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Genetics

Genetics. Genetics is the science of inheritance.  It requires sexual reproduction.. wherein a sperm and egg combine to form a zygote. Patterns of Inheritance: Genetics Chapt. 10. Interest in genetics is as old as humankind… Modern genetics began in 1860’s

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Genetics

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  1. Genetics Genetics is the science of inheritance.  It requires sexual reproduction.. wherein a sperm and egg combine to form a zygote.

  2. Patterns of Inheritance: Genetics Chapt. 10 • Interest in genetics is as old as humankind… • Modern genetics began in 1860’s • Czech Monk- Gregor Mendel • Playing with peas in his garden

  3. Gregor Mendel • Used peas to study how physical traits passed from parent to offspring • Mendel measured 7 traits in peas, each trait with 2 forms. • How were these traits passed on? • Mendel came up with rules…. Examples of two Pea traits (Shape & Color) that Mendel studied • Text pg. 178

  4. Mendel’s 1st Rule The Law of Segregation: • For each trait (i.e. pod color or plant height) an individual has 2 factors • The 2 factors may be the same or different • When making kids, each parent will contribute only 1 factor • The 2 factors a parent has will separate when making a kid (plant or human)

  5. The Law of Segregation • Each parent will pass on 1 factor during sex (gamete production) • Kids get 1 factor (for each trait) from each parent... Text pg 181

  6. The Factors • Each individual has 2 factors for each trait…pod color, height, eyes, hair... • If both factors for a trait are the same, you are homozygous for that trait… • If you have 2 different factors for a trait, you are heterozygous for that trait

  7. How to Label these factors? • G for Green pods • Y for yellow pods • B for brown hair • x for blond hair But…we don’t do this!!

  8. The Factors • You have 2 factors, but only 1 factor for each trait is typically used (expressed).. • This is the dominant factor • The other one is the recessive factor

  9. So; How we do Label the factors? • Dominant factor is written in upper case… i.e. “B” • Recessive factor in lower case, using the dominant abbreviation.. i.e. “b” • B is for brown hair (which is dominant) • b is for blond

  10. Quiz • If the you are heterozygous for brown hair, what two factors will you have? • If homozygous, what two factors?

  11. How to Predict which factor you’ll give your kids? • Each parent has 2 factors for each trait • But, each gamete you produce has only 1 factor for each trait • Which factor goes to which kid? • Best described by a Punnett Square

  12. B B b b Punnett Square.. • Used to predict how offspring will get their share of factors… • Parents mate (x): BB X bb • What possible offspring will each make? Male Gametes Female Gametes

  13. Possible Offspring…. Or, F1 Generation B B b Bb Bb Bb Bb b Each F1 Offspring has the same traits for hair color… Bb

  14. Another Example..Trait for Seed Shape (S) Text pg 181

  15. Mendel’s 2nd Law • Factors for each trait segregate into gametes independently of each other • The factor for hair color (B or b) will segregate independently of the factor for height (T or t) • Consider a dihybrid cross… Two traits at once • Example: Say Parents are Bbtt x bbTT

  16. Dihybrid Cross • If a Bbtt male mates with a bbTT female? • What are the possible gametes for each?

  17. Male Bbtt x Female bbTT Bt bt gametes bT BbTt bbTt New individuals (with two factors for each trait) gametes bbTt bT BbTt

  18. So What? • What does Mendel and his Peas have to do with you? • Chromosomes and Heredity…

  19. Mendel’s Factors = Genes • Every normal human has thousands of genes • Each gene describes the information for one human trait. • You have two genes for each trait • Where are these genes located?

  20. On Chromosomes • We each have 46 chromosomes in each cell • 23 chromosomes came from Mom, 23 from Dad • Each chromosome contains hundreds of genes… An example using the FISH technique of identifying the location of one gene on a chromosome.

  21. Gene location on Chromosomes

  22. Quiz • If the human trait for Hairy knuckles is located on 1 gene…how many copies of this gene will you have? • If Hairy knuckles is a dominant trait, how would you characterize the genotype? • Use H for Hairy knuckles • HH or Hh

  23. Why should you care about Chromosomes?…Have a Baby! • Karyotype…spread out a fetus’s chromosomes to check for normalcy • Amniocentesis (Text pg. 768-769) …Enables us to karyotype a fetus • What are they looking for?

  24. Chromosomal Abnormalities: Downs Syndrome • An extra chromosome # 21 (3 copies) • Also referred to as Trisomy 21 • Slow development, flat face, slanted eyes, intelligence varies greatly • 50% of children die before age 1 • Karyotype tests can predict the disorder but not its severity

  25. Karyotyping reveals lots of information • Normal 23 pairs of chromosomes • Of the 23 pairs, 22 are autosomal pairs and 1 pair are the sex chromosomes • Females have two identical sex chromosomes (XX), • While males have one X and one smaller chromosome called Y Sex Chromosomes

  26. Male vs. Female • Females are determined by XX chromosomes • Males by XY chromosomes • Males get the X from Mom, the Y from Dad • Females get one X from each parent Sex Chromosomes

  27. Male or Female?

  28. Sex-linked Traits • Each X chromosome carries ~1,000 genes, whereas Y contains very few • So, if a male gets an X chromosome from his Mom with a bad gene, he is going to suffer from it • A female has a second X copy to work with…

  29. Example: Hemophilia • A sex-linked recessive disorder in which blood does not clot effectively • Therefore, cuts are slow to heal • Disease is carried on the X chromosome • Queen Victoria and extended family suffered from this

  30. Female Carriers for Hemophilia

  31. Genetic Defects:Can be due to chromosomal disorders…

  32. Genetic Defects:Or, at the level of Genes Sickle Cell anemia; autosomal recessive. 9 % of US blacks are heterozygous, while 0.2% are homozygous recessive. The recessive allele causes a single amino acid substitution in the beta chains of hemoglobin. When oxygen concentration is low, sickling of cells occurs. Heterozygotes make enough good beta-chain hemoglobin that they do not suffer as long as oxygen concentrations remain high, such as at sea-level.

  33. Genetic Defects:at the level of Genes Huntington’s Disease; (also referred to as Woody Guthrie's disease) is an autosomal dominant resulting in progressive destruction of brain cells. If a parent has the disease, 50% (or more) of the children will have it. The disease usually does not manifest until after age 30. Cystic Fibrosis; CF is the most common genetic disease in Caucasians. An individual must inherit a defective copy of the CF gene from each parent to have cystic fibrosis. CF causes the body to produce an abnormally thick, sticky mucus, due to the faulty transport of sodium and chloride (salt) within cells

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