Biology Chaptwr 9.1

telophase I

After ____________, the two resulting daughter nuclei are haploid, meaning they each contain one chromosome from each homologous pair.

trisomy 21

An example of nondisjuction in autosomes is ______, also called Down Syndrome.

random fertilization

Another level of genetic variation is added by ________, since we can't predict which sperm will fertilize a given egg.

characteristics of Turner syndrome

Caused by a lack of an X chromosome. Female. Characteristics include short stature, broad chest, and webbed neck. Underdeveloped ovaries, oviducts, and uterus.

characteristics of Klinefelter syndrome

Caused by an extra X chromosome. Underdeveloped testes and prostate gland. Male. Characteristics include large hands and feet and long arms and legs.

chromosome 21; egg

Down syndrome results from an extra copy of _____________, usually donated from the _____ in approximately 80 percent of the cases.

anaphase II

During ________, the sister chromatids separate and move towards the poles.

prophase

During _________, the nuclear envelope fragments, spindle fibers begin to form, and condensed homologues undergo synapsis.

prophase II

During ___________, each duplicated chromosome attaches to the spindle.

telophase II

During ___________, the spindle disappears and four haploid daughter cells result.

anaphase I

During ____________, homologues separate and dyads move to poles.

metaphase I

During ____________, tetrads align independently along the equator.

metaphase II

During ____________, the dyads line up at the equator.

homologous

During meiosis I, ____________ chromosomes line up side-by-side and may shuffle genetic material between themselves.

homologous chromosomes

During meiosis I, _______________ separate and move towards opposite ends of the poles.

characteristics of metaphase II

Dyads align at the spindle equator. Sister chromatids face opposite spindle poles.

Overall process of mitosis

Dyads are at spindle equato, sister chromatids separate, diploid daughter nuclei are genetically identical to parent cell.

nondisjunction

However, sometimes chromosomes fail to separate and _____________ occurs.

monosomy

If an egg that contains 22 chromosomes instead of 23 chromosomes is fertilized by a normal sperm, the result is ________ because one type of chromosome is present in a single copy.

trisomy

If an egg that contains 24 chromosomes instead of 23 chromosomes is fertilized by a normal sperm, the result is ________ because one type of chromosome is present in three copies.

autosomes; sex chromosomes

In humans, there are 22 pairs of chromosomes called ________, which are the same in both males and females, and one pair of chromosomes called __________, which contain genes that determine gender.

mental disabilities

Individuals with Down Syndrome tend to have the following similar characteristics: short stature, and extra eyelid fold, stubby fingers, a fissured tongue, and sometimes __________.

abnormal

Nondisjunction results in cells with _________ numbers of chromosomes.

characteristics of meiosis II

Results in four genetically diverse haploid nuclei. A haploid number of dyads align at the spindle equator during metaphase.

characteristics of meiosis I

Results in two genetically diverse haploid nuclei. Crossing-over occurs during synapsis. Homologous chromosomes pair up during prophase. Tetrads align at the spindle equator during metaphase.

Characteristics of Mitosis

Results in two genetically identical diploid nuclei. A diploid number of dyads align at the spindle equator during metaphase.

Overall process of meiosis

Synapsis and crossing-over occur, Tetrads are at spindle equator, Homologues separate, Haploid daughter nuclei are not genetically identical to parent cell.

characteristics of metaphase I

Tetrads align at the spindle equator. Chromosomes are shuffled into new combinations. Crossing-over occurs during synapsis. Homologous chromosomes face opposite spindle poles.

increases

The chance of having a child with Down syndrome _____________ rapidly with maternal age, starting at about the age of 40.

meiosis; sperm; eggs

The nuclear division used in sexual reproduction is called ________ and it serves tow major functions: (1) reducing the chromosomes and genes to produce genetically different gametes, called _____ (males) and ______(females).

X

The sex chromosomes in females are two _____ chromosomes.

Y

The sex chromosomes in males are X and ______.

nonsister

These chromosomes stay close together and _______ chromatids can exchange genetic material.

tetrad; synapsis

This alignment, called a(n) ______, forms during _______.

crossing-over

When this genetic swap occurs, it is called __________ and results in genetic recombination in the gametes.

sister chromatids

during meiosis II, ______________ separate and move towards opposite ends of the poles.