Organismal Biology Chapter 13

What is a key difference between meiosis and mitosis?

The homologous chromosomes are paired in meiosis but not mitosis.

The region of a chromosome where microtubules connect to a chromosome pair is called the .

centromere

Which of the following will lead to trisomy?

The chromosomes in each homologous pair don't separate from each other during the first meiotic division.

What is the difference between synapsis and a chiasma?

Synapsis is the physical pairing of two homologous chromosomes during the prophase I of meiosis; a chiasma is the x-shape structure formed during meiosis by crossing over between the non-sister chromatids of homologous chromosomes.

A 42-year-old woman is pregnant with her second child. Her first child has Down syndrome. What are the odds that her second child will also have Down syndrome?

1/70, because having another child has no bearing on the question.

Which of the following statements about asexual reproduction is not true?

Results in offspring that have chromosome complements unlike those of their siblings or their parents

Which of the following is not a possible outcome as the result of meiotic non-disjunction?

A normal number of chromosomes in all gametes.

If the kidney cells of an animal have 12 chromosomes, the sperm cells would have how many chromosomes?

6

Haploid cells or species are simply labeled n because they have just one set of chromosomes. Humans are diploid, therefore, for us:

2n=46

How do microtubules move chromosomes in anaphase?

They are degraded at the kinetochore.

Based on this graph, at what age does a mother have a 1.6% chance of having a child with Down syndrome?

42

The number and types of chromosomes present in a cell are called a .

Karyotype

What is the most common result of gamete trisomy, when that gamete is used to form a zygote?

Failure of the zygote to develop into an embryo

What process leads to independent assortment?

The random separation of maternal and paternal homologous chromosomes during meiosis I.

What would happen to genetic variation if maternal chromosomes always lined up together on one side of the metaphase plate during meiosis I, and paternal chromosomes always lined up on the other side?

Genetic variation would decrease.

A karyotype reveals that a developing rat fetus, which died before birth, carried an extra copy of chromosome 1. Genetically, this individual would best be described as showing .

trisomy

Which of the following statements best describes homologous chromosomes?

Chromosomes that have the same genes in the same position and are the same size and shape.

When do homologous chromosomes pair in meiosis?

Prophase 1

A pair of chromosomes made of members from two parents is called .

homologous chromosomes

proteins hold sister chromatids together along their full length whereas, a network of proteins called the hold together homolog pairs during synapsis.

Cohesin, synaptonemal complex

Sexual reproduction is best defined as .

the production of offspring through the production and fusion of gametes

When are homologous chromosomes separated during meiosis?

Anaphase 1

A plant species has a diploid number of 40. Which of the following chromosome counts represents monosomy in this species?

39

In 1883, German biologist, August Weismann, formally proposed a hypothesis; during the formation of gametes, if sperm and egg contribute equal number of chromosomes to the fertilized egg, then each must contain .

half of the usual number of chromosomes

Fertilization was first observed in .

sea urchins, because the eggs are large and semi-translucent

An individual plant that exhibits self-fertilization can produce offspring different from itself primarily as a result of .

independent assortment and crossing over during the formation of spores

Which of the following statements best describes a phase that occurs in meiosis II?

Sister chromatids separate and begin moving to opposite sides of the cell.

Which of the following statements helps to explain why sexual reproduction is favored in many groups?

Sexually reproducing parents can produce offspring that are unique and lack deleterious alleles.

Gametes .

fuse to form a zygote

What conclusion can be drawn from John Maynard Smith's mathematical model comparing asexual and sexual reproduction?

Asexual organisms can produce more offspring than sexually reproducing organisms.

Some males have an abnormal karyotype consisting of 47 chromosomes with an extra Y chromosome. This condition is most likely caused by .

nondisjunction in the production of the male gamete

The cells that produce sperm in humans contain 46 chromosomes. If one of these cells undergoes meiosis to form sperm cells and chromosomal nondisjunction occurs in chromosome 22 during meiosis II, what is the chromosome number in each of the resulting sperm?

23, 23, 22, and 24

When a sperm and egg combine, the resulting embryo has .

half of the mother's genetic information and half of the father's

Which hypothesis explains why many instances of aneuploidy in humans involve chromosome 21?

Aneuploidy tends to be lethal in embryos if it involves chromosomes with a large number of genes.

A segment of DNA that is found at a specific place on a chromosome and influences hereditary traits is called .

a gene

What is the end result of meiosis and the subsequent fertilization of gametes?

An offspring with a chromosome complement unlike that of either parent

At the end of meiosis I, .

the cells are haploid

Bacteria, archaea, and many algae and fungi have cells that contain just one of each type of chromosome. These cells and organisms are called __________.

haploid

Which of the following statements about crossing over is true?

Chromosomes that result from crossing over have a mixture of paternal and maternal alleles.

Which of the following organisms would most likely be affected by a mutation that occurred at a single locus on one chromosome?

A haploid yeast

The cells that produce sperm in humans contain 46 chromosomes. If one of these cells undergoes meiosis to form sperm cells and chromosomal nondisjunction occurs in chromosome 22 during meiosis I, what is the chromosome number in each of the resulting sperm?

24, 24, 22, and 22

Crossing over occurs .

between chromatids of homologous chromosomes

If a cell has a diploid number of 50, how many chromosomes are present in the nucleus at the beginning of meiosis? How many chromosomes are present in each resulting nucleus at the end of meiosis?

Beginning: 50; End: 25

Some plants are triploid. If a plant has a haploid chromosome number of 42, how many chromosomes would be present in a triploid plant's somatic cells?

126

Which of the following statements is a leading hypothesis to explain why many organisms reproduce sexually?

The offspring that result from sexual reproduction are genetically variable, and some of them can fight off diseases more easily than genetically identical offspring.

During sexual reproduction, a male reproductive cell, a , and a female reproductive cell, a , unite in a process called to form a new individual.

sperm, egg, fertilization

If a fatal disease were to infect a grove of aspen trees that reproduced asexually (e.g., the trees are clones), which of the following effects on the aspen grove would be most likely?

The entire grove would die as a result of infection.

.