Human Heredity. Human Chromosomes Humans have 46 total chromosomes Two Categories –Autosomes-...
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Transcript of Human Heredity. Human Chromosomes Humans have 46 total chromosomes Two Categories –Autosomes-...
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
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?