Non-Mendelian Inheritance…another pattern Genes rarely operate in isolation from other genes. Epistasis = the action of one gene affects whether another gene will be turned “on”

cc= has NO color (despite what B gene is) Epistasis Cc or CC= has color cc= has NO color (despite what B gene is) Bb or BB= Black bb= brown

Epistasis

PEDIGREES AP Biology Ms. Gaynor

Many human traits follow Mendelian patterns of inheritance Humans are not convenient subjects for genetic research However, We use pedigrees!

The Study of Human Genetics Continues to Advance… Can’t use humans We use pedigrees A family tree that describes the interrelationships of parents and children across generations Can also be 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

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.

Recessively Inherited Disorders Many genetic disorders are inherited in a recessive manner Need 2 recessive alleles (ex: ff) Some people can be carriers heterozygous individuals, who carry recessive allele but are show “normal” phenotype Ff  carry the cf gene (“f”) but don’t have the disorder b/c you have to be ff (recessive)

Mating of Close Relatives Matings between relatives Can increase the probability of the appearance of a genetic disease…especially recessive traits! Are called consanguineous matings Increases changes of inheriting mutated alleles (ex: lethal mutations)

HUMAN DISORDERS AP Biology Ms. Gaynor

Cystic Fibrosis Example of recessive autosomal disorder Affect mostly people of European descent Symptoms Mucus buildup in the some internal organs Abnormal absorption of nutrients in the small intestine

Sickle-Cell Disease Another recessive autosomal disorder Affects one out of 400 African-Americans Is caused by the substitution of a single amino acid in the hemoglobin protein in red blood cells Symptoms Physical weakness, pain, organ damage, and even paralysis

Autosomal dominant Inherited Disorders Some human disorders due to autosomal dominant alleles  only need 1 dominant allele Ex: Achondroplasia Lethal when homozygous for the dominant allele AA’s CAN’T live

Another Autosomal Dominant Disorder Huntington’s disease (HD) degenerative disease of nervous system No obvious phenotypic effects until about 35 to 40 years of age 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)

Alterations of Chromosome Structure Breakage of a chromosome can lead to four types of changes in chromosome structure Deletion Duplication Inversion Translocation

Alterations of chromosome structure Figure 15.14a–d A B C D E F G H Deletion Duplication M N O P Q R Inversion Reciprocal translocation (a) A deletion removes a chromosomal segment. (b) A duplication repeats a segment. (c) An inversion reverses a segment within a chromosome. (d) A translocation moves a segment from one chromosome to another, nonhomologous one. In a reciprocal   translocation, the most common type, nonhomologous chromosomes exchange fragments. Nonreciprocal translocations also occur, in which a chromosome transfers a fragment without receiving a fragment in return.

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

Triple X Syndrome XXX individuals Females Healthy Same phenotype as XX individuals 1/1000 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

Cri Du Chat Caused by a deletion of part of chromosome #5 Mentally retarded; small head Cries like a cat sound

Disorders Caused by Translocations Certain cancers caused by translocations of chromosomes Example: Chronic Myelogenous Leukemia Short Chromosome #22/ Long Chromosome #9 Figure 15.16 Normal chromosome 9 Reciprocal translocation Translocated chromosome 9 Philadelphia chromosome Normal chromosome 22 Translocated chromosome 22

Genetic Testing and Counseling Genetic counselors Can provide information to prospective parents concerned about a family history for a specific disease

Tests for Identifying Carriers For a growing number of diseases Tests are available that identify carriers and help define the odds more accurately Examples Tay Sachs & CF

Blood test @ 10 weeks after conception

Can make karyotypes, too! Fetal Testing In amniocentesis The liquid that bathes fetus is removed & tested In chorionic villus sampling (CVS) A sample of the placenta is removed and tested Can make karyotypes, too!

(b) Chorionic villus sampling (CVS) (a) Amniocentesis Amniotic fluid withdrawn Fetus Placenta Uterus Cervix Centrifugation A sample of amniotic fluid can be taken starting at the 14th to 16th week of pregnancy. (b) Chorionic villus sampling (CVS) Fluid Fetal cells Biochemical tests can be Performed immediately on the amniotic fluid or later on the cultured cells. Fetal cells must be cultured for several weeks to obtain sufficient numbers for karyotyping. Several weeks Biochemical tests hours Chorionic viIIi A sample of chorionic villus tissue can be taken as early as the 8th to 10th week of pregnancy. Suction tube Inserted through cervix Karyotyping and biochemical tests can be performed on the fetal cells immediately, providing results within a day or so. Karyotyping Fetal testing Figure 14.17 A, B

Newborn Screening Some genetic disorders can be detected at birth Simple tests are now routinely performed in most hospitals in the United States Example- PKU test