1. Gender Determination Autosomes All chromosomes other
Than sex chromosomes
Pairs #1-22
Sex chromosomes
Chromsomes that
determine an organism’s
gender
Pair #23

2. Gender Determination Females: XX 2 large, X-shaped sex chromosomes
Males: XY
1 large, X-shaped &
1 small, hook-shaped
Y chromosome

3. What’s the probability of getting a male or female child?X

4. What’s the probability of getting a male or female child?X
All eggs receive an X
Half of Sperm receive an X
Half receive a Y X Y

5. What’s the probability of getting a male or female child?X
Who determines the gender
of the offspring?
DAD! % female
50% Male X Y XX XY

6. Trait determined by a gene located
Autosomal trait
Trait determined by a gene located
on an autosome (#1-22)
Will appear in males & females equally.

7. Sex-linked traits Gene is located on the X sex chromosome (#23)
Trait will appear in more males than females!
WHY?

8. If it carries the recessive allele, they MUST express it.
Sex–Linked Traits
More males exhibit recessive, sex-linked traits because they only receive 1 X chromosome.
If it carries the recessive allele, they MUST express it.
Females, receive 2 X chromosomes, so they must receive two recessive alleles to express them.

9. Example of Sex-Linkage:Colorblindness
XN XN Woman with normal vision
XN Xn Woman who is heterozygous for colorblindness ( a “carrier”)
Xn Xn Woman who is colorblind
XN Y0 Man with normal vision
Xn Y0 Man who is colorblind
Notice that males CANNOT be carriers! Why?

10. Pedigree
A diagram showing how a trait is inherited over several generations of a family. (Fig 12)
Used to:
Detect a carrier – person who is heterozygous for a recessive trait. (Don’t have the disorder but may pass the allele to offspring).
Determine if a trait is dominant or recessive
Determine if a gene is autosomal or sex-linked

11. Pedigree = Male = Female = Exhibits trait of interest I. II. III.
Mating I.
II.
Offspring oldest to youngest from left to right
III.
= Male
= Female
= Exhibits trait of interest

12. Dominant or Recessive?
If an offspring exhibits traits that neither parent does  it’s recessive.
Recessive traits tend to skip generations
Dominant traits tend to appear in every generation.

13. Autosomal or Sex-Linked?
If more males exhibit the trait than females it’s sex-linked (The gene is on the X sex-chromosome)
If there seem to be equal numbers of males & females with the trait, it’s autosomal. (The gene is on #1-22)

14. Dominant or Recessive? Autosomal or Sex-Linked?

15. Can you determine the genotype of each individual?
Red hair is caused by a recessive allele on chromosome #16.
B = Non-red hair (Black, Brown, Blonde)
b = Red hair
bb bb bb

16. Can you determine the genotype of each individual?
Red hair is caused by a recessive allele on chromosome #16.
B = Non-red hair (Black, Brown, Blonde)
b = Red hair
B_ B_
B_ bb bb B_ B_
B_ B_ bb

17. Can you determine the genotype of each individual?
Red hair is caused by a recessive allele on chromosome #16.
B = Non-red hair (Black, Brown, Blonde)
b = Red hair
Bb Bb
B_ bb bb B_ B_
B_ B_ bb

18. Can you determine the genotype of each individual?
Red hair is caused by a recessive allele on chromosome #16.
B = Non-red hair (Black, Brown, Blonde)
b = Red hair
Bb Bb
B_ bb bb B_ B_
Bb Bb bb

19. Can you determine the genotype of each individual?
Red hair is caused by a recessive allele on chromosome #16.
B = Non-red hair (Black, Brown, Blonde)
b = Red hair
Bb Bb
B_ bb bb Bb B_
Bb Bb bb