Human Genetics Biology Waggy

Chapter Objectives 1. sex linked traits 2. Linked Genes 3. polygenic traits 4. Epistasis 5. Pleiotropy 6. pedigree charts 7. germ cell mutation & a body cell mutation 8. chromosome mutations & gene mutations

Sex Linked Traits A trait found on the X or Y chromosome is called a sex linked trait Since females have two X chromosomes (XX), they would need to be homozygous recessive for a recessive trait to be expressed physically

males only have one X chromosome (XY), they showed the recessive traits much more frequently Most sex linked traits are carried on the X chromosome Add to this that other sex linked traits are carried on the Y chromosome which only boys have... For these reasons, boys have more sex linked traits/disorders than girls

Linked Genes Genes that are on the same chromosome tend to be inherited together Crossing over in meiosis helps to add genetic variability by ‘mixing up’ some of these genes How ‘mixed up’ they get depends on how close they are to each other on the chromosome

Polygenic Traits Most traits are determined by many genes instead of one or two as we did in the monohybrid and dihybrid punnetts Skin color is determined by 6 genes Eye color is determined by 20 genes This accounts for the wide range of color variability humans have

Epistasis Epistasis is when one genes modifies or suppresses another gene In other words, more than one gene affects a phenotype outcome example: agouti coat color in rodents

Pleiotropy This is when one allele can cause multiple different phenotypic results example: sickle cell anemia affects 1out of every 400 African Americans It causes hemoglobin protein to fold improperly (same for everyone) But gives different symptoms to different people

Pedigree Charts Geneticists can trace genetic diseases from one generation to another by studying pedigree charts A pedigree chart is a diagram that shows how a trait is inherited over several generations

Color filled = individual has the disease A person who does not have a disease themselves but carries the gene for it is called a carrier Symbols of a Pedigree chart: Squares = males circles = females Color filled = individual has the disease Empty = individual does not have the disease Half filled = carrier

Mutation Basics Germ-cell mutations: occur in the gametes -They don’t affect the individual itself, but can be passed onto offspring Body-cell mutations: occur in the body cells -They do affect the organism, but can not be passed onto offspring Skin cancer, leukemia, etc.

Lethal mutations: cause death, usually before birth Beneficial mutations: most mutations are this type Organisms with this type of mutation have an evolutionary advantage over others

Chromosome mutations This type of mutation involves the entire chromosome There are four kinds: 1. Deletion: the loss of a piece of a chromosome due to breakage

2. Inversion: a piece of a chromosome breaks off, flips over & reattaches

3. Translocation: a piece of a chromosome breaks off & attaches to a different chromosome

4. Nondisjunction: this happens when two homologous pairs fail to separate during meiosis One gamete ends up with an extra chromosome while another ends up with none

Gene Mutations 1. Substitution: one nucleotide replaces another a change in a single gene There are three kinds: 1. Substitution: one nucleotide replaces another 2. Insertion: an extra nucleotide is added 3. Frame-shift: if a nucleotide is missing or an extra is added the others will shift, changing all of the remaining base pairs