Gregor Mendel and Genetics Gregor Mendel was a Swiss Monk who studied genetic traits in Pea Plants.
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Gregor Mendel and Genetics Gregor Mendel was a Swiss Monk who studied genetic traits in Pea Plants
Inheritance We each inherit 2 forms of each gene –1 from each parent in the sex cells (sperm and egg) –The genes code for the same traits (eyes, ears, fingers) but variations of those traits –Blue or Brown eyes, hairy knuckles, non-hairy knuckles, sickle cell /non-sickle cell –These variants are called alleles
Mendel’s “Laws” Law of Independent Assortment –Genes are usually inherited independent of each other (so you can be tall and blond, etc) –Mendel used Pea plants – he saw that each trait (flower color, height, seed color, seed shape) were all inherited separately from each other Law of Segregation – The genes are separated into gametes (sex cells) and reunited during fertilization
Types of Inheritance Complete dominance: –One allele is dominant over the other – inheriting only one dominant allele will show this trait –The other allele is considered recessive – one needs to inherit this variant from both parents
Other Inheritance patterns Co-Dominance – neither gene is completely dominant – blood typing – type A, B, AB or i or type O X- linked – traits carried on the X chromosome Women’s genotype is XX ( and X from each parent) Men are XY – X from the mother, Y from father tend to be more likely in men because they have only 1 X-chromosome.
X- linked traits Women can be carriers – because they can have an X chromosome that doesn’t have the trait The trait won’t show but they can pass it on
Eye color Eye color is a complete dominance inheritance pattern: Brown is represented by B Blue is represented by b The genotype of a person with brown eyes could be: BB or Bb –One “B” from each parent and –a second “B” or ‘b’ from each parent The phenotype of BB or Bb is brown eyes
Heterozygous and Homozygous If both copies of the allele are the same, one is considered to be homozygous for that trait (BB OR bb) If one has two different alleles for a gene one is considered to be heterozygous for that trait (Bb)
Punnett Squares A heterozygous parent has genotype: Bb A parent homozygous for blue eyes has genotype: bb \ \ \ \
Genetics is about Probabilities Bb x bb Look at the boxes that show all of the possible results: BB = Bb/bB = Bb = Genotype – what their allele distribution is: Phenotype probabilities- what they will look like:
Heterozygous black guinea pigs are mated to homozygous white guinea pigs. Do the punnett square for this cross. (Use B for black and b for white) Genotype Ratios % BB %Bb %bb Phenotype Ratios % Black % White
Genetics Is Probabilities Each mating is a new “throw of the dice” Every time it is the same Women are XX Men are XY XY x XX What are the chances of having a boy?
Monohybrid Crosses When we look at the inheritance patterns of a single gene we call this a monohybrid cross When we look at the inheritance patterns of two genes at the same time we call this a dihybrid cross
Dihybrid Crossing What happens when you look at 2 different traits? When Mendel looked at the inheritance of two separate traits, he discovered that the outcome for each trait was unchanged from his examination of individual traits. He determined that most traits are inherited independently of others. This became his Principle of Independent Assortment
There are 4 different ways that the alleles for the seed color and seed shape can be combined. RY rY Ry ry These 4 possible combinations can result in 16 different genotypes R = Round r = wrinkled Y = Yellow y = green
Of the sixteen possible outcomes: How many are round and yellow? How many are wrinkled and yellow? How many are round and green? How many are wrinkled and green? Which color is dominant? __________ Which shape is dominant? ________________________
How we indicate a X-linked trait We use a regular X with a subscript Indicator letter: Hemophilia is indicated As X h - it is recessive X h Y – This male will have hemophilia X h X – This female will not have hemophilia
Hemophilia – X-linked trait Hemophilia is a disease of bleeding. Why is it called an “X-linked” trait? X h – to show that the gene for hemophilia is on the chromosome.
Carriers Hemophilia is a recessive gene – it needs to be on both X chromosomes for a female to have the disorder. If only 1 chromosome has it she is a Carrier We indicate a carrier this way: XX h – Notice only 1 of the X chromosomes carries the disorder X h X h - Female who HAS the disorder
Females are Carriers Why can’t males be carriers? We indicate a male with hemophilia this way: X h Y
Punnett squares A female carrier and a normal male: Female carrier ______ Normal Male _________
Phenotype Ratios: Affected Males: Female carriers Affected Females Genotype Ratios: XY _____ Xhx _____ XX_____ XhXh___ Probability of having a child with hemophilia
Pedigrees Which are the males? Which are the females? Which is the unaffected family member? What kind of inheritance is this? = affected female = unaffected female = affected male = unaffected male
Solving a Pedigree Problem A)What are the likely genotypes of III1 and III2? B) What are the likely genotypes of offspring of III1 and III2? The black hair of guinea pigs is produced by a dominant gene B and white by its recessive allele b. Assume that II1 and II4 do not carry the recessive allele. Using this hint – Use text boxes to write the genotypes that you can determine