Chapter 10: Meiosis (The Basis of Sexual Reproduction)

karyotype

the complete set of chromosomes from a single eukaryotic cell

homologues

the two chromosomes that make up a pair

diploid

cells with pairs of homologous chromosomes

haploid

cells that contain only one member of each pair of homologues

autosomes

pairs of chromosomes with nearly identical DNA sequences that are found in diploid cells of both sexes

sex chromosomes

animals and some plants have one pair of this

X
X, Y

in mammals, including humans, each individual’s karyotype includes either two _ chromosomes (in females) or an _ and _ chromosome

gene

sequence of nucleotides, found at a specific location on a chromosome

alleles

the slightly different sequences of a gene

mutations

______ can occur in two ways:
1. cells sometimes make mistakes when copying DNA
2. DNA is damage by factor such as ultraviolet light from the sun or harmful chemicals from environment

sexual reproduction

haploid reproductive cells called gametes from two parent organisms unite to produce offspring that are genetically different from one another

meiotic

haploid gametes are produced through ______ cell division, in which a diploid cell gives rise to haploid daughter cells; then two gametes fuse at fertilization and forming a diploid zygote

meiosis

a type of nuclear division process in which a diploid nucleus divides twice to produce four haploid nuclei

meiosis I

separates the homologues of each pair of homologous chromosomes into two daughter nuclei

meiosis II

separates the chromatids into individual chromosomes

prophase I

homologous chromosomes pair and exchange DNA during which phase

crossing over

the exchange of DNA between maternal and paternal chromosomes at chiasmata

metaphase I

paired homologous chromosomes line up at the equator of the cell during what phase

homologous pairs

unlike mitosis, in metaphase I of meiosis, _______ ______. line up along the equator; this randomness, along with new genetic combinations caused by crossing over ensures that the haploid cell produce by meiosis are genetically diverse

mosquitoes

have three pairs of homologous chromosomes

recombination

two members of a pair of homologous chromosomes may have different alleles of some genes; if so, crossing over may produce genetic _________

nondisjunction

errors in meiosis; can effect the number of chromosomes in a gamete

Turner’s syndrome

about 1 in every 2,500 female babies has only one X chromosome, a condition called _______ ______; also called monosomy X; treatment with estrogen can help

Trisomy X

about 1 in every 1,000 women has 3 X chromosomes, a condition known as ______ _

Klinefelter syndrome

about 1 in every 500-1,000 males born with two X chromosomes and one Y chromosome, a condition know as _______ ____; usually have small testes and so not produce much testosterone

Jacob syndrome

about 1 in every 1,000 males is born with one X chromosome and two Y chromosomes, a condition known as ______ ________

autosomes

some disorders are caused by abnormal numbers of this

nondisjunction of autosomes

produces eggs or sperms that are missing an autosome or that have two copies of an autosome; fusion with a normal gamete results in a zygote with 1 or 3 copies of the affected autosome

13, 18, 21

a small fraction of embryos with three copies of chromosomes __, __, or __ survive to birth

trisomy 21

an extra copy of chromosome 21 results in a condition called _______ __ or down syndrome