Chapter 10: Meiosis and Sexual Reproduction

pg. 164/ pg. 162

What is meiosis?

Type of nuclear division that reduces the chromosome number from 2n to n; daughter cells receive the haploid number of chromosomes in varied combinations

• Reduces the chromosome number of the cell by 50%

What is haploid and diploid?

Haploid (n) - number of chromosomes represents a single set of chromosomes

Diploid (2n) - in many eukaryotic organisms. total number of chromosomes in a cell. Cell condition in which two of each type of chromosome are present

How many chromosomes do humans have? What does meiosis reduce the chromosomes to?

23 chromosomes (n) that exist in two sets (2n).

Meiosis reduces the diploid number of 46 chromosomes to the haploid number of 23 chromosomes

What are gametes?

A haploid sex cell such as egg or sperm

• in plants and animals

Sexual Reproduction

Reproduction involving meiosis, gamete formation, and fertilization

• produces offspring with chromosomes inherited from each parent with a unique combination of genes.

Zygote

Diploid cell formed by the union of two gametes; the product of fertilization.

Process in sexual reproduction

Haploid gametes, which are produced during meiosis, merge into a diploid cell called a zygote.

• in plants and animals, the zygote undergoes development to become an adult organism

Why undergo meiosis?

Each parent needs to contribute a single copy of each chromosome so the zygote will be in a diploid state.

Karyotype

A pictorial display of human chromosomes arranged by pairs according to their size, shape, and general appearance in mitotic metaphase. Each pair is called homologous chromosomes.

homologous chromosomes

homologues

Member of a pair of chromosomes that are alike and come together in synapsis during prophase of the first meiotic division.

• have the same length and centromere position

Alleles

alternative forms of a gene

To properly produce a haploid number of chromosomes in gametes, you have to…

double the amount of DNA

What happens when a chromosome is duplicated? Where are these held together?

It’s composed of two identical parts called sister chromatids, each containing one DNA double-helix molecule.

• sister chromatids are held together at a common region called the centromere.

autosomes

Chromosome pairs that are the same between the sexes; in humans, all but the X and Y chromosomes. 22 pairs. one pair is a sex chromosome.

sex chromosome

differ between the sexes.

• X and Y chromosomes in humans

How do geneticists identify homologues and why?

They use the chromosome’s length and centromere location because chromosomes do not have color

Difference between the zygote and body cells' and the gametes’ chromosomes?

Zygote and Body Cells: homologous pairs of chromosomes

Gametes: have only one chromosome

What is the purpose of meiosis? What is required and produced?

To reduce the chromosome number from 2n to n.

• meiosis requires two nuclear divisions and produces four haploid daughter cells, each having one kind of chromosome.

The two nuclear divisions?

Meiosis I—prior to this, DNA replication already happened; each chromosome has two sister chromatids. homologous chromosome come together and line up side by side, forming a synaptonemal complex, a process called "synapsis" and resulting in a bivalent.

meiosis II — sister chromatids separate, becoming daughter chromosomes that move to opposite poles. the chromosomes in each of the four daughter cells have one DNA double helix molecule in a haploid chromosome

Synaptonemal Complex

Protein structure that forms between the homologous chromosomes of prophase I of meiosis; promotes the process of crossing-over.

Synapsis

Pairing of homologous chromosomes during meiosis I

Bivalent

Homologous chromosomes, each having sister chromatids that are joined by a nucleoprotein lattice during meiosis; also called a tetrad (four).

Crossing Over

exchange of genetic material between nonsister chromatids of a bivalent during meiosis I.

• humans have two to three crossovers occur between the nonsister chromatids during meiosis

Genetic Recombination

Process in which chromosomes are broken and rejoined to form novel combinations; in this way, offspring receive alleles in combinations different from their parents.

Independent Assortment

Alleles of unlinked genes segregate independently of each other during meiosis, so that the gametes can contain all possible combinations of alleles.

Fertilization

union of male and female gametes

Interkinesis

Period of time between meiosis I and meiosis II during which no DNA replication takes place.

Gametophyte

Haploid generation of the alternation-of-generations life cycle of a plant; produces gametes that unite to form a diploid zygote

Sporophyte

Diploid generation of the alternation-of-generations life cycle of a plant; produces haploid spores that develop into the haploid generation.

Gametogenesis

Development of the male and female sex gametes

Spermatogenesis

Production of sperm in males by the process of meiosis and maturation

Oogenesis

Production of eggs in females by the process of meiosis and maturation.

Oocytes

Immature egg that is undergoing meiosis; upon completion of meiosis, the oocyte becomes an egg.

Secondary oocyte

In oogenesis, the functional product of meiosis I; becomes the egg.

Polar Body

Nonfunctional product of oogenesis produced by the unequal division of cytoplasm in females during meiosis; in humans three of the four cells produced by meiosis are polar bodies

Euploidy and Aneuploidy

Euploidy — Condition in which a cell contains the correct number, and combinations, of chromosomes.

Aneuploidy — Condition in which a cell does not contain the correct number, or combinations, of chromosomes.

Monosomy and Trisomy

Monosomy - Chromosome condition in which a diploid cell has one less chromosome than normal; designated as 2n − 1.

Trisomy - Chromosome condition in which a diploid cell has one more chromosome than normal; designated as 2n + 1

Primary and Secondary Nondisjunction

Primary - happens during meiosis I whenboth members of a homologous pair go into the same daughter cell

Secondary — during meiosis II when sister chromatids fail to break apart and both daughter chromosomes go into the same gamete

Deletion

When an end of a chromosome breaks off or when two simultaneous breaks lead to the loss of an internal segment

Duplication

presence of a chromosomal segment more than once in the same chromosome

Inversion

Change in chromosome structure in which a segment of a chromosome is turned around 180 degrees; this reversed sequence of genes can lead to altered gene activity and abnormalities.

Translocation

movement of a chromosome segment from one chromosome to another, nonhomologous chromosome.