1. Sex-Linked Traits Objective 53: I can describe sex-linked traits

2. The Sex Chromosomes (pair 23)
The sex chromosomes carry genes that determine whether a person is male or female
They also carry genes that determine other traits.

3. Is it a girl or a boy? Eggs carry X chromosomes (female)
Half of the male’s sperm carry the X and half carry the Y
If an egg fertilizes with a sperm cell carrying an X, it will be a girl (X from mom, X from dad)
If an egg fertilizes with a sperm cell carrying a Y, it will be a boy (X from mom, Y from dad)
The father (sperm cell) determines the gender of the baby

4. Sex-Linked Genes
Genes on the X and Y chromosomes are often called sex-linked genes because their alleles are passed from parent to child on a sex chromosome Try this:
Traits controlled by sex-linked genes are called sex-linked traits

5. Why do sex linked traits happen?
The X chromosome from the mother is bigger than the Y chromosome from the father. Remember the chromosomes pair up…
Mom = X Dad = Y when the X and the Y pair up it looks like this
These genes don’t have a match

6. Sex-Linked Genes One sex-linked trait is red-green colorblindness
A person with this trait cannot distinguish between red and green
Recall that females have two X chromosomes, whereas males have one X chromosome and one Y chromosome

7. Sex-Linked Genes
Unlike most chromosome pairs, the X and Y chromosomes have different genes
Most of the genes on the X chromosome are not on the Y chromosome
Therefore, an allele on an X chromosome may have no corresponding allele on a Y chromosome
Because males have only one X chromosome, males are more likely than females to have a sex-linked trait that is controlled by a recessive allele

8. Color Blindness

9. Color Blindness
Colorblindness is a trait controlled by a recessive allele on the X chromosome
More males have it
Notice, however, that the mother is a carrier of colorblindness
A carrier is a person who has one recessive allele for a trait and one dominant allele

10. Color Blindness

11. Normal Color Vision vs. Color Blindness
Top – 25, 29, 45
Bottom – 56, 6, 8
Color Blindness
Top – 25, spots, spots
Bottom – 56, spots, spots

12. Selective Breeding
Objective 54: I can describe selective breeding

13. Selective Breeding
Selecting desirable traits and using the organisms with those desirable traits to produce offspring with the same traits
Think about the article you read in LA about choosing gender and specific traits for their children – this is an example of selective breeding

14. Dogs have been breed to be friendly
Cats which are small
and not aggressive
and can play
the piano?
How man has changed the traits of organisms through Selective Breeding.
Dogs have been breed to be friendly
Gold-colored fish
Cows to produce
more milk
Horses for speed

15. If you wished to breed the prettiest guppies, how would you do it?
By only selecting the most colorful guppies and those with the longest tails, then breeding them generation after generation.
Wild guppies
Guppy which has been
selectively bred.

16. Dog breeders have been selectively breeding for desirable traits for centuries.

17. Farmers have cultivated many popular vegetables from wild mustard,
by artificially selecting for certain attributes.

18. Selective Breeding
nature provides variation, humans select variations of genes that are useful.
Example - a farmer breeds only his best livestock

19. In essence, when humans selectively breed organisms for certain traits, they are selecting for certain genes.

20. Genetics VS. Environment
Objective 55: I can describe how environmental factors can have an impact on a person’s genetic makeup.

21. The Effect of Environment
the effects of genes are often influenced by the environment—an organism’s surroundings
Many of a person’s characteristics are determined by an interaction between genes and the environment

22. Examples of Environmental Factors
Athletic ability – some may be genetic but most come from hard work and dedication
Height can be affected by diet, smoking, damage to a growth plate, ingestion of large amounts of caffeine at a young age
Cancer – UV exposure and skin cancer
Singing ability – same as athletics – hard work and dedication – singing lessons with some natural ability

23. Other examples
Diet plays a HUGE role in determining many factors that may have an effect on our genetics such as:
Obesity
Cholesterol
Heart Disease
Other environmental factors such as alcohol and drug use can affect a person’s genetics