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Chapter 13 Objectives
1. Explain why organisms only reproduce their own kind, and why offspring more
closely resemble their parents than unrelated individuals of the same species.
Organisms are asexual, which means they can reproduce without the help of another
organism. Therefore, when they reproduce their offspring would look exactly like them.
While the rest of the species is able to sexually reproduce, which means that it take two to
make an offspring. By doing this each parent are donating 23 chromosomes making the
offspring a mixture of both the parents.
2. Distinguish between asexual and sexual reproduction.
I already know this
3. Diagram the human life cycle and indicate where in the human body that mitosis and
meiosis occur; which cells are the result of meiosis and mitosis; and which cells are
haploid.
4 Distinguish among the life cycle patterns of animals, fungi, and plants.
1. Human
a) Fertilization
(1)Sperm (1n) + Ovum (1n)
(2)1n = haploid
(3)Produces fertilized egg (2n)
b) Fertilized egg
1)Diploid (2n)
(2)Divides by mitosis to produce many cells
c) Adult female
(1)Diploid
(2)Ovaries produce eggs
(3)Eggs produced by meiosis
(4)Meiosis divides chromosome number in half
d) Adult male
(1)Diploid
(2)Testes produce sperm
(3)Sperm produced by meiosis
(4)Meiosis divides chromosome number in half
2. Animals
a) Figure 12.5 page 249
b) Gametes are the only haploid cells; all other cells diploid
c) Meiosis occurs during gamete production
d) Fertilization produces diploid zygote; zygote divides by mitosis; results in diploid
multicellular animal
3. Fungi
a)
b)
c)
d)
e)
Figure 12.5 page 249
Only diploid state is zygote
Meiosis occurs immediately after zygote forms
Haploid cells divide by mitosis resulting in haploid multicellular organism
Gametes produce by mitosis; haploid organism produces haploid gametes
4. Plants
a) Alternate between multicellular haploid and diploid generations
b) Alternation of generations
c) Multicellular diploid stage
(1)Called sporophyte
(2)Produces spores by meiosis
(3)Spores are haploid
d) Haploid spores divide by mitosis resulting in multicellular haploid stage
e) Multicellular haploid stage
(1)Called gametophyte
(2)Produces gametes by mitosis
f) Fertilization produces diploid zygote
5. List the phases of meiosis I and meiosis II and describe the events characteristic of
each phase.
1. Interphase I
a) Precedes meiosis
b) Chromosomes replicate
c) Each duplicate chromosome consists of 2 identical chromatids attached at
centromere
d) In animal cells, centrioles pairs duplicate
2. Meiosis I
a) Prophase I
(1)Chromosomes condense and attach at their ends to nuclear envelope
(2)Synapsis occurs
(a)Homologous chromosomes come together in pairs
(b)Homologous chromosomes – pair of chromosomes of
(i) Same size
(ii) Same centromere position
(iii) Same staining pattern
(iv) Same gene loci (except sex chromosomes)
(3)Chromosomes condense further; appear as tetrad
(a)Appear as tetrad
(b)Tetrad
(i) 4 chromatids
(ii) 2 pr. of homologous chromosomes
(c) In tetrad
(i) Sister chromatids attached by centromeres
(ii) Nonsister chromatids linked by X-shaped chiasmata
(iii) Chiasma
(a)Site of crossing over
(b)Site where homologous strand exchange occurs
(4)Cell prepares for nuclear division
(a)Centriole pairs move apart
(b)Spindle microtubules form
(c) Nuclear envelope and nucleoli disperse
(d)Chromosomes begin moving to metaphase plate
(5)Prophase I consumes more than 90% of time required for meiosis
b) Metaphase I
(1)Tetrads line up on metaphase plate
(2)Centromeres of homologous chromosomes point to opposite poles
(3)Each homologue attached to kinetochore microtubules
c) Anaphase I
(1)Homologues split & move toward opposite poles
(2)Sister chromatids remain attached at centromeres; move as unit
d) Telophase I & cytokinesis
(1)Homologous chromosomes reach poles
(2)Each pole has haploid set of chromosomes
(3)Chromosomes
(a)Consists of two sister chromatids
(b)Chromatids still attached by centromere
(4)Cytokinesis occurs simultaneously with telophase I
(a)Cleavage furrow in animals
(b)Cell plate in plants
(c) Produces 2 haploid cells
e) Interkinesis
(1)May occur before meiosis II
(2)Nuclear membrane & nucleoli reform
(3)No DNA replication occurs
3. Meiosis II
a) Prophase II
(1)Nuclear envelope & nucleoli disperse
(2)Spindle forms
(3)Chromosomes move toward metaphase plate
b) Metaphase II
(1)Chromosomes align along metaphase plate
(2)Kinetochores of sister chromatids point toward opposite poles
c) Anaphase II
(1)Centromeres of sister chromatids separate
(2)Sister chromatids (now called chromosomes) move toward opposite poles
d) Telophase II and cytokinesis
(1)Nuclear envelopes form at each pole
(2)Cytokinesis
(3)4 haploid cells formed
6. Recognize the phases of meiosis from diagrams or micrographs.
I already know this
7. Describe the process of synapsis during prophase I, and explain how genetic
recombination occurs.
Synapsis occurs in prophase I.
(a)Homologous chromosomes come together in pairs
(b)Homologous chromosomes – pair of chromosomes of
(i) Same size
(ii) Same centromere position
(iii) Same staining pattern
(iv) Same gene loci (except sex chromosomes)
8. Describe key differences between mitosis and meiosis; explain how the end result of
meiosis differs from that of mitosis.
1. Meiosis
a) Reduction division
(1)2n to 1n
(2)Diploid to haploid
b) Creates genetic variation
(1)Gametes carry half of chromosomes
(2)When egg & sperm fuse, new genetic combination produced
c) Two divisions
d) Synapsis occurs; tetrads produced
e) Homologous pairs (tetrads) align on metaphase plate
f) Metaphase I
(1)Separates homologous chromosomes
(2)Sister chromatids pulled toward same pole
g) Metaphase II – separates sister chromatids
2. Mitosis
a) Maintains chromosome number
(1)2n to 2n
(2)Diploid to diploid
b) Daughter cells clones of mother cells
c) One division
d) No synapsis; no tetrads
e) Individual chromosomes align on metaphase plate
f) Metaphase separates sister chromatids
9. Explain how independent assortment, crossing over, and random fertilization
contribute to genetic variation in sexually reproducing organisms.
1. Independent assortment of chromosomes
a) In each cell
(1)50% of chromosomes came from mother
(2)50% of chromosomes came from father
b) Homologous chromosomes
(1)1 set (2 chromatids) came from mother
(2)1 set (2 chromatids) came from father
c) During synapsis – orientation of homologues is random
d) 50-50 chance that daughter cell of meiosis I will get maternal set & 50-50 chance that
daughter cell of meiosis I will get paternal
e) Each homologous pair of chromosomes orients & separates independently of other
homologous chromosomes
f) Gamete contains 1 possible combination of maternal/paternal chromosomes
g) Independent assortment
(1)Random distribution of maternal & paternal homologues to gametes
(2)Assortment refers to random distribution of genes located on different
chromosomes
(3)Possible combinations = 2n
(a) n = haploid number
(b) 223 (about 8 million) combinations
(c) Each human gamete contains 1 of 8 million possible assortments of
chromosomes
(4)Genetic variation results from reshuffling of chromosomes during gamete
production
2.
a)
b)
c)
Crossing over
Exchange of genetic material between homologues
Pieces of homologues exchange place
Occurs
(1)During prophase I
(2)During synapsis
(3)Formation of X-shaped chiasmata
d) Produces chromosomes with genes from both parents
e) In humans, average of 2 or 3 crossovers per chromosome pair
f) Synapsis
(1)Precise
(2)Homologues align gene by gene
(3)Mechanism unknown – involves formation of synaptonemal complex (protein
structure that brings chromosomes into close association)
3.
a)
b)
c)
Random fertilization
Egg 1 of 8 million different possibilities
Sperm 1 of 8 million different possibilities
Zygote
(1)1 of 64 trillion different possible combinations
(2)(8x106) x (8x106) = 64x1012
Chapter 14 Objectives
1. State, in your own words, Mendel's law of segregation.
Two alleles for a character are packaged into separate gametes.
2. Use a Punnett square to predict the results of a monohybrid cross and state the
phenotypic and genotypic ratios of the F2 generation.
I already know this.
3. Distinguish between genotype and phenotype; heterozygous and homozygous;
dominant and recessive.
I already know this.
4. Explain how a testcross can be used to determine if a dominant phenotype is
homozygous or heterozygous.
I already know this.
5. Define random event, and explain why it is significant that allele segregation during
meiosis and fusion of gametes at fertilization are random events.
6. State, in your own words, Mendel's law of independent assortment.
Each allele pair segregates independently of other gene pairs during gamete formation.
7. Use a Punnett square to predict the results of a dihybrid cross and state the phenotypic
and genotypic ratios of the F2 generation.
I already know this.
8. Give an example of incomplete dominance and explain why it is not evidence for the
blending theory of inheritance.
a) 1 allele not completely dominant over other
b) heterozygote intermediate between homozygous dominant and homozygous recessive
c) Example – Snapdragons
(1) Red x white  pink
(2) RR x rr  Rr
d) Blending theory
(1)Traits in offspring are a blending of those from parents
(2)Red x red  pink
(3)Pink x pink  pink
(4)Pink x white  lighter pink
(5)Pink x light pink  medium pink
e) Reality
(1)Red x red  pink
(2)Pink x pink  1 red to 2 pink to 1 white
(3)Red allele (R) not lost, shows up in next generation
(4)Alleles maintain integrity
9. Explain how the phenotypic expression of the heterozygote is affected by complete
dominance, incomplete dominance and codominance.
10. Describe the inheritance of the ABO blood system and explain why the IA and IB
alleles are said to be codominant.
11. Define and give examples of pleiotropy.
1. Definition – ability of a single gene to have multiple phenotypic effects
2. Example – sickle-cell anemia
3. One gene can also influence a combination of seemingly unrelated characteristics
a) In tigers and Siamese cats
b) Gene that controls fur pigmentation influences connections between cat’s eyes
and brain.
c) Defective gene causes both pigmentation and cross-eyed condition
12. Explain, in your own words, what is meant by "one gene is epistatic to another."
a) Interaction of several genes that control phenotypic expression of single trait
b) Gene at one locus alters phenotypic expression of a second gene
13. Describe how environmental conditions can influence the phenotypic expression of a
character.
14. Given a simple family pedigree, deduce the genotypes for some of the family
members.
I already know this (think of song).
Chapter 15 Objectives
1. Define linkage and explain why linkage interferes with independent assortment.
1. Linkage
a) Linked genes
b) Genes located on same chromosome
c) Tend to be inherited together
d) Do not assort independently
e) F2 phenotypic ratio of dihybrid cross not 9:3:3:1
2.
a)
b)
c)
Genetic recombination
Production of offspring with new combination of traits
Different from combination in parents
Results from events in meiosis & random fertilization
2. Explain how crossing over can unlink genes.
If crossing over occurs randomly then probability of crossing over directly proportional
to distance between genes
3. Describe sex determination in humans.
The 23rd pair of chromosome determines the sex of the offspring. The father usually
determines the sex of the baby. The mother is X X while the father is X Y, because of
this the mother will always give the X and the father can only give the Y. This is why the
father determines the sex of the offspring.
4. Describe the inheritance of a sex-linked gene such as color-blindness.
Sex-linked disorders in humans usually refers to X linked. X is always larger then the Y,
because of this more X-linked genes have no homologous loci on U.
5. Explain why a recessive sex-linked gene is always expressed in human males.
The X is larger then the Y.
6. Distinguish among nondisjunction, aneuploidy, and polyploidy; explain how these
major chromosomal changes occur and describe the consequences.
1. Nondisjunction
a) Meiotic or mitotic accident
b) Homologous chromosomes or sister chromatids fail to separate
c) In meiosis
(1)1 gamete has 2 of same type of chromosome
(2)1 gamete missing chromosome
2. Aneuploidy
a) Condition of having abnormal number of certain chromosomes
b) May result if normal gamete fuses with 1 produced from nondisjunction
c) Example
(1)Trisomy 21
(2)2 copies of chromosome 21
3.
a)
b)
c)
d)
e)
(3)Down’s syndrome
Polyploidy
More than 2 complete sets of chromosomes
Triploidy
(1)3n
(2)Abnormal diploid egg fuses with normal sperm
Tetraploidy
(1)4n
(2)Diploid zygote undergoes mitosis with out cytokinesis
Common in plants – important in plant evolution
Rarely occurs in animals
7. Distinguish among deletions, duplications, translocations, and inversions.
(1)Deletion – piece of chromosome lost
(2)Duplication – lost piece joins homologous chromosome
(3)Translocation – if lost piece joins nonhomologous chromosome
(4)Inversion – if lost piece reattaches to original chromosome but in reverse order