1 / 14

Beyond Dominant & Recessive Alleles

Beyond Dominant & Recessive Alleles. Since Mendel’s work, scientists have learned that not all genes follow a simple inheritance pattern. There are some exceptions to Mendel’s principles!. Non-Mendelian Genetics. Multiple Alleles. When MORE than 2 alleles for a gene exist

lea
Download Presentation

Beyond Dominant & Recessive Alleles

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Beyond Dominant & Recessive Alleles • Since Mendel’s work, scientists have learned that not all genes follow a simple inheritance pattern. • There are some exceptions to Mendel’s principles!

  2. Non-Mendelian Genetics

  3. Multiple Alleles • When MORE than 2 alleles for a gene exist • Each individual organism can only carry 2 alleles (1 from mom & 1 from dad), BUT more than 2 alleles may exist for a gene! The gene for human blood type consists of 4 alleles (versions): A, B, AB, & O!

  4. Multiple Alleles

  5. Polygenic Traits • Traits that are determined by alleles from MORE than 1 gene • These traits usually have a range of phenotypes. Skin color & height in humans are both controlled by multiple genes!

  6. Incomplete Dominance • Cases in which there is no dominant allele • A heterozygous phenotype is somewhere in between the 2 homozygous phenotypes!

  7. Codominance • Both alleles contribute to the phenotype & can be observed in the offspring.

  8. Sex Determination • There are 2 types of chromosomes: • Autosomes: Of the 46 chromosomes, 44 of them (22 pairs) are non-sex chromosomes. • Sex Chromosomes: The last 2 chromosomes determine the sex of the person. Females have 2 X chromosomes (XX), while males have 1 X and 1 Y chromosome (XY).

  9. Sex Linked Traits • Traits that are determined by alleles that are found on the X or Y chromosome • The Y chromosome is shorter & does not carry the same genes as the X chromosome!

  10. Sex Linked Traits • Females are XX & males are XY. • Females can be homozygous or heterozygous for a trait carried on the X chromosome, but males (only having 1 X chromosome) are hemizygous.

  11. Sex Linked Traits • If males inherit a defective gene (on the sex chrom.) from a parent, they will express the trait, because they cannot inherit a second gene to mask it! A healthy male can’t “hide” a bad allele (even if it’s recessive), because they only have 1 X chromosome or 1 Y chromosome.

  12. Baldness is a sex linked trait (B=not bald, b=bald)! The baldness gene is located on the X chromosome. • A woman can be a carrier of the baldness allele, but she may not express it (if the other X chromosome carries the dominant allele). • Men inherit their single X chromosome from their mother, so if the mother is a carrier, she could pass that on to her son. • If inherited, a man will express the baldness allele, even though it’s recessive! This is why MOSTLY men are affected by sex linked traits (but not always).

  13. Sex Linked Punnett Square – Color Blindness (B=normal, b=color blind) • XBXb(heterozygous female with normal vision) • XBY (hemizygous male with normal vision)

More Related