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

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.

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

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

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

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

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

Color Blindness

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

Color Blindness

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

Selective Breeding Objective 54: I can describe selective breeding

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

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

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.

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

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

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

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

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

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

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

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