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BIOL 102 > Chapter 13 > Flashcards

Chapter 13 Flashcards

1
Q

What is heredity?

A

the transmission of traits from one generation to the next

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2
Q

What is variation?

A

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

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3
Q

What is genetics?

A

the scientific study of heredity and variation

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3
Q

What is sexual reproduction?

A

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

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3
Q

What is asexual reproduction?

A

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

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4
Q

What is a clone?

A

a group of genetically identical individuals from the same parent

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5
Q

What are genes?

A

units of heredity, made up of DNA segments

  • each gene has a specific location (=locus) on a certain chromosome
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6
Q

What is a locus?

A

specific location of a gene on a specific chromosome

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7
Q

how are genes passed on?

A

chromosomes are passed to the next generation via gametes (reproductive cells)

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8
Q

What is a genome?

A

all the DNA in a cell

  • genome can consist of one DNA molecule (prokaryotes) or several molecules
  • DNA molecules in a cell are packaged into chromosomes
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9
Q

What is chromatin?

A

a complex of DNA and protein that condenses during cell division
- in eukaryotic chromosomes

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10
Q

What are somatic cells and gametes?

A
  • somatic cells = nonreproductive cells, have two sets of chromosomes
  • gametes = reproductive cells, have half as many chromosomes (one set)
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11
Q

What are sister chromatids?

A

each duplicated chromosome has two sister chromatids (= joined copies of the original chromosome)

  • separate during cell division
  • once separated, the chromatids are called chromosomes
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12
Q

What is a centromere?

A

narrow waist of the duplicated chromosome, where the two chromatids are most closely attached

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13
Q

what are homologous chromosomes?

A

two chromosomes in each pair

  • chromosomes have the same length and shape, they carry genes controlling the same inherited characters
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14
Q

What is a karyotype?

A

an ordered display of the pairs of chromosomes from a cell

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15
Q

What are the differences in the 23 pairs of chromosomes in a human somatic cell?

A
  • 22 pairs of autosomes
  • 1 pair of sex chromosomes

each pair of homologous chromosomes includes one chromosome from each parent

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16
Q

diploid cell

A

(2n)
two sets of chromosomes
humans: (2n = 46)

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17
Q

What is a life cycle?

A

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

  • from its conception to the production of its own offspring
  • the alternation of meiosis and fertilization is common to all organisms that reproduce sexually
18
Q

What is fertilization?

A

the union of gametes

  • the fertilised egg is called zygote -> has one set of 23 chromosomes from each parent
19
Q

What are germ cells?

A

they are the cells that the gametes come from

20
Q

How is the chromosome number maintained?

A

by the alternation of fertilization and meiosis in sexual life cycles

21
Q

sexual life cycles in animals

A
  • gametes are the only haploid cells
  • gametes are produced by meiosis and undergo no further cell division before fertilization
  • gametes fuse to form a diploid zygote that divides by mitosis to develop into a multicellular organism
22
Q

sexual life cycles in plants (and some algae)

A
  • they exhibit an alternation of generations
  • includes both a diploid and haploid multicellular stage
  • the diploid (= sporophyte) makes haploid spores by meiosis
  • each spore grows by mitosis into a haploid organism (=gametophyte)
  • gametophyte makes haploid gametes by mitosis
  • fertilization of gametes results in a diploid sporophyte
23
Q

sexual life cycles of fungi

A
  • no multicellular diploid stage
  • single-celled zygote produces haploid cells by meiosis
  • each haploid cell grows by mitosis into a haploid multicellular organism
  • the haploid adult produces gametes by mitosis
  • only the diploid cells can undergo meiosis
24
Q

What are the stages of meiosis?

A

-chromosomes duplicate
- meiosis I
- meiosis II

-> 4 haploid daughter cells with unreplicated chromosomes

25
Q

meiosis I

A
  • homologous chromosomes separate
  • results in two haploid daughter cells with replicated chromosomes
  • reductional division (reduces the number of chromosomes from diploid to haploid )
26
Q

meiosis II

A
  • sister chromatids separate
  • results in 4 haploid daughter cells with unreplicated chromosomes
  • equational division
  • similar to mitosis
27
Q

Prophase I

A
  • typically occupies more than 90% of the time required for meiosis
  • chromosomes begin to condense
  • Synapsis = homologous chromosomes loosely pair up, aligned gene by gene
  • crossing over = nonsister chromatids exchange DNA segments
  • each pair of chromosomes forms a tetrad, a group of four chromatids
  • each tetrad usually has one or more chiasmata, X-shaped regions where crossing over occurred
28
Q

Metaphase I

A
  • tetrads line up 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
  • microtubules from the other pole are attached to the kinetochore of the other chromosome
29
Q

Anaphase I

A
  • pairs of homologous chromosomes separate
  • one chromosome moves toward each pole, guided by the spindle apparatus
  • sister chromatids remain attached at the centromere and move as one unit toward the pole
30
Q

Telophase I and Cytokinesis

A
  • in the beginning, each half of the cell has a haploid set of chromosomes, each chromosome still consists of two sister chromatids
  • cytokinesis usually occurs simultaneously, forming two haploid daughter cells
    – animals: cleavage furrow
    – plant cell: cell plate

-> no chromosome replication between end of meiosis I and beginning of meiosis II (because the chromosomes are already replicated )

31
Q

Prophase II

A
  • spindle apparatus forms
  • chromosomes move toward the metaphase plate
32
Q

Metaphase II

A
  • sister chromatids are arranged at the metaphase plate
  • because of crossing over in meiosis I, the two sister chromatids of each chromosome are not genetically identical
  • kinetochores of sister chromatids attach to microtubules extending from opposite poles
33
Q

Anaphase II

A
  • sister chromatids separate
  • the sister chromatids of each chromosome move as two newly individual chromosomes toward opposite poles
34
Q

Telophase II and cytokinesis

A
  • the chromosomes arrive at opposite poles
  • nuclei form, and the chromosomes begin decondensing
  • cytokinesis separated the cytoplasm
35
Q

What are the main differences between mitosis and meiosis?

A
  • mitosis conserves the number of chromosome sets, producing cells that are genetically identical to the parent cell
  • meiosis reduces the number of chromosome sets from diploid to haploid, producing cells that differ genetically from each other and from the parent cell
36
Q

What events are unique to meiosis?

A

all these events in meiosis I:

  • synapsis and crossing over ( homologs physically connect and exchange genetic info)
  • at metaphase plate, there are paired homologs (tetrads) instead of individual replicated chromosomes
  • in anaphase I, it is homologs instead of sister chromatids that separate
37
Q

How can sister chromatids stay together through meiosis I?

A

through sister chromatid cohesion

due to cohesins

38
Q

What are cohesins?

A

protein complexes responsible for sister chromatid cohesion

  • are cleaved at the end of metaphase in mitosis
  • are cleaved along chromosome arms in anaphase I and at the centrometers in anaphase II in meiosis
39
Q

What are the origins of genetic variations?

A
  • mutations
  • reshuffling of alleles
  • most variation due to behaviour of chromosomes during meiosis and fertilization

-> independent assortment of chromosomes
-> crossing over
-> random fertilization

40
Q

Independent Assortment of Chromosomes

A
  • homologous pairs of chromosomes orient randomly at metaphase I
  • each pair of chromosome sorts maternal and paternal homologs into daughter cells independently of the other pairs
  • number of possible combinations: 2^n (n= haploid number)

-> humans: 2^23 = over 8 million possible combinations

41
Q

Crossing over:

A
  • produces recombinant chromosomes, which combine DNA inherited from each parent
  • begins in early prophase I
  • homologous portions of two sister chromatids trade places
  • by combining DNA from two parents into a single chromosome, crossing over contributes to genetic variation
  • about 1-3 crossover events per chromosome pair (depends on size of chromosome and position of centromere)
42
Q

Random fertilization

A
  • adds to genetic variation because any sperm can fuse with any ovum
  • the fusion of two gametes (with 8.4 mio possible combinations) produces a zygote with any of about 70 trillion diploid combinations
  • each zygote has a unique genetic identity
43
Q
A

BIOL 102 (3 decks)

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