1 / 19

Section 7-1 “Human genetics ”

Section 7-1 “Human genetics ”. Write everything that is BLACK. KEY CONCEPT The chromosomes on which genes are located can affect the expression of traits. Two copies of each gene affect phenotype. Mendel studied autosomal (body cell) gene traits, like hair texture. (dominant).

ion
Télécharger la présentation

Section 7-1 “Human genetics ”

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. Section 7-1“Human genetics” Write everything that is BLACK

  2. KEY CONCEPT The chromosomes on which genes are located can affect the expression of traits

  3. Two copies of each gene affect phenotype • Mendel studied autosomal (body cell) gene traits, like hair texture

  4. (dominant) • A heterozygote for a recessive disorder is a carrier • Disorders caused by dominant alleles are uncommon • Mendel’s rules of inheritance apply to autosomal genetic disorders.

  5. Males and females can differ in sex-linked traits • Genes on sex chromosomes are called sex-linked genes • Y chromosome genes in mammals are responsible for male characteristics • X chromosome genes in mammals affect many traits

  6. Our chromosomes: • Recall … • In humans the diploid number of chromosomes is 46 (23 pairs) • 22 pairs of homologous (matching) chromosomes called autosomes • The 23rd pair are sex chromosomes

  7. Sex Chromosomes: • Females are XX • Have 2 X chromosomes that are alike • Males are XY • Have 1 X and 1 Y chromosome • The Y chromosome is smaller (just says be a male)

  8. Males have an XY genotype • All of a male’s sex-linked genes are expressed • Males have no second copies of sex-linked genes

  9. Females have an XX genotype • Expression of sex-linked genes is similar to autosomal genes in females • X chromosome inactivation randomly “turns off” one X chromosome

  10. After meiosis there are gametes (sperm or egg cells) that each have only one chromosome • All female eggs will have one X • All males will have half their sperm with X chromosomes and half with Y

  11. Now write everything on the next slide for your genetics book …

  12. “How a zygote is made as male or female” Female XX Male XY Eggs Y X X X Sperm XY boy XX girl XX girl XY boy 50 % chance of a girl 50% chance of a boy

  13. Problems … • Nondisjunction: The failure of homologous chromosomes to separate properly during meiosis • This can happen in the autosomes or sex chromosomes

  14. If one homologous pair fails to separate, half of the sex cells produced will have one too many chromosomes while the other half has one less chromosome • Trisomy: has one too many chromosomes

  15. When an extra chromosome is at #21 the result is Down Syndrome • This person will have 47 chromosomes instead of 46. These are in the autosomes (not sex cells) • People with Down Syndrome usually survive, but will have mental retardation

  16. Monosomy: one less chromosome • These organisms usually do not survive (except in Turner’s Syndrome)

  17. When 2 gametes with an extra set of chromosomes fuse we it is called polyploidy • Its rare in animals and results in death • It is seen frequently in plants. Flowers and fruits tend to be bigger and plants healthier

  18. True hermaphrodites (both male and female organs) are very rare and are not caused by abnormal chromosome numbers

  19. There are many X-linked traits like: • Muscular Dystrophy, color-blindness • These are more prevalent in males because they don’t have another normal X to cover up the bad one

More Related