Chapter 16 – Heredity
16.1 – What is genetics? Pg. 428
Heredity – the passing of traits from parent to offspring
- genes are made up of DNA
- located on chromosomes
Alleles – different forms of genes
- meiosis separates chromosome pairs
- gives each sex cell 1 allele for each trait
Genetics – the study of how traits are inherited through
the actions of alleles
- Gregor Mendel – father of genetics
o Austrian monk (1822)
o Experimented with garden peas
o Thought is was possible to predict outcome of
flowers
o “Experiments with Plant Hybrids”
o Worked with large numbers to create more
accurate predictions (30,000 pea plants over 8
years)
 Purebreds – an organism that always
produces the same traits generation to
generation
 Cross-pollination – taking pollen off male
and placing it on female reproductive
organ of different plant
 Dominant traits
o A factor that dominates or
covers up the other traits
o The trait expressed/shown
 Recessive traits
o The trait that disappears
(doesn’t show)
o Can show if recessive traits
combine from both parents
- Punnett square
o Dominant and recessive alleles are represented
by letters
o Capital letters represent dominant traits
o Lowercase letters represent recessive traits
o Genotype
 The genetic make-up of an organism
 Homozygous
 Two alleles exactly the same
 Ex. BB or bb
 Heterozygous
 One allele dominant and one
recessive
 Ex. Bb
o Phenotype
 The physical expression of a particular
genotype
 Color, shape, physical attribute expressed
16.2 Genetics Since Mendel
Incomplete dominance
- the production of a phenotype that is intermediate to
those of the two homozygous parents
- ex. Crossing red homozygous flowers with white
homozygous flowers and the offspring expressing pink
flowers
- one allele is not able to be dominant over the other
Multiple alleles
- a trait controlled by more than two alleles
- ex. Blood type in humans
o A, B, O
o A & B are both dominant
o O is recessive
o Possible phenotypes:
 A – could have AA or AO
 B – could have BB or BO
 AB – only AB
 O – only OO
Polygenic inheritance
- when a group of gene pairs acts together to produce
a single trait
o eye color
o fingerprints
o height
o weight
o body build
o shapes of features
o skin color
- not limited to humans, plants have traits controlled by
polygenic inheritance
- genes may influence a small amount but creates the
variety that is expressed
o many different skin tones in ethnic grouping
o many different shades of blue eyes
o many different shades of brown hair
o etc
16.3 Human Genetics
Recessive Genetic Disorders
- sickle-cell anemia
o homozygous recessive
o red blood cells are sickle-shaped instead of a
disc-shape
o cannot deliver enough oxygen to cells of body
o cannot move through vessels easily
o usually found in tropical areas
o heterozygous carriers do not express the trait
but are known to be resistant to malaria
- Cystic fibrosis
o Homozygous recessive
o Thick mucus in areas of the lungs and digestive
tract
o Builds up in lungs and makes it hard to
breathe
o Reduces the flow of digestive enzymes to break
down food
o Mostly Caucasians
Sex determination
- x and y chromosomes
- females produce eggs with only x chromosome
- males produce sperms with x or y chromosome
Sex – linked disorders
- color-blindness linked to x chromosome
- more males with color blindness than females
o all sexes have x chromosome
o more chances to pass on trait
- sex-linked gene
o an allele inherited on a sex chromosome
- hemophilia
o an allele inherited on the x chromosome
Pedigrees
- a tool for tracing the occurrence of a trait in a family
Genetic engineering
- scientists experimenting with biological and chemical
methods to change the DNA sequence that makes up
a gene
- helped produce large quantities of medicines
- improve crop production
- resistant to diseases