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Basic Genetics

Basic Genetics. Allele A version of a gene Dominant Allele that may mask the presence of another Recessive Allele that may be masked by another Heterozygous The 2 alleles are different Homozygous The 2 alleles are identical. P Extra Fingers. P Extra Fingers. ♂. ♀.

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Basic Genetics

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  1. Basic Genetics

  2. Allele A version of a gene Dominant Allele that may mask the presence of another Recessive Allele that may be masked by another Heterozygous The 2 alleles are different Homozygous The 2 alleles are identical P Extra Fingers P Extra Fingers ♂ ♀ DNA in a Normal Cell(one chromosome from each parent) F Free f Attached Earlobe Gene a albino a albino Melanin Gene Polydactyly Gene

  3. Genotype The set of alleles an organism possesses Phenotype The outcome resulting from the genotype P Extra Fingers P Extra Fingers ♂ ♀ DNA in a Normal Cell(one chromosome from each parent) F Free f Attached Earlobe Gene a albino a albino Melanin Gene Polydactyly Gene

  4. f f f f f f F F F F F F Meiosis Maternal/Paternal alleles segregate

  5. Geneticists perform crosses to predict what offspring will result from two parents. Determine parent genotypes. Determine possible gametes. Place the male gametes along the top of the Punnett Square and the female gametes along the side. Combine gametes in each box. List possible offspring genotypes. List possible offspring phenotypes. A woman with attached earlobes has a child with a man who is heterozygous. f f ♀ x F f ♂ f or f F or f Mendelian Genetics

  6. Practice Problems • Y = yellow pea seeds y = green pea seeds Perform this cross: Y y x Y y • What is the probability of the first offspring having green seeds? • What about the 5th? • What are the chances of the first 5 plants having green seeds? • Out of 1000 offspring, how many would you expect to have green seeds?

  7. Practice Problems • Cystic fibrosis is a recessive genetic disease caused by buildup of mucus in the lungs, liver, and pancreas. If two normal people have a child with cystic fibrosis, what are the chances of their next child having CF? • People with the nervous system disorder Huntington’s disease (caused by a dominant allele) usually don’t show symptoms until their 30’s. A 27-yr-old man’s family has no history of the disease. His 26-yr-old wife’s grandmothers both had the disease though her parents do not. What are the chances of their 1st kid having HD?

  8. Codominance • Both alleles are detectable in a specimen • Gene: Cattle coat color Alleles CR = red CW = White Genotypes CRCR = red coat CWCW = white coat CRCW = roan coat

  9. Multiple Alleles • More than two alleles exist for a gene • Human blood type

  10. Multiple Alleles Genotype Antibodies Blood Type

  11. Practice Problem A child with blood type A needs a blood transfusion. Her mother is blood type B, and her father is type AB. What is the probability that her brother (if we don’t have time to test his blood) could donate a compatible supply of blood to her?

  12. Sex-Linkage (X-Linkage) • Somatic cells have 2 alleles per gene for… • Genes on autosomes • Genes on the x-chromosome in females • Somatic cells in males have only one allele per x-linked gene. A M A M b n B N

  13. Sex-Linkage (X-Linkage) • Colorblindness is caused by a recessive x-linked allele. • What are the possible genotypes? • What phenotypes correspond to these genotypes? • What are the expected offspring from a cross between a carrier female and a colorblind male?

  14. P p P p P p P p Y y Y y Y y OR Y y P p P p P p y Y y Y y Y Law of Independent Assortment GametesPY py PpYy Py pY

  15. Dihybrid Crosses P: FfTt♂ x FfTt♀ F = Free earlobes f= attached earlobes T= 2nd toe longest t = great toe longest F1 Genotypes F1 Phenotypes

  16. Blood Typing, Part 2 • Rh Factor • Rh+ RBCs have Rh proteins; Rh- don’t. • A type AB- mother and a type B+ father really want to have a type A+ child. How likely are they to do it on the first shot? • The man’s mother is O-. + Anti-Rh antibodies

  17. Pedigrees • Determining nature of inheritance using family histories

  18. Tribrachiosis Dibrachiosis Practice Pedigree

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