1. Chromosomes and Inheritance
Chapter 12-1

2. Objectives Distinguish among inheritance patterns
Dominant, recessive, codominant, sex-linked, polygenic, incomplete dominance, multiple alleles
Explain how mutations in the DNA sequence can sometime result in change of an organism
Explain how mutations in gametes can result in change in the offspring

3. Vocabulary Amniocentesis Lethal mutation Single-allele trait Carrier
Monosomy
Somatic mutation
Chromosome map
Nondisjunction
Substitution
Pattern of inheritance
Deletion
Translocation
Frame shift mutation
pedigree
Trisomy
Point mutation
Genetic disorder
Polygenic trait
Germ-cell mutation
Sex-influenced trait
Inversion
Sex linkage

4. Sex Determination X is female and Y is male (smaller chromosome)
After meiosis II, one cell gets X and one get Y (from male parent)
50% chance of being male or female

5. Sex Linkage Sex linkage is on sex chromosome
More genes on X chromosome than on Y
When on X, called X-linked genes
When on Y, called Y-linked genes

6. Linkage Groups
Genes located on one chromosome and are inherited together
Crossing over is the exchange of genes
Causes new gene combinations

7. Chromosome Mapping
The farther apart on the chromosome, the likelier crossover will happen
Chromosome map shows the linear sequence of genes on the chromosome through breeding experiments
One map unit are 2 genes separated by crossing over 1% of the time (closer together, less likely to be seperated)

9. Mutation Change in DNA of an organism
Germ mutation- no affect, in gametes (offspring?)
Somatic mutations- in body cells, do not affect offspring
Lethal mutations- cause death usually before birth
Some mutations are beneficial

10. Chromosome Mutations Deletion is the loss of a piece of chromosome
Inversion is when a piece breaks off and reattaches backwards
Translocation is when a breaks off and reattaches to another nonhomologous chromosome
Nondisjunction is when the chromosome doesn’t separate and the gamete gets an extra

12. Gene Mutations
Point mutation-substitution, addition, or removal of a nucleotide
Substitution- one nucleotide is replaced with another and makes a new codon
Sickle cell anemia- adenine is substituted for thymine
Insertion is when a nucleotide is added and deletion is when one is lost
Both are serious and cause frame shift mutation (all codons moved)

13. Human Genetics
Chapter 12-2

14. Studying Human Inheritance
Geneticists focus on disease
Usually study phenotype of members of the same family and make a pedigree
Patterns of inheritance are predictable patterns throughout generations
Carriers do not express allele but can pass it on to offspring (recessive)

15. Pedigree Chart

16. Genetic Traits and Disorders
Genetic disorders are diseases or debilitating conditions that have genetic basis

17. Traits Controlled by a Single Allele
Single allele traits controlled by a single allele of a gene
Huntington’s Disease controlled by a dominant allele
Most people do not know they have the disease until after they have children (in their 30s or 40s)
Discovered genetic marker (short section of DNA that is known to have association with nearby gene)
Others are controlled by homozygous recessive traits
Cystic fibrosis and sickle-cell anemia

18. Traits Controlled by Multiple Alleles
3 or more alleles of the same gene for a single trait
ABO blood type (IA, IB, i)
A has A antigen, B has B antigen, AB has both, O has none
A person with Rh- blood cannot receive Rh+ blood
Blood Typing

19. Polygenic Traits Controlled by 2 or more genes
Show many degrees of variation
Also influenced by environment (ex: height)

20. X-Linked Traits Found on the X chromosome
Colorblindness, Hemophilia, Duchenne muscular dystrophy
Not all are diseases, mostly code for protein

21. Sex-Influenced Traits
The presence of male or female sex hormones influence traits
Ex: male pattern baldness
Both male and female homozygous will lose hair
Heterozygous males will lose hair, female will not

22. Disorders Due to Nondisjunction
Usually causes death
Monosomy -1, trisomy +1 chromosome
Down Syndrome (trisomy-21) has an extra chromosome 21
Klinefelter’s Syndrome (XXY) has feminine characteristics, mental retardation, infertile
Turner’s Syndrome (X) is female but does not mature, infertile
Just Y does not survive

23. Detecting Human Genetic Disorders
Genetic screening examines the genetic make-up through karyotype or blood tests (+ or – proteins)
Genetic counseling is medical guidance for people at risk

24. Or immediately after birth
Can also test fetus
Amniocentesis removes fluid from around fetus
Chorionic villi sampling removes tissue from between the uterus and placenta
Or immediately after birth
Some babies have phenylketonuria (PKU) which prevents the digestion of phenylananine and can cause brain damage
Can be prevented by removing from the diet