8.11-8.17: Meiosis and Crossing Over

Question 1

What is a somatic cell defined by?

Answer 1

Having a certain number of chromosomes for the species (in humans, 46). It is a typical body cell. any cell of a living organism other than the reproductive cells.

Question 2

Fill the blank: a human cell at metaphase contains _____ sets of duplicated chromosomes.

Answer 2

23

Question 3

What are homologous chromosomes (shortened: homologs)

Answer 3

Chromosomes of possibly different constructions that mirror each other in length, centromere location, and staining (when specific chemicals
are added). These chromosomes control the same characteristics of the body.

Question 4

What is a locus, in the context of genetics?

Answer 4

A part of a chromosome that codes for a specific trait. In different chromosomes, the codes may be different, but the subject is the same.

Question 5

What distinguishes sex chromosomes from non-sex chromosomes, known as autosomes?

Answer 5

They are considered homologous but do not mirror themselves in shape and construction if the sex chromosomes determine someone to be male (XX female, XY male)

Question 6

End of 8.11 question: Are all your chromosomes fully homologous?

Answer 6

If you are female, yes. If you are male, no.

Question 7

Define life cycle

Answer 7

The development of a fertilized egg to an adult

Question 8

What is a key factor in the life cycle of species that reproduce sexually?

Answer 8

inherited chromosomes from mother and father.

Question 9

What is the diploid number? For humans?

Answer 9

2n; 46

Question 10

Define diploid.

Answer 10

organisms that contain somatic cells with a certain number of pairs of homologous chromosomes. the presence of two complete sets of chromosomes in an organism’s cells, with each parent contributing a chromosome to each pair

Question 11

What is the umbrella term for sperm and egg?

Answer 11

Gametes (gam-meets)

Question 12

Describe the chromosomal structure of a gamete for humans

Answer 12

22 autosomes (singular) and a single sex chromosomes X or Y (always X for an egg)

Question 13

What is a cell with a single chromosome set, such as gametes, called?

Answer 13

A haploid cell

Question 14

What is the haploid number? For humans?

Answer 14

n; 23

Question 15

Define fertilization

Answer 15

The process in which a haploid sperm cell meets with a haploid egg cell.

Question 16

What is a zygote? Is it a haploid or a diploid?

Answer 16

A fertilized egg. Diploid, because it has two sets of chromosomes from a male and a female.

Question 17

The zygote is the _____ cell of a human.

Answer 17

First. Mitosis expands it.

Question 18

What types of cells does meiosis produce?

Answer 18

Gametes.

Question 19

Where does meiosis occur?

Answer 19

Reproductive organs.

Question 20

End of 8.12 question: How many autosomes are found in a human sperm cell? How many and which sex chromosomes?

Answer 20

22 autosomes plus either an X or Y sex chromosomes.

Question 21

What does interphase look like (meiosis)?

Answer 21

the same as mitosis: DNA doubles, cell gets larger.

Question 22

What does prophase I look like?

Answer 22

1. Chromatin coils up into sister chromatids, but it does not stop there. The sister chromatids find their homologous pairs (synapsis)
2. The tetrads cross over
3. Spindle forms
4. Nuclear envelope starts dissolving
5. Spindles begin to move tetrads to center of the cell.

Question 23

What is synapsis?

Answer 23

The process in which sister chromatids find their homologous pairs in prophase I.

Question 24

What is a tetrad

Answer 24

Found in prophase I, these are the two sets of sister chromatids together. (total four chromatids)

Question 25

What is crossing over?

Answer 25

The process is which locus points in DNA are switched when the sister chromatids are in the form of tetrads. It rearranges genetic information. "the exchange of corresponding segments between nonsister chromatids of homologous chromosomes"

Question 26

What does metaphase I look like?

Answer 26

Like in mitosis, spindle fibers attach to the kinetochores of the (meiosis) tetrads. Note that they attach to individual kinetochores of homologous chromosomes, meaning that the tetrads are poised to break up with each other.

Question 27

What does anaphase I look like?

Answer 27

The tetrads (which alleles are mixed because of crossing over), are split into sister chromatids (compare this to mitosis, where sister chromatids are split into individual chromosomes)

Question 28

What is a centromere

Answer 28

where the kinetochore is located, waist.

Question 29

What happens during telophase I and the concurrent cytokinesis.

Answer 29

Happens just like in mitosis, except this time the sister chromatids move to opposite ends of the cell, become chromatin, and the nuclear membrane reappears. Cytokinesis occurs, and before the 2nd cycle, in some organisms, an interphase occurs.

Question 30

Meiosis II occurs exactly like...

Answer 30

Mitosis.

Question 31

What is the main difference between Meiosis 2 and Mitosis.

Answer 31

Meiosis 2 starts with a haploid cell, and ends with 23 chromosomes in each gamete.

Question 32

When two haploid cells are combined (like in fertilization), what is the resulting cell?

Answer 32

Diploid.

Question 33

Fill in the blanks. Meiosis divides the diploid cell ____ times, resulting in cells with ______ individual chromosomes

Answer 33

2; 23

Question 34

What triggers crossing over?

Answer 34

physical contact of homologous chromosomes.

Question 35

End of 8.13 question: A cell has the haploid number of chromosomes, but each chromosome has two chromatids. The chromosomes are arranged singly at the center of the spindle. What is the mitotic stage?

Answer 35

Metaphase II (because the chromosome line up two by two in metaphase I)

Question 36

End of 8.14 question: Which stage of meiosis shown here most closely resembles mitosis?

Answer 36

The movement of chromosomes during meiosis II very closely matches mitosis (except with half as many chromosomes).

Question 37

List the state of the genetic material in mitosis until its end.

Answer 37

Chromosomes (duplicated during S-phase) --> become sister chromatids --> sister chromatids split during metaphase --> same amount of chromosomes in daughter cells.

Question 38

List the state of the genetic material in meiosis until its end.

Answer 38

Chromosomes duplicate during s-phase --> sister chromatids --> sister chromatids pair up with other sister chromatids (homologous chromosomes) --> tetrads --> (meiosis I) --> sister chromatids in daughter cells (same amount of genetic material as daughter cells in mitosis, just in a different form)---> sister chromatids separate, making 4 haploid cells.

Question 39

sister chromatids contain the genetic material of one or two people? (meiosis)

Answer 39

One, they are a duplicated chromosome from one cell

Question 40

tetrads contain the genetic material of one or two people? (meiosis)

Answer 40

Two, the homologous pair of sister chromatids from the maternal and paternal cell.

Question 41

What is one way that genetic variation occurs in the creation of gametes (8.15)

Answer 41

When homologous chromosomes match up, there is a 50% of the sister maternal/paternal chromatid ending up near a certain pole, so that when the cell divides, they can end up in different sister chromatid pairs (see 141)

Question 42

Fill in the blank: for a species with more than two pairs of chromosomes, such as humans, all the chromosome pairs _______ ____________ at metaphase I.

Answer 42

orient independently

Question 43

(8.15) For any organism that undergoes meiosis, what is the formula that determines the possible amounts of gamete combinations?

Answer 43

2^n, where n is the haploid number.

Question 44

Using the formula from 8.15, how many possible gamete combinations do humans have?

Answer 44

Humans have 46 chromosomes, and 23 chromosomes pairs. 23 is the haploid number. 2^23 is 8 million. Each gamete made is one in eight million.

Question 45

How many possibilities are there when a gamete from one individual unites with a gamete from another individual in fertilization?

Answer 45

one in 8 million for egg,*one in 8 million for sperm. 64 trillion.

Question 46

End of 8.15 question: A particular species of worm has a diploid number of 10. How many chromosomal combinations are possible for the gametes formed by meiosis?

Answer 46

2n=10, n=5, 2^5=32

Question 47

What is the plural of locus?

Answer 47

loci

Question 48

What makes gametes-- and therefore offspring-- different from each other.

Answer 48

The fact that homologous chromosomes have different genetic material at loci. Might inherit one eye color from mom, different from dad, but they are still located within the chromosome that determines eye color. Crossing over and independent orientation.

Question 49

What is a chiasma? (pl. chiasmata)

Answer 49

the site of crossing over between tetrads. Looks like an "X"

Question 50

When does crossing over occur in meiosis?

Answer 50

Beginning of prophase I. There, homologous chromosomes are paired all along their lengths, with a precise gene-by-gene alignment.

Question 51

What is a large determinant for genetic variation?

Answer 51

random fertilization, ie. which sperm which egg.

Question 52

What is genetic recombination?

Answer 52

the production of gene combinations different from those carried by the original parent chromosomes.

Question 53

How many crossing over events occur per homologous pairs?

Answer 53

1-3.

Question 54

If one was to examine the genetic material from a gamete of theirs, would it look like any of their chromosomes?

Answer 54

no, rather a patchwork of of segments derived from a pair of homologous chromosomes.

Question 55

List what a parental type of chromosome may have instructions for (see page 143). Then do a recombinant chromosome.

Answer 55

E, C vs. E, c

Question 56

End of 8.17 Question: Describe how crossing over and the random alignment of homologous chromosomes on the metaphase I plate account for the genetic variation among gametes found in meiosis.

Answer 56

Crossing Over creates recombinant chromosomes having a combination of genes that were originally on different, though homologous, chromosomes. Homologous chromosomes pair are oriented randomly at metaphase of meiosis I.

Question 57

What are the three sources of genetic variability?

Answer 57

Independent orientation at metaphase I, random fertilization, and crossing over during prophase I of meiosis.

Question 58

What is responsible for genetic diversity in humans?

Answer 58

Genetic mutation.