LECTURE 5 <ul><li>2.2.5  Lethal Genes </li></ul><ul><li>2.2.6 Linked Genes </li></ul>
OBJECTIVES <ul><li>At the end of the lesson, students should be able to : </li></ul><ul><li>Explain dominant and recessive...
Lethal Genes <ul><li>lethal   genes  -  genes that leads to the death. </li></ul><ul><li>Types of lethal genes. </li></ul>...
If we cross two heterozygotes, expect a 3:1 ratio in progeny But, in yellow x yellow cross, get: 2 yellow : 1 nonyellow Ex...
 
 
Coat color of rodents P :  Yellow  X  Yellow Yy  Yy G :  Y  y  Y  y F1: YY Yy yY yy Yellow   Yellow   Yellow   Grey (Die)
<ul><li>Example of dominant lethal allele </li></ul><ul><li>Hungtinton’s disease </li></ul><ul><li>A degenerative disease ...
Inheritance of Huntington’s allele
Linked Genes <ul><li>Genes that are  on the same </li></ul><ul><li>chromosome  are linked.  </li></ul><ul><li>Such genes d...
Linked genes in  Drosophila
SEX DETERMINATION IN HUMANS <ul><li>Human sex is determined by a pair of  sex chromosomes  called  X  and  Y .  </li></ul>...
<ul><li>Females  have two large X chromosomes ( XX ),  males  have one X chromosome and one Y chromosome ( XY ). </li></ul...
 
 
Sex Linked Genes <ul><li>Human have 22 pairs of autosomes and a pair of sex chromosome. </li></ul><ul><li>Genes carried on...
<ul><li>In males, the Y chromosome is smaller  and cannot mirror all the genes found on the X chromosome, so males have on...
 
X c X c Color blind  X X C Y Normal  X C X c X C X c X c Y X c Y Parent gamete progeny 100% carrier 100% color blind X c X...
 
Transmission of sex-linked genes
Upcoming SlideShare
Loading in …5
×

Hour 5new

390 views

Published on

Published in: Lifestyle, Technology
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
390
On SlideShare
0
From Embeds
0
Number of Embeds
5
Actions
Shares
0
Downloads
1
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

Hour 5new

  1. 1. LECTURE 5 <ul><li>2.2.5 Lethal Genes </li></ul><ul><li>2.2.6 Linked Genes </li></ul>
  2. 2. OBJECTIVES <ul><li>At the end of the lesson, students should be able to : </li></ul><ul><li>Explain dominant and recessive lethal allele. </li></ul><ul><li>Calculate genotypic and phenotypic ratios for recessive lethal alleles (2:1) </li></ul><ul><li>Explain linked genes. </li></ul><ul><li>Show the effect of linked genes on the dihybrid test cross (3:1) in the absence of crossing over. </li></ul><ul><li>Show the effect of linked genes with crossing over on the dihybrid test cross ratio. </li></ul><ul><li>Explain sex-linked genes. </li></ul>
  3. 3. Lethal Genes <ul><li>lethal genes - genes that leads to the death. </li></ul><ul><li>Types of lethal genes. </li></ul><ul><li>- Dominant lethal allele </li></ul><ul><li>- recessive lethal allele </li></ul><ul><li>Example for recessive lethal allele </li></ul><ul><li>E.g: gene for coat color of rodents (mice). </li></ul><ul><li>Wild mice have grey-colored fur (agouti) while mutants, yellow. </li></ul><ul><li>A self cross between mice with yellow fur produces offspring in the ratio of 2 yellow to 1 agouti. </li></ul><ul><li>These results suggest that the allele for yellow ( Y ) is dominant to the allele for agouti ( y ). </li></ul><ul><li>So, although the Y allele is dominant for fur color , it is recessive for the lethal characteristic . </li></ul><ul><li>Genotypic and phenotypic ratio is 2:1 </li></ul>
  4. 4. If we cross two heterozygotes, expect a 3:1 ratio in progeny But, in yellow x yellow cross, get: 2 yellow : 1 nonyellow Explanation:
  5. 7. Coat color of rodents P : Yellow X Yellow Yy Yy G : Y y Y y F1: YY Yy yY yy Yellow Yellow Yellow Grey (Die)
  6. 8. <ul><li>Example of dominant lethal allele </li></ul><ul><li>Hungtinton’s disease </li></ul><ul><li>A degenerative disease of the nervous system </li></ul><ul><li>Has no obvious phenotypic effect until certain age. </li></ul><ul><li>If Hh x hh , with H is dominant allele for Hungtinton’s disease, 50% of child born inheriting the allele & the disorder. </li></ul>
  7. 9. Inheritance of Huntington’s allele
  8. 10. Linked Genes <ul><li>Genes that are on the same </li></ul><ul><li>chromosome are linked. </li></ul><ul><li>Such genes do not obey Mendel’s laws because they do not undergo </li></ul><ul><li>independent assortment. </li></ul><ul><li>They are inherited together unless </li></ul><ul><li>separated by crossing over during </li></ul><ul><li>prophase 1 of meiosis. </li></ul>
  9. 11. Linked genes in Drosophila
  10. 12. SEX DETERMINATION IN HUMANS <ul><li>Human sex is determined by a pair of sex chromosomes called X and Y . </li></ul><ul><li>Because these chromosomes do not look alike, they are called heterosomes . </li></ul><ul><li>All other chromosomes are called autosomes . </li></ul><ul><li>Every human cell contains 23 pairs of chromosomes. </li></ul>
  11. 13. <ul><li>Females have two large X chromosomes ( XX ), males have one X chromosome and one Y chromosome ( XY ). </li></ul><ul><li>During meiosis, the sex chromosomes pair up and segregate into the daughter cells. </li></ul><ul><li>Males are heterogametic sex because they produce different sperm : approximately 50% contain an X chromosome and 50% have a Y chromosome. </li></ul><ul><li>Females produce homogametic sex because all of their egg contain an X chromosome. </li></ul>
  12. 16. Sex Linked Genes <ul><li>Human have 22 pairs of autosomes and a pair of sex chromosome. </li></ul><ul><li>Genes carried on the sex chromosomes are said to be sex-linked . </li></ul><ul><li>Human females have two X chromosomes , meaning they have two sex-linked alleles. </li></ul>
  13. 17. <ul><li>In males, the Y chromosome is smaller and cannot mirror all the genes found on the X chromosome, so males have only one sex-linked allele. </li></ul><ul><li>This is why males suffer from the effects of X-linked genetic diseases more often than females. </li></ul><ul><li>There are no known Y-linked traits, probably because the Y chromosome carries so few genes. </li></ul>
  14. 19. X c X c Color blind X X C Y Normal X C X c X C X c X c Y X c Y Parent gamete progeny 100% carrier 100% color blind X c X c X C Y
  15. 21. Transmission of sex-linked genes

×