1. Basic principles of genetics
Genetics from the beginning!
Basic principles of genetics
University of Utah Review of Genes etc!

2. Genetics Inheritance The study of traits of coded for by Heredity
genes

3. All the genes
in a given
population
What is a gene pool?

4. caused by similarities
Evidence for Heredity
Similar phenotype
caused by similarities
in genotype

5. Gregor Mendel
Austrian Monk!

6. Could tell tall from short easily
Mendel’s
Pea
Plants
Showed
Traits
that were
Markedly
Contrasting
Could tell tall from short easily

7. Traits studied by Mendel
Markedly contrasting

8. Male part with pollen
Female part with egg

9. Cross Pollination/Cross Fertilization
Pollen from anther transferred to
stigma of female part

10. Gregor Mendel Cross pollinated pea plants
Studied traits whose expression were markedly contrasting
eg Height: tall vs. short…..no in between
Pure Tall X Pure Short…….cross 1
All offspring Tall

11. Gene for tall is dominant Gene for short is recessive
He then crossed offspring from cross 1
Offspring: 75% Tall : 25% Short
He reasoned that……
Gene for tall is dominant
Gene for short is recessive

12. Summary of Mendel’s Cross
TT x tt Tt
Tt x Tt Tall : 1 Short
Parents referred to as P1
First generation referred to as F1 (F=Filial)
Second generation referred to as F2

13. Monohybrid Cross: Involving 1 trait
Punnett
Square t Tt Tt t Tt Tt
Phenotypes
All Tall
Genotypes
All Tt
Heterozygous

14. Monohybrid Cross T t T TT Tt t Tt tt Phenotypes Genotypes
3Tall: 1Short
Genotypes
1 TT : 2 Tt : 1 tt

15. Genotypes of parents F1 F2
Punnett Square

16. Crossing Tall and Short Plants
Which characteristic appears to be recessive?

17. Genetics Terminology Physical appearance = phenotype
Genetic make up causing pheno = genotype
Genotype described using minimum of 2 letters
All traits controlled by at least 2 genes
These referred to as alleles of a pair
For height: alleles are T and t

18. Heterozygous dominant…why??
If genotype is TT, plant is tall (homozygous dominant)
If genotype is Tt, plant is also tall but also a carrier for short (heterozygous)
Hybrid
& Heterozygous
often confused
Heterozygous dominant…why??
No need to say

19. More terminology…Yikes!!.
If genotype is tt, plant is short (homozygous recessive or just recessive)
Phenotypic ratio in cross 1 = all tall
Phenotypic ratio in cross 2 = 3 tall : 1 short
Genotypic ratio in cross 2 = 1 TT: 2 Tt: 1 tt
G.R. & P.R. found easily using punnett square

20. Identify the recessive allele & phenotype
Using the following punnett square

21. Monohybrid Cross t t Tt T Tt t tt tt Phenotypes 1 Tall: 1 Short
Genotypes
1 Tt : 1 tt

22. Conclusions from Mendel’s work
Inherited characteristics controlled by factors (genes) found in gametes
All traits controlled by 2 alleles (minimum).
Some alleles mask effect of others.
These are called dominant alleles

23. Law of Segregation: Pairs of genes segregate when homologous chromosomes move to opposite poles during meiosis
Law of Independent Assortment: Different pairs of alleles segregate independently of each other

24. Mendel’s law of segregation

25. Independent Assortment

26. Test Cross Cross with homozygous recessive
Used to determine genotype of individual expressing dominant characteristic
eg. If pea plant is tall
Genotype could be TT or Tt
Only one way to find out!
Cross with homozygous recessive

27. Test Cross t t No short Tt T Tt offspring T Tt Tt Phenotypes Genotypes
All Tall
Genotypes
All Tt

28. Test Cross t t Short Tt T Tt offspring t tt tt Phenotypes Genotypes
2 Tall : 2 short
Genotypes
2 Tt : 2 tt

29. Summary of Test Cross Results
If some recessive individuals show up…..
Genotype of unknown must be heterozygous
If no recessives show up….
Genotype is probably homozygous dominant

30. Testcross with monohybrids

31. White is dominant, black recessive
Test Crossing Sheep
Sheep ranchers like producing white wool
Easier to dye and less brittle than black
White is dominant, black recessive
If farmer suspects white sheep in herd are heterozygous…what can she/he do????

32. Farmer may find out for certain by crossing suspected carriers with homozygous recessive (ww)
If some black sheep show up as offspring…
Sheep was a carrier for black wool! (heterozygous)
These sheep make better meat!!!!