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Regents Biology
14.1 – Human Heredity
Originally prepared by Kim B. Foglia Revised and adapted by Nhan A. Pham
Regents Biology
Objectives § Explain how pedigrees are used to study human
traits. § Describe examples of the inheritance of human traits. § Explain how small changes in DNA cause genetic
disorders.
Regents Biology
Human Chromosomes
§ a karyotype § 2 of the 46 human
chromosomes are sex chromosomes.
§ The remaining 44 chromosomes are autosomal chromosomes, or autosomes.
Regents Biology
§ Males and females are born in a roughly 50:50 ratio.
§ Do you know why?
§ … because of the way sex chromosomes segregate during meiosis.
Regents Biology
Human Traits and Pedigrees § In order to apply
Mendelian genetics to humans, a trait must be: - controlled by a single
gene - inherited and NOT
the result of environmental influences
§ A pedigree shows how a trait is passed on from one generation to the next.
Regents Biology
Human Traits and Pedigrees
§ Applications of a pedigree? § Probability of a child with widow’s peak? With widow’s
peak and attached earlobes?
Regents Biology
Recessively Inherited Disorders § shows up only in homozygous individuals (aa) § Many disorders are caused by autosomal recessive
alleles.
Regents Biology
Recessively Inherited Disorders
http://www.youtube.com/watch?v=l0dDhKFk2HU
Regents Biology
Dominantly Inherited Disorders § expressed even when
the recessive allele is present
§ Many are caused by autosomal dominant alleles.
Regents Biology
From Gene to Molecule § An allele responsible for
a genetic disorder codes for: - a malfunctioning
protein or - no protein at all
§ Such changes are due to small changes in the DNA.
§ In CF, 3 bases missing à no phenylalanine (Phe)
Regents Biology
§ predominant in African Americans (1 in 400)
§ 3 phenotypes - SS (sickle cell
anemia) - Ss (resistance to
malaria) Heterozygote advantage
- ss (normal) § Codominant?
Sickle Cell Disease
http://www.youtube.com/watch?v=Qd0HrY2NlwY
Regents Biology
Heterozygote Advantage
Regions where malaria is common Regions where the sickle cell allele is common
Regents Biology
Dominant ≠ most common allele
Polydactyly
§ Because an allele is dominant does not mean… - it is better, or - it is more common
Regents Biology
Polydactyly § The allele for >5 fingers/
toes is dominant. § The allele of 5 digits is
recessive. § Recessive alleles are far
more common than dominant.
§ Only 1 individual out of 500 has more than 5 fingers toes (499 out of 500 people are homozygous recessive (aa))
Regents Biology
Hound Dog Taylor