BIO 121 - Chapter 13, 14, and 15

In prophase 1

1. Synapsis occurs, forming tetrads 2. Crossing over occurs between homologous chromosomes in the tetrads 3. Crossing over increases genetic variation 4. Areas of crossing over form chiasmata 5. The nuclear envelope disintegrates

If a heterozygous plant is allowed to self-pollinate, what proportion of the offspring will also be heterozygous?

1/2

In werewolves (hypothetically), pointy ears (P) are dominant over round ears (p). The gene is on the X chromosome. (Sex determination in werewolves is the same as for "other" humans.) A certain female werewolf has pointy ears even though her father had round ears. What percentage of her sons will have round ears if she mates with a werewolf with round ears?

50%

Why did Morgan choose Drosophila for his genetics experiments?

A single mating can produce many offspring and Drosophila chromosomes can be easily distinguishable under a light microscope.

Human blood groups are governed by three alleles, A, B, and O. A and B are codominant and O is recessive to both. A man who has type B blood and a woman who has type A blood could have children of which of the following phenotypes?

A, B, AB, or O

Alleles

Alternative versions of genes (flower color; white and purple)

__________ are a group of genetically identical individuals produced by a process called __________.

Clones; asexual reproduction

Queen Victoria was a carrier of a recessive sex-linked allele for hemophilia. Which of the following possibilities could explain the presence of the hemophilia allele in her genotype?

Either her mother was a carrier or her father had hemophilia.

What is the result when a diploid cell undergoes meiosis?

Four haploid cells

Which of the following occurs in meiosis, but not mitosis?

Homologous chromosomes separate.

Ignoring crossover, how many kinds of gametes can be produced by an organism with a diploid number of 8?

Ignoring crossover, there are 16 different kinds of gametes that can be produced by an organism with a diploid number of 8.

In a certain fish, fin rays (supporting structures for the fins) can be either bony or soft in adult fish. Sex linkage in a fish is similar to that in humans. What evidence would most strongly support the idea that the ray locus is on the X chromosome?

Matings of soft ray males and bony ray females give different results from the matings of bony ray males and soft ray females.

Which of the following is a function of mitosis in humans?

Multiplication of body cells

__________ is the failure of __________ to separate in meiosis I or the failure of __________ to separate in meiosis II.

Nondisjunction; homologous chromosomes; sister chromatids

In a typical pea experiment, two true-breeding plants with distinct traits of a single character are called the __________, and the offspring are called the __________, which will always be __________.

P (or parental) generation; F1 (or first filial) generation; hybrid

What kind of protection does the Genetic Information Nondiscrimination Act of 2008 provide the public with regard to the use of genetic information?

The law prohibits the use of genetic test information to deny insurance coverage or employment to individuals.

What is a locus?

The precise location of a gene on a chromosome.

Pea plants are tall if they have the genotype TT or Tt, and they are short if they have genotype tt. A tall plant is mated with a short plant. Which outcome below would indicate that the tall parent plant was heterozygous?

The ratio of tall offspring to short offspring is 1:1.

Which of the following statements about homologous chromosomes is correct?

They have genes for the same traits at the same loci.

The life cycle called __________ in plants has two multicellular stages: the __________ and the __________.

alternation of generations; haploid gametophyte; diploid sporophyte

Down syndrome is an example of __________, and the child is __________ for chromosome 21.

aneuploidy; trisomic

Linked genes __________.

are located near each other on the same chromosome

Homologous chromosomes

both chromosomes of each pair carry genes that control the same inherited characteristics

Mendel studied __________, heritable features that vary among individuals; each variant is called a __________.

characters; trait

The __________ states that genes have specific positions on chromosomes and that chromosomes undergo both __________ and __________.

chromosomal theory of inheritance; segregation; independent assortment

Somatic cells in humans differs from gametes in that human somatic cells __________.

contain two sets of each of the 23 chromosome types

Polyploidy

containing more than two paired (homologous) sets of chromosomes. Most species whose cells have nuclei (Eukaryotes) are diploid, meaning they have two sets of chromosomes—one set inherited from each parent.

Regardless of whether an organism is an animal, a plant, a fungus, or an algal cell, all zygotes are __________ and are formed during the __________ of two __________ gametes.

diploid; fertilization; haploid

Darwin realized the importance of heritable variation to evolution __________.

even though he never read any of Gregor Mendel's work

epistasis

expression of a gene at one locus alters the phenotypic expression of a gene at a second locus

In X-linked patterns of inheritance, __________.

fathers pass X-linked alleles only to their daughters, and mothers pass X-linked alleles to both their daughters and their sons

Achondroplasia

form of dwarfism caused by a rare dominant allele

The chromosome theory of inheritance states that __________.

genes occupy specific positions on chromosomes, homologous chromosomes segregate from each other during meiosis, and chromosomes assort independently during meiosis

Allelic variation is an important source of __________ in a population.

genetic diversity

Gene silencing is called __________.

genomic imprinting. Genomic imprinting occurs during gamete formation and results in the silencing of a particular allele of certain genes.

Carriers

heterozygous individuals who carry the recessive allele but are phenotypically normal

If a plant variety is true-breeding for a dominant trait, then __________.

if the plant were allowed to self-pollinate, all of the progeny would have the dominant trait

The major contribution of sex to evolution is that __________.

it provides a method to increase genetic variation

The process called __________ reduces the chromosome number by __________.

meiosis; two consecutive cell divisions

Human ABO groups are best described as an example of __________.

multiple alleles

In meiosis, __________ of __________ cross over and form __________.

nonsister chromatids; homologous pairs; chiasmata

Complete dominance

occurs when phenotypes of the heterozygote and dominant homozygote are identical

Nondisjunction

pairs of homologous chromosomes do not separate normally during meiosis • As a result, one gamete receives two of the same type of chromosome, and another gamete receives no copy

A family tree that describes traits in families is called a __________.

pedigree analysis

true-breeding

plants that produce offspring of the same variety when they self-pollinate

In a cross between wild-type (red-eyed) female flies and mutant white-eyed male flies, the F1 generation should always produce females with __________ eyes and males with __________ eyes.

red; white

The ability to observe meiosis in gamete production supported Mendel's first law of __________, which applies when __________ separate, and supported Mendel's second law of __________, which applies when __________ sort __________.

segregation; homologous pairs; independent assortment; alleles; independently

Besides the fact that pea plants have a short generation time, the key to Mendel's successful plant-breeding experiments was that pea plants usually __________.

self-pollinate

Monosomy

the condition of having a diploid chromosome complement in which one (usually the X) chromosome lacks its homologous partner.

Wild type

the most common phenotype thought to be found in the natural population

incomplete dominance

the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties

aneuploidy

the presence of an abnormal number of chromosomes in a cell

Mendel's law of segregation states that __________.

the two alleles for a heritable character segregate (separate from each other) during gamete formation and end up in different gametes

trisomy

there are three instances of a particular chromosome, instead of the normal two

codominance

two dominant alleles affect the phenotype in separate, distinguishable ways

In incomplete dominance, the offspring __________.

will have an appearance that's intermediate between those of the two parental types

Crossing Over

• Crossing over produces recombinant chromosomes • Increases genetic variation • DNA from one homolog is cut and exchanged with an exact portion of DNA from the other homolog • Chiasmata form where crossing over occurred • Chiasmata hold homologs together until Anaphase 1

Three mechanisms contribute to genetic variation:

• Independent assortment of chromosomes (Metaphase 1) • Crossing over (Prophase 1) • Random fertilization (Unique egg/unique sperm)

Mendel's Laws

• Law of Segregation: the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes • Law of Independent Assortment: Each pair of alleles will segregate (separate) independently during gamete formation (Anaphase 1)

Events unique to meiosis I

• Synapsis and crossing over in prophase I: Homologous chromosomes physically connect and exchange genetic information • Homologous pairs at the metaphase plate • Separation of homologs during anaphase I