Download Sexual Reproduction Homologous Chromosomes have different

Sexual Reproduction
„3
steps to reproduction
– Meiosis
– Gametes produced
– Fertilization (two gametes join)
„ All
three steps help to create genetic
variation in offspring
Homologous Chromosomes
have different traits
„ Allele
„ Cell
– variation of a gene
has two of each chromosome
– one from mom & one from dad
„ Paternal
and maternal chromosomes carry
different alleles
Meiosis: Two Divisions
„ Two
nuclear divisions
– Meiosis I & Meiosis II
DNA is NOT duplicated between meiosis I
and II
END RESULT: Four haploid cells are formed
1
Meiosis
Meiosis I
Meiosis II
„
Prophase I
„
Prophase II
„
Metaphase I
„
Metaphase II
„
Anaphase I
„
Anaphase II
„
Telophase I
„
Telophase II
Meiosis I
Meiosis II
2
Crossing Over/Recombination PROPHASE I
•Chromosomes link
with homologue while
in sister chromatid
stage
•Homologues trade
segments
Crossing Over
„ With
genetic recombination, each
chromosome has maternal and parental
sections
„ Creates
genetic variation
Random
Alignment –
Independent
Assortment
When chromatids pair with homologues and line up
during metaphase I they do so randomly
So genes from mom and dad can go to either pole
leading to a blend of genes from mom and dad in
gamete
3
Fertilization
„ Male
and female gametes join
„ Two
haploid cells make a diploid cell
„ Mom
provides the cellular components
(e.g. mitochondria)
„ The
two gametes that join is random
Genetic Variation
Comes from:
„
Genetic recombination during prophase I
„
Random alignment at metaphase I
„
Random combination of gametes at
fertilization
4
Results of Mitosis and Meiosis
„ Mitosis
– Two diploid cells produced
– Each identical to parent
„ Meiosis
– Four haploid cells produced
– Differ from parent and one another
What are the key differences between
male and female gamete production?
5
Asexual Reproduction
„ Single
parent produces offspring
– Fission
– Vegetative reproduction
– Regeneration
„ All
offspring are genetically the same
(clones)
Dominance
It’s not just dominant and recessive
„ Complete
dominance
dominance
„ Incomplete
– Heterozygote phenotype is in between – like
the blending theory
„ Codominance
– Heterozygote (two different alleles) are both
expressed
6
Continuous Variation
„A
more or less continuous range of small
differences in a given trait among
individuals
„ The
greater the number of genes and
environmental factors that affect a trait,
the more continuous the variation in
versions of that trait
7
Genetics & Environment
„A
phenotype results from the interaction
of the genotype with the environment
„ Environmental
factors may control the
expression or inhibition of a gene
Potentilla
Category
Genetics & IQ scores
Predicted
Correlation
Bouchard (1997)
Actual Median
Correlation
# of studies
Identical twins
reared together
1.0
0.85
34
Identical twins
reared apart
1.0
0.75
5
Fraternal twins
reared together
0.5
0.58
41
Siblings reared
together
Parents and
offspring
0.5
0.45
69
0.5
0.39
32
Parents and
adoptive offspring
0.0
0.18
6
8
Garter Snakes
Arnold. A. (1980)
% of snakes
Newborn eating patterns
80
70
60
50
40
30
20
10
0
Inland
Coastal
0
1
2
3
4
5
6
7
8
9 10
# slug chunks eaten
9