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Flashcards in Chapter 13 Deck (123):
1

Living organisms are distinguished by

their ability to reproduce their own kind

2

Genetics is the

scientific study of heredity and variation

3

Heredity is the

transmission of traits from one generation to the next

4

Variation is

demonstrated by the differences in appearance that offspring show from parents and siblings

5

Offspring acquire genes from parents by

inheriting chromosomes

6

In a literal sense, children do not

inherit particular physical traits from their parents

7

It is

genes that are actually inherited

8

Genes are the

units of heredity, and are made up of segments of DNA

(Genes are generic categories, but they have specific locations)

9

Genes are passed to the next generation via reproductive cells called

gametes (sperm and eggs)

10

Each gene has a specific location called a

locus, on a certain chromosome

11

Most DNA is packaged into

chromosomes

12

One set of chromosomes is inherited from

each parent

13

Every person has

specific details (alleles)

14

In asexual reproduction (mitosis),

a single individual passes genes to its offspring without the fusion of gametes

15

A clone is

a group of genetically identical individuals from the same parent

16

In sexual reproduction,

two parents give rise to offspring that have unique combinations of genes inherited from the two parents

17

Fertilization and Meiosis alternate in

sexual life cycles

18

A life cycle is the

generation-to-generation sequence of stages in the reproductive history of an organism

19

Human somatic cells (any cell other than a gamete) have

23 pairs of chromosomes.

(have 2 of every chromosome)

20

A karyotype is an

ordered display of the pairs of chromosomes from a cell

21

The two chromosomes in each pair are called

homologous chromosomes, or homologs

22

Chromosomes in a homologous pair are the

same length and shape and carry genes controlling the same inherited characters ((but slightly different information??))

23

The sex chromosome, which determine the sex of the individual, are called

X and Y

24

Human females have a

homologous pair of X chromosomes (XX)

25

Human males have

one X and one Y chromosome (XY)

26

The remaining 22 pairs of chromosomes are called

autosomes

(not a sex chromosome)

27

Each pair of homologous chromosomes includes

one chromosome from each parent

28

The 46 chromosomes in a human somatic cell are

two sets of 23: one from the mother and one from the father

29

A diploid cell (2n) has

two sets of chromosomes

30

For humans, the diploid number is

46 (2n = 46)

31

In a cell in which DNA synthesis has occurred,

each chromosome is replicated

32

Each replicated chromosome consists of

two identical sister chromatids

33

A gamete (sperm or egg) contains a

single set of chromosomes, and is haploid (n)

34

For humans, the haploid number is

23 (n = 23)

35

Each set of 23 consists of

22 autosomes and a single sex chromosome

36

In an unfertilized egg (ovum),

the sex chromosome is X

37

In a sperm cell,

the sex chromosome may be either X or Y

38

Fertilization is the

union of gametes (the sperm and the egg)

(when the egg and sperm come together)

39

The fertilized egg is called a

zygote and has one set of chromosomes from each parent

40

The zygote produces

somatic cells by mitosis and develops into an adult

41

At sexual maturity,

the ovaries and testes produce haploid gametes

42

Gametes are the only types of human cells produced by

meiosis, rather than mitosis

43

Meiosis results in

one set of chromosomes in each gamete

44

Fertilization and meiosis alternate in

sexual life cycles to maintain chromosome number

45

The alternation of meiosis and fertilization is common to

all organisms that produce sexually

46

The three main types of sexual life cycles differ in

the timing of meiosis and fertilization

47

Gametes are the only haploid cells in

animals

48

The gametes are produced by meiosis and undergo no further

cell division before fertilization

49

Gametes fuse to form a diploid zygote that

divides by mitosis to develop into a multicellular organism

50

Plants and some algae exhibit an

alternation of generations

51

This life cycle (plants) includes both a

diploid and haploid multicellular stage

52

The diploid organism, called the

sporophyte, makes haploid spores by meiosis

53

Each spore grows by mitosis into a

haploid organism called a gametophyte

54

A gametophyte makes

haploid gametes by mitosis

55

Fertilization of gametes results in a

diploid sporophyte

56

In most fungi and some protists,

the only diploid stage is the single-celled zygote; there is no multicellular diploid stage

57

In most fungi, the zygote produces haploid cells by

meiosis

58

Each haploid cell grows by

mitosis into a haploid multicellular organism

59

The haploid adult produces gametes by

mitosis

60

Depending on the type of life cycle,

either haploid or diploid cells can divide by mitosis

61

However, only diploid cells can

undergo meiosis

62

In all three life cycles,

the halving and doubling of chromosomes contributes to genetic variation in offspring

63

Meiosis reduces the

number of chromosome sets from diploid to haploid

64

Like mitosis, meiosis is preceded by

the replication of chromosomes

65

Meiosis takes place in two sets of cell divisions, called

meiosis I and meiosis II

66

The two cell divisions result in

four daughter cells, rather than the two daughter cells in mitosis

67

Each daughter cell has only

half as many chromosomes as the parent cell

68

Meiosis Stages

1. Replicate DNA (DNA synthesis)
2. meiosis I
P-prophase I
M- metaphase I
A- anaphase I
T- telophase I and cytokinesis
3. meiosis II
P-prophase I
M- metaphase I
A- anaphase I
T- telophase I and cytokinesis

69

After chromosomes duplicate, two divisions follow

-Meiosis I (reductional division: homologs pair up and separate, resulting in two haploid daughter cells with replicated chromosomes
-Meiosis II (equational division): sister chromatids separate

-The result is four haploid daughter cells with unreplicated chromosomes

70

Meiosis I is preceded by

interphase, when the chromosomes are duplicated to form sister chromatids

71

The sister chromatids are

genetically identical and joined at the centromere

72

The single centrosome replicates, forming

two centrosomes

73

Division in meiosis I occurs in four phases

P-prophase I
M- metaphase I
A- anaphase I
T- telophase I and cytokinesis

((they are generally the same as in Mitosis, but there are a few differences))

74

Prophase I typically occupies more than

90% of the time required for meiosis.

75

In prophase I,

chromosomes begin to condense

76

In synapsis,

homologous chromosomes loosely pair up, aligned gene by gene

77

In crossing over,

nonsister chromatids exchange DNA segments

78

Each pair of chromosomes forms a

tetrad, a group of four chromatids

79

Each tetrad usually has one or more

chiasmata, X-shaped regions where crossing over occurred

80

3 things that make meiosis different/unique from mitosis

1. prophase I- synapsis/crossing over
2. metaphase I- homologs line up
3. Anaphase I- homologs separate

81

In metaphase I,

tetrads line up at the metaphase plate, with one chromosome facing each pole

82

Microtubules from one pole are attached to the

kinetochore of one chromosome of each tetrad

83

Microtubules from the other pole are attached to

the kinetochore of the other chromosome

84

In anaphase I,

pairs of homologous chromosomes separate

85

One chromosome moves toward

each pole, guided by the spindle apparatus

86

Sister chromatids remain attached at the

centromere and move as one unit toward the pole

87

In the beginning of telophase I,

each half of the cell has a haploid set of chromosomes; each chromosome still consists of two sister chromatids

88

Cytokinesis usually occurs

simultaneously, forming two haploid daughter cells

-In animal cells, a cleavage furrow forms
-In plant cells, a cell plate forms

89

No chromosome replication occurs between the

end of meiosis I and the beginning of meiosis II because the chromosomes are already replicated

90

Division in meiosis II also occurs in four phases

P- prophase II
M- metaphase II
A- anaphase II
T- telophase II and cytokinesis

91

Meiosis II is very similar to

mitosis

92

In prophase II,

a spindle apparatus forms

93

In late prophase II,

chromosomes (each still composed of two chromatids) move toward the metaphase plate

94

In metaphase II,

the sister chromatids are arranged at the metaphase plate

95

Because of the crossing over in meiosis I,

the two sister chromatids of each chromosome are no longer genetically identical

96

The kinetochores of sister chromatids attach to

microtubules extending from opposite poles

97

In anaphase II,

the sister chromatids separate

98

The sister chromatids of each chromosome now move as

two newly individual chromosomes toward opposite poles

99

In telophase II,

the chromosomes arrive at opposite poles

100

Then in telophase II,

nuclei form, and the chromosomes begin decondensing

101

Cytokinesis separates the

cytoplasm

102

At the end of meiosis,

there are four daughter cells, each with a haploid set of unreplicated chromosomes

103

Each daughter cell is genetically distinct from

the others and from the parent cell

104

Mitosis conserves the number of

chromosome sets, producing cells that are genetically identical to the parent cell

105

Meiosis reduces the number of

chromosomes sets from two (diploid) to one (haploid), producing cells that differ genetically from each other and from the parent cell

106

Three events are unique to meiosis, and all three occur in meiosis I

-synapsis and crossing over in prophase I: Homologous chromosomes physically connect and exchange genetic information
-At the metaphase plate, there are paired homologous chromosomes (tetrads), instead of individual replicated chromosomes
-At anaphase I, it is homologous chromosomes, instead of sister chromatids, that separate

107

Genetic variation produced in sexual life cycles contributes to

evolution

108

Mutations (changes in an organism's DNA) are the

original source of genetic diversity

109

Mutations create

different versions of genes called alleles

110

Reshuffling of alleles during sexual reproduction produces

genetic variation

111

The behavior of chromosomes (DNA) during meiosis and fertilization is responsible for

most of the variation that arises in each generation

112

Three mechanisms contribute to genetic variation
(reasons why kids look different from parents and other siblings)

1. independent assortment of chromosomes
2. crossing over
3. random fertilization

113

Homologous pairs of chromosomes orient

randomly at metaphase I of meiosis

114

In independent assortment,

each pair of chromosomes sorts maternal and paternal homologs into daughter cells independently (differently) of the other pairs

(chromosomes can line up differently)

115

The number of combinations possible when chromosomes assort independently into gametes is

2^n, where n is the haploid number

116

For humans (n = 23), there are more than

8 million (2^23) possible combinations of chromosomes

117

Crossing over produces

recombinant chromosomes, which combine DNA inherited from each parent

118

Crossing over beings very early in prophase I, as

homologous chromosomes pair up gene by gene

119

In crossing over,

homologous portions of two nonsister chromatids trade places

120

Crossing over contributes to

genetic variation by combining DNA from two parents into a single chromosome

121

Random fertilization adds to

genetic variation because any sperm can fuse with any ovum (unfertilized egg)

122

The fusion of two gametes (each with 8.4 million chromosome combinations from independent assortment) produces a

zygote with any of about 70 trillion diploid combinations

123

Each zygote has a

unique genetic identity