AP Bio Chapter 13

The muscle cells of a dog have 78 chromosomes. Fill in the correct chromosome number in a: Sperm

39 in a sperm cell

How many chromosomes are in human cells?

46

What is a somatic cell?

Any cell other than those involved in gamete formation.

Female Gamete

Haploid cells.

Male Gamete

Haploid cells.

Gamete

Haploid sex cells that are used for reproduction.

What are alleles? Give an example.

Alleles are any of the alternative versions of a gene that may produce distinguishable phenotypic effects, such as freckles.

Explain alternation of generations.

Alternation of generations is a life cycle of plants and some algae involving both diploid (sporophyte) and haploid (gametophyte) stages that are multicellular.

Maternal Chromosome

Egg with 23 chromosomes

Daughter cells

Either of the two cells formed when a cell undergoes cell division by mitosis.

Sister Chromatids

Either of the two identical copies formed by the replication of a single chromosome, with both copies joined together by a common centromere.

Mitosis: Role in the animal body

Enables multicellular adult to arise from zygote; produces cells for growth, repair, and asexual reproduction

By what process are gametes produced?

Gametes are produced through meiosis.

Where are the gametes of an animal produced? Be specific as to male and female gametes.

Gametes, the only cells of the human body not produced by mitosis, develop from specialized cells called germ cells in the gonads (ovaries in females produce eggs; testes in males produce sperm).

Is the cell haploid or diploid: Gamete

Haploid

Is the cell haploid or diploid: Sex Cell

Haploid

Is the cell haploid or diploid: Sperm

Haploid

Is the cell haploid or diploid: egg

Haploid

Explain what is meant by homologous chromosomes.

Homologous chromosomes are a pair of chromosomes of the same length, centromere position, and staining pattern.

There will be two divisions in meiosis.

Homologous chromosomes separate in the first division of meiosis I. Sister chromatids separate during meiosis II.

What are homologs (homologous chromosomes)?

Homologs (homologous chromosomes) are a pair of chromosomes of the same length, centromere position, and staining pattern that possess genes for the same characters at corresponding loci.

What occurs in synapsis?

In synapsis, duplicated homologous chromosomes are paired and physically connected during prophase I.

What happens to chromosome number in meiosis?

In the meiosis I stage of meiosis, the number of chromosomes are reduced by half.

What is the purpose of meiosis?

Meiosis is a type of cell division in sexually reproducing organisms consisting of two rounds of cell division but only one round of DNA replication, resulting in daughter cells with half the number of chromosome sets as the mother cell. Meiosis produces gametes and enhances genetic variability.

During which division is the chromosome number reduced?

Meiosis reduces the number of sets of chromosomes from two to one in gametes.

Meiosis: Number of daughter cells

4

The muscle cells of a dog have 78 chromosomes. Fill in the correct chromosome number in a: Bone Cell

78 chromosomes in a bone cell

The muscle cells of a dog have 78 chromosomes. Fill in the correct chromosome number in a: Somatic Cell

78 in a somatic cell

The muscle cells of a dog have 78 chromosomes. Fill in the correct chromosome number in a: Zygote

78 in a zygote.

Parent cell

A cell that is the source of other cells, as a cell that divides to produce two or more daughter cells.

What is a chromosome?

A cellular structure carrying genetic material, found in the nucleus of eukaryotic cells

Mitosis: Number of DNA replications

1

Mitosis: Number of divisions

1

Meiosis: Number of DNA replications

1 (during interphase)

Meiosis: Number of divisions

2

Mitosis: Number of daughter cells

2

Mitosis: Chromosome number of daughter cells

2n

The number of different gametes that can be formed because of independent assortment is

2n, where n = the number of homologous pairs

The muscle cells of a dog have 78 chromosomes. Fill in the correct chromosome number in a: Haploid Cell

39 in a haploid cell

Mitosis

A part of the cell cycle when replicated chromosomes are separated into two new nuclei.

Meiosis

A specialized type of cell division that reduces the chromosome number by half, creating four haploid cells, each genetically distinct from the parent cell that gave rise to them.

Autosome

Any chromosome that is not a sex chromosome.

Haploid Cell

Cells that have only one of each homologous pair.

Diploid Cell

Cells that have two of each homologous pairs (2n).

Homologous Chromosomes

Chromosome pairs (one from each parent) that are similar in length, gene position, and centromere location. May contain different alleles.

Is the cell haploid or diploid: Liver Cell

Diploid

Locus

Location of gene on chromosome.

How many times do the chromosomes duplicate?

Once

Asexual Reproduction

One parent cell, cloning.

Meiosis: Role in the animal body

Produces gametes; reduces number of chromosomes by half; introduces genetic variability among gametes.

Meiosis II

Produces two haploid cells from each haploid cell.

Synapsis and crossing over are unique to meiosis. During what specific phase do these occur?

Prophase I

Gene

Segments of DNA that code for a protein or RNA molecule.

How many times does the cell divide in meiosis?

The cell divides twice in meiosis, the chromosomes do not duplicate themselves, and 4 daughter cells formed.

How many daughter cells are formed? What is the chromosome number?

The chromosome number is n

What is a karyotype?

The number and visual appearance of the chromosomes in the cell nuclei of an organism or species.

Sexual Reproduction

Two parent cells, variation.

How does a somatic cell compare to a gamete in terms of chromosome number?

Unlike somatic cells, gametes contain a single set of chromosomes. Such cells are called haploid (rather than diploid) cells, and each has a haploid number of chromosomes (n).

Meiosis always begins with cells that...

are diploid, and as a result of meiosis, daughter cells are formed that are always haploid.

Meiosis: Chromosome number of daughter cells

n

Which type of reproduction will result in genetically identical offspring?

Asexual reproduction.

How is karyotype prepared?

Biologists photograph cells in mitosis, cut out the chromosomes from the photographs, and group them together in pairs. They then check whether any chromosomes are missing or have extra copies.

Give examples of two human somatic cell types.

Blood cells and skin cells.

Meiosis I

Chromosomes in a diploid cell resegregate, producing four haploid daughter cells. It is this step in meiosis that generates genetic diversity. DNA replication precedes the start of meiosis I. During prophase I, homologous chromosomes pair and form synapses, a step unique to meiosis.

What is crossing over?

Crossing over is the reciprocal exchange of genetic material between nonsister chromatids during prophase I.

Explain the physical events of crossing over. You may wish to make a sketch of the event. Include these terms: synaptonemal complex, chiasmata, homologs, sister chromatids.

Crossing over, a genetic rearrangement between nonsister chromatids involving the exchange of corresponding segments of DNA molecules, begins during pairing and synaptonemal complex formation, and is completed while homologs are in synapsis. A chiasma forms at the point where a crossover has occurred.

Is the cell haploid or diploid: Skin Cell

Diploid

Is the cell haploid or diploid: Somatic Cell

Diploid

Is the cell haploid or diploid: zygote

Diploid

How is the arrangement of chromosomes in metaphase 1 different from the metaphase of mitosis?

During mitosis, individual chromosomes line up at the metaphase plate. During meiosis, pairs of homologous chromosomes line up at the metaphase plate.

Explain the events of prophase I

Synapsis is the pairing and physical connection of duplicated homologous chromosomes. Crossing over is the reciprocal exchange of genetic material between nonsister chromatids. A chiasma is an X-shaped, microscopically visible region where crossing over has occurred earlier in prophase I between homologous nonsister chromatids. Chiasmata become visible after synapsis ends, with the two homologs remaining associated through sister chromatid cohesion.

random fertilization

The collection of genes within one gamete (such as a sperm cell) do not give that gamete a lesser or better chance than any of the other sperm cells of fusing with an egg cell to produce a zygote.

Therefore, since humans have 46 chromosomes or 23 homologous pairs, what is the number of possible gametes that can be formed due to independent assortment of chromosomes?

The number of possible combinations of maternal and paternal chromosomes in the resulting gametes is 223, or about 8.4 million.

Synapsis

The pairing of two homologous chromosomes that occurs during meiosis. It allows matching-up of homologous pairs prior to their segregation, and possible chromosomal crossover between them. Takes place during prophase I of meiosis.

independent assortment of chromosomes

The process of random segregation and assortment of chromosomes during anaphase I of meiosis resulting in the production of genetically unique gametes

Centromere

The region of a chromosome to which the microtubules of the spindle attach, via the kinetochore, during cell division.

What are three things that can be determined from a karyotype?

The size of the chromosomes, the position of the centromeres, and the pattern of the stained bands.

Now study the chromosomes in anaphase I and telophase I carefully. How many chromosomes are in each cell at the end of the first meiotic division? Are the resultant daughter cells haploid, or diploid?

Three chromosomes remain in each cell at the end of the first meiotic division. The resultant daughter cells are haploid.

Sex chromosome

X and Y chromosomes; responsible for determining individual's sex.

What is another term for a fertilized egg? __________________What is the chromosome number of the fertilized egg? (Answer this in general terms, haploid, n, or diploid, 2n.)

Zygotes are diploid cells with 2n chromosomes.