Karyotypes and Pedigrees

KARYOTYPES AND PEDIGREESChapter 14

Chromosome Review• All of an organism’s DNA can be packaged into chromosomes• Humans - 23 pairs or 46 total chromosomes

• Each pair of chromosomes contain genes with 2 alleles (1 from each parent)

Chromosome Review• All of an organism’s DNA can be packaged into chromosomes• Humans - 23 pairs or 46 total chromosomes

• Each pair of chromosomes contain genes with 2 alleles (1 from each parent)

• Chromosome Numbers• 1-22 autosomes• Sex chromosomes “#23”

• XX – Female• XY - Male

Pedigree• A pedigree is a chart for tracing genes in a family

• Phenotypes are used to infer genotypes on a pedigree

Pedigree Basics

Circle – FemaleSquare – MaleHorizontal Line – MatingVertical Line – OffspringShaded – Has traitUnshaded – No trait

Human Genome• Human Genes- human genome contains 20,000 to 30,000 genes.• 99.9% of all nucleotide

bases are exactly the same in all people

• Less than 2% of genome actually codes for proteins

Karyotypes• Karyotypes- picture of all chromosomes in a cell for one

organism

Creating a Karyotype

Karyotype Uses•  Used to identify certain genetic disorders in which there

are extra or too few chromosomes (i.e. Down syndrome 

Identifying Gender by Karyotype

Male Female

Autosome Disorders

Trisomy 21 (Down’s Syndrome)• Extra 21st chromosome• Male or female (47XX or

47XY)• 1/700 births• characteristic facial features,

short stature; heart defects • susceptibility to respiratory

disease, shorter lifespan • prone to developing early

Alzheimer's and leukemia • often sexually underdeveloped

and sterile, usually some degree of mental retardation.

Patau Syndrome (trisomy 13)• Extra 13th chromosome• Male or female (47XX or

47XY)• serious eye, brain,

circulatory defects as well as cleft palate.

• 1:5000 live births. • Children rarely live more

than a few months.

Edward’s Syndrome• Extra 18th chromosome• Male or female (47XX or

47XY)• almost every organ

system affected • 1:10,000 live births. • Most are stillborn or

miscarried• Children with full Trisomy

18 generally do not live more than a few months.

Alterations in Chromosome Structure• Sometimes, chromosomes break, leading to 3 types of

changes in chromosome structure:1. Deletion: a portion of one chromosome is lost during

cell division. That chromosome is now missing certain genes. When this chromosome is passed on to offspring the result is usually lethal due to missing genes.

Alterations in Chromosome Structure- Example: Cri du chat (cry of the cat): A specific deletion of a

small portion of chromosome 5; these children have severe mental retardation, a small head with unusual facial features, and a cry that sounds like a distressed cat.

Alterations in Chromosome Structure2. Duplication: if the fragment joins the homologous

chromosome, then that region is repeatedExample - Fragile X: the most common form of mental

retardation. The X chromosome of some people is unusually fragile at one tip - seen "hanging by a thread" under a microscope. Most people have 29 "repeats" at this end of their X-chromosome, those with Fragile X have over 700 repeats due to duplications. Affects 1:1500 males, 1:2500 females.

Alterations in Chromosome Structure3. Translocation: a fragment of a

chromosome is moved ("trans-located") from one chromosome to another - joins a non-homologous chromosome.

• The balance of genes is still normal (nothing has been gained or lost) but can alter phenotype as it places genes in a new environment.

• Can also cause difficulties in egg or sperm development and normal development of a zygote.

Sex Chromosome Disorders

Only 1 X chromosome

Turner’s Syndrome• In females,(45XO) sex organs fail to develop at puberty• Occurs 1/ 2,000 births• http://www.youtube.com/watch?v=ldjb-FR-PKo

Triple X Syndrome• In females (47XXX)• Have normal development• Usually taller for their age• Occurs 1/ 1,00 births

Klinefelter’s Syndrome• In males (47XXY)• Sterile, feminine qualities (higher voice, breast

development)• Little facial hair• Taller than average• Occurs 1/ 1,000 male births

Jacob’s Syndrome • Male (47XYY)• Lead normal lives (most don’t even know they have this)• Produce more testosterone more facial hair, taller• Occurs 1/ 1,500 births?