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Biology 101 > Meiosis and Sexual Life Cycle > Flashcards

Meiosis and Sexual Life Cycle Flashcards

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1
Q

Why is meiosis necessary

A

To reduce the chromosome number

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2
Q

Why is it necessary to reduce the chromosome number?

A

To make gametes (eggs and sperm)

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3
Q

Why is it necessary to make gametes?

A

To complete the sexual life cycle

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4
Q

a organism passes all of its genes to its offspring

A

asexual reproduction

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5
Q

, a small freshwater animal, reproduces by budding; offspring are therefore clones, all genetically identical; many simple animals reproduce asexually

A

Hydra

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6
Q

is when an organism produces sex cells called gametes

A

Sexual reproduction/meiosis

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7
Q

The gametes combine at fertilization to form a

A

zygote

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8
Q

The female and male gametes may be from __ individuals or, in plants, from the __ individual

A

different, same

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9
Q

Zygote eventually turns into an adult by

A

mitotic cell divisions

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10
Q

The cells of the human body (the somatic cells) have __ sets of chromosomes

A

2

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11
Q

One set came from the mother and was in the egg

A

maternal chromosomes

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12
Q

other set came from the father and was in the sperm;

A

Paternal chromosomes

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13
Q

A set has how many chromosomes

A

23

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14
Q

double set?

A

46

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15
Q

Human cells contain a maternal chromo-some 1 and a paternal chromosome 1

A

homologous chromosomes (or just homologs)

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16
Q

are the same length, have the same centromere position and carry the same genes in the same order

A

chromosomes in a homologous pair

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17
Q

humans, there are __ homologous pairs of chromosomes

A

23

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18
Q

X and Y in most animals in and some plants

A

sex chromosomes

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19
Q

Females have a homologous pair of X chromosomes (XX);

A

homogametic sex

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20
Q

Males have one X and one Y (XY);

A

heterogametic sex

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21
Q

The other 22 pairs of chromosomes are called

A

autosomes

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22
Q

Organisms with two sets of chromosomes are said to be

A

diploid or 2n

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23
Q

diploid number in humans?

A

46, 2n=46

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24
Q

make gametes with a single set of chromosomes

A

diploid organisms

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25
Q

Gametes are thus

A

haploid

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26
Q

In humans, the haploid number is

A

23 (n = 23)

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27
Q

Disadvantages of the sexual life cycle

A

more complicated, requiring meiosis
meiosis is error-prone

takes more energy

may entail more risk

often requires two individuals

may spread disease

causes a loss of genetic representation

involves a “two-fold cost of sex”

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28
Q

only half of each parent’s genes are passed to the offspring; “loss of genetic representation”

A

In sexual reproduction

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29
Q

all the genes are passed to the offspring

A

asexual reproduction

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30
Q

asexually reproducing organisms can potentially produce offspring much faster than sexually reproducing organisms

A

two-fold cost of sex

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31
Q

Do asexuals or sexuals produce faster?

A

asexuals

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32
Q

is necessary to make haploid gametes

A

meiosis

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33
Q

Cutting the chromosome in half by ____ maintains the diploid (2n) chromosome number

A

meiosis

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34
Q

involves copying the chromosomes once (in the S phase of interphase) followed by two divisions of the chromosomes:

A

A meiotic cell cycle

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35
Q

the chromosome number is reduced from 2n to n

A

meiosis I

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36
Q

in the chromosome number is unchanged

A

meiosis II

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37
Q

One diploid (2n) cell will thus divide twice to produce

A

four cells, each haploid (n)

38
Q

Before the S phase, each chromosome consists of one

A

one chromatid

39
Q

After the S phase, each chromosome consists of two

A

identical sister chromatids

40
Q

two sister chromatids are held together at the

A

centromere

41
Q

Chromatids from homologous chromosomes are called

A

nonsister chromatids

42
Q

are not identical; their DNA sequences will differ

A

Nonsister chromatids

43
Q

the chromosomes are copied once and divided twice

A

meiotic division

44
Q

the chromosomes are copied once and divided once

A

mitotic division

45
Q

preceded by an interphase

A

meiosis

46
Q

the chromosomes are copied

A

During S phase of interphase

47
Q

each chromo-some consists of two identical sister chromatids

A

At the end of the S phase

48
Q

the homologous chromosomes pair up

they are then pulled apart

this cuts the chromosome number in half (2n–>n)

A

Meiosis I

49
Q

the two sister chromatids making up each chromosome are pulled apart

this does not further reduce the chromosome number (still n)

A

Meiosis II

50
Q

Preceded by interphase

Homologous chromosomes pair up

Maternal #1 pairs up with paternal #1, maternal #2 pairs up with paternal #2, etc

A

Prophase I

51
Q

The phase that Chromatids from homologous chromosomes overlap, break and rejoin

Most complex

A

This is called crossing over. Prophase I

52
Q

Each pair of homologous chromosomes aligns on the equatorial plane of the cell
The homologous chromosomes are now ready to be pulled apart…

A

Metaphase I

53
Q

The homologous chromosomes are pulled apart

The maternal chromosome goes to one pole and the paternal chromosome to the other pole

This cuts the chromosome number in half

The original cell had two sets of chromosome (2n)

All subsequent cells will have one set (n)

A

Anaphase I

54
Q

The chromosomes arrive at the opposite poles

Nuclear membranes form

The cell now divides into two cells, each with one set of chromosomes

A

Telophase I and Cytokinesis

55
Q

After telophase I, there may be a short resting phase

A

interkinesis

56
Q

The chromosomes may condense further

A

Prophase II

57
Q

The chromosomes align on the equatorial plane

A

Metaphase II

58
Q

The two sister chromatids are pulled apart and move to opposite poles

A

Anaphase II

59
Q

The chromosomes arrive at the opposite poles and nuclear membranes form

A

Telophase II

60
Q

The cell membrane pinches the cell into two new daughter cells

A

Cytokinesis

61
Q

Occurs in only in reproductive tissues (ovaries and testes

A

Meiotic cell cycle

62
Q

independent assortment of homologous chromosomes during meiosis I

A

The sexual life cycle generates and maintains genetic diversity

63
Q

random fertilization between gametes

A

The sexual life cycle generates and maintains genetic diversity

64
Q

crossing over between homologous chromosomes during prophase I of meiosis

A

The sexual life cycle generates and maintains genetic diversity

65
Q

maternal vs. paternal chromosomes occurs independently for all the pairs of homologous chromosomes

A

chromosome assortment

66
Q

At the end of meiosis there are ___ combinations of maternal and paternal chromosomes in the gametes, each occur-ring with equal probability:

A

8 possible

67
Q

The number of combinations of maternal and paternal chromosomes in the gametes is 2n, where n is the haploid number of chromosomes

A

For n = 3, 2(3) = 8

68
Q

how many possible chromosomal combinations in every fertilizations

A

70 trillion

69
Q

crossing over occurs between what?

A

sister chromatids of homologous chromosomes

70
Q

during crossing over, how many of four gametes will be recombined

A

2

71
Q

Purpose of crossing over?

A

increases total number of possible genetic combinations

72
Q

The point of crossing over is called

A

chiasma (plural chiasmata)

73
Q

Chiasmata are visible under the microscope during the later stages of what phase

A

Prophase I

74
Q

crossing over between homologous chromosomes during meiosis (prophase I)

A

causes genetic uniqueness

75
Q

independent assortment of homologous chromosomes during meiosis (meta-phase & anaphase I)

A

causes genetic uniqueness

76
Q

the fusion of gametes made by different organisms (fertilization)

A

causes genetic uniqueness

77
Q

each parent donates his or her own set of genetic material

A

Alleles come from two parents

78
Q

The homologs and sister chromatids distributed to each daughter cell during meiosis are a random mix of maternal and paternal genetic material

A

assortment of homologues

79
Q

So why don’t sexually reproducing organisms give up sex and reproduce asexually?

A

Females could make “eggs” without reducing the chromosome number by meiosis.

80
Q

Fertilization would become unnecessary.

Females would give birth to their genetic clones, all daughters

A

parthenogenesis

81
Q

common in some insects, including aphids and some bees, but is rare among vertebrates

A

parthenogenesis

82
Q

asexual animal

15 species are all-female

a courtship ritual is still required for ovulation

A

American whiptail lizard

83
Q

Suggested advantages of sex

A

It generates and maintains genetic diversity.

It eliminates harmful mutant alleles.

It increases the resistance to harmful parasites.

84
Q

Meiosis shuffles the chromosomes

Crossing over further recombines the genes

Fertilization brings together gametes from unrelated individuals

The offspring are genetically unique: different from each other and from both parents

The new genetic combinations created each generation may allow rapid adaptation to changing environments

A

Generation of genetic diversity

85
Q

Meiosis with crossing over can bring the most beneficial alleles from the maternal and paternal chromosomes together onto one chromosome

A

Generation of genetic diversity

86
Q

Mutations occur during the lifetime of an organism, creating harmful alleles in cells throughout the body

A

Elimination of harmful mutant alleles

87
Q

By asexual reproduction, these “somatic mutations” might be passed to the off-spring

A

Elimination of harmful mutant alleles

88
Q

In sexual reproduction, the genes are passed to the next generation through a single cell, the gamete

A

Elimination of harmful mutant alleles:

89
Q

The gamete would not have any of the somatic mutations

The offspring thus start with a “clean slate”

A

Elimination of harmful mutant alleles

90
Q

the number of mutations “ratchets up” irreversibly over time

A

Muller’s Ratchet

91
Q

Harmful parasites may infect cells throughout the body

By asexual reproduction, these parasites could be passed to the offspring

In sexual reproduction, the genes are passed to the next generation through a single cell, the gamete

A

Increased resistance to parasites

92
Q

The gamete would be free of the para-sites

The offspring thus start with a “clean slate”

The shuffling of alleles by meiosis would also create combinations that give greater resistance to parasites

A

Increased resistance to parasites

Biology 101 (6 decks)

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