1. Human Genetics

2. Earlobe Variation
Whether a person is born with attached or detached earlobes depends on a single gene
Gene has two molecular forms (alleles)

3. Earlobe Variation
You inherited one allele for this gene from each parent
Dominant allele specifies detached earlobes
Recessive allele specifies attached lobes

4. Dominant & Recessive Alleles
If you have attached earlobes, you inherited two copies of the recessive allele
If you have detached earlobes, you may have either one or two copies of the dominant allele

5. Alleles denoted as…
shorthand notation to show genes and the two copies of each in a cell
Dominant called D- for detached earlobes
Recessive called d- for attached earlobes
So person can be- DD, Dd or dd

6. Gregor Mendel Strong background in plant breeding and mathematics
Using pea plants, found how parents transmit genes (units of information) to offspring

7. The Garden Pea Plant Self-pollinating
True breeding (different alleles not introduced)
Can be experimentally cross-pollinated

8. Genes Units of information about specific traits
Passed from parents to offspring
Each has a specific location (locus) on a chromosome

9. Alleles Different molecular forms of a gene Arise by mutation
Dominant allele masks a recessive allele that is paired with it

10. A pair of homologous chromosomes
A gene locus
A pair of alleles
Three pairs of genes

11. Allele Combinations Homozygous Heterozygous
having two identical alleles at a locus
AA or aa
Heterozygous
having two different alleles at a locus Aa

12. Genotype & Phenotype
Genotype refers to particular genes an individual carries
Phenotype refers to an individual’s observable traits
Cannot always determine genotype by observing phenotype

13. Tracking Generations Parental generation P mates to produce F1
First-generation offspring F1
mate to produce F2
Second-generation offspring F2

14. F1 Results of True-breeding lineages Crossed

15. F2 Results of Monohybrid Cross

16. Mendel’s Monohybrid Cross Results
5,474 round
1,850 wrinkled
6,022 yellow
2,001 green
882 inflated
299 wrinkled
428 green
152 yellow
F2 plants showed dominant-to-recessive ratio that averaged 3:1
705 purple
224 white
651 long stem
207 at tip
787 tall
277 dwarf

17. Mendel’s Theory of Segregation
An individual inherits a unit of information (allele) about a trait from each parent
During gamete formation, the alleles segregate from each other (meiosis!!)

18. Punnett Square of a Monohybrid Cross
Female gametes
Male
gametes
A a A a Aa AA aa
Dominant
phenotype can
arise 3 ways,
recessive only
one

19. Test Cross
Individual that shows dominant phenotype is crossed with individual with recessive phenotype
Examining offspring allows you to determine the genotype of the dominant individual

20. Dihybrid Cross
Experimental cross between individuals that are homozygous for different versions of two traits

21. A Dihybrid Cross - F1 Results
purple
flowers, tall
white
flowers,
dwarf
TRUE-
BREEDING
PARENTS:
AABB x
aabb
GAMETES: AB AB ab ab
AaBb
F1 HYBRID
OFFSPRING:
All purple-flowered, tall

22. F1 Results of Mendel’s Dihybrid Crosses
All plants displayed the dominant form of both traits
All plants inherited one allele for each trait from each parent
All plants were heterozygous (AaBb)

23. Phenotypic Ratios in F2 Four Phenotypes: Tall, purple-flowered (9/16)
AaBb X
AaBb
Four Phenotypes:
Tall, purple-flowered (9/16)
Tall, white-flowered (3/16)
Dwarf, purple-flowered (3/16)
Dwarf, white-flowered (1/16)

24. Explanation of Mendel’s Dihybrid Results
If the two traits are coded for by genes on separate chromosomes, sixteen gamete combinations are possible
1/4
1/4
1/4
1/4 AB Ab aB ab
1/4
1/16
1/16
1/16
1/16 AB
AABB
AABb
AaBB
AaBb
1/4
1/16
1/16
1/16
1/16 Ab
AABb
AAbb
AaBb
Aabb
1/4
1/16
1/16
1/16
1/16 aB
AaBB
AaBb
aaBB
aaBb
1/4
1/16
1/16
1/16
1/16 ab
AaBb
Aabb
aaBb
aabb

25. Independent Assortment
Mendel concluded that the two “units” for the first trait were to be assorted into gametes independently of the two “units” for the other trait

26. Impact of Mendel’s Work
Mendel presented his results in 1865
Paper received little notice
Mendel discontinued his experiments in 1871
Paper rediscovered in 1900 and finally appreciated

27. Dominance Relations Complete dominance Incomplete dominance
Heterozygote phenotype is somewhere between that of two homozyotes
Codominance
Non-identical alleles specify two phenotypes that are both expressed in heterozygotes

28. Flower Color in Snapdragons: Incomplete Dominance
Red-flowered plant X White-flowered plant
Pink-flowered F1 plants
(homozygote)
(homozygote)
(heterozygotes)

29. Flower Color in Snapdragons: Incomplete Dominance
Pink-flowered plant X Pink-flowered plant
White-, pink-, and red-flowered plants
in a 1:2:1 ratio
(heterozygote)
(heterozygote)

30. Flower Color in Snapdragons: Incomplete Dominance
Red flowers - two alleles allow them to make a red pigment
White flowers - two mutant alleles; can’t make red pigment
Pink flowers have one normal and one mutant allele; make a smaller amount of red pigment

31. Co-dominance - Multiple alleles
Gene that controls ABO type codes for enzyme that dictates structure of a glycolipid (called A or B) on blood cells
3 alleles total = A gene makes A glycolipid, B gene makes B glycolipid and O gene means neither A nor B genes are present

32. ABO Blood Type: Allele Combinations
Type A – AA or Ai
Type B – BB or Bi
Type AB - AB
Type O - ii

33. ABO Blood Type: Glycolipids on Red Cells
Type A - Glycolipid A on cell surface
Type B - Glycolipid B on cell surface
Type AB - Both glyocolipids A & B
Type O - Neither glyocolipid A nor B

34. Environmental Effects on phenotype
Siamese cats- heat sensitive enzyme works only in cooler areas of the body
Height of a person- can have gene for more height but nutrition can also dictate height