1. Mendelian Exceptions Not all genes show simple patterns of
Objective: F3 - Predict possible outcomes of non-Mendelian inheritance & explain how sex is determined
Not all genes show simple patterns of
dominant and recessive alleles
Because the majority of traits are controlled by more than one gene/alleles

2. Codominance Cases in which both alleles are expressed
White cow x Brown cow =
Speckled (white and brown) cow

3. Incomplete dominance Neither allele is dominant
Red flower x White flower = Pink flower

4. codominance Practice Problems
In a certain cactus, prickly spines can be two pronged or one pronged. If a true breeding (homozygous) one-pronged cactus is crossed with a true breeding two-pronged cactus, the F1 generation has a mixture of spines, some are two-pronged, some are one-pronged.
Is this an example of codominance or incomplete dominance?
codominance

5. In snapdragons, the combined expression of both alleles for flower color produces a new phenotype that is pink. This illustrates incomplete dominance. The Punnett square above shows that both the white and red snapdragons are homozygous. Which of the following would be the correct product from a cross between two heterozygous pink snapdragons? [VA05 EOC]
A 1 red, 2 pink, 1 white
B 2 red, 2 white
C 2 red, 1 pink, 1 white
D 1 red, 1 pink, 2 white

6. Sex-linked Genetics

7. Section 12.2 Summary – pages 315 - 322
Sex Determination
If you are female, your 23rd pair of chromosomes are homologous, XX.
XY Male X Y X
XX Female
XY Male X X
XX Female
Female
If you are male, your 23rd pair of chromosomes XY, look different. X Y X
Male
XX Female
XY Male
Section 12.2 Summary – pages

8. Section 12.2 Summary – pages 315 - 322
Sex-linked inheritance
Traits controlled by genes located on sex chromosomes are called sex-linked traits.
The alleles for sex-linked traits are written as superscripts of the X or Y chromosomes.
Section 12.2 Summary – pages

9. Sex Linked Traits
When genes are located on the X chromosome, females receive two alleles for these genes, but males only receive one.
In males, the genotype is automatically known.
Colorblind male - XbY (recessive)
Normal male - XBY (dominate).
A female can be:
XBXB - normal
XBXb - carrier
XbXb - colorblind

10. The following shows a cross between a normal man and a woman who is a carrier.

12. Based only on the sex chromosomes in typical human egg and sperm cells at fertilization, the probability of producing a female is -
50%
[CA EOC]

13. In certain species of roses, white roses and red roses are incompletely dominant to each other. When a red rose and a white rose are crossed, a pink rose is produced. What is the probability of producing a white rose when a red rose is crossed with a pink rose? 0%

14. The allele for having a bent pinky finger is dominant to the allele for having a straight pinky finger. If two people who are both heterozygous for the trait of a bent pinky finger have a child, what is the percent probability that the child will have straight pinky fingers?
25%

15. Polycystic kidney disease is a dominant trait
Polycystic kidney disease is a dominant trait. What are the chances that a child will develop polycystic kidney disease if one parent is heterozygous and the other is normal?
50%

16. A gene that is sex-linked is BEST described as which of the following?
A It results in all male offspring.
B It results in all female offspring.
C It is located on the X chromosome.
D It is located inside the mitochondria.
[GA04 EOC]