Human Inheritance

The sex chromosome As we stated before the human has 46 chromosomes Chromosome set #23 determines the sex of the human.

Boy or Girl? If chromosome set #23 is….. XX- girl XY- boy Demo

Predicting the sex of the offspring. Mom’s Genotype XX Dad’s Genotype XY Draw the Punnett Square.

Review What is the male sex chromosome? X M Y T

Karyotype A karyotype is an x-ray picture of the chromosomes. Scientist use this as a tool to study the chromosomes.

Human Karyotype Looking at the picture what is the sex of this offspring? Male (XY)

Single Alleles Some traits are controlled by a single pair of alleles. One will be dominant and one will be recessive. EX: hitch-hikers thumb, dimples….

Multiple Alleles Some genes are controlled by many different alleles. They may have three or more forms (think of flavors of pudding!) EX: Height & Blood types exist in many gene forms

Codominance Often times genes have equal effects and both traits will show. EX: a breed of chicken will have both black and white feathers.

Review Co-dominance is when… Neither trait is dominant Both traits are dominant Both traits show Both B & C

Blood Types Blood Type is controlled by multiple alleles It also expresses co-dominance Type A – co-dominant Type B – co-dominant Type AB Type O – recessive Food Coloring Demo

Incomplete dominance Some times genes are in similar forms and the two traits will blend together. EX: Red flowers will be crossed with white flowers and make Pink flowers.

Sex Linked Genes Genes on the X and Y chromosomes are called sex linked genes. These traits appear more often in one sex than the other

Color Blindness The color blindness is a sex-linked trait found on the X chromosome. Color-blindness is most common in males Why?

Color-blindness There is no gene for colorblindness on the Y chromosome! It only takes one recessive allele for men to be colorblind

Mutations Mutations happen when there is a mistake in the DNA Can be harmful or beneficial

Review What is a mutation? a mistake in the DNA an error in the cell’s membrane a mistake in the mitochondria

Pedigree Charts Scientist use Pedigree Charts to trace the inheritance of traits in humans. The chart or family tree will track which member of the family have a particular trait.

Pedigree Chart