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General Biology I > lecture 11: sexual reproduction > Flashcards

lecture 11: sexual reproduction Flashcards

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1
Q

What is asexual reproduction?

A

Produce clones: genetically identical individuals

  • Several mechanisms for asexual reproduction exist
  • Those mechanisms involve mitotic cell division in both uni-multicellular eukaryotes & binary fission in prokaryotes
  • Produce offspring form unfertilized eggs
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2
Q

What is selfing (self-fertilization)?

A

Sexual reproduction where sperm and egg are produced by same individual

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3
Q

What is sex, where is it observed, and what does it require?

A
  • Sexual reproduction: fusion of two cells and genetic information of each to create a new organism
  • Observed in eukaryotes (not in prokaryotes) that evolved 1 BYA
  • Requires meiosis in the lifecycle of the organism
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4
Q

Sexual reproduction requires what type of cell division?

A

Meiosis

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5
Q

Asexual reproduction requires what type of cell division?

A

Mitosis

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6
Q

What is a life cycle?

A

Steps of development for one generation —> period where an organisms is formed, develops, and reproduces an offspring of its own

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7
Q

Mitosis produces…

A

genetically identical cells (same ploidy)

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8
Q

Meiosis produces…

A

genetically unique cells with half o f the number of chromosomes

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9
Q

What is a homologous pair of chromosomes?

A

1 from mother and 1 from father: each carries genes for the same traits

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10
Q

What is a gene?

A

Segment of DNA located in a specific site on a specific chromosome that contain information for producing a particular polypeptide

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11
Q

What are alleles?

A

Different versions of a gene —> pair of alleles = 1 form mother and other from father

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12
Q

What are the 5 main steps of a meiotic cell division?

A
  1. Interphase: chromosomes are replicated (46 —> 92 in one cell)
  2. Meiosis I
  3. Cytokinesis I (2 cells with 46 chromosomes each)
  4. Meiosis II (without replication of chromosomes)
  5. Cytokinesis II (4 cells with 23 chromosomes each)
    —> Meiosis = TWO cell divisions
    —> Produce 4 haploid cells
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13
Q

Meiosis steps following ploidy

A

INTERPHASE
1 diploid cell (single chromosomes: 46) —> Replication —> 1 diploid cell (double chromosomes: 92)
MEIOSIS I
1 diploid cell (double chromosomes: 92) —> 2 haploid cells (double chromosomes: 46 each)
MEIOSIS II
2 haploid cells (double chromosomes: 46 each) —> 4 haploid cells (single chromosomes: 23 each)

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14
Q

How does meiosis differ from mitosis?

A

MITOSIS:
- produces 2 genetically identical and diploid daughter cells
- involves one division of nucleus and one division of cytoplasm
- involve one chromosomes replication
MEIOSIS:
- produces 4 genetically different and haploid daughter cells
- involves two divisions of nucleus and two divisions of cytoplasm
- involves one chromosome replication
- homologous chromosomes exchange regions

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15
Q

What is “crossing over”?

A

Homologous chromosomes exchange regions during prophase 1 —> ensures that each haploid cell will be genetically unique

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16
Q

What happens in meiosis I in early prophase I that does not happen in mitosis?

A

Replicated homologous chromosomes pairs form tetrads —> 4 chromosomes together
—> Stay in tetrads until end of anaphase (when the 2 homologous pairs are pulled to opposite poles)

17
Q

What happens in meiosis I in late prophase I that does not happen in mitosis?

A

Crossing over occurs between chromatids of the homologous chromosomes —> “shuffling” —> infinite combinaisons of alleles

18
Q

What happens during meiosis II?

A

Is essentially mitosis but without replicated chromosomes (prophase, metaphase, anaphase, telophase —> 4 haploid daughter cells)

19
Q

Gamete production requires and what are the two types of production of gametes? (2)

A
  1. Meiosis
  2. Differentiation (maturation)
  3. Spermatogenesis in testes
  4. Oogenesis in ovaries
20
Q

What is the outcome of meiosis and sexual reproduction? (3)

A
  • Meiosis produces genetically unique sex cells
  • Fusion of these sex cells produces genetically unique zygotes giving rise to genetically unique offspring
  • Sexual reproduction produces genetic variation which in turn produces genetic variation in population (only reason why there is meiosis in sexual reproduction)
21
Q

How does sexual reproduction produce genetic variability? (3)

A
  1. Maternal and paternal chromosomes are randomly assorted —> variation in gametes
  2. Crossing over creates recombinant chromosomes —> variation in gametes
  3. Fertilization is random —> variation in zygotes
22
Q

How does meiosis produce genetic variation in gametes? (2)

A
  1. Random distribution of homologues during meiosis in gametes —> variation in the combination of maternal and paternal chromosomes
  2. Crossing over varies combinations of maternal and paternal alleles within each chromosome type
23
Q

How does distribution of homologues produce genetic variation?

A
  • Orientation of a pair (which side is the maternal/paternal chromosome is on?) is random
  • So homologues will line up in ONE of millions of possible ways before they are package into different cells
  • So millions of combinations of maternal and paternal chromosomes to be packaged into gametes by meiosis —> millions of combinations of alleles for the genes on our chromosomes
  • 2^23 = 8.4 millions of combination possible
24
Q

How does crossing over produce genetic variation?

A
  • When homologues pair and lineup in meiosis I, corresponding portionsof these chromosomes are exchanged making recombinant chromosomes
  • So alleles are shuffled into unique combinations
  • So allows even more unique combinations of alleles to be packaged into gametes by meiosis
  • Much more than 8.4 million combos can be created for humans
25
Q

How does fertilization produce genetic variation?

A
  • Individuals are likely to contain different alleles for genes
  • Each unique gamete from individuals has an equal chance of coming together
  • Two unique gametes combine to form a unique zygote that develops into an offspring
  • 8.4 million X 8.4 million = 70.6 X 10^12 genetically distinct offspring can result from any one human mating (WITHOUT taking into account crossing over!)
26
Q

What is genetic linkage?

A
  • Physical association of two or more genes found on the same chromosome
  • Alleles for linked genes = inherited as a package
  • Linked genres = too close together on the same chromosome —> crossing over between the genes rarely occurs
  • Crossing over occurs frequently between genes that are far apart
27
Q

Can all possible combinations of alleles be packaged into gametes?

A

No, because of genetic linkage

28
Q

Why does sexual reproduction exist?

A

For genetic uniqueness and variation in traits

29
Q

Why is asexual reproduction most convenant than sexual reproduction? (2)

A
  1. All individuals in a population can directly produce offspring
  2. More efficient —> do not need time or energy to find mate
30
Q

Why do some organisms reproduce sexually when they can reproduce asexually?

A

Only reproduce sexually in response to environmental cues —> as last resort because of bad conditions

31
Q

Why is sexual reproduction less efficient?

A
  1. Only half of the individuals of a population can directly produce offsprings
  2. Use time and energy to find mate
32
Q

What are the advantages to sexual reproduction?

A

Environment is always changing to need Genetic variation for survival

  • Fuel for evolution
    1. Asexual reproduction: genetically identical population with identical traits —> all may die if change in environment
    2. Sexual reproduction: genetically different population with variation in traits —> some may survive because of advantageous traits
33
Q

What is one important change to the environment that alters selection pressures on organisms?

A

Evolution of parasites

General Biology I (19 decks)

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