1. Sex-linked Traits

2. REVIEW!!!!! What is it…Incompete Dominance or Codominance????
Zebra (black and white coat)
White dog + black dog → gray dog
Red flower + blue flower → purple flower
Indian Corn

3. Mendel studied autosomal gene traits, like hair texture
REMINDER:
Mendel studied autosomal gene traits, like hair texture
Two copies of each autosomal gene affect phenotype. RR= Red flower
Autosomes are chromosome pairs
# 1-22

4. These are genetic disorders carried on chromosomes # 1-22
Mendel’s rules of inheritance apply to autosomal genetic disorders as well.
These are genetic disorders carried on chromosomes # 1-22
A heterozygote for a recessive disorder is a carrier.
Disorders caused by dominant alleles are uncommon.
(dominant)

5. Sex-linked Traits Traits (genes) located on the sex chromosomes
23 chromosome pair
Sex chromosomes are X and Y
XX genotype for females
XY genotype for males
Many sex-linked traits carried on X chromosome because Y chromosome contains very few genes and is mainly involved in sex determination

6. Genes on sex chromosomes are called sex-linked genes.
Males and females can differ in there 23rd chromosomal pair (which are their sex chromosomes).
Genes on sex chromosomes are called sex-linked genes.
Y chromosome genes in mammals are responsible for male characteristics.
250 known genes
X chromosome genes in mammals affect many traits.
1100 known genes,
including many that cause
Genetic disorders

7. Several methods help map human chromosomes.
X Y
A karyotype is a picture of all chromosomes in a cell.

8. Females can carry sex-linked genetic disorders.
Males (XY) express all of their sex linked genes.
Expression of the disorder depends on which parent carries the allele and the sex of the child. X Y

9. (normal vision male) x (Normal vision, carrier female) XCY x XCXc
Because Males have just one X chromosome, all X linked alleles are expressed in males, even if they are recessive.
(normal vision male) x (Normal vision, carrier female) XCY x XCXc
Remember: the Y chromosome
in males does not carry traits.
CC = normal
Cc = Normal, carrier
cc = colorblindness XC y Xc

10. Sex-linked Trait Solution:XC y Xc
¼ normal vision female
¼ normal vision, carrier female
¼ normal male
¼ colorblind male
XC XC
XC Xc
XC y
Xc y

11. Example: Color Blindness
Various tests for color blindness.

12. Examples of Sex-Linked Recessive Disorders
Red/Green Colorblindness – Difficulty perceiving differences between colors (red or green, blue or yellow).
Hemophilia – Absence of one or more proteins necessary for normal blood clotting.
Deafness
Cataracts – opacity in the lens that can lead to blindness
Night blindness – (Nyctalopia) rods do not work so that can not see in the dark
Glaucoma – pressure in the eye that can lead to optic nerve damage and blindness
Duchenne Muscular Dystrophy – progressive weakness and degeneration of skeletal muscles that control movement due to absence of dystrophin (protein that maintains muscle integrity). Mainly in boys, onset 3-5 yrs, by 12 years can’t walk, and later needs respirator.