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Gregor Mendel and Genetics

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Presentation on theme: "Gregor Mendel and Genetics"— Presentation transcript:

1 Gregor Mendel and Genetics
Gregor Mendel was a Swiss Monk who studied genetic traits in Pea Plants

2 Inheritance We each inherit 2 forms of each gene
1 from each parent (from 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

3 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

4 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

5 Other Inheritance patterns
Incomplete dominance – blending of genetics – black cat + white cat = gray cat 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 tend to be seen in men who have only 1 x-chromosome

6 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

7 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)

8 Punnett Squares A heterozygous parent has genotype: Bb
A parent homozygous for blue eyes has genotype: bb \ \ \ \

9 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:

10 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

11 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?

12 Seed Shape Pod Shape

13 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

14 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


16 There are 4 different ways that the alleles for the seed color and seed shape can be combined.
These 4 possible combinations can result in 16 different genotypes

17 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? ________________________

18 X- linked traits The X carries more information than the Y-Chromosome
Females are XX Males are XY Therefore, any additional information on the male’s X chromosome will show, even if it is recessive

19 X-Chromosome/ Y Chromosome

20 How we indicate a X-linked trait
We use a regular X with a subscript Indicator letter: Hemophilia is indicated As Xh - it is recessive XhY – This male will have hemophilia Xh X – This female will not have hemophilia

21 Hemophilia – X-linked trait
Hemophilia is a disease of bleeding. Why is it called an “X-linked” trait? Xh – to show that the gene for hemophilia is on the chromosome.

22 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: XXh – Notice only 1 of the X chromosomes carries the disorder XhXh - Female who HAS the disorder

23 Females are Carriers Why can’t males be carriers?
We indicate a male with hemophilia this way: XhY

24 Punnett squares A female carrier and a normal male: Female carrier
______ Normal Male _________

25 Affected Males: Female carriers Affected Females Genotype Ratios:
Phenotype Ratios: Affected Males: Female carriers Affected Females Genotype Ratios: XY _____ Xhx _____ XX_____ XhXh___ Probability of having a child with hemophilia

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