Chapter 13
Vocabulary
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heredity
variation
gene
gamete
somatic cell
asexual vs sexual
reproduction
autosomes
sex chromosomes
allele
dominant vs recessive
diploid vs haploid
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parental generation
filial generation
heterozygous
homozygous
phenotype
genotype
sex-linked gene
Locus
Trait
true-breeding
hybrid
 Where does genetic diversity come from?
 original source is mutations (mistakes in DNA)
that result in different alleles
 sexual reproduction causes reshuffling of the
alleles to produce a population with a unique
combination of traits
Chromosome Anatomy Revisited
 Humans = 46 chromosomes
(23 pairs)
 for analysis, chromosomes
organized into karyotypes
 homologous chromosomes
(pairs), each contain genes
controlling the same
inherited characteristics
 one chromosome is
inherited from each parent
(dominant allele is
expressed--usually)
Meiosis
 cell division in sperm and egg cells (produces haploid
cells)
 In humans, 23 chromosomes
 two cells unite during fertilization to produce diploid
cell (zygote)
 In humans, 46 chromosomes
 goal to ensure genetic diversity in sexually
reproducing organisms
(figure 13.8)
 Meiosis I (separates
homologous
chromosomes)
 crossing over occurs
during prophase I
 otherwise identical steps
to mitosis (non-identical
haploid cells produced)
 Meiosis II (separates
sister chromatids)
 identical steps to mitosis
(produces non-identical
haploid cells)
Gametogenesis
 Production of gametes (sperm/egg cells)
 Within the testes/ovaries precursor cells
(spermatocytes and oocytes) exist in the diploid form
 These precursor cells then go through meiosis to form
haploid sperm/egg cells which are used in sexual
reproduction to produce offspring
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Spermatogenesis
Oogenesis
Meiosis…again.
 Reduction Division (creates haploid cells)
 Meiosis I
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Two HAPLOID cells produced
Chromosomes have crossed over
 Meiosis II
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Four HAPLOID cells produced
Genetically unique cells
 Ensures genetic diversity of a species through…
 Independent assortment of homologous chromosomes
 Crossing over of homologous chromosomes
Independent
Assortment
 During Meiosis I, maternal and
paternal chromosomes align
randomly on metaphase plate
(daughter cell has 50/50 chance
of getting either)
 each pair of chromosomes is
sorted independently from one
another (daughter cells will have
various combinations of
chromosomes from mom/dad)
 In humans there are over 8
million different combinations
with 23 chromosomes from two
parents (223)
Crossing Over
 occurs during prophase I
 two non-sister chromatids (tetrad) trade alleles thus combining genetic
information from two parents
 Chiasma: site of crossing over
 results in genetic recombination (offspring with different
combination of traits than parents)
 Coupled with independent assortment, this results in over 23 trillion
different combinations from both parents
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You are 1 in 23 trillion!
 recombinant chromosomes: individual chromosomes that carry
genes derived from two different parents
 1-3 cross-over events per pair of chromosomes at most
 Mr. Knuffke Meiosis Prezi Link
 Awesome meiosis square dancing video!
https://prezi.com/el-sh-qgrgsj/ap-bio-information-7meiosis/
Mitosis vs. Meiosis
 (figure 13.9)