Biology 8.11-8.23

tetrads-

sets of four chromatids

Independent orientation of chromosomes at metaphase I and random fertilization are most like

shuffling cards and dealing out hands of poker

If we assume that crossing over does not occur, how many different combinations of chromosomes are possible in a zygote derived from diploid parents who each have three pairs of chromosomes?

64

Which of the following statements regarding the differences between mitosis and meiosis is false?

Crossing over is a phenomenon that creates genetic diversity during mitosis.

Scientists commonly choose white blood cells that are going through mitosis to prepare karyotypes. Why?

During mitosis, chromosomes are more condensed than during interphase.

Which of the following statements regarding genetic diversity is false?

Genetic diversity is enhanced by mitosis.

Which of the following statements regarding mitosis and meiosis is false?

Meiosis provides for asexual reproduction.

During meiosis I, homologous chromosomes form a tetrad. What does this accomplish?

This brings the chromosomes into alignment so that crossing over can create new combinations of genes present on a single chromosome.

Although in humans there are 22 pairs of autosomal chromosomes, only three different chromosomal trisomies are commonly seen in newborns. Of the remaining 19 autosomes, many trisomies have not been seen in newborns. Why not?

Trisomy for the other autosomal chromosomes is often lethal, and the affected embryos are miscarried.

In theory, when a nondisjunction for chromosome 18 occurs during meiosis I, four gametes can be produced. If these gametes are fertilized with unaffected gametes from the second parent, what observations would you make concerning the resulting embryos?

Two of the embryos will be trisomic for chromosome 18, and two will contain a single copy of chromosome 18.

haploid-

a cell containing a single set of chromosomes

diploid-

a cell containing two homologous sets of chromosomes

zygote-

a fertilized egg

gamete-

a sex cell, haploid egg or sperm

somatic cell-

a typical body cell which has 46 chromosomes

trisomy 21-

also known as Down syndrome

crossing over-

an exchange of corresponding. segments between nonsister chromatids and homologous chromosomes

karyotype-

an ordered display of an individual's chromosomes in pairs

Karyotyping

can reveal alterations in chromosome number.

sex chromosomes-

determine an individual's sex

At a chiasma, two ________ are attached to each other.

homologous or non-sister chromatids

Independent orientation of chromosomes at metaphase I results in an increase in the number of

possible combinations of characteristics

autosomes-

the remaining 22 pairs of chromosomes in both males and females

locus-

the site where a gene is found on a chromosome

chiasma-

the sites of crossing over

In a cell with eight chromosomes, one chiasma develops during meiosis I in only one particular pair of homologs. How many recombinant chromosomes will there be at the completion of meiosis II?

two

homologous chromosomes-

two chromosomes in a matching pair

nondisjunction-

when members of a chromosome pair fail to seperate