BIO 311C Meiosis and Genes

Define down syndrome

Trisomy 21 A human genetic disease caused by presence of an extra chromosome 21. Most cases are due to nondisjunction in meiosis I. Characteristics include developmental delays, heart defects, characteristic facial features

True or false? The same phenotype can be produced by more than one genotype.

True

Determine whether the following about crossing over are true or false As a result of crossing over, sister chromatids are no longer identical to each other. Crossing over prevents homologous chromosomes from separating during meiosis I. Crossing over occurs at the ends of chromosomes, rather than near the centromeres. For crossing over to occur, homologous chromosomes must align precisely early in prophase I so that nonsister chromatids can exchange corresponding segments of DNA.

True False True True

Define gene

Unit of DNA that transmits genetic information and codes for a specific protein or RNA molecule

Define Punnett Square

a diagram that is used to predict an outcome of a particular cross or breeding experiment

If crossing over did not occur, which of the following statements about meiosis would be true? Select all that apply. Assume that an organism exists in which crossing over does not occur, but that all other processes associated with meiosis occur normally. Consider how the absence of crossing over would affect the outcome of meiosis. A) The four daughter cells produced in meiosis II would all be different. B) There would be less genetic variation among gametes. C) Independent assortment of chromosomes would not occur. D) The daughter cells of meiosis I would be diploid, but the daughter cells of meiosis II would be haploid. E) The two daughter cells produced in meiosis I would be identical. F) The two sister chromatids of each replicated chromosome would no longer be identical.

B

Before Mendel's work, what was the current model of genes?

Blended model

How could you determine the genotype of a purple plant using test cross?

Breed purple plant (Pp or PP?) with white plant (pp): -If all offspring are purple then know purple plant was PP -If some offspring were white, then know purple plant was Pp

Define testcross

Breeding or an organism of unknown genotype with a homozygous recessive individual to determine the unknown genotype. The ratio of phenotypes in the offspring will reveal unknown genotypes

Which statement correctly describes how cellular DNA content and ploidy levels change during meiosis I and meiosis II? A) DNA content is halved only in meiosis I. Ploidy level changes from diploid to haploid in meiosis I, and remains haploid in meiosis II. B) DNA content is halved in both meiosis I and meiosis II. Ploidy level changes from diploid to haploid only in meiosis II. C) DNA content is halved in both meiosis I and meiosis II. Ploidy level changes from diploid to haploid in meiosis I, and remains haploid in meiosis II. D) DNA content is halved only in meiosis I. Ploidy level changes from diploid to haploid only in meiosis II. E) DNA content is halved only in meiosis II. Ploidy level changes from diploid to haploid in meiosis I, and remains haploid in meiosis II.

C During anaphase of both meiosis I and meiosis II, the DNA content in a cell is halved. However, the ploidy level changes only when the number of unique chromosome sets in the cell changes. This occurs only in meiosis I (where separation of homologous chromosomes decreases the ploidy level from 2n to n and produces daughter cells with a single chromosome set).

Which of these cells is (are) haploid?

C and D

What is the difference between heterozygous and homozygous individuals? A) The homozygote will express the dominant trait and the heterozygote will express the recessive trait. B) Homozygotes have one chromosome while heterozygotes have two similar chromosomes. C) All of the gametes from a homozygote carry the same version of the gene while those of a heterozygote will differ. D) Heterozygotes carry two copies of a gene while homozygotes only carry one.

C) All of the gametes from a homozygote carry the same version of the gene while those of a heterozygote will differ.

When constructing a Punnett square, the symbols on the outside of the boxes represent _______, while those inside the boxes represent _______. A) progeny, gametes B) gametes, parents C) gametes, progeny D) parents, gametes

C) gametes, progeny

Homologous pairs of chromosomes are lined up independently of other such pairs during _____. A) telophase II B) anaphase I C) prophase II D) metaphase I E) metaphase II

D) metaphase I

Describe what happens in anaphase I of meiosis I

-Breakdown of proteins that are responsible sister chromatid cohesion along chromatid arms allowing homologs to separate -Sister chromatid cohesion still occurs at the centromere so two chromatids are still held together

Review: How many chromosomes are there? How many pairs of homologous chromosomes are there and identify them. Label the sister chromatids and non sister chromatids. Is this a diploid or haploid.

6 chromosomes 3 pairs of homologous chromosomes Maternal chromosomes and paternal chromosomes are both duplicated. Each duplicated chromosome contains 2 sister chromatids paired along length. Each homologous pair is composed of a duplicated chromosome from the maternal set and one from paternal set. A chromatid from each one would be nonsister chromatids.

Define haploid

A cell containing only one set of chromosomes(n) ex. humans n = 23

Define aneuploidy

A chromosomal aberration in which one or more chromosomes are present in extra copies or are different in number

Define polyploidy

A chromosome alteration in which the organism possesses more than two complete chromosome sets. It is the result of an accident of cell division

Define recombinant chromosomes

A chromosome created when crossing over combines DNA from wo parents into a single chromosome

Define sex chromosomes

A chromosome responsible for determining the sex of an individual Female: XX Male: XY Egg contains X chromosome; sperm contains X or Y chromosome

Define autosomes

A chromosome that is not directly involved in determining sex; not a sex chromosome

Define deletion

A deficiency in a chromosome resulting from the loss of a fragment through breakage

Define pedigree

A diagram of a family tree with conventional symbols, showing the occurrence of heritable characters in parents and offspring over multiple generations

Define dominant disorder

A disorder found in individuals that are homozygous dominant or heterozygous for a particular trait.

Define recessive disorder

A disorder found in individuals that are homozygous recessive for a particular trait. Generally, the recessive disorder allele codes for a nonfunctional or nonexistent protein. The normal dominant allele codes for the normal protein. If the normal dominant allele is present, enough of the right protein is produced. If not, the organism does not have the protein.

Define karyotype

A display of the chromosome pairs of a cell arranged by size and shape

Define cri du chat

A genetic disorder that results from a specific deletion in chromosome 5 and causes the child to have a small head and distressed car. Such individuals usually die in early childhood

Define Achondroplasia

A human genetic disease caused by a dominant allele; caused by a single amino acid change that results in an overactive fibroblast growth factor receptor that causes premature differentiation from cartilage into bone

Define Huntington's disease

A human genetic disease caused by a dominant allele; characterized by uncontrollable body movements and degeneration of the nervous system; usually fatal 10 to 20 years after onset of symptoms

What are the 4 alterations of chromosome structure?

Deletion, Duplication, Inversion, Translocation

How does genotype contribute to phenotype?

Different genes code for different proteins/enzymes that produce different traits

Define Chronic myelogenous leukemia

Disease that occurs from a translocation of large portion of chromosome 22 with small portion of chromosome 9 in pre-white blood cells which causes cancer by leading to a new "fused" gene that contributes to uncontrolled cell cycle progression

Explain how alternative versions of genes account for variations in phenotype

Each gene contains a specific DNA nucleotide sequence and different DNA sequences code for different proteins

Define non-sister chromatids

Either of the two chromatids of any of the paired homologous chromosomes

What are other factors that influence phenotype besides genotype?

Environment

True or false? In diploid organisms, a dominant phenotype will only be expressed if the individual is homozygous dominant for that trait.

False

Define zygote

Fertilized egg. Formed in fertilization when haploid gametes unite and form a gamete

Explain the life cycle of fungi and protists

Fungi and protists are haploids -Zygote (diploid) will produce non-gamete haploids via MEIOSIS (2n -> n) -Haploid cell will produce gametes (haploid) by MITOSIS

Define cystic fibrosis

A human genetic disease caused by a recessive allele for a chloride channel protein; the recessive allele codes for a defective or absent chloride channel protein which causes high amount of intracellular chloride ions which causes high water uptake via osmosis which causes mucus thickening; characterized by an excessive secretion of music and consequent vulnerability to infection; fatal if untreated

Define Turner's Syndrome

A human genetic disorder in which a female has only one X chromosome

Define Klinefelter Syndrome

A human genetic disorder in which a male has an extra X chromosome

Define alternation of generations?

A life cycle in which there is both multicellular diploid form, the sporophyte, and a multicellular haploid form, the gametophyte; characteristic of plants and some algae

Define meiosis

A modified type of cell division in sexually reproducing organisms consisting of two rounds of cell division but only one round of DNA replication. It results in cells with half the number of chromosome sets as the original cell

Define homologous chromosomes

A pair of chromosomes of the same length, centromere position, and staining pattern that possess genes for the same characters at corresponding loci

Define sickle cell disease

A recessively inherited human blood disease in which a single nucleotide change in the B globin gene causes hemoglobin to aggregate, changing red blood cell shape and causing multiple symptoms such as anemia, weakness, pain, strokes, paralysis

Define gamete

A reproductive cell, such as an egg or a sperm. -HAPLOID -produced through meiosis

Define multiplication rule

A rule of probability stating that the portability of two or more independent events occurring together can be determined by multiplying the individual probabilities

Define addition rule

A rule of probability stating that the probability of any one of two or more mutually exclusive events occurring can be determined by adding their individual probabilities

Define locus

A specific place along the length of a chromosome where a given gene is located

Define synaptonemal complex

A zipper like structure composed of proteins which connects a chromosomes to its homolog tightly along their lengths during part of prophase I of meiosis

Crossing over, resulting in an increase in genetic variation, occurs between _____. A) nonsister chromatids of homologous chromosomes B) sister chromatids of homologous chromosomes C) sister chromatids of nonhomologous chromosomes D) nonsister chromatids of nonhomologous chromosomes E) sex cells and somatic cells

A) nonsister chromatids of homologous chromosomes

List two examples of dominant disorders

Achondroplasia Huntington's disease

What is the life cycle of plants and algae called?

Alternation of generations

Define duplication

An aberration in chromosome structure due to fusion with a fragment from a homologous chromosome, such that a portion of a chromosome is duplicated

Define translocation

An aberration in chromosome structure resulting from attachment of a chromosomal fragment to a nonhomologous chromosome

Define inversion

An aberration in chromosome structure resulting from reattachment of a chromosomal fragment in a reverse orientation to the chromosome from which it originated

Define dominant allele

An allele that is fully expressed in the phenotype of a heterozygote Ex. purple flower in Mendel's experiment

Define recessive allele

An allele whose phenotypic effect is not observed in a heterozygote Ex. white flower in Mendel's experiment

Define nondisjunction

An error in meiosis or mitosis in which members of a pair of homologous chromosomes (meiosis I) or sister chromatids (meiosis II, mitosis) fail to separate properly from each other

Define character

An observable heritable feature that may vary among individuals Ex. flower color

Define homozygote

An organism that has a pairs of identical alleles for a gene encoding a character

Define heterozygote

An organism that has two different alleles for a gene encoding a character

Explain the life cycle of animals

Animals are diploid multicellular organisms. -They will produce GAMETES (haploid) from germ cells (diploid) by MEIOSIS (2n -> n) -ZYGOTES (diploid) will form by fertilization via fusion of 2 gametes (n + n -> 2n) -They will grow via MITOSIS (diploid) (2n -> 2n)

Define diploid

Any cell containing two sets of chromosomes (2n), one set inherited from each parent ex. humans 2n = 46

Define somatic cell

Any cell in a multicellular organism except a sperm or egg or their precursors; -DIPLOID -produced through MITOSIS

How are homologous chromosomes similar and different?

Homologous chromosomes share the same structure (length, centromere position, genes for same characteristic at corresponding loci) but are not genetically identical.

Define independent assortment

Homologous pairs orient themselves randomly at metaphase plate independent of each other which gives rise to more genetic variation

How does nondisjunction contribute to aneuploidy?

If nondisjunction occurs and resulting abnormal gametes unite with normal gametes, the zygote will exhibit aneuploidy

Explain how different alleles interact to affect phenotype

In each homologous chromosome there is a gene on each chromosome (one paternal one maternal) at the same locus that codes for a characteristic. If the genetic sequences are different, the dominant gene will be expressed. If the genetic sequences are the same, then the gene will be expressed

Define carrier

In genetics, an individual who is heterozygous at a given genetic locus for a recessively inherited disorder. The heterozygote is phenotypically normal for the disorder but can pass on the recessive allele to offspring

What is hybridization?

In genetics, the mating or crossing of two true-breeding varieties

Why are dominant disorders usually not passed down?

In most cases, lethal dominant alleles cause death of afflicted individuals before they can pass it on. Dominant disorders may be passed on if the lethal symptoms are not seen until later (ex. Huntington's disease) or if the disorder is not lethal

Why is inbreeding a problem?

Increase the occurrence of recessive disorders because individuals in interrelated families are more likely to carry recessive alleles

Are sex chromosomes homologous?

No, they differ in size and genetic composition

If an organism with the genotype AaBb produces gametes, what proportion of the gametes would be Bb?

None Alleles of the same gene must separate during gamete formation; thus, the two B alleles would be distributed to different gametes.

Define phenotype

Observable physical characteristics of an organism ex/ brown eyes

Where do the chromosomes in homologous pairs come from?

One homologous chromosome from father One homologous chromosome inherited from mother They have the same structure but may have different genetic code.

Define trait

One or two or more detectable variants in a genetic character

Explain the difference between the P generation, F1 generation, and F2 generation

P generation = true-breeding parental generation F1 generation = The first filial, hybrid (heterozygous) offspring arising from a parental generation F2 generation = The offspring resulting from inbreeding (or self pollination ) of hybrid F1 generation

Explain the life cycle of plants and some algae

Plants can be haploids (gametophyte) or diploids (sporophyte) -Sporophytes will produce SPORES (haploid) by MEIOSIS (2n -> n) -Spores (haploid) divide by mitosis to produce the gametophyte (n -> n) -Gametophytes produce GAMETES (haploid) by MITOSIS (n -> n) -ZYGOTES (diploid) form by fertilization via fusion 2 gametes (n+n->2n)

Why are plants unique in terms of their life cycle?

Plants can exist as both haploid multicellular organisms and diploid multicellular organisms.

How do prokaryotes reproduce?

Prokaryotes reproduce asexually via binary fission.

Define monosomic

Referring to a diploid cell that has only one copy of a particular chromosome instead of the normal two; 2n - 1

Define trisomy

Referring to a diploid cell that has three copies of a particular chromosome instead of the normal two; 2n + 1

What is a true breeding variety?

Referring to organisms that produce offspring of the same variety over many generations of self-pollination

Define sexual reproduction

Reproduction arising from fusion of two gametes

How is sexual reproduction different from asexual reproduction?

Sexual reproduction leads to variation while asexual reproduction produces genetically identical cells

How do single celled eukaryotes reproduce?

Single celled eukaryotes reproduce asexually via mitosis

What is the difference between sister chromatids and non-sister chromatids?

Sister chromatids are identical copies of the same chromosomes that are joined together along their length. -1 sister chromatid = 1 chromosome -2 sister chromatids together = 1 duplicated chromosome Non-sister chromatids are chromatids from different chromosomes in a homologous pair.

What is the result of meiosis I?

The duplicated homologous chromosomes separate and 2 haploid cells with duplicated chromosomes.

Define meiosis I

The first division of a two-stage process of cell division in sexually reproducing organisms that results in cells with half the number of chromosome sets as the original cells

Define asexual reproduction

The generation of offspring from a single parent that occurs without the fusion of gametes. In most cases, the offspring are genetically identical to the parent

Define genotype

The genetic makeup of an organism ex. gene for eye color

Define fertilization

The joining of two gametes

Define allele

different versions of the same gene

What is the sporophyte generation?

diploid, produces spores by meiosis

What is the gametophyte generation?

haploid; produce gametes by mitosis

A tall, purple-flowered pea plant (TtPp) is allowed to self-pollinate. (The recessive alleles code for short plants and white flowers.) The phenotypic ratio of the resulting offspring is 9:3:3:1. What is the genotype of the plant whose phenotype appeared once out of every 16 offspring (the "1" in the 9:3:3:1 ratio)?

ttpp

Explain the process of crossing over

-After interphase, chromosomes are duplicated and sister chromatids held together by cohesins; homologs are associated along length allele by allele -DNA molecules of non-sister chromatids broken at corresponding points -The synaptonemal complex forms and closes the DNA breaks by attaching one end to corresponding segment of nonsister chomatid

What did Mendel conclude from his pea color experiment?

-Alternative versions of genes account for variations -For each character, there are two alleles, one from each parent -Dominant alleles determine organism's appearance while recessive alleles have no noticeable effect in heterozygous organisms -Law of Segregation

Describe what happens in anaphaseII of meiosis II

-Breakdown of proteins holding sister chromatids together at the centromere allows the chromatids to separate and move toward pole -Each chromatid becomes an individual chromosome

Describe what happens in metaphase II of meiosis II

-Chromosomes line up at the metaphase plate -all kinetochores are attached to microtubules

Describe what happens in prophase I of meiosis I

-Crossing over -Nuclear envelope breaks down -Spindle begins to form as centromeres travel toward poles, microtubules elongate, and microtubules attach to kintetochores

List two examples of recessive disorders

-Cystic fibrosis -Sickle Cell Disease

List three disorders caused by nondisjunction

-Down syndrome -Turner Syndrome -Klinefelter syndrome

Describe what happens in telophase I and cytokinesis of meiosis I

-Each half of cell has complete haploid set of duplicated chromosomes (2 sister chromatids) -Cell splits into two

How do parental genes affect gametes?

-Egg or sperm only has one allele from parent -If parent has identical alleles, that allele is present in all gametes and all offspring will look that way -If parent has different alleles, then 50% gametes receive dominant allele and 50% receive recessive allele

Explain the law of segregation in terms of Mendel's peas

-In the P generation, each parent is a true breeding variety. The purple plant will only produce gametes with the P allele. The white plant will only produce gametes with the p allele. -In the F1 generation, all the plants will be purple and have Pp genotype. The hybrid alleles will segregate into P and p gametes. -In the F2 generation 3 plants will be purple PP, Pp, and Pp and 1 plant will be white pp.

What are the three sources of genetic variation?

-Independent assortment -Crossing over -Random fertilization

Two mice are heterozygous for albinism (Aa) . The dominant allele (A) codes for normal pigmentation, and the recessive allele (a) codes for no pigmentation. What percentage of their offspring would have an albino phenotype?

25%

How many possibilities are possible under independent assortment?

2^n where n is the haploid number of the species. This is because each chromosome has two orientations with either maternal or paternal chromosome oriented toward one pole and opposite toward other pole

Describe what happens in prophase II of meiosis II

-Nuclear envelope breakdown -Spindle begins to form as centromeres travel toward poles, microtubules elongate, and microtubules attach to kinetochores of chromosomes (duplicated; sister chomatids attach at centromere)

Describe what happens in telophase II and cytokinesis of meiosis

-Nuclei reform -Chromosomes decondense -Divide into haploid cells with unduplicated chromosomes

Describe what happens in metaphase I of meiosis I

-Pair of homologous chromosomes are arranged at the metaphase plate; random orientation (independent assortment) -Both chromatids of one homolog are attached to kinetochore microtubules of one pole; other homolog attached to microtubules of opposite pole

Sort each daughter cell into the appropriate bin depending on which arrangement at metaphase I would create it.

1: 8,3 2: 5, 1 3: 2, 6 4: 7, 4

Explain how each source gives rise to genetic variation -Independent assortment -Crossing over -Random fertilization

Independent assortment: homologous chromosomes orient themselves independently of each other at metaphase plate; this creates more combinations Crossing over: chromosomes contain DNA from both parents; creates more combinations Random fertilization: many many gametes; creates more combinations

What did Mendel conclude from his pea color/pea shape experiemnt

Law of independent assortment

Is nondisjunction more impactful in mitosis or meiosis?

Meiosis

Explain Mendel's experiment with pea color and shape

Mendel used true breeding varieties (RRYY, rryy) and cross bred them looking at two traits: pea color, and pea size In the F1 generation he found only yellow round peas In the F2 generation he found a 9:3:3:1 ratio

Explain Mendel's experiment with pea color

Mendel used two true-breeding varieties, one purple and one white, and cross bred them (hybridization). In the F1 generation, all plants were purple. In the F2 generation 3/4 plants were purple and 1/4 plants were white.

Define the law of segregation

Mendel's first law, stating that the two alleles for a heritable feature segregate into different gametes during gamete formation

Define the law of independent assortment

Mendel's second law, stating that each pair of alleles segregates, or assorts, independently of each other pair during gamete formation..

Compare Mitosis vs Meiosis

Mitosis -During prophase, there is no crossing over -During metaphase, individual duplicated chromosomes (sister chromatids) line up at metaphase plate -During anaphase, sister chromatids separate -2 identical diploid (2n) cells formed Meiosis -During prophase, crossing over occurs between non-sister chromatids -During metaphase I, duplicated pairs of homologs line up at metaphase -During metaphase II, individual duplicated chromosomes line up at metaphase plate (same as metaphase in mitosis) -During anaphase I, homologs separate -During anaphase II, sister chromatids separate -4 unique haploid (n) cells formed

Is there any chromosome duplication between meiosis I and meiosis II?

No

Why are chiasmata important? (Fact check this)

They help hold the homologs together.

Define synapsis

The pairing and physical connection of one duplicated chromosome to its homolog during prophase I of meiosis

What occurs before meiosis?

The parent cell will have pairs of homologous chromosomes. Theses chromosomes will duplicate (2 sister chromatids paired along length). Homologous chromosomes will associate along their length.

Define chiasmata

The points of attachment where crossover has occurred

Define crossing over

The reciprocal exchange of genetic material between NONSISTER chromatids during prophase I of meiosis

Define meiosis II

The second division of a two-stage process of cell division in sexually reproducing organisms that results in cells with half the number of chromosomes sets as the original cell

What is the result of meiosis II?

The sister chromatids of each duplicated chromosome separate and 4 haploid cells with unduplicated chromosomes

What does n represent? (ex. 2n = 12)

n represents the number of chromosomes in a single set; each species has a characteristic haploid/diploid number n = haploid (1 set) 2n = diploid (2 sets)

Is polyploidy more common in plants or animals?

plants

What is oogenesis?

production of female gametes

What is spermogenesis?

production of male gametes