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Exceptions to Mendel’s Principles

Exceptions to Mendel’s Principles. Incomplete Dominance or Blending Inheritance – When an organism is heterozygous for a trait and both genes are expressed but not completely. Example: Snap Dragon Flowers. Codominance. When 2 different alleles are present and both alleles are expressed.

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Exceptions to Mendel’s Principles

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  1. Exceptions to Mendel’s Principles • Incomplete Dominance or Blending Inheritance • – When an organism is heterozygous for a trait and both genes are expressed but not completely.

  2. Example: Snap Dragon Flowers

  3. Codominance • When 2 different alleles are present and both alleles are expressed. • Example: Dalmatians • Dalmatians that are black and white have an allele for black and an allele for white • If a 2 Dalmatians that are black and white mate they will only have a 50% chance of having a black and white Dalmatian

  4. Bloodtypes • Blood types vary and your immune system recognizes your own blood type as being self. Other blood types are recognized as non-self. • Antigens are the markers on the cell that the immune system “looks” for to identify the cell.

  5. Antibody and Antigens • Antibodies are chemicals that are a part of the immune system that attaches to the antigens. • The antigen-antibody complex sends a signal to the immune system that something does not belong. The immune system tries to kill and remove the item.

  6. Antibody Antigen

  7. Bloodtypes Antigens & Antibodies

  8. Bloodtype Alleles • Allele IA produces antigen A • Allele IB produces antigen B • Allele i produces no antigen. 

  9. Codominance and Bloodtypes • Blood types are an example of codominance. • Both alleles are fully expressed (both antigens appear completely when the genotype is heterozygous). • Example: Bloodtype AB

  10. Exception to Independent Assortment Linked Traits = • Genes that are next to each other on the same chromosome have a greater chance of being passed on together. • Red hair and freckles

  11. Linkage Maps – • Created from linked relationships • Based on the number of “crossovers” we can determine the order of the genes and their relative distance to each other. • Greater % of cross over = farther apart b and cn =9%, cn and vg = 9.5%, b and vg = 18.5%

  12. Sex Linked or X-Linked Traits • Traits that are more often found on one sex than the other is said to be sex linked. • If the gene on an X chromosome is recessive it would take two of those genes to show up on a female. While it would only take one gene for that trait to show up on the male (since he only has one X).

  13. Examples of Sex Linked Traits • Color Blindness • Hemophilia

  14. Exceptions to Principle of Segregation • Passing on of multiple chromosomes = nondisjunction • Polysomy = more than 2 genes/trait • examples: Down syndrome (extra #21 chromosome = trisomy)

  15. XXY = Klinefelter syndrome • XO = Turner syndrome (monosomy) • XXX = triple-X syndrome • Chromosomal mutations results in multiple or missing genes • examples: deletion and duplication

  16. Polygenic Inheritance • Several genes influence a character (trait) • May be scattered on different chromosomes or on the same chromosome • Examples: Hair color, weight, height, and eye, hair and skin color

  17. Environmental Influences • Phenotypes often depend on environmental conditions • examples: Hydrangea plants in acidic soil have blue flowers and those in basic soil have pink flowers • artic fox fur, Himalayan rabbit fur, and Siamese cat fur color • Human height and skin color

  18. Sex-influenced • traits expressed differently in the two sexes. • autosomal (not on the sex chromosomes) • male-pattern baldness • Sex-limited • expressed in only one sex. • example lactation, or milk production. • genes in both males and females, only lactating females express these genes (LH –hormone)

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