Quiz 4 Flashcards
1
Q
genetics
A
scientific study of heredity and variation
2
Q
heredity
A
transmission of traits from one generation to the next
3
Q
variation
A
differences in appearance of offspring from parents and siblings
4
Q
how are traits inherited?
A
through genes, specific sites on chromosomes
- physical characteristics (like big muscles) not inherited
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)
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!
7
Q
clone
A
group of genetically identical individuals from the same parent (created via mitosis)
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
9
Q
exceptions to rules of asexual/sexual reproduction
A
some protists reproduce “sexually” without sperm/egg gametes
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
11
Q
karyotype
A
ordered display of pairs of chromosomes from a cell
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)
13
Q
autosomes
A
remaining 22 pairs of chromosomes in humans
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
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
16
Q
how do organisms maintain chromosome number?
A
fertilization and meiosis alternate in organisms with sexual life cycles
- 3 main types
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
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
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
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
21
Q
which types of cells can undergo mitosis/meiosis?
A
- all cells can divide by mitosis
- only diploid cells can divide by meiosis
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
tetrad
pair of homologous chromosomes (4 chromatids) with chiasmata, x-shaped regions where crossing over occurred
26
metaphase I
- 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
anaphase I
- 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
telophase I and cytokinesis
- 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
prophase II
- spindle apparatus forms
| - chromosomes move towards metaphase plate
30
metaphase II
- 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
anaphase II
- sister chromatids separate, move as newly individual chromosomes toward opposite poles
32
telophase II and cytokineiss
- 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
main differences in mitosis vs meiosis
Mitosis: conserves # of chromosome sets, produces genetically identical cells
Meiosis: reduces # of chromosome sets, producing cells that differ genetically
34
roles of mitosis and meiosis in organisms
Mitosis: asexual reproduction, development from zygote, growth, repair
Meiosis: reduces # of chromosomes, increases genetic variability
35
3 events unique to meiosis
- 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
importance of mutations for genetic variation
- 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
3 mechanisms contributing to genetic variation
- independent assortment of chromosomes
- crossing over
- random fertilization
38
independent assortment of chromosomes
- homologous chromosomes orient randomly during metaphase I
- each pair of chromosomes sorts into daughter cells independently
- 2^n combinations possible
39
what does crossing over produce?
produces recombinant chromosomes, combining DNA inherited from each parent
40
random fertilization
- any sperm can fuse with any ovum (unfertilized egg)
| - natural selection results in accumulation of genetic variation favored by the environment
41
2 theories for passing of traits
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
advantages of Mendel's quantitative approach with pea plants
- 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
characteristic vs trait
characteristics are recognizable features on organisms (e.g. flower color) whereas traits are variants of characteristics (e.g. purple or white flower)
44
Mendel's general methodology
* ***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
results of Mendel's crosses
- all F1 hybrids purple
| - many F2 were purple, but some were white (3:1 ratio)
46
Mendel's general learnings from the experiment
- 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
4 concepts of Mendel's Model
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
punnet squares and examples of genetic makeups
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
phenotype vs genotype
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
test crosses and their importance
***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
law of independent assortment
***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
monohybrid vs dihybrid
- 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
usefulness of dihybrid crosses
can be used to determine whether 2 characters are transmitted together (on the same chromosome) or independently
54
enzyme
