1. Take notes on the following slides on your foldable.
Patterns of Heredity
Take notes on the following slides on your foldable.

2. White or Red Offspring, Right?
Patterns of Heredity
Based on what we have learned, what offspring phenotypes would you expect from a cross between these two horses?
White or Red Offspring, Right?
Not necessarily…
White Horse
Red Horse
Strawberry Roan

3. Patterns of heredity How did this happen?
Most of the time, traits display more complex patterns of heredity than the simple dominant-recessive pattern
What is the simple dominant-recessive pattern known as?
Mendelian Genetics
Let’s look at Mendelian Genetics one more time…and then let’s look at the other patterns of inheritance!

4. Mendelian Genetics
Again, Mendelian genetics shows a pattern where a clear dominant trait masks a recessive trait.
Cleft chins, dimples, and freckles are all examples of traits that follow Mendelian patterns.

5. Mendelian Genetics D d Genotype: 1:2:1 Phenotype: 3:1 D DD Dd Dd dd d
Punnett Square Dimples (D) are dominant over no dimples (d) Cross two parents that are heterozygous for dimples. Complete the ratios for genotype and phenotype. D d
Genotype: 1:2:1
Phenotype: 3:1 D DD Dd Dd dd d

6. Incomplete Dominance
Occurs when the heterozygous allele combination results in a blend of the dominant and recessive trait.
Remember the horses…

7. Incomplete Dominance
Straight, wavy and curly hair is one example of incomplete dominance.
Another example is carnation color. If the red and white alleles are both present, the resulting offspring will be pink (a blend of red and white).

8. Incomplete Dominance R r RR Rr R r Rr rr Punnett Square
Red flower color (R) is incompletely dominant over white flower color (r) in carnations.
Cross two parents that are heterozygous for flower color. Complete the ratios for genotype and phenotype. R r RR Rr R r Rr rr
Genotype: 1:2:1
Phenotype:1:2:1

9. Co-dominance
Occurs when both alleles are expressed when the heterozygous allele combination is present.
Not a Blend!!
Human blood is an example of co-dominance. A and B alleles are both dominant over the recessive allele, O. If both the A and B alleles are present, both will be expressed.

10. Co-dominance IA IB Genotype: 1:2:1 Phenotype:1:2:1 IA IAIA IAIB IAIB
Punnett Square
Cross two parents that are co-dominant for blood type. Give the ratios for genotype and phenotype. IA IB
Genotype: 1:2:1
Phenotype:1:2:1 IA
IAIA
IAIB
IAIB
IBIB IB

11. Sex-linked (X) Traits XRY XrY XRXR XRXr XrXr
Occurs when a trait is passed on from generation to generation on one of the sex- determining chromosomes (X, Y)
The dominant and recessive representative alleles are written as superscripts on the X and Y.
XRY XrY
Only females can be carriers of X-Linked traits. What is a carrier?
Why can’t males be carriers of X-Linked traits?
XRXR
XRXr
XrXr

12. Sex-linked Traits XB Xb XB XBXB XBXb y XBy Xby Punnett Square
Cross a female carrier for colorblindness with a normal male. List the possible phenotypes.
B – not affected
b - affected XB Xb XB
XBXB
XBXb
Possible Phenotypes: Normal Female
Carrier Female
Normal Male Colorblind Male y
XBy
Xby

13. Polygenic Traits So POLY GENIC means MANY GENES!!!
What does Poly mean?
Many
Genic looks like?
Genes!
Occurs when several genes influence a trait
The genes may be on the same chromosome or on different chromosomes
So POLY GENIC means MANY GENES!!!

14. Polygenic Traits
Eye color, height, weight, and hair and skin color are all polygenic traits.

15. Multiple Alleles i i How many possible genotypes for blood? 6
How many possible phenotypes? 4
Genes with three or more alleles are said to have multiple alleles.
Human blood has 3 alleles: A, B, and O.
i i

16. Multiple Alleles IA IO IB IAIB IBIO IAIO IOIO IO
Punnet Square Cross a parent with an IAIO genotype with a parent that has the genotype IBIO for blood. List the possible phenotypes. IA IO
Possible Phenotypes: Type AB Blood
Type A Blood
Type B Blood
Type O Blood IB
IAIB
IBIO
IAIO
IOIO IO