1. Patterns of Inheritance
Chapter 9

2. Gregor Mendel Deduced the fundamental principles of genetics
Cross-fertilization

4. What’s with the Peas? Little spontaneous variation between generations
Can self-fertilize
Easy to control pollination
Possessed several easily observable traits
Pea form
Pea color
Flower location
Flower color
Stem size

5. What do we get?? Genetic cross P generation F1 generation
Bb x Bb
P generation
F1 generation
F2 generation

6. Monohybrid Cross
Cross between parent plants that differ in only one characteristic
Mendel developed four hypotheses from the monohybrid cross:
There are alternative forms of genes
Alleles
For each characteristic, an organism inherits two alleles
One from each parent
Alleles can be dominant or recessive
Gametes carry only one allele for each inherited characteristic

7. Mendel’s Laws
Genes
Set of instructions that determine characteristics of an organism
Segments of nucleic acid that specifies a trait
Found at designated place on chromosomes
Locus
Not all copies of a gene are identical

8. Mendel’s Laws
Alternative forms of a gene lead to the alternative form of a trait
Alleles
way of identifying the two members of a gene pair which produce opposite contrasting phenotypes
Chromosomes that are homologous are members of a pair and carry genes for the same traits in the same order

9. Genes v. alleles Genes Alleles Basic instruction Sequence of DNA
General
Hair color
Alleles
Variations of that instruction
Specifics
Brown hair

10. Genotype verse Phenotype
the alleles an individual receives at fertilization
Homozygous
an organism has two identical alleles at a gene locus
Heterozygous
an organism has two different alleles at a gene locus
Phenotype
the physical appearance of the individual

11. Describing Genotypes Homozygous Dominant
when both alleles are dominant BB
Homozygous Recessive
when both alleles are recessive bb
Heterozygous
when one allele is dominant and one is recessive Bb

12. Punnet Square…..
Genetic cross determines arrangement

13. Pedigree Chart

14. Phenotypes are not always a direct translation of genotype
Phenotypes may also be influenced by the environment
Examples?
skin color influenced by sun
height/weight influenced by nutrition
animal coat influenced by climate

15. Remember…..
P = G + E

16. Types of Phenotypic Traits
Discrete traits
Quantitative traits

17. Types of Phenotypic Traits
1) Discrete Traits: determined by the action of a single gene
Only a few distinct categories exist for trait

18. Shape of human hairline is a discrete trait
There are 2 alleles and 2 varieties:
No Widow’s Peak = recessive
Widow’s Peak = dominant

19. Human earlobe type is a discrete trait
There are 2 alleles and 2 varieties:
Free earlobe = dominant
Attached earlobe = recessive

20. Types of Phenotypic Traits
2) Quantitative Traits: determined by 2 or more genes
Has a range of phenotypes for that trait

21. Height is a quantitative trait There’s a range of possible values
Others: weight, skin color

22. Past the Peas: Types of Dominance
1) Complete Dominance: 1 or other
2) Incomplete Dominance: 3rd effect
3) Codominance: some of both

23. Complete Dominance Dominant Allele is always expressed when present
Recessive Allele is only expressed as homozygote

24. Incomplete Dominance
Alleles have combined (equal) effect on phenotype of heterozygote
Phenotype is intermediate

25. Codominance
Both alleles are visible in the phenotype of the heterozygote

26. Multiple Allelism: existence of more than 2 alleles of gene
Example: Blood type (A, B, O)
Remember: Each person still only has 2 alleles for that trait, but more than 2 exist

27. Multiple Allelism: Blood typing
ABO Blood Type in Humans exhibits multiple allelism
Phenotype Genotype
O OO
A AA or AO
B BB or BO
AB AB *
How many ALLELES are there?
3 ( A, B, O)
How many Phenotypes are there?
4 (A, B, AB, O)
How many Genotypes are there? 6
What is the relationship between A and B alleles?
codominance

28. Question: If a woman with blood type O marries a man with blood type B, can they have a child with blood type A?
Phenotype Genotype
O OO
A AA or AO
B BB or BO
AB AB*
No. The mother’s genotype must be OO and the father’s either BB or BO. Their child will either be type B (BO) or type O (OO)

29. Sex-linked Traits Female XX Male XY
Genes located on the X or Y chromosome are sex-linked
X and Y chromosomes are not homologous, they contain different genes

30. Sex-linked traits Sex chromosomes Sex-linked genes
Are designated X and Y
Determine an individual’s sex
Influence the inheritance of certain traits
Sex-linked genes
Are any genes located on a sex chromosome

31. Sex-Linked Traits
Females (XX) have 2 copies of each gene on the X chromosome
Males (XY) have only 1 copy of each gene on the X chromosome
Females can show a dominant condition if present on 1 or both X chromosomes
Females can only show a recessive condition if present on both X chromosomes
Males ALWAYS show X-linked alleles, regardless of dominance

32. Sex-Linked Disorders in Humans
number of human conditions result from sex-linked (X-linked) genes
Red-green color blindness
characterized by a malfunction of light-sensitive cells in the eyes

33. Question…..
Will a mother that is colorblind automatically have a son that is colorblind?

34. Question…..
Will a mother that is colorblind automatically have a son that is colorblind?
Yes!!!!!

35. Beyond Simple Inheritance Patterns
Polygenic Inheritance
Occurs when a trait is governed by two or more sets of alleles

36. Mutations
Changes to the nucleotide sequence of the genetic material of an organism
Can be caused by:
copying errors in the genetic material during cell division
exposure to UV light or chemical mutagens
Viruses
can be induced by the organism itself
Create variety within gene pool
Less favorable verse more favorable

37. Recessive Disorders Most human genetic disorders are recessive
Individuals can be carriers of these diseases

38. Dominant Disorders Some human genetic disorders are dominant
Achondroplasia is a form of dwarfism
Huntington's disease