BGSU Genetics Exam 3

What meant by ‘diploid’? Are most of your cells diploid?

has two complete sets of chromosomes; yes most cells are diploid

What is meant by ‘haploid’? Are most of your cells haploid?

only one set of chromosomes; only the gametes (sex cells) are the gametes

How many chromosomes do we have in most of our cells?

Cells contain 46 chromosomes arranged in 23 pairs

What are the three essential elements of a eukaryotic chromosome?

1. Origin of Replication

2. Centromere

3. Telomeres

What is the role of the centromere during cell division?

What are the two major phases of the cell cycle?

1. Interphase

2. Mitotic phase (M phase)

List the six stages of M phase?

1. Interphase

2. Prophase

3. Prometaphase

4. Metaphase

5. Anaphase

6. Telophase

On pg 25 right bottom of the pre-class reading, the text states: “the resulting cells are genetically identical with each other and their parent cell because DNA synthesis… creates an exact copy of each DNA molecule…”? Is this true? Please explain why/why not?

What is the end-product of meiosis?

4 haploid cells

What are the main differences between mitosis and meiosis?

Mitosis produces 2 diploid cells while meiosis produces 4 haploid cells

Mitosis happens in the somatic cells and meiosis happens in the gametes

What does the term “crossing over” refer to? During what phase in meiosis does crossing over occur?

The DNA exchange between non-sister chromatids. Occurs in Meiosis I in Prophase !.

What is the role of cohesion in the separation of sister chromatids?

Cohesion holds sister chromatids together until they are pulled apart in Meiosis.

What is the meaning of benign?

non cancerous and not harmful

What is the meaning of malignant?

cancerous and can undergo metastasis

What are three observations that suggest cancer results from genetic damage, or that genes play a role in cancer, also known as the “genetic theory of cancer”?

• mutagenizing agents

• chromosome abnormalities

• cancers tend to have familial prevalence

What are some of the problems with the genetic theory of cancer as presented?

1. Not all cancer cells have the same mutations

2. Many mutations are found in normal cells

3. The number of mutations does not always correlate with cancer development

4. Non-genetic factors like the cellular environment and epigenetic changes

5. Changes in gene regulation

What is meant by “clonal evolution” of tumors?

accumulation of mutations; when a tumor develops from one original abnormal cell that aquires mutations and begins diving uncontrollably

What are some environmental factors that contribute to cancer?

carcinogens, UV rays

What is an oncogene? Who is responsible for discovery of the first known oncogene?

An oncogene is a mutated or overactive version of a normal gene that promotes uncontrolled cell growth and division, which can lead to cancer.

Why are oncogenes usually dominant in their action, whereas tumor-suppressor genes are recessive?

Oncogenes are usually dominant because a mutation in just one copy of the gene can promote cell growth and contribute to cancer.

How can aberrant activation of the enzyme telomerase contribute to the progression of cancer?

Aberrant activation of telomerase allows cancer cells to maintain their telomeres and avoid senescence. As a result, they can continue dividing indefinitely, contributing to tumor growth and cancer progression

How can a retrovirus cause cancer?

can cause cancer by altering the expression of genes that control cell growth and division after it inserts its genetic material into the host cell's DNA.

• Carrying an onogene

• Insertional mutagenesis

What type of organism did Mendel use in his heredity experiments? What are some advantages of Mendel’s choice of model?

He used pea plants
- easy to grow

• produce many offspring

• short generation time

• Controlled mating is possible

• Easily observable traits

What is meant by ‘genotype’?

genetic traits an individual has

How many alleles are included in the genotype at a single locus?

2

What is the difference between a genotype that is heterozygous vs. one that is homozygous?

A homozygous genotype contains two identical alleles (AA or aa), whereas a heterozygous genotype contains two different alleles (Aa) at the same gene locus.

What is a monohybrid cross?

A monohybrid cross is a genetic cross involving a single trait (one gene) and is used to study the inheritance of one pair of alleles.

Mendel derived two major conclusions from his work with monohybrid crosses in pea plants (Pisum savitum) (also see question #1 above). One of these is referred to as “Mendel’s First Law”. What are these conclusions and the significance of each in the context of “heritable material”?

Mendel concluded that hereditary traits are controlled by pairs of alleles, with one allele inherited from each parent. He also proposed the Law of Segregation (Mendel's First Law), which states that the two alleles for a gene separate during gamete formation so that each gamete receives only one allele. These findings demonstrated that heritable material is passed as discrete units rather than blending together.

What is a dihybrid cross?

A dihybrid cross is a genetic cross involving two traits (two genes) simultaneously. It is used to study how two pairs of alleles are inherited and helped establish Mendel's Law of Independent Assortment.

A third major conclusion was derived from Mendel’s work with dihybrid crosses (“Mendel’s Second Law”). What is described by this principle?

Mendel's Second Law (Law of Independent Assortment) states that alleles of different genes segregate independently during gamete formation. This demonstrated that different hereditary factors are inherited separately, allowing new combinations of traits to arise in offspring.

What is dominance? Recessive?

A dominant allele is expressed whenever it is present in the genotype, whereas a recessive allele is expressed only when an individual has two copies of that allele. For example, in Tt, the dominant allele T masks the recessive allele t.

How is complete dominance distinguished from incomplete dominance?

Complete dominance occurs when the dominant allele completely masks the recessive allele in a heterozygote. Incomplete dominance occurs when neither allele is fully dominant, causing the heterozygote to display an intermediate phenotype.

True or False: An allelic interaction describes interactions between the products of genes at the same locus (alleles).

true

True or False: Dominance is an allelic interaction

True

True or False: The sorting of alleles in new combinations (i.e. the independent assortment of alleles) is due to effects of recombination between those genetic loci (as Mendel observed).

True

Who is Walter Sutton? What theory did he put forth in 1903?

proposed a biological basis for Mendel's principles, called the chromosome theory of heredity.

What is the ‘Chromosome Theory of Heredity’?

Genes are found on chromosomes

What is meant by the term ‘linkage group’? Do linked genes sort independently?

Genes located together on the same chromosome. They do not sort independently

Why do you think that Mendel observed each of his traits did indeed sort independently?

His genes were not close together on the same chromosome

Why are linked genes NOT expected to sort independently? Along these lines, are genes in very close proximitymore or less likely to be linked?

They travel together in meiosis and end up in the same place in the gametes. Gene should be linked

What did Bateson, Saunders, and Punnett observe in 1905?

They observed two homologous traits that when crossed in the F2 generation, did not follow the 9:3:3:1 ratio as Mendel said

True or False: A testcross can be utilized to reveal the effects of linkage.

True

How would one perform a testcross? What is the significance of the utilizing a true-breeding homozygous recessive plant in a testcross?

Take 2 homozygous plants, 1 for just the dominant traits and 1 for just the recessive traits. This will produce offspring that are heterozygous for both traits.

There are no dominant alleles that can mask the other alleles

How do non-recombinant and recombinant gametes differ?

non-recombinant only has original combinations, and recombinant only has new combinations

Which cross would produce a 3:1 ratio of phenotypes in the next generation?

Aa x Aa

What occurs in sporadic retinoblastoma?

Two mutations are successively acquired in RB1 leading to the loss of both functional alleles