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BIO 102 > Quiz 4 > Flashcards

Quiz 4 Flashcards

1
Q

genetics

A

scientific study of heredity and variation

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2
Q

heredity

A

transmission of traits from one generation to the next

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3
Q

variation

A

differences in appearance of offspring from parents and siblings

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4
Q

how are traits inherited?

A

through genes, specific sites on chromosomes

- physical characteristics (like big muscles) not inherited

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5
Q

what are genes and how are they passed on

A

units of heredity; made up of segments of DNA packaged into chromosomes

  • each has a specific location on a chromosome (locus)
  • passed on to the next generation via reproductive cells called gametes (sperm and egg)
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6
Q

asexual reproduction and its benefits

A

mitosis - single individual passes genes to offspring without fusion of gametes
*good in times of environmental uncertainty!

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7
Q

clone

A

group of genetically identical individuals from the same parent (created via mitosis)

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8
Q

sexual reproduction

A

meiosis - two parents give rise to offspring with unique combinations of genes (from both parents) through the fusion of gametes

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9
Q

exceptions to rules of asexual/sexual reproduction

A

some protists reproduce “sexually” without sperm/egg gametes

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10
Q

homologous chromosomes and how many do humans have

A

the 2 chromosomes in each pair; one from mother and one from father

  • same length/shape and carry genes controlling the same inherited characteristics
  • humans have 23 pairs of chromosomes; females have 23 homologous pairs and males have 22 homologous pairs
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11
Q

karyotype

A

ordered display of pairs of chromosomes from a cell

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12
Q

sex chromosomes

A

determine biological sex of an individual

  • females are homologous (XX)
  • males are XY (Y is shorter, may have broken off ancestral X)
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13
Q

autosomes

A

remaining 22 pairs of chromosomes in humans

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14
Q

what happens to homologous chromosomes during DNA replication?

A

each chromosome is replicated and each replicated chromosome makes 2 identical sister chromatids

*4 chromatids for a homologous pair

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15
Q

what are haploid cells and where are they produced in humans

A

haploid cells: single set of chromosomes

  • gametes (sperm or egg) are human haploid cells (haploid number: 23)
  • gametes produced by cells in gonads (testes and ovaries) that undergo meiosis
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16
Q

how do organisms maintain chromosome number?

A

fertilization and meiosis alternate in organisms with sexual life cycles
- 3 main types

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17
Q

life cycle

A

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

  • in organisms with sexual life cycles, fertilization and meiosis alternate to maintain chromosome #
  • 3 main methods of alternation
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18
Q

life cycles in animals

A
  • gametes are only haploid cells; undergo no further division before fertilization
  • gametes fuse during fertilization to become a diploid zygote
  • zygote divides by mitosis to form a multicellular organism
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19
Q

life cycles in plants/some algae

A

includes both diploid and haploid multicellular stage!

  • diploid sporophyte makes haploid spores by meiosis
  • spores grow by mitosis to form a haploid gametophyte
  • gametophyte makes haploid gametes by mitosis
  • fertilization of 2 gametes results in a diploid sporophyte
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20
Q

life cycles in fungi/some protists

A
  • only diploid stage is the single-celled zygote
  • zygote produces haploid cells by meiosis
  • haploid cells grow by mitosis to form multicellular organisms
  • haploid adults produce gametes by mitosis that fuse to create diploid zygotes
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21
Q

which types of cells can undergo mitosis/meiosis?

A
  • all cells can divide by mitosis

- only diploid cells can divide by meiosis

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22
Q

significance of fertilization and meiosis in all 3 life cycles

A
  • contributes to genetic variation in offspring

- maintain chromosomes number

23
Q

divisions and result of meiosis (overview)

A
  • 2 sets of cell divisions result in 4 daughter cells with 1/2 as many chromosomes as the parent
  • meiosis I (reductional division): homologs form a tetrad and separate; results in 2 haploid daughter cells with replicated chromosomes attached at centromere
  • meiosis II (equational division): sister chromatids separate; results in 4 haploid daughter cells with unreplicated chromosomes
24
Q

prophase I

A
  • typically >90% of meiosis time; chromosomes condense
  • synapsis: homologous chromosomes loosely pair up, align gene by gene to form a tetrad
  • crossing over: nonsister chromatids exchange DNA segments
25
Q

tetrad

A

pair of homologous chromosomes (4 chromatids) with chiasmata, x-shaped regions where crossing over occurred

26
Q

metaphase I

A
  • tetrads line up at metaphase plate with 1 chromosome facing each pole
  • microtubules from 1 pole attach to kinetochore of 1 chromosome of tetrad; microtubules from other pole attach to kinetochore of other chromosome
27
Q

anaphase I

A
  • pairs of homologous chromosomes separate
  • one chromosome moves towards each pole, guided by spindle apparatus
  • sister chromatids remain attached at the centromere and move as one unit towards pole
28
Q

telophase I and cytokinesis

A
  • each cell half has a haploid set of chromosomes (each w/ 2 sister chromatids)
  • cytokinesis occurs simultaneously, forming 2 haploid daughter cells (cleavage furrow or cell plate)

***no chromosome replication occurs between end of meiosis I and beginning of meiosis II

29
Q

prophase II

A
  • spindle apparatus forms

- chromosomes move towards metaphase plate

30
Q

metaphase II

A
  • chromosomes at metaphase plate
  • **due to crossing over, sister chromatids no longer genetically identical
  • kinetochores of sister chromatids attach to microtubules from opposite poles
31
Q

anaphase II

A
  • sister chromatids separate, move as newly individual chromosomes toward opposite poles
32
Q

telophase II and cytokineiss

A
  • chromosomes arrive at opposite poles and decondense; nuclei form
  • cytokinesis separates cytoplasm
  • end result is 4 haploid daughter cells that are genetically distinct from each other and the parent
33
Q

main differences in mitosis vs meiosis

A

Mitosis: conserves # of chromosome sets, produces genetically identical cells

Meiosis: reduces # of chromosome sets, producing cells that differ genetically

34
Q

roles of mitosis and meiosis in organisms

A

Mitosis: asexual reproduction, development from zygote, growth, repair

Meiosis: reduces # of chromosomes, increases genetic variability

35
Q

3 events unique to meiosis

A
  • synapsis (chromosomes connect and exchange genetic info)
  • tetrads line up at metaphase plate (paired homologous chromosomes instead of individual replicated chromosomes)
  • homologous chromosomes separate instead of sister chromatids
36
Q

importance of mutations for genetic variation

A
  • original source of genetic diversity (even asexual), change in organism’s DNA
  • create different versions of genes at the same locus called alleles
  • reshuffling of alleles during crossing over produces variation
37
Q

3 mechanisms contributing to genetic variation

A
  • independent assortment of chromosomes
  • crossing over
  • random fertilization
38
Q

independent assortment of chromosomes

A
  • homologous chromosomes orient randomly during metaphase I
  • each pair of chromosomes sorts into daughter cells independently
  • 2^n combinations possible
39
Q

what does crossing over produce?

A

produces recombinant chromosomes, combining DNA inherited from each parent

40
Q

random fertilization

A
  • any sperm can fuse with any ovum (unfertilized egg)

- natural selection results in accumulation of genetic variation favored by the environment

41
Q

2 theories for passing of traits

A

blending hypothesis - genetic material from 2 parents “blends” together, like paint colors

particulate hypothesis - parents pass on “discrete heritable units” (what we now call genes); offspring inherit a unit from each parent

  • documented by Mendel
  • explains how genes can skip generations
42
Q

advantages of Mendel’s quantitative approach with pea plants

A
  • many varieties of pea with different traits of distinct heritable characteristics
  • mating can be controlled; each flower has sperm-producing stamens and egg-producing carpels
  • cross-pollination involves dusting one plant with pollen from another
  • he could track characteristics with only 2 distinct forms
43
Q

characteristic vs trait

A

characteristics are recognizable features on organisms (e.g. flower color) whereas traits are variants of characteristics (e.g. purple or white flower)

44
Q

Mendel’s general methodology

A
  • ***used true-breeding varieties (produce off spring of the same variety during self-pollination; a pure lineage)
  • **tracked only characteristics with 2 distinctive forms
  • mated 2 contrasting, true-breeding varieties (P generation) to produce a F1 generation
  • F1 generation either self- or cross-pollinated to produce a F2 generation
45
Q

results of Mendel’s crosses

A
  • all F1 hybrids purple

- many F2 were purple, but some were white (3:1 ratio)

46
Q

Mendel’s general learnings from the experiment

A
  • reasoned only purple factor affected F1 color, but the factor for white flowers must not have been destroyed since it reappeared in the F2 generation
  • called the purple color a dominant trait and the white color a recessive trait
  • same pattern of inheritance observed with 6 other characters
47
Q

4 concepts of Mendel’s Model

A
  1. alternative versions of genes (alleles) result in variations of characteristics
  2. organism inherits 2 alleles at a locus, one from each parent, which may be identical or differ
  3. if the 2 alleles differ, the dominant allele determines appearance and the recessive allele had no effect
  4. law of segregation: the 2 alleles of a single trait segregate during gamete formation and end up in either egg or sperm
    * **(corresponds to knowledge today about how chromosomes are sorted into gametes, but he didn’t know about chromosomes!!)
48
Q

punnet squares and examples of genetic makeups

A

diagrams for predicting results of a cross between individuals of a known genetic makeup

homozygous: 2 identical alleles at a locus
heterozygous: 2 different alleles at a locus (not true-breeding)

49
Q

phenotype vs genotype

A

because dominant and recessive alleles are expressed differently, an organism’s traits don’t always reveal genetic makeup

genotype: genetic makeup (which alleles)
phenotype: physical appearance (which traits expressed)

50
Q

test crosses and their importance

A

***allow us to tell if an individual with a dominant phenotype is homozygous or heterozygous!

test cross: mystery individual bred with homozygous recessive individual; if any offspring display recessive phenotype the mystery parent must be heterozygous

51
Q

law of independent assortment

A

***Mendel’s 2nd law of inheritance; relates to dihybrid crosses

  • each pair of alleles segregates independently of other pairs during gamete formation
  • only applies to genes on different, non-homologous chromosomes
  • genes located near each other on the same chromosome actually tend to be inherited together (less likely for only one to cross-over)
52
Q

monohybrid vs dihybrid

A
  • monohybrids produced by true-breeding parents that differed in a single character (F1 heterozygous for 1 character)
  • F2 is the result of a monohybrid cross
  • dihybrids produced by true-breeding parents differing in 2 characters (F1 heterozygous for 2 characters)
  • F2 is the result of a dihybrid cross
53
Q

usefulness of dihybrid crosses

A

can be used to determine whether 2 characters are transmitted together (on the same chromosome) or independently

54
Q

enzyme

A

BIO 102 (14 decks)

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