1. GREGOR MENDEL
Founder of Genetics

2. GENES ARE GROUPED TOGETHER ON CHROMOSOMES DURING CELL DIVISION
One type of map uses the cytogenetic location to describe a gene’s position. The cytogenetic location is based on a distinctive pattern of bands created when chromosomes are stained with certain chemicals.
Locate genes using
the bands on a
stained chromosome

3. GENES COME IN ALTERNATE FORMS CALLED ALLELES

4. GENES DETERMINE TRAITS

5. phenotypes
genotypes
homozygous
hybrid, heterozygote

6. MAKING HYPOTHESES: via a punnett square
F1 heterozygous parents
1:2:1 genotype ratio
3:1 phenotype ratio
gamete possibilites

7. A a X A a A A A a a A a a Or use F.O.I.L. (first, outer, inner, last)
25% : % : %
: :

8. 9.3
Recessive allele
reappears in the
F2 phenotype
Potter Punnetts?

9. The letters represent the pair of alleles for a gene in each parents DNA
1 gene, 2 alleles
post-DNA replication
metaphase I
Metaphase gametes
Meiosis serves to SEGREGATE the alleles, so each gamete has a single copy of every gene

10. Meiosis also INDEPENDENTLY ASSORTS the alleles on different chromosomes
2 genes
2 alleles each
2 chromosomes
post-replication
metaphase metaphase gametes

11. Predict the inheritance of multiple traits? (2+ genes)
Need a much larger Punnett square!
Expected frequencies:

12. Trihybrid? Yikes!

13. Multiply probabilities in lieu of a large Punnett square*
9/16 (0.56)
show both dominant traits
* decimals are better; use 0.25

15. Other gene and allele Interactions

16. Pleiotrophy – one mutation, many effects
Sickle Cell (HbSHbS)
anemia
heart failure
brain damage
rheumatism
kidney failure
spleen damage
Albinism - lack pigment in skin, hair
Higher freq. crossed eyes

17. Multiple alleles – more than 2 in a population
6 genotypes
4 phenotypes

18. Incomplete dominance – heterozygote is a blend/
Incomplete dominance – heterozygote is a blend/ intermediate expression

19. Codominance – both expressed 100%, in 50% of phenotype (not a blend)

20. Polygenic trait – many genes interacting to influence the expression of a single trait

21. Melanin pigment production in
cells is clearly polygenic.
If two genes (4 alleles) determine
pigment, 5 phenotypes result
Three genes (6 alleles) creates 4 phenotypes
Three genes have been identified
thus far

22. Skin pigmentation reflects two different (and selective) responses to solar radiation
Higher latitude native populations have lighter skin to maximize vitamin D production
Indigenous population skin reflectivity
UV radiation
Jablonski:
As humans dispersed outside of the tropics, there was [an] intense evolutionary pressure to lose pigmentation. Modern genetics, and specifically genomic studies, have shed a lot of light on this process. People like me, who are interested in the history of evolution, or the history of adaptation—we’ve made inferences based on the fossil record [about] what we thought probably happened in human evolution. But the genomics experts have actually been able to establish unequivocally that there were independent genetic mutations that occurred in the ancestors of Western Europeans and Eastern Asians that led to loss of pigmentations as people dispersed into those areas. That’s really interesting, because both of these groups today have lightly pigmented skin, but it’s not from the same set of genetic changes. It’s from independent genetic changes that brought about loss of melanin pigment in the skin.
And, not only do we see different pathways in modern Europeans and modern Eastern Asians, but [researchers have] been able to look at the ancient DNA in Neanderthals and diagnose that they, in fact, had de-pigmented skin that was due to yet a different set of mutations. So the evolutionary pressure to lose pigment at high latitudes was great, and in at least three different instances—two groups of modern humans and one group of fossil relatives—we see three different genetic trajectories for achieving loss of pigmentation.
Equatorial indigenous people have dark skin to prevent UV from breaking down folate