Sex linked traits

STEM Lesson

1. OBSERVATION I

2. OBSERVATION II

3. SEX LINK TRAITS AND RECOMBINATION

4. Sex linked trait . The gene (pair) that determines a character (e.g. hemophilia) is located on the sex chromosomes

5. X-linked trait . A sex-linked trait is where the gene or allele for the trait is found on the X chromosome.

6. In humans, males and females are represented by different sex chromosomes • Females have two X chromosomes in the nucleus of their cells. • Males have one X chromosome and one Y chromosome in the nucleus of their cells. • Depending on whether the trait is dominant or recessive, the expression pattern of the trait differs in males and females

7. Colorblindness in humans as an example of sex-linked trait

8. The alleles responsible for colorblindness is found on the X chromosome only.

9. The dominant allele is the normal allele; the recessive allele causes colorblindness • Females need two copies of the recessive allele, one from each of the two X chromosomes, for the trait to be manifested. If they only have one copy of the recessive allele, they have normal color vision. However, they are carriers for the trait in that they may pass it on to their offspring. • Males only need one recessive allele in their sole X chromosome for the trait to be expressed.

10. Y-linked trait. A sex-linked trait where the gene or allele for the trait is found on the Y chromosome

11. Hypertrichosis pinnae auris A Y-linked trait where affected males have hair growing from their external ears

12. Other sex-related traits A. Sex-influenced trait- Any trait in a diploid organism whose expression is affected by an individual’s biological sex; a trait that occurs at a higher frequency in one sex over the other. B. Sex-limited trait- Any trait in a diploid organism whose expression is limited to just one biological sex.

13. SEX INFLUENCED TRAITS Sex - influenced traits  are autosomal  traits  that are influenced  by  sex . If a male has one recessive allele, he will show that  trait , but it will take two recessive for the female to show that same  trait . One such gene is baldness. A lot of  sex - limtied   traits  can determine parental carriers by using a pedigree.

14. SEX LINKED TRAITS-HEMOPHILIA

15. SEX LIMITED TRAITS The traits limited to only one sex due to anatomical differences are called a sex limited trait. Such trait affects a structure or function of the body of males or females only. These traits are controlled by sex-linked or autosomal genes. For example: ( i ).       Genes for milk production in dairy cattle affect only cows. (ii).      Beard growth in humans is limited to men. A woman does not grow a beard herself but she can pass the genes of heavy beard growth to her sons.

16. SEX LIMITED TRAITS FUNCTONAL MAMMARY GLANDS