1. 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

2. Most multicellular organisms reproduce sexually.
fertilization of egg by sperm
Fig. 19-4

3. After fertilization, the diploid zygote then undergoes
rounds of mitosis
to generate a new
multicellular
adult.
Fig. 19-5

4. Meiosis differs from mitosis in also having a reductive division.
non-reductive
division
reductive
division
non-reductive
division
Fig. 19-6

5. Physical Basis of reductive division:
separation of chromosome homologues
Fig. 19-7

6. holds homologues together
Paired chromosome
homologues after
duplication (one
from each parent)
Cohesin holds sister
chromatids together
Synaptonemal Complex
holds homologues together
Fig. 19-9

7. Physical Basis of reductive division:
separation of chromosome homologues
Fig. 19-8

8. Meiosis generates genetic diversity in two ways.
Law of
Independent
Assortment
Fig

9. Recombination by strand invasion/copying mechanism
Fig

10. Cohesin holds sister chromatids together through Meiosis I.
Fig

11. Cohesin cleavage allows sister chromatid separation during Meiosis II.
Fig

12. Failure to separate in Meiosis I (or II) generates
aneuploid gametes, like those responsible
for Down’s Syndrome.
Fig

13. Mendel used pea plants to uncover the laws of genetics.
Fig

14. Law of Segregation (alleles separate during meiosis)
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.
Law of Segregation
(alleles separate
during meiosis)
Fig

15. Crosses of F1 progeny showed that recessive trait is still present
in F1 progeny.
It reappeared in
F2 progeny.
Fig

16. Alleles for two different genes can segregate independently
Law of Independent
Assortment
(multiple chromosome
homologue pairs
segregate independently)
Fig

17. The same laws apply to other diploid
multi-cellular organisms, including us.
A gene encodes
enzyme needed
for melanin
production.
Fig

18. Examples of how mutations can generate
recessive vs. dominant phenotypes
Example:
G protein lost ability to bind GTP retains GTP binding
but lost GTPase
GTP-binding &
GTPase domains
recessive dominant

19. Frequency of recombination between two
genes depends on distance between them.
will appear to
segregate
independently
will almost
always co-segregate
Fig

20. Recombination frequency used to map genes on chromosomes
T.H. Morgan and students responsible
for establishing this principle
Panel 19-1

21. 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.

22. Single Nucleotide Polymorphisms (SNPs)
provide genetic markers for mapping
mutations in human genes that cause disease.
Fig

23. SNPs inherited in chromosomal blocks (Haplotypes)
Karp, Cell and Molecular Biology, Wiley & Sons

24. 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

25. Genome-Wide Association Studies (GWAS)
identify SNPs associated with disease phenotypes.
Fig
disease-associated
mutation located in
this haplotype block
SNP and disease gene in
linkage disequilibrium