Genetics and Inheritance
Chapter 29 (pg 1098-1105)
Genes or DNA segments contain the blueprints for protein synthesis and many of these are enzymes that dictate the synthesis of virtually all of the body's molecules.
Genetics:

The nuclei of all human cells (except chromosomes

Genotype
______) contain the diploid # of

Phenotype

Homologous chromosomes – two members of each pair o 22 are autosomal o 23 rd chromosomes are the
Karyotype (figure 29-14) typically shown as homologous chromosome pairs
Gene pairs (alleles)
 alleles (genotype) may code for the same or for alternative forms of a trait
 each of us receives 2 genes:
 homozygous
 heterozygous o if the allele is dominant ,

genetic disorders caused by dominant genes are fairly uncommon o an allele that is recessive o incomplete dominance is a phenotype that is different from phenotypes of homozygous for either allele
• intermediate between homozygous dom and homozygous recess.

• sickling gene (s):
• ss: • Ss: o codominance is a heterozygous allele that shows both traits in its phenotype
•ex: ABO blood type:
I A , I B i
•each receives 2 of these IA and IB are codominant and i is recessive ii = I B I B or I B i =
I A I A or I A i = I A I B =
Even so, genotype doesn’t always affect the phenotype the same way

mainly from the effects of environmental factors, expressivity, and teratogens
Predicting Inheritance (figure 29-15)
Punnett Square
– box diagram to help predict
Simple Inheritance vs Polygenic Inheritance

amount of brown pigment in the iris (determines eye color) is also regulated by polygenes as are intelligence and height.
Genetic Variation : not always 50/50

chance determines the alignment & orientation of the tetrads

in male testes the # of gamete types produced by independent assortment is 2 23 =
8.5 million
1. Gene Recombination a. crossing-over -

each crossover causes recombination of many genes not just 2; many crossovers during synapsis.

b. chromosomal abnormalities -
2. Mutations a. spontaneous mutations

random errors

responsible for increased mortality rates of pre-embryos and embryos carrier –
Sex-Linked Inheritance
• inherited traits determined by genes on sex chromosome are sex linked
XX = XY =
• Y chromosome contains the genes that determine maleness
• X chromosome is large and has more genes
• a gene found only on the X chromosome is said to be sex linked
• for colorblindness which is a recessive x linked disorder:
 male inherits a bad x-linked recessive allele
 the female must have 2 bad X's to express the disorder

X-linked traits passed from mothers to sons
Human Genome Project
- 13 Chromosomes have been completely mapped; 38,000 tentatively identified.
- Began in 1990 to identify the full compliment of our chromosomes
- Disorders and diseases can now be screened for (fig 29-19)
Check out www.ornl.gov/sci/techresources/Human_Genome/home.shtml
and www.ncbi.nlm.nih.gov/genome/guide/human/ for further information
Read Genetic Engineering and Gene Therapy in the Applications Manual