14.1 – human heredity - quia · regents biology! 14.1 – human heredity originally prepared by...

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