is random assortment?

Answer 24

Chromosomes will independently/randomly separate from each other during anaphase.

Question 25

How can the same genotypes result in different phenotypes?

Answer 25

Two individuals might have the same genotype, but different environmental conditions and different selective pressures might cause different phenotypes to arise.

Question 26

What is aneuploidy?

Answer 26

Too many or too few chromosomes in a cell.

Question 27

What is independent assortment?

Answer 27

The random orientation of chromosomes at the metaphase plate.

Question 28

How does genetic variation give rise to evolution?

Answer 28

Mutations and Meiosis create genetic variation in a population. That genetic variation will translate into the variation of phenotypes expressed in the population. Then natural selection will select for individuals with one type of phenotype and against those with another phenotype. Individuals with the favorable phenotype will survive longer in the current environment compared to those without that phenotype (differential survival). The individuals that survive longer will be able to reproduce more than those without the trait (differential reproduction). They will be able to get more of their favorable genes into the next generation (heritability). And if natural selection continues, evolution of a population will occur.