Meosis Notes

Every cell of an organism that reproduces by sexual reproduction has _ copies of each autosome.

2

In humans, sex chromosomes are either X or Y. Females have _ _ chromosomes and males normally have an _ chromosomes and a _ chromosome.

2 X X Y

Humans have ____ total chromosomes that exist as __ _____.

46 23 pairs.

__________ occurs between gametes when 1 sperm is allowed into the egg to fertilize it.

Fertilization

______ is the process of nuclear division that reduces the number of chromosomes in new cells to half the number in the original cell.

Meiosis

The stages of the first cell division are called _____ _ and the stages of the second cell division are called________ __.

Meiosis I Meiosis II

______ reproductionistheformationofoffspringthrough meiosis and the union of a sperm and an egg.

Sexual

The two chromatids are attached at a point called a ______.

centromere

Chromatids form as the DNA makes a ___ of itself before cell division.

copy

Offspring produced by sexual reproduction are genetically _____ from the parents due to the combination of inherited genes and the _______ _____ that occurs during meiosis.

different crossing over

Cells having two sets of chromosomes are _____ (2n). In humans the diploid number is ___.

diploid 46

Meiosis produces 4 _____, or sex cells.

gametes

The DNA of each chromosome contains sections called ____ that contain instructions for our traits.

genes

Four _____ cells result.

haploid

Sperm and egg cells are _____ cells (1n), which only contain one set of 23 chromosomes.

haploid

Because gametes are ________ (only 23 chromosomes in humans), the end result is a cell that is _____- (all 46 chromosomes that are found in humans).

haploid diploid

The two copies of each autosome are called _____ chromosomes, or homologs.

homologous

In Meiosis I _________ __________ separate. In Meiosis II, _______ separate.

homologous chromosomes chromatids

Cells preparing to divide by meiosis undergo the G1, S, and G2 phases of _________.

interphase

In metaphase I: a. Tetrads line up randomly along the ____ _____ of the dividing cell b. Spindle fibers attach to the centromere of one _________ chromosome

mid line homologous

Meiosis II includes four phases that are just like _____ ; sister chromatids separate.

mitosis

In telophase I and cytokinesis: a. Chromosomes reach opposite ends of the cell b. Cytoplasm division begins c. New _____ membranes form

nuclear

Each species has a characteristic _______ of chromosomes in each cell.

number

In anaphase I: Each homologous chromosome (consisting of two chromatids) moves to the _______ pole of the dividing cell.

opposite

The organism receives a copy of each autosome from each _______ (one from the egg and one from the sperm).

parent

Chromosomes consist of two identical halves. Each half is called a ________ __________.

sister chromatid.

Human gametes are _____ ___ and ____ ____.

sperm cells and egg cells.

Homologous chromosomes are the same size and shape and carry genes for the same _____.

traits

Because we get half of our chromosomes from our mother's egg and half of our chromosomes from our father's sperm, we have ___ forms of the genes for all of our characteristics

two

In Prophase I: a. ________ coils tightly into chromosomes. b. ______ fibers appear c. Nucleolus and nuclear membrane _______. d. Homologous chromosomes pair up, which is called a ____ and crossing over occurs.

Chromatin Spindle tetrad

_______ are rod-shaped structures made of DNA and protein.

Chromosomes

_____ _______, when portions of homologous chromosomes exchange genetic material, occurs during prophase I and results in genetic ______.

Crossing over variation

All of the other chromosomes in an organism are _______-.

autosomes

Human and animal chromosomes are categorized as either sex chromosomes or _______.

autosomes