Human Heredity

Human Chromosomes Humans have 46 total chromosomes Two Categories –Autosomes- first 22 pairs –Sex Chromosomes- 23rd pair, determine sex (gender) X and Y Males- XY Females- XX

Punnett Square of Gender

Karyotype Picture of chromosomes paired up with it’s homologous chromosome –Commonly used for genetic testing

Taken during mitosis when chromosomes are visible Dye added to show banding of genes

Karyotype Activity Utah Website

Types of Disorders Major Categories –Chromosomal –Single Allele (single gene) Chromosomal Disorders- gaining or losing a piece/entire chromosome –Gaining= 47 chromosomes –Losing= 45 chromosomes

Why Chromosomal Disorders Occur Non-disjunction- error in meiosis in which chromosomes fail to separate –Monosomy- only getting one copy of a chromosome –Trisomy- getting three copies of a chromosome

Examples Down Syndrome- trisomy 21 –Having 3 copies of chromosome number 21

Turner’s Syndrome- monosomy X, girl only having one X chromosome

Single-Allele Traits Disorder caused by a single gene Types –Autosomal Dominant –Autosomal Recessive –Sex-Linked

Autosomal Dominant- if present will be expressed –Only need one bad copy to be expressed Autosomal Recessive- can be masked –Must have two bad copies to be expressed –Can skip generations

Carrier- a person who is healthy but has a faulty gene –Heterozygous –Has no symptoms, but can pass on to children

Sex-linked Disorder found on X or Y chromosome –Found more in men because only have 1 X chromosome Men need just one bad copy to be expressed

Pedigree Chart used to determine inheritance patterns within a family –Family genetic tree –Males-squares –Females- circles

Autosomal Dominant

Autosomal Recessive

Sex-Linked

Pattern of Inheritance- patterns seen in a pedigree –A. Dominant- in every generation –A. Recessive- can skip generations –Sex-linked- found more in males

Other Patterns of Inheritance Sex-Influenced- having the same genotype but different expressions of that gene –Presence of hormones alters expression

Example: Pattern Baldness In Males –NN- Normal hair –Nn- baldness –nn- baldness In Females –NN- Normal hair –Nn- normal hair –nn- baldness The heterozygous is different between males and females

X Chromosome Inactivation Females turn “off” one of their X chromosomes –Why? To compensate for males only having one X –Barr body- name of dense region in nucleus created by turned off X

What Causes Disorders? Simple Answer- Mutations Germ-cell Mutation- change in DNA of a gamete cell Somatic cell Mutation- change in DNA of a body cell

Chromosomal Mutations Changes in the structure of a chromosome or loss/gain of a chromosome Types –Deletion- loss of a piece –Duplication- repeating a piece –Inversion- piece breaks off, reverses, then reattaches

–Translocation- chromosome piece breaks off, then attaches to another chromosome –Non-disjunction- failure of chromosomes to separate during meiosis

Gene Mutations Changes to nucleotides of DNA Types –Substitution- exchanging one base for another –Frame Shift- causes changes to the reading of codons Addition- adding a base Deletion- removing a base

Remember DNA sequence is read three bases at a time (codon) THE CAT ATE THE RAT- normal THE BAT ATE THE RAT- substitution

THE CAT ATE THE RAT- normal THE CCA TAT ETH ERA T- addition THE ATA TET HER AT- deletion

End Result Frameshift Mutations will make a wrong protein or one that is deficient Substitution- can result in no change or wrong amino acid

Genetic Disorders See handout sheet –Write down how they are inherited and a general description

Linked Genes Each chromosome is actually a group of linked genes –During meiosis the chromosomes separate independently, not genes

Linked Forever? No, crossing over separates and exchanges information –Further apart of chromosome= more likely to be exchanged

Gene Map Shows the relative locations of known genes for a chromosome

Detecting Human Disorders Genetic Markers- short section of DNA that is related to a particular gene Genetic Screening- examination of a person’s genetic make-up –Using- karyotypes, pedigrees, and genetic markers

Genetic Counselor- medical guidance that informs a couple about problems that can affect offspring –Amniocentesis- test used to withdraw fluid while baby is still in womb to test for genetic disorders

Human Genome Project- worldwide effort to determine the entire nucleotide sequence for the entire human genome –Determined humans to have about 35,000 genes –Created gene maps for each chromosome

Gene Therapy Treatments for genetic disorders in which the faulty gene is replaced with a normal gene

Ethical Issues Gene Therapy Cloning- producing a new individual from one cell –Has exact same genetic make-up Genetic Screening- how will information be used?