PEDIGREES AP Biology Ms. Gaynor

The Study of Human Genetics Continues to Advance… Can’t use humans We use pedigrees A family tree describes the interrelationships of parents and children across generations used to make genetic predictions about future offspring

Inheritance patterns of particular traits can be traced and described using pedigrees Ww ww WW or First generation (grandparents) Second generation (parents plus aunts and uncles) Third generation (two sisters) Ff ff FF or Ff FF Widow’s peak No Widow’s peak Attached earlobe Free earlobe (a) Dominant trait (widow’s peak) (b) Recessive trait (attached earlobe) Figure 14.14 A, B

GENERATIONS

Example of Pedigree Charts Is it Autosomal or X-linked? Take a minute and try to decide if this slide is autosomal or X-linked.

Is it Autosomal or X-linked?

Recessively Inherited Disorders Many genetic disorders are inherited in a recessive manner Need 2 recessive alleles (ex: ff) Some people are carriers heterozygotes, who carry recessive allele but are show “normal” phenotype Can pass down recessive allele to offspring

HUMAN DISORDERS

recessive autosomal disorder Cystic Fibrosis (ff) recessive autosomal disorder Affect mostly Caucasians Symptoms Mucus buildup organs Abnormal absorption of nutrients in small intestine

Sickle-Cell Disease (dd) recessive autosomal disorder Affects mostly African-Americans Caused by point mutation in hemoglobin protein in red blood cells Symptoms Physical weakness pain organ damage/paralysis

Achondroplasia (Aa only) Autosomal dominant only need 1 dominant allele In Achondroplasia…homozygous dominant embryos DIE in utero AA’s CAN’T be born

Achondroplasia Genetic Problems What chance does 2 parents w/ achondroplasia have of: having a normal heighted child? AA = ¼ Aa = ½ aa = ¼ AA die in utero so never born So…1/3 chance of having “normal” height Aa x Aa AA Aa aa 1/3 2/3

Achondroplasia Genetic Problems What chance does 2 parents w/ achondroplasia have of: having a child who looks like them? AA = ¼ Aa = ½ aa = ¼ AA die in utero so never born So…2/3 chance Aa x Aa AA Aa aa 1/3 2/3

Huntington’s Disease (HH or Hh) Autosomal dominant Huntington’s disease (HD) degenerative disease of nervous system No obvious phenotypic effects until about ~35 yo HD Normal

Nondisjunction of sister chromatids in meiosis II Figure 15.12a, b Meiosis I Nondisjunction Meiosis II Gametes n + 1 n  1 n – 1 n –1 n Number of chromosomes Nondisjunction of homologous chromosomes in meiosis I Nondisjunction of sister chromatids in meiosis II (a) (b)

Human Disorders Due to Chromosomal Alterations Down syndrome Is usually the result of an extra chromosome 21 trisomy 21

Klinefelter syndrome a result of an extra chromosome in a male, producing XXY individuals 1/2000 live births

Turner syndrome Is the result of monosomy X, producing an X0 karyotype 1/5000 live births Only known monosomy in humans Normal intelligence Sterile