1. Human Genetics Biology Waggy

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

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

9. 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

10. 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

12. 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.

13. 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

14. 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

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

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

17. 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

18. 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