Chapter 9: Sexual Reproduction & Meiosis

Asexual Reproduction

Cannot create/maintain genetic diversity. Reproduction that does not involve the union of gametes and in which a single parent produces offspring that are genetically identical to the parent

Sexual Reproduction

process by which cells from two different parents unite to produce the first cell of a new organism

Conjugation

the process in which a unicellular organism transfers some of its genetic material to another unicellular organism

Diploid

(2n), (genetics) an organism or cell having two sets of chromosomes or twice the haploid number

Haploid

(1n), term used to refer to a cell that contains only a single set of chromosomes and therefore only a single set of genes

Somatic Cells

46 chromosomes. any cell in multicellular organism except an egg or sperm

Germ Cells

the only cells that can undergo meiosis. A special type of diploid cell that will divide by mitosis to produce replacements but also divide by meiosis to produce gametes.

gametes

reproductive cells, have only half the number of chromosomes as body cells

Meiosis

Germ cells-process by which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell

Fertilization

process in sexual reproduction in which male and female reproductive cells join to form a new cell

Zygote

the cell resulting from the union of an ovum and a spermatozoon (including the organism that develops from that cell)

meiosis 1

results in 2 haploid daughter cells with half the number of chromosomes as the original cell, the daughter cells have a set of chromosomes and alleles that are different from each other an from the original diploid cell

Meiosis 2

the function of M2 is to seperate the sister chromatids. each daughter cell ends up with single stranded chromosomes. Prophase 2 - Metaphase 2 - Anaphase 2 - Telophase - daughter cells

homologous pairs

(2 chromosomes one male one female but they are the same) are important because in the end cells each need to have one of each gene (no two "reds" instead of 1 "red" and 1 "blue")

Sex chromosomes

one of the 23 pairs of chromosomes in the human, contains genes that will determine the sex of the individual

interphase

the period of the cell cycle during which the nucleus is not undergoing division, typically occurring between mitotic or meiotic divisions.

prophase

the first stage of mitosis or meiosis in eukaryotic cell division, during which the nuclear envelope breaks down and strands of chromatin form into chromosomes

metaphase

the stage in mitosis or meiosis in which the duplicated chromosomes line up along the equatorial plate of the spindle

anaphase

the stage of meiosis or mitosis when chromosomes move toward opposite ends of the nuclear spindle

telophase

the final stage of mitosis or meiosis, during which a nuclear membrane forms around each set of new chromosomes

cytokinesis

organic process consisting of the division of the cytoplasm of a cell following karyokinesis bringing about the separation into two daughter cells

homologs

Same as homologous chromosomes; chromosomes with identical sets of genes or loci

Meiosis 2

spindle fibers contract, splitting the centromeres. sister chromatids move to opposite poles

prophase 2

DNA does not replicate. Chromosomes condense, spindles form in each new cell, and spindle fibers attach to chromosomes.

metaphase 2

Centromeres of chromosomes line up randomly at the equator of each cell.

anaphase 2

the sister chromatids separate and move to opposite poles

telophase 2

chromosomes are single stranded, end up with 4 new cells, cells are Haploid (hybrid), genetically different, nucleus DOES reappear.

polyploidy

A chromosomal alteration in which the organism possesses more than two complete chromosome sets.

nondisjunction

error in meiosis in which homologous chromosomes don't separate; gametes end up with wrong number of chromosomes

trisomy 21

condition in which an individual has three number 21 chromosomes, resulting in Down syndrome

trisomy 18 and 13

Extra 18 or 13, heart defects, cleft pallet (Autosomal nondisjunction)

XXX

Tall, thin, blonde women, higher incidence of learning disability, can have children, tend to be speech delayed and have trouble with reading

klinefelter syndrome

an extra X chromosome in a male (XXY) produces the disorder called ________ ___________, where male have sex organs, but the testes are abnormally small and the man is sterile

jacobs syndrome

47 chromosomes: (XYY); tall, persistent acne, speech and reading problems

turner syndrome

Chromosome disorder in females. a x chromosome is missing or part of one x is deleted. short stature and webbed neck.

deletion

(1) A deficiency in a chromosome resulting from the loss of a fragment through breakage. (2) A mutational loss of one or more nucleotide pairs from a gene.

duplication

An aberration in chromosome structure resulting from an error in meiosis or mutagens; duplication of a portion of a chromosome resulting from fusion with a fragment from a homologous chromosome.

inversion

(genetics) a kind of mutation in which the order of the genes in a section of a chromosome is reversed

translocation

the movement of a segment of DNA from one chromosome to another, which results in a change in the position of the segment

spermatogonium

(diploid), A diploid cell that can undergo mitosis to form more spermatogonium, and can also be triggered to undergo meiosis to form sperm.

primary spermatocyte

(diploid), the product of a mitotic division of a spermatogonium under the influence of FSH (follicle-stimulating hormone) after puberty. this cell is destined to undergo meisosis. it under goes a growth phase and then meiosis I takes place (DNA replicates before the division)

Secondary spermatocyte

(haploid), the result of meiosis I of the primary spermatocyte is this haploid which is smaller in size. two are made out of one primary spermatocyte, they are destined to undergo meiosis II (DNA is not replicated before division)

spermatids

haploid, 23c, spermiogenisis, form from secondary spermocytes and form 4 spermatozoons or sperm cells

sperm

(haploid), male gamete

Oogonium

(diploid), A precursor cell that undergoes mitosis during fetal development to produce more oogonium. These cells are then activated to produce primary oocytes, which remain dormant until stimulated to undergo meiosis I during some future menstrual cycle.

primary oocyte

diploid cell in prophase 1 of meiosis that can be hormonally triggered to develop into an ovum

secondary oocyte

(haploid), A haploid cell resulting from the first meiotic division of oogenesi (not that the cytoplasmic division in this case is unequal, producing one large cell with almost all of they cytoplasm - the secondary oocyte- and one smaller cell with virtually no cytoplasm - the first polar body.). The secondary oocyte (along with some follicular cells) is released from the ovary during ovulation.

Ovum

the female reproductive cell

polar body

(haploid), a small cell containing little cytoplasm that is produced along with the oocyte and later discarded

autosomes

Any chromosome that is not a sex chromosome

crossing over

the interchange of sections between pairing homologous chromosomes during the prophase 1 of meiosis

chiasma

The point of overlap. The X-shaped, microscopically visible region representing homologous chromatids that have exchanged genetic material through crossing over during meiosis.

alleles

different forms of a gene

random alignment

The second major source of genetic variation that occurs in Metaphase I. Either the maternal or paternal member of a homologous pair can end up at either pole, the chromosomes in a gamete are a mix of chromosomes from the two parents.

random fertilization

source of genetic variation caused by the unlimited number of possible sperm & egg combinations

monozygotic

developed from a single fertilized ovum, as identical twins

dizygotic

twins who are formed when two separate ova are fertilized by two separate sperm at roughly the same time (fraternal twins)

spore

(1n), a small usually single-celled reproductive body produced by many plants and some protozoans and that develops into a new individual

gametophyte

(1n), In organisms (plants and some algae) that have alternation of generations, the multicellular haploid form that produces haploid gametes by mitosis. The haploid gametes unite and develop into sporophytes.

synapsis

the side by side pairing of homologous maternal and paternal chromosomes at the start (prophase 1) of meiosis

spindle apparatus

Dynamic, temporary array of microtubules that moves chromosomes in precise directions during mitosis or meiosis.

kinetochores

Protein structures located on chromosomes and are sites where spindle fibres attach during division to pull the chromosomes apart