Transcript PATTERNS OF HEREDITY AND HUMAN GENETICS

PATTERNS OF HEREDITY
AND HUMAN GENETICS
CHAPTER 11
☺ You will compare the inheritance of recessive
and dominant traits in humans.
☺ You will analyze the inheritance of incompletly
dominant and codominant traits.
☺ You will determine the inheritance of sex linked traits.
Mendelian Inheritance of
Human Traits
Making a Pedigree
▪ Pedigrees illustrate inheritance: a graphic representation of
genetic inheritance.
▸Made up of a set of symbols that identify males, females and the
trail being studied and family relationships.
☐= male; ❍ = female
☐┬❍ = parents ▄ affected male
┌┴┐
●affected female
☐ ❍ = siblings Half shaded square or
circle means a carrier of trait
Simple Recessive Heredity
▪ Most genetic disorders are caused by recessive
alleles. Allele must be inherited from both parents.
▪ Many of the alleles are relatively rare.
▪ Few are common in certain ethnic groups
▸Cystic fibrosis - most common genetic disorder among
white Americans. 1 in 20 carry, 1 in 2000 inherit disorder.
▸Tay-Sachs - Amish and Ashkenzic Jews. Disorder of
the central nervous system.
▸Phenylketnuria (PKU) - Norway, Sweden. Disorder that
results from the absence of an enzyme that converts an
amino acid to another amino acid.
Simple Dominant Heredity
▪ Trait only has to be inherited from one parent
▸Simple dominant traits - Tongue rolling, hitchhiker’s
thumb, attached earlobes, and Hunington’s disease.
When Heredity Follows
Different Rules
Complex Patterns of Inheritance
▪ Incomplete dominance: a third genotype: A dominant red
flower and a dominant white flower produce a pink flower.
▸Both flowers have incomplete dominance patterns, neither allele is
dominant.
▪ Codominance: Expression of both alleles.
▸The phenotype of both homozygotes to be produced in heterozygote
individuals. Both alleles are expressed equally.
▪ Traits controlled by more than two alleles have multiple
alleles.
Sex Determination
1:1 Ratio; 50 - 50 Chance
▪ 22 pairs of matching homologous chromosomes
called autosomes; look exactly alike.
▸23rd pair differ in males and females. Females have a
“XX” pair males have a “XY” pair.
– These are the chromosomes that control the inheritance of sex
characteristics.
▸Females only produce the “X” gamete while males
produce both the “X” and the “Y” gamete.
Sex-linked Traits &
Polygenic Inheritance
Traits carried on the 23rd pair
▪ Traits dependent on genes that follow the
inheritance pattern for a sex chromosome.
▸Color blindness
▪ Traits that are controlled by two or more
genes
▸May be on the same chromosome or on different
chromosomes
– Skin color, height .
Environmental Influences
External and Internal
▪ External influences: Temperature,
nutrition, light, chemicals, infection all
can change the way a gene is expressed.
▪ Internal influences: hormones and
structural differences, organisms age can
change a gene’s expression.
Complex Inheritance