Alberts • Bray • Hopkin • Johnson • Lewis • Raff • Roberts • Walter
Essential
Cell Biology
FOURTH EDITION
Chapter 19
Sexual Reproduction and the
Power of Genetics
Copyright © Garland Science 2014
Most multicellular organisms
reproduce sexually.
fertilization of egg by sperm
Fig. 19-4
After fertilization,
the diploid zygote
then undergoes
rounds of mitosis
to generate a new
multicellular
adult.
Fig. 19-5
Meiosis differs from mitosis in also having
a reductive division.
non-reductive
division
reductive
division
Fig. 19-6
non-reductive
division
Physical Basis of reductive division:
separation of chromosome homologues
Fig. 19-7
Paired chromosome
homologues after
duplication (one
from each parent)
Synaptonemal Complex
holds homologues together
Fig. 19-9
Cohesin holds sister
chromatids together
Physical Basis of reductive division:
separation of chromosome homologues
Fig. 19-8
Meiosis generates genetic diversity in two ways.
Law of
Independent
Assortment
Fig. 19-15
Recombination by strand invasion/copying mechanism
Fig. 19-10
Cohesin holds sister chromatids together
through Meiosis I.
Fig. 19-13
Cohesin cleavage allows sister
chromatid separation during Meiosis II.
Fig. 19-13
Failure to separate in Meiosis I (or II) generates
aneuploid gametes, like those responsible
for Down’s Syndrome.
Fig. 19-16
Mendel used pea plants to uncover the laws of genetics.
Fig. 19-20
He started with true-breeding plants.
They were
homozygous
for the genes
of interest.
These crosses revealed two
versions of genes (alleles);
some are dominant
and some are recessive.
Fig. 19-21
Law of Segregation
(alleles separate
during meiosis)
Crosses of F1
progeny showed
that recessive trait
is still present
in F1 progeny.
It reappeared in
F2 progeny.
Fig. 19-23
Alleles for two different genes can
segregate independently
Law of Independent
Assortment
(multiple chromosome
homologue pairs
segregate independently)
Fig. 19-27
The same laws apply to other diploid
multi-cellular organisms, including us.
A gene encodes
enzyme needed
for melanin
production.
Fig. 19-25
Examples of how mutations can generate
recessive vs. dominant phenotypes
GTP-binding &
GTPase domains
recessive
Example:
G protein
lost ability to bind GTP
dominant
retains GTP binding
but lost GTPase
Frequency of recombination between two
genes depends on distance between them.
will appear to
segregate
independently
Fig. 19-29
will almost
always co-segregate
Recombination frequency used to map
genes on chromosomes
T.H. Morgan and students responsible
for establishing this principle
Panel 19-1
Morgan established fruit flies as model
system for mapping genes on chromosomes.
Visible phenotypes (such as eye color) provided a
whole array of genetic markers that can be used to map
the positions of new genes.
Single Nucleotide Polymorphisms (SNPs)
provide genetic markers for mapping
mutations in human genes that cause disease.
Fig. 19-36
SNPs inherited in chromosomal blocks
(Haplotypes)
Karp, Cell and Molecular Biology, Wiley & Sons
Haplotype blocks reflect our evolutionary history.
- Closely linked SNPs co-segregate into populations.
- Size of haplotype block reflects # generations since
emergence of SNPs in the block.
- Information used to map histories of different human
populations after exiting Africa.
larger
haplotype
blocks
smaller
haplotype
blocks
larger
haplotype
blocks
Fig. 19-37
Genome-Wide Association Studies (GWAS)
identify SNPs associated with disease phenotypes.
Fig. 19-38
disease-associated
mutation located in
this haplotype block
SNP and disease gene in
linkage disequilibrium