1. Heredity and Genetic Analysis
When you look at the seeds below you see the results of gametogenesis and fertilization. They represent a fraction of this plants potential progeny. In this chapter we will learn how Gregor Mendel experimented with pea plants to develop one of the key principles of Biology.
8/22/2019

2. Unit 8: Concepts Probability (C) Mendel's work (I)
8/22/2019
Unit 8: Concepts
Probability (C)
Mendel's work (I)
Monohybrid crosses (E)
Dihybrid crosses (C)
Special patterns of inheritance (E)
Environmental considerations (C)

3. 8/22/2019
The passing of genes from one generation to the next is called heredity.
Gregor Mendel experimented on hereditable patterns in pea plants.
Mendel began with monohybrid crosses.
All of the plants he used were purebred.
These purebred plants were used for the Parental generation (P).
Mendel cross pollinated two parental plants that had contrasting traits (white flowers with purple flowers) and produced an F1 generation.
Each of Mendel’s F1 plants showed only one form of the trait (the dominant trait).
He allowed each F1 plant to self pollinate and produce an F2 generation.
Each of Mendel’s F2 generations showed a 3:1 ratio of dominant to recessive traits (recessive is the trait that hides in the F1).

4. Mendel’s Experimental design
8/22/2019
Mendel’s Experimental design
Parental generation (P)
Purebred for contrasting traits
F1 Generation –
All Purple
F2 Generation –
3:1 – Purple : White

5. Mendel’s findings have been put in modern terms.
8/22/2019
Mendel’s findings have been put in modern terms.
Each trait is given a letter to represent both of its different versions (alleles) (‘F’ and ‘f’ for the freckle gene).
If an individual has two of the same letter, they are said to be homozygous (FF or ff).
If an individual has two different letters, they are said to be heterozygous (Ff).
The set of alleles that an organism has is known as its genotype (FF, Ff, or ff).
The result (physical manifestation) of that genotype is called the phenotype (Freckles or no freckles).
The dominant phenotype may be coded for by 2 genotypes (FF and Ff).
The recessive phenotype can only be reached by one genotype (ff).

7. Unit 8: Concepts Probability (C) Mendel's work (I)
8/22/2019
Unit 8: Concepts
Probability (C)
Mendel's work (I)
Monohybrid crosses (E)
Dihybrid crosses (C)
Special patterns of inheritance (E)
Environmental considerations (C)

8. There are 3 types that we’ll consider:
8/22/2019
A Punnett square is a diagram that predicts the outcome of a genetic cross.
There are 3 types that we’ll consider:
Monohybrid: one characteristic (4 blocks)
Dihybrid: two characteristics (16 blocks)
Trihybrid: three characteristics (64 blocks)

9. Continued… There are a few simple rules when using a Punnett square:
8/22/2019
Continued…
There are a few simple rules when using a Punnett square:
The cross must be written above the square (HH x Hh).
All possible parental gametes must be predicted (along the left and top of the Punnett square).
The results are EXPECTED outcomes for each genotype, NOT the actual number and type of offspring that WILL be born.
Answers must be written in the proper form: genotypes or phenotypes as requested.

10. 8/22/2019
If purple flower color is dominant, what phenotypes are expected in the F1 and F2 generations if a purebred purple flowered plant is crossed with a purebred white flowered plant?

11. 8/22/2019
It is possible to determine the genotype of a dominant phenotype by performing a test cross with that individual.
A dominant phenotype may be either XX or Xx.
When this unknown genotype is crossed with a homozygous recessive individual (xx), the results will reflect the presence or absence of a recessive allele.
If the unknown individual produces any recessive phenotype offspring, it must have been a heterozygote (Xx).
If the unknown individual produces all dominant phenotype offspring, it is probably homozygous dominant (XX).

12. 8/22/2019
Most traits are not controlled by simple dominant-recessive single gene alleles.
Polygenic traits are influenced by many genotypes affecting the same phenotype.
The phenotypes of these traits demonstrate continuous variation.
Examples: height, weight, skin color, intelligence.

13. Unit 8: Concepts Probability (C) Mendel's work (I)
8/22/2019
Unit 8: Concepts
Probability (C)
Mendel's work (I)
Monohybrid crosses (E)
Dihybrid crosses (C)
Special patterns of inheritance (E)
Environmental considerations (C)

14. Mendelian Inheritance : Independent assortment.
Click to watch video –
Mendelian Inheritance : Independent assortment.

15. Unit 8: Concepts Probability (C) Mendel's work (I)
8/22/2019
Unit 8: Concepts
Probability (C)
Mendel's work (I)
Monohybrid crosses (E)
Dihybrid crosses (C)
Special patterns of inheritance (E)
Environmental considerations (C)

16. 8/22/2019
Genes carried on the X chromosome are referred to as Sex-linked traits.
Males inherit only one copy of sex-linked genes (XAY), while females inherit two copies (XAXA).
Since males receive one less copy of these genes, the genotypes responsible for each phenotype are influenced.
Males can be recessive phenotypes with only one recessive phenotype (XaY).
Females are more likely to inherit a dominant disorder since they receive two X chromosomes (XAXa or XAXA).
Punnett squares predict not only the probabilities of phenotypes being passed on, but also correlate them with gender.

17. 8/22/2019

18. 8/22/2019
A Pedigree is a family tree that shows the pattern of inheritance of a particular genetic disorder.
A pedigree can be used to determine how a disorder will be passed on to the next generation.
It shows who has the disorder, and helps to predict who will be a carrier of the disorder.
Carriers have the normal phenotype but carry the defective allele (heterozygous genotypes).

19. Pedigree example Unaffected female Carrier female Affected Male
8/22/2019
Pedigree example
Unaffected female
Carrier female
Affected Male

20. A pedigree can allow you to determine whether a trait is autosomal, or sex-linked.
Autosomal disorders affect males and females equally.
Sex-linked traits are carried on the X chromosome, and therefore affect one gender or the other in disproportionately high numbers.
Sex-linked recessive traits affect males in higher numbers.
Since they have only one X chromosome, if males receive a single copy of this recessive allele, they will show the phenotype.
Females must still receive two recessive versions to show the phenotype.
Sex-linked dominant traits affect females in higher numbers
A female has two X chromosomes, and therefore is twice as likely to receive the trait

21. Incomplete dominance occurs when neither allele takes a fully dominant role (blending of phenotypes).
8/22/2019
Two distinctly different phenotypes blend together to produce the heterozygous phenotype.
Alleles may be written in several different ways:
BB (black), WW (white) and BW (grey)
HH (curly), HIH (wavy) and HIHI (straight)
CBCB(black), CWCW(white), CBCW(grey/blue)
Sample Phenotypes:
Black and white chickens combine to grey
Straight and curly hair combine to wavy

22. 8/22/2019

23. 8/22/2019
Co-dominance occurs when two alleles are expressed normally, but at the same time.
Two distinctly different phenotypes are both expressed together in the heterozygous genotype.
Examples:
Certain blood types
Roan coats in horses
Brindle coats in dogs

24. 8/22/2019
Codominance example: In the U.S. it is generally considered disadvantageous to have the sickle cell trait or the sickle cell disease. This hasn’t always been the case globally. (see LEQ 6.2)

25. Multiple allelism exists when there are 3 or more alleles for a gene.
8/22/2019
Multiple allelism exists when there are 3 or more alleles for a gene.
Human blood type is expressed by 3 alleles: IA, IB and i.
IA and IB are Co-dominant, and i is recessive.
Combinations of the 3 alleles can produce 4 phenotypes.

26. 8/22/2019
Question: What genotypes are responsible for producing the following blood group phenotypes?
Type O: Type A: Type B: Type AB: ii
IAi, IAIA
IBi, IBIB
IAIB

27. Codominance in blood groups
8/22/2019
Codominance in blood groups