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BIOLOGY: Genetics (unit three) > Sexual Reproduction (lesson three) > Flashcards

Sexual Reproduction (lesson three) Flashcards

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1
Q

Sexual Reproduction

A

Sexual reproduction is a form of reproduction in which individuals are produced from the fusion of two sex cells

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2
Q

why are off-springs produced by sexual reproduction genetically unique?

A

because they obtain half of their genetic material from each of their two parents

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3
Q

disadvantages to reproducing sexually

A
  • Specialized organs are required to produce the sex cells
  • Specialized mating calls or bright colours to attract mates can also attract predators
  • May require the loss of resources, like nectar in flowers
  • The combining of genetic information may make the offspring weak and unable to survive
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4
Q

advantages to sexual reproduction

A
  • Individuals that rely on sexual reproduction can adapt to a changing environment, due to their genetic variability which is not possible in organisms that reproduce asexually
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5
Q

what are the two key processes involved with Sexual Reproduction?

A
  • The formation of haploid cells, or gametes, which contain genetic information from the parents
  • Two sex cells join to form a zygote, the first cell of a genetically unique individual, through fertilization
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6
Q

Meiosis

A
  • the process through which haploid gametes are formed
  • Meiosis is a process that involves two divisions that produce 4 haploid gametes from 1 diploid parent cell
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7
Q

the difference between meiosis and mitosis

A
  • In mitosis, the chromosome number in each generation stays the same
  • and in meiosis, the chromosome number is cut in half
  • For ex: sex cells produced in humans contain only 23 (haploid or n), not 46 (diploid or 2n), chromosomes
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8
Q

what happens in the combination of two gametes

A

The combination of two gametes (sperm and egg - both haploid) will result in a complete set of chromosomes (diploid, 2n = 46)

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9
Q

homologous chromosomes

A

You receive a complete set of DNA from each parent (one version of each gene) known as homologous chromosomes

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10
Q

what does homologous chromosomes ensure

A

ensures the offspring is genetically unique from each parent

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11
Q

gametogenesis

A

The formation of sex cells is called gametogenesis

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12
Q

what are the two types of gametogenesis in humans?

A
  • Formation of sperm by spermatogenesis
  • Formation of egg cells or ova by oogenesis
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13
Q

how are the two types of gametogenesis formed?

A

Both are produced through a process called meiosis

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14
Q

Interphase

A
  • Cell grows to nearly twice in size
  • Nucleus makes a copy of its DNA
  • Organelles are also replicated
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15
Q

Meiosis I: Prophase I

A
  • Chromatin condenses into chromosomes
  • The nuclear membrane dissolves
  • Centrioles move to opposite sides of the cell
  • Spindle fibres begin to grow
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16
Q

synapsis

A
  • Homologous chromosomes come together and intertwine to form a tetrad by a process called synapsis
  • Each chromosome is made of 2 sister chromatids, and you have 1 chromosome from each parents
  • These four sister chromatids together is called a tetrad
17
Q

what happens to Homologous chromosomes in prophase I

A

Homologous chromosomes come together and intertwine to form a tetrad by a process called synapsis

18
Q

explain crossing over which occurs during Meiosis I: Prophase I

A
  • This is when intertwined chromatids from different chromosomes break off and reattach at the chiasmata
  • This causes an exchange of genetic material in certain sections
  • This works to mix or recombine genetic information further increasing genetic variation in the gene pool
19
Q

Meiosis I: Metaphase I

A
  • During this phase, the tetrads migrate towards the center of the cell, called the equatorial plate
  • This is done through spindle fiber attachment at the centromeres like in mitosis
  • The tetrads align their centromeres at the middle of the cell
20
Q

Meiosis I: Anaphase I

A
  • Homologous chromosomes move to opposite poles of the cell when the spindle fibers shorten
  • This means that only one of the two chromosomes from each homologous pair will be in each new daughter cell and therefore are genetically unique
  • EX. Each of your sperm or egg has only the chromosome you received from your mom or your dad, not both!
21
Q

Meiosis I: Telophase I

A
  • The nuclear membranes reform, spindle fibers dissolve and the cell begins to divide via the first cycle of cytokinesis
  • Each new cell has only 1 (not two) duplicated copy of a chromosome at this point
  • Only the maternal or paternal chromosome is in each new cell
  • Therefore the cells are haploid
22
Q

Meiosis II: Prophase II

A
  • Each haploid cell has one chromosome made of two sister chromatids at this point
  • The sister chromatids are not genetically identical though, due to the crossing over that occurred during prophase I
  • Once again, the nuclear membrane dissolves, centrioles move to opposite poles and spindle fibers reform
23
Q

Meiosis II: Metaphase II

A
  • Again, the one chromosome made of two sister chromatids move to center of the cell, called the equatorial plate
  • This is accomplished through spindle fiber attachment at the centromeres like in mitosis
  • The chromosomes align their centromeres at the middle of the cell
24
Q

Meiosis II: Anaphase II

A
  • Sister chromatids now separate and move to opposite poles of the cell
  • Each cell now has a single sister chromatid, not a duplicate copy
  • These will not be identical due to the genetic exchange that occurred in crossing over
25
Q

Meiosis II: Telophase II

A
  • Just like in mitosis, the nuclear membrane reforms around the chromatids, the DNA relaxes into chromatin and the spindle fibers dissolve
  • The second nuclear division is now completed
  • Soon after, cytokinesis will occur for the second time
  • This will result in 4 haploid daughter cells (that are NOT identical)
26
Q

Genetic Variation

A
  • There are many parts of meiosis that allows for genetic variation through random assortment of chromosomes
  • In Prophase I, crossing over occurs randomly
  • In Metaphase I and II, it is random as to which side each chromosome goes to

BIOLOGY: Genetics (unit three) (11 decks)

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