1. Observing Patterns in Inherited Traits
Chapter 10

2. Before you go on…
Review the answers to the following questions to test your understanding of previous material.
Most organisms are diploid. What does this mean in terms of inheritance?
What is the smallest unit of inheritance, and how do they function?
What do you call alternate forms of a gene? How do these arise? Can there be more than two?
How are gametes produced, and how do you describe the genetic information that is normally contained in each?
Explain Independent Assortment, which describes the behavior of genes (on different chromosomes) during Meiosis.
Discuss linked genes, and the significance of crossing over. When and how does this happen?

3. Learning Objectives
Explain the process Mendel used in his experiments with garden peas, and what his results added to our understanding of inheritance.
Construct a Punnett square demonstrating a monohybrid cross between one homozygous dominant individual and one homozygous recessive individual. Then use this method to predict the genotypes and phenotypes of a cross between 2 of these offspring (F1 = first filial generation). Use correctly the terms: parental generation, first filial (F1) generation and second filial (F2) generation. What is the predicted phenotypic ratio in the F2 generation?
Construct a Punnett square demonstrating a dihybrid cross between heterozygotes for both traits. Predict the phenotypes that would result. What is the predicted phenotypic ratio? Is this a good illustration of the principle of independent assortment?
Discuss the effect on the phenotype for traits governed by codominant alleles, alleles which demonstrate incomplete dominance, and multiple allele systems. Provide some examples of each.
Differentiate between polygenic inheritance and pleiotrophy, with examples.
How is gender inherited, and what is the predicted phenotypic ratio? What are sex-linked genes: how are they inherited, how does one become a “carrier” for a sex-linked trait, and how do you predict the inheritance pattern for these genes?

4. Model Organisms Rapid Reproduction Produce large # of offspring)
Few chromosomes
Ease of propagation

5. Model Organisms *
* Although not all of these code directly for the production of proteins.

6. p. 152
Mendelian Genetics
Gregor Mendel ( )
A botanist and mathematician
To this day, Mendel’s principles accurately describe the inheritance of traits.
Described the variation in sexually reproducing species.

7. The Garden Pea Plant Self-pollinating
True-breeding (normally self-pollinating, so different alleles not introduced)
Can be experimentally cross-pollinated
p. 153

8. Mendel’s Peas
p. 154
Mendel studied these 7 characters. How many traits were studied?
What do these results tell us about allele dominance for these characteristics?

9. Independent Assortment
Mendel recognized “units” of inheritance that governed specific traits
e.g. pink or white flowers
We know these units as alleles
Mendel concluded that the two “units” for the first character were to be assorted into gametes independently of the two “units” for the other character
This is true if the genes for the two characters are located on different chromosomes
e.g. flower color and pod shape are not linked
In other words, homologous chromosomes separate and are sorted into gametes at random during meiosis

10. p. 153
Genetic Terms
A pair of homologous chromosomes
(one from egg; one from sperm)
Dominant allele (Y) will mask a recessive allele (y) that it is paired with as a result of fertilization.
(Yy, YY, or yy)
Genotypes:
If both alleles the same: homozygous
If alleles different:
heterozygous
A gene locus (i.e. location)
A pair of alleles
Three pairs of genes
What is the difference between the terms phenotype and genotype?

11. What did Mendel learn from this experiment?
Monohybrid Cross:
What did Mendel learn from this experiment?
p. 154
True-breeding True-breeding
yellow pea green pea
(pollen) (eggs)
Generation
Parental (P)
First Filial (F1)
Second Filial (F2) x
grow plants,cross pollinate
allow to self-fertilize
all yellow
6022 yellow : 2001 green
3 : 1

12. Alleles… …on Homologous Chromosomes y Y Pea color alleles
What color are the peas in this plant?
When this diploid plant produces a gamete, what allele(s) might the gamete contain?
If allowed to self-pollinate, and fertilization is random, what are the possible combinations of alleles in the resulting offspring, and what will their peas look like?
Pea color alleles y Y
…on Homologous
Chromosomes

13. p. 153
Genotype
Phenotype

14. Punnett Square of a Monohybrid cross
Yellow x Yellow
YY x Yy = ?
During gamete formation, the alleles segregate from each other
Y Y Y y YY Yy
Genotypic ratio?
Phenotypic ratio?
1:1, YY:Yy
4:0, yellow: green
p. 155

15. Punnett Square of a Monohybrid Cross
Aa X Aa
Female gametes a A aa Aa AA
Genotypic ratio?
Phenotypic ratio?
Male
gametes
1:2:1
3:1
p. 155

16. Test Cross Yy Pea with unknown genotype Y? x yy
the phenotype of the offspring will reveal the genotype of the unknown parent.
If offspring result in ½ yellow and ½ green what is the parental genotype? Y y y Yy yy
p. 155

17. Complete Dominance Unattached earlobes Widow’s peak Long eyelashes
Freckles
Cleft chin
Certain diseases: e.g. cystic fibrosis
p. 153

18. Many traits are not expressed via complete dominance.
Sex linked traits
Which chromosome(s) carries these alleles?
Incomplete dominance (p. 158)
Is this the same as “equally dominant” aka co-dominant?
Polygenic inheritance (p. 158)
“poly” means….
Pleiotrophy & Epistasis (p. 159)
Differentiate between these forms of gene expression.
Environmental controls (p. 162)
Provide at least one example of how the environment can affect gene expression.

19. Sex linked genes
Fathers pass sex linked alleles to all of their daughters but none of their sons. Mothers pass alleles to both.
X Y b
X X b
Color blindness
Hemophilia
Male pattern baldness
p. 169, 175

20. 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)
p. 158

21. Incomplete Dominance Hair texture in Caucasians RR: curly Rr: wavy
rr: straight
Curly hair is shaped like an elongated oval and grows at a sharp angle to the scalp.

22. ABO Blood Type: Co-dominance in a Multiple Allele System
Type A - IAIA or IAi
Type B - IBIB or IBi
Type AB - IAIB
Type O - ii
Identify the blood type known as the:
Universal donor…
Universal recipient …
p. 158

23. Polygenic Inheritance & Continuous Variation
The cumulative effect of multiple genes on one phenotype.
Genes A, B, C each contribute a unit of darkness.
AABBCC: very dark
AaBbCc: intermediate darkness
aabbcc: very light
The cumulative effect of multiple genes on one phenotype.
p. 160

24. Pleiotropy
Alleles at a single locus may have effects on two or more traits
Classic example is the effects of the mutant allele at the beta-globin locus that gives rise to sickle-cell anemia
Cell shape and resistance to malaria
Why has this disease not been eliminated by natural selection?
p. 159

25. Epistasis: gene expression dependent upon two or more genes.
Melanin
BB = black lab
Bb = black lab
bb = brown lab
How much melanin?
EE = full deposition
Ee = full deposition
ee = no deposition
p. 160

26. Epistasis cont. BBEE, BbEE, BBEe, or BbEe = black
BBee, Bbee, or bbee = yellow
bbEE = chocolate
bbEe = chocolate
Must have at least one dominant allele at both loci for black pigment to be deposited
Pigment is not deposited
Brown pigment is deposited

27. Don’t for get the world around you
Acidity of the soil changes the color of hydrangea flowers.
The expression of some genes is heavily influenced by environmental factors.
p. 162

28. Don’t for get the world around you
Being in the sun darkens our skin
Ratio of red : white blood cells are affected by exercise, injury, and illness.
Siamese cat and Himalayan rabbit: fur color is dependent upon temperature.