Patterns of Human Inheritance

Describe dominant and recessive patterns of inheritance in human disease traits. Describe how sex is inherited in humans and the pattern of inheritance observed for sex-linked genes Explain X chromosome inactivation

Learning Outcomes

The inheritance patterns – DOMINANT or RECESSIVE of most human traits has been determined by pedigree analysis

red numbers - feet

black numbers - hands

Autosomal Dominant

Huntington’s disease

Sickle cell cystic fibrosis

Autosomal Recessive

Autosomal Dominant

dominant - the presence of the dominant allele WILL produce the phenotype

normal mother

affected father

meiosis and gamete formation

affected child normal child

disorder-causing allele (dominant)

Autosomal Recessive

recessive - both the alleles MUST BE recessive to produce the phenotype

million

Sickle Cell Anemia

Cystic Fibrosis

over 1500 known mutations

Pleiotropy

a single gene affects multiple traits

Sickle Cell Cystic Fibrosis

severe anemia sickle crisis (extremely painful) swelling of hands/feet more infections stroke

thick/sticky mucus in lungs repeated lung infections pneumonia pancreatitis intestinal blockage

Sex-linked traits

hemophilia, red-green color blindness

Sex-linked traits

(green-deficient color blind)

dystrophin (muscular dystrophy)

(anhidrotic ectodermal dysplasia)

IL2RG (SCID-X1)

XIST X chromosome inactivation control

(hemophilia B)

(hemophilia A)

(red-deficient color blind) X

~10% of protein coding genes are on the X chromosome

Sex-linked traits

When we talk about sex-linked traits, we are really talking about genes on the X chromosome.

There are only a few genes on the Y chromosome where mutations are known to cause genetic diseases.

Queen Victoria 1819-1901

The Romanov Family ca. 1931

Cleft chin (dominant) Cheek dimples (dominant) Free (dominant) or attached (recessive) earlobes Freckles (dominant) Hitchhiker's thumb (recessive) Widow's peak (dominant)

Human Traits that are simple Mendelian inheritance

X Chromosome Inactivation— A Colorful Story

XX cells XY cells

X Chromosome Inactivation

In XX cells, one X chromosome in each cell is permanently inactivated during embryonic development.

Nuclei of:

Epistasis

Gene #1 -- codes for cat fur color -- 2 alleles -- black or orange

One gene regulates/controls the expression of another.

Gene #2 -- dilute - controls how much expression -- get lighter or darker variations

Gene #3 -- white spotting -- completely turns off Gene #1 in some spots