Ch.13: Meiosis Flashcards
In asexual reproduction, one parent produces genetically identical offspring
A clone
This is done by _______
Cellular division
Mitosis
two parents give rise to offspring that have unique combinations of genes inherited from the two parents
Sexual reproduction (Meiosis)
What is the result of sexual reproduction
variation
the scientific study of heredity and variation
genetics
the transmission of traits from one generation to the next
heredity
are the units of heredity, and are made of DNA
genes
Each gene has a specific location called a______on a certain chromosome
locus
Genes are passed from parent to offspring through reproductive cells called ______ (sperm and eggs)
gametes
The two chromosomes in each pair are called
homologous pairs
Human somatic (body) cells have how many pairs of chromosomes?
23 pairs of chromosomes
Homologous pairs carry genes controlling the same inherited characters
Thus we all carry ??
two genes for each trait
The 23rd chromosome pair are called the
sex chromosome
human female and human male
XX & XY
The 22 pairs of chromosomes that do not determine sex are called _________
autosomes
Meiosis is preceded by the
replication of chromosomes
Meiosis takes place in two sets of cell divisions: two cell divisions result in four haploid cells
Each daughter cell has only half as many chromosomes as the parent cell
meiosis I and meiosis II
Meiosis is sometimes called ______ ________ because the chromosome condition is reduced from diploid (2n) to haploid (n).
nuclear reduction
A gamete (sperm or egg) contains a single set of chromosomes, and is
haploid
the haploid number is
23
is the union of gametes (the sperm and the egg)
fertilization
The fertilized egg is called a _________ and has one set of chromosomes from each parent
The _______ produces somatic cells by mitosis and develops into an adult
zygote
conserves the number of chromosome sets, producing cells that are genetically identical to the parent cell
Mitosis
reduces the number of chromosomes sets from two (diploid) to one (haploid), producing cells that differ genetically from each other and from the parent cell
Meiosis
Three mechanisms contribute to genetic variation:
Independent assortment of chromosomes
Crossing over
Random fertilization
Independent Assortment of Chromosomes deal with
Homologous pairs of chromosomes orient randomly during metaphase I Each pair of chromosomes sorts maternal and paternal homologues into daughter cells independently of the other pairs For humans (n = 23), there are more than 8 million (223) possible combinations of chromosomes
Crossing over produces
recombinant chromosomes
Crossing over occurs in __________, as homologous chromosomes pair up gene by gene
Crossing over contributes to genetic variation by combining DNA from two parents into a single chromosome
prophase I
also adds to genetic variation;
any sperm can fuse with any egg
random fertilization
