Download PPT NOTES_AP Biology Chapter 13 Notes

AP Biology Chapter 13 Notes
Meiosis
What you need to know:
 The differences between ___________________ and ____________________ reproduction
 The role of ___________________ and fertilization in sexually reproducing organisms
 The importance of ___________________________ chromosomes to meiosis
 How the chromosome number is reduced from ___________________ to ________________
through the stages of meiosis
 Three important differences between _____________ and __________________
 The importance of _____________________________, ____________________ assortment,
and _______________________ fertilization to increasing genetic variability.
13.1: Offspring acquire genes from parents by inheriting chromosomes
 ___________________ are the units of heredity, and are made up of segments of DNA
 Genes are passed to the next generation through reproductive cells called
______________________ (sperm and eggs)
 Each gene has a specific location called a __________________ on a certain chromosome
 Most DNA is packaged into ___________________
 One _________ of chromosomes is inherited from each __________
 Asexual vs Sexual Reproduction
o ___________________________ - one parent produces genetically identical offspring
by mitosis
 A ________________ is a group of genetically identical individuals from the same
parent
o ___________________________ - two parents give rise to offspring that have unique
combinations of genes inherited from the two parents
13.2: Fertilization and meiosis alternate in sexual life cycles
 Human _________________________ (any cell other than a gamete) have 23 pairs of
chromosomes
 ______________________ - an ordered display of the pairs (_______________________
chromosomes) of chromosomes from a cell
 __________ chromosomes are called X and Y
o Human females have a homologous pair of X chromosomes (______)
o Human males have one X and one Y chromosome (______)
o The 22 pairs of chromosomes that do not determine sex are called ________________
 A _______________ cell (2n) has two sets of chromosomes
 Each replicated chromosome consists of two identical ________________________
 Label the Picture

 ________________ (sperm or egg) contains a single set of chromosomes, and is
______________ (n)
o For humans, the haploid number is ______ (n = 23)
o Each set of 23 consists of 22 ________________ and a 1 ________ chromosome
o In an unfertilized egg (ovum), the sex chromosome is ____
o In a sperm cell, the sex chromosome may be either ____ or ____
o Gametes are the only types of human cells produced by _____________, rather than
mitosis
Alternation of Generations
 ______________ and some _______________ exhibit an alternation of generations
o This life cycle includes both a _____________ and ________________ multicellular
stage
o The diploid organism, called the ______________________, makes haploid spores by
meiosis
o Each spore grows by ________________ into a haploid organism called a
_______________
o A gametophyte makes haploid gametes by ______________
o Fertilization of gametes results in a diploid ______________________
 Label the picture



_______________ and some _________________, the only diploid stage is the single-celled zygote; there is no
multicellular diploid stage
o The zygote produces _____________________ cells by meiosis
o Each haploid cell grows by ______________________ into a haploid multicellular organism
o The haploid adult produces gametes by ____________________
Label the Picture

13.3: Meiosis reduces the number of chromosome sets from diploid to haploid
 Meiosis takes place in two sets of cell divisions, called ___________________ and _________________
 The two cell divisions result in __________ daughter cells, rather than the two daughter cells in mitosis
 Each daughter cell has only _____________ as many chromosomes as the parent cell
 Meiosis I
o Prophase I
 Prophase I typically occupies more than 90% of the time required for meiosis
 Chromosomes begin to _____________
 In synapsis, homologous chromosomes loosely _________ up, aligned gene by gene
 In ___________________, nonsister chromatids exchange DNA segments
 Each pair of chromosomes forms a tetrad, a group of __________ chromatids
 Each tetrad usually has one or more _______________________, X-shaped regions where
crossing over occurred
o Metaphase I
 _______________ line up at the metaphase plate, with one chromosome facing each pole
 Microtubules from one pole are attached to the __________________ of one chromosome of
each tetrad
 _______________________ from the other pole are attached to the kinetochore of the other
chromosome
o Anaphase I
 Pairs of homologous chromosomes __________________
 One chromosome moves toward each pole, guided by the __________________ apparatus
 _______________________________ remain attached at the centromere and move as one unit
toward the pole
o Telophase I and Cytokinesis
 In the beginning , each half of the cell has a ____________________ set of chromosomes; each
chromosome still consists of ___________ sister chromatids
 ______________________ usually occurs simultaneously, forming two haploid daughter cells
 Meiosis II
o Prophase II



__________________ apparatus forms
In late prophase II, ____________________ (each still composed of two chromatids) move
toward the metaphase plate
o Metaphase II
 _________________________________ are arranged at the metaphase plate
 Because of crossing over in meiosis I, the two sister chromatids of each chromosome are no
longer genetically ___________________
 _____________________________ of sister chromatids attach to microtubules extending from
opposite poles
o Anaphase II
 The sister chromatids _______________
 The sister chromatids of each chromosome now move as two newly individual chromosomes
toward opposite poles
o Telophase II and Cytokinesis
 chromosomes arrive at ______________________ poles
 _______________ form, and the chromosomes begin decondensing
Mitosis vs Meiosis
o Mitosis
 conserves the number of chromosome sets, producing cells that are genetically
____________________ to the parent cell
o Meiosis
 reduces the number of chromosomes sets from two (__________________) to one
(____________________), producing cells that ______________ genetically from each other
and from the parent cell
o The mechanism for separating sister chromatids is virtually _______________ in meiosis II and mitosis
13.4: Genetic variation produced in sexual life cycles contributes to evolution
 _______________________ (changes in an organism’s DNA) are the original source of genetic diversity
o Mutations create different versions of genes called alleles
o _____________________ of alleles during sexual reproduction produces genetic variation
 Three mechanisms contribute to genetic variation:
o ___________________________________________ of chromosomes
 (Next couple Slides) _____________________ pairs of chromosomes orient randomly at
metaphase I of meiosis
 Each pair of chromosomes sorts maternal and paternal homologues into daughter cells
__________________________________ of the other pairs
o ___________________________________________
 (Next Couple Slides) Produces _____________________________ chromosomes, which
combine genes inherited from each parent
 Crossing over begins very early in ___________________ I, as homologous chromosomes pair
up gene by gene
 In crossing over, homologous ___________________ of two nonsister chromatids trade places
 Crossing over contributes to genetic variation by _______________________ DNA from two
parents into a single chromosome

o ___________________________________________
 (Next Couple Slides) adds to genetic variation because any ________________ can fuse with
any _________________ (unfertilized egg)