Human Genetics

Human Heredity Studying human genetics

Karyotypes Picture of chromosomes that are paired up Humans have 46 chromosomes in each somatic cell arranged in 23 pairs 2 chromosomes are sex chromosomes because they determine an individual’s sex –Females – 2 large-sized X chromosomes – XX –Males – 1 large-sized X and 1 small-sized Y chromosome – XY 44 other chromosomes are autosomal chromosomes, or autosomes

Karyotype Autosomes Sex Chromosomes Is this person a male or female? How do you know? How are these chromosomes arranged?

Karyotype Is this person a male or female? How do you know? Is this a “normal” karyotype? How do you know? What genetic disorder does this person have?

Males vs. Females Males and females are born in a 50/50 ratio: XX x XY XX X Y X X XX X X YY Who determines the gender of the baby? How do you know?

Pedigree Charts Show the relationships within a family and are used to study how the trait is passed on from one generation to the next

Pedigree Chart A circle represents a female. A square represents a male. A horizontal line connecting a male and female represents a marriage. A vertical line and a bracket connect the parents to their children. A half-shaded circle or square indicates that a person is a carrier of the trait. A completely shaded circle or square indicates that a person expresses the trait. A circle or square that is not shaded indicates that a person neither expresses the trait nor is a carrier of the trait. I II III Roman numerals represent generation #s Numbers underneath individuals are for identification purposes.

Albinism in Humans Below is a pedigree on Albinism, which is a defect on the 11th homologous pair in humans. People with albinism lack melanocytes, which produce the pigment melanin. Melanin helps protect the skin from harmful UV rays, and also gives skin its color.

Albinism in Humans Start with the shaded symbols. They are individuals who are affected with the observed trait. If it is recessive then their genotype can be only one form (two lower case letters). A carrier is an individual who carries the recessive trait. They are also known to be heterozygous for the trait. Aaa A AAAA AAA A AAaaaaa Using Pedigrees: Since all the rest are not shaded, then they have to have at least one dominant letter. If an affected individual has children, then they must be donating a recessive allele to the offspring. If a child is affected, then they must inherit a recessive allele from each parent. a aa At this point, all of the rest are unknown and only a test cross can be done to determine the genotype. ? ?? ?

Dominant or Recessive Trait? Is the above pedigree that of a recessive form or of a dominant form? How do you know?

Pedigrees (continued) Not all traits are easily “trackable” –Some traits are controlled by many genes (polygenic) –Many personal traits are only partially controlled by genetics –We don’t understand all traits enough to be able to use pedigrees for them