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TH- meiosis Flashcards

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1
Q

What is heredity/inheritance?

A

The transmission of traits from one generation to the next

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2
Q

what is variation?

A

a change or slight difference

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3
Q

What is a genome? and is it comprised of?

A
  • organism’s complete set of genetic instructions.

- comprised of many genes from mother and father.

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4
Q

what are genes? and where are they found on a chromosome?

A
  • segments of DNA

- found at its locus

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5
Q

State the difference between asexual and sexual reproduction.

A
  • organisms that reproduce asexually can produce offspring that are exact copies of themselves.
  • sexual reproduction, two parents produce offspring that have unique combinations of genes inherited from the two parents.
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6
Q

What is a clone?

A

a group of genetically identical individuals.

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7
Q

How may clones differ?

A

Due to mutations

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8
Q

What is a somatic cell?

A

all cells except reproductive cells

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9
Q

What is a karyotype display?

A

images of 46 chromosomes arranged in pairs in order of size.

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10
Q

What do two chromosomes in a pair need to have in common?

A

have the same length, centromere position, and staining pattern.

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11
Q

what is a homologous chromosome pair?

A

carry genes that control the same inherited characters.

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12
Q

what are the 2 distinct sex chromosome?

A

X and Y

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13
Q

what are the exception to the general pattern of homologous chromosomes in human somatic cells?

A

the sex chromosomes

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14
Q

what are autosomes?

A
  • chromosomes other than X and Y

- so the 22 other pairs in humans cells.

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15
Q

what homologous pair of sex chromosomes do females and males have?

A
  • M= XY

- F= XX

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16
Q

what is a diploid cell?

A

• Any cell with two sets of chromosomes, 2n

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17
Q

what is a haploid cell?

A

• A gamete with a single chromosome set, n

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18
Q

How many sets of chromosomes and what type do we have in somatic cells?

A

-two sets of 23, a maternal set and a paternal set

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19
Q

How many and what type of chromosomes do sperm cells and ovum have?

A
  • sperm= 22 autosomes and X or Y

- ovum= 22 autosomes and X

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20
Q

what is syngamy?

A

the fusion of two cells, or of their nuclei, in reproduction.

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21
Q

what occurs in fertilisation?

A

Fertilization occurs when the nucleus of both a sperm and an egg fuse (synagmy) to form a diploid cell, known as zygote.

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22
Q

what is a zygote?

A

fertilised egg

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23
Q

what is gonads?

A

male and female primary reproductive organs.

24
Q

By which process are gametes produced?

A

meiosis

25
Q

why are gametes produced by this process?

A
  • If gametes were produced by mitosis, the fusion of gametes would produce offspring with four sets of chromosomes after one generation, eight after a second, and so on.
  • however by meiosis they are halved instead.
26
Q

Briefly describe life cycle from gamete to adult

A
  • gametes divide by meiosis
  • haploid sperm and egg cell fuse
  • fertilization takes place
  • most cells in diploid zygote now divides via mitosis to grow and develop
  • forming eventually a adult
  • their gametes still divide via meiosis
27
Q

What is the 2nd life cycle of plants and algae called?

A

alternation of generations.

28
Q

what does the life cycle of plants and algae include?

A

two multicellular stages, one haploid and one diploid.

29
Q

Describe the alternation of generations

A
  • The multicellular diploid stage is called the sporophyte.
  • Meiosis in the sporophyte produces haploid spores that develop by mitosis into the haploid gametophyte stage.
  • Gametes produced via mitosis by the gametophyte fuse to form the zygote, which grows into the sporophyte by mitosis.
30
Q

describe the third life cycle of most fungi and protoctists

A
  • Gametes fuse to form a zygote, which is the only diploid phase.
  • The zygote undergoes meiosis to produce haploid cells.
  • These haploid cells grow by mitosis to form the haploid multicellular adult organism.
  • The haploid adult produces gametes by mitosis.
31
Q

which type of cells can undergo meiosis?

A

Diploid cells

32
Q

which feature do all 3 cell cycles share?

A

each cycle of chromosome halving and doubling contributes to genetic variation among offspring.

33
Q

what does meiosis I result in?

A

separation of homologous chromosomes forming a haploid cell

34
Q

what does meiosis II result in?

A

separates sister chromatids so form 4 daughter cells.

35
Q

what 2 things happenn in interphase before meiosis I?

A
  • chromosomes are replicated to form sister chromatids.

- single centrosome is replicated, forming two centrosomes.

36
Q

Describe Meiosis I

A
  • Prophase I:
  • the chromosomes begin to condense.
  • Homologous chromosomes loosely pair up along their length, precisely aligned gene for gene.
  • In crossing over, nonsister chromatids exchange DNA segments
  • a protein structure called the synaptonemal complex forms between homologues, holding them tightly together along their length.
  • As the synaptonemal complex disassembles in late prophase, each chromosome pair becomes visible as a tetrad, or group of four chromatids.
  • Each tetrad has one or more chiasmata, sites where the chromatids of homologous chromosomes have crossed, and segments of the chromatids have been traded
  • Spindle microtubules form from the centrosomes, which have moved to the poles
  • The breakdown of the nuclear envelope and nucleoli take place.
  • Kinetochores of each homologue attach to microtubules from one of the poles.
  • Metaphase I:
  • tetrads are all arranged at the metaphase plate, with one chromosome facing each pole.
  • Microtubules from one pole are attached to the kinetochore of one chromosome of each tetrad, while those from the other pole are attached to the other.
  • Anaphase I:
  • homologous chromosomes separate
  • One chromosome moves toward each pole, guided by the spindle apparatus.
  • Sister chromatids remain attached at the centromere and move as a single unit toward the pole.
  • Telophase I and cytokinesis:
  • movement of homologous chromosomes continues until there is a haploid set at each pole.
  • In animal cells, a cleavage furrow forms. In plant cells, a cell plate forms.
37
Q

Does chromosome replication occur after meiosis I? explain why/ why not

A

no, chromosomes are already replicated.

38
Q

Describe Meiosis II

A
  • Prophase II:
  • spindle apparatus forms and attaches to kinetochores of each sister chromatid.
  • Spindle fibers from one pole attach to the kinetochore of one sister chromatid, and those of the other pole attach to kinetochore of the other sister chromatid.
  • Metaphase II:
  • sister chromatids are arranged at the metaphase plate.
  • kinetochores of sister chromatids attach to microtubules extending from opposite poles.
  • Anaphase II:
  • centromeres of sister chromatids separate
  • two newly individual chromosomes travel toward opposite poles.
  • Telophase II:
  • chromosomes arrive at opposite poles.
  • Nuclei form around the chromosomes, which begin expanding
  • cytokinesis separates the cytoplasm.
39
Q

Explain the synapsis process

A

-During prophase I of meiosis, replicated homologous chromosomes line up and become physically connected along their lengths by a zipperlike protein complex, the synaptonemal complex

40
Q

state the differences between meiosis and mitosis

A
  • chromosome number is reduced from diploid to haploid in meiosis but is conserved in mitosis.
  • mitosis produces genetically identical daughter cells to parents but Meiosis produces cells that are genetically distinct
  • Synapsis and crossing over do not occur in mitosis.
  • In mitosis, individual replicated chromosomes line up along the metaphase plate however in Meiosis I homologous pairs line up
  • At anaphase I of meiosis, it is homologous chromosomes that separate and are carried to opposite poles of the cell however In mitosis, sister chromatids separate to become individual chromosomes.
41
Q

What is synaptonemal complex ?

A

zipperlike protein complex used in synapsis

42
Q

What is crossing over?

A

Genetic rearrangement between nonsister chromatids

43
Q

What is the origin of genetic variation?

A

Mutations are the original source of genetic diversity

44
Q

What are the three mechanisms contribute to genetic variation?

A
  1. Independent assortment of chromosomes.
  2. Crossing over.
  3. Random fertilization.
45
Q

Describe Independent assortment of chromosomes (how it affects genetic variation)

A
  • each pair of chromosomes sorts maternal and paternal homologues into daughter cells independently of the other pairs
  • Therefore, the first meiotic division results in independent assortment of maternal and paternal chromosomes into daughter cells.
  • causing the number of combinations possible.
46
Q

what is the formula for calculating the number of possible combinations for Independent assortment of chromosomes?

A
  • 2^n

- n= haploid number

47
Q

What are recombinant chromosomes?

A

DNA are broken and recombined to produce new combinations of alleles.

48
Q

Describe crossing over and when it takes place?

A
  • begins very early in prophase I
  • homologous portions of two nonsister chromatids trade places
  • paired chromosomes from each parent align so that similar DNA sequences from the paired chromosomes cross over one another.
49
Q

how do crossing over and Independent assortment of chromosomes help provide variation together?

A
  • Crossing over, by combining DNA inherited from two parents into a single chromosome brings about nonidentical sister chromatids
  • At metaphase II, nonidentical sister chromatids sort independently from one another, increasing by even more the number of genetic types of daughter cells that are formed by meiosis.
50
Q

Describe Random fertilization

A

• Any sperm can fuse with any egg.

51
Q

What are the three sources of genetic variability in a sexually reproducing organism?

A
  1. Independent assortment of homologous chromosomes during meiosis I and of nonidentical sister chromatids during meiosis II.
  2. Crossing over between homologous chromosomes during prophase I.
  3. Random fertilization of an ovum by a sperm.
52
Q

what is natural selection?

A

Natural selection is the process through which populations of living organisms adapt and change.

53
Q

what is phenotype?

A

individual’s observable traits

54
Q

What develops from natural selection?

A

adaptation

55
Q

what is adaptation?

A

A change in structure, function, or behavior by which a species or individual improves its chance of survival in a specific environment

56
Q

What can cause new genes to arise and former ones to decrease?

A

If the environment changes or a population moves to a new environment, new genetic combinations that work best in the new conditions will produce more offspring, and these genes will increase.

57
Q

Why is adaptation important?

A

Only those individuals best suited to the local environment will leave the most offspring, transmitting their favorable genes in the process.

Biology (15 decks)

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