3 Main Questions:
- What is the chromosome theory of inheritance?
It is a basic principle in biology stating that genes are located on chromosomes and that the behavior of chromosomes during meiosis accounts for inheritance patterns.
- What is sex-linked gene?
A gene located on either sex chromosome.
- What is hemophilia?
It is a sex-linked recessive disorder defined by the absence of one or more of the proteins required for blood clotting.
5 Main Facts:
- Whether we are male or female is one of our more obvious phenotypic characters.
- In humans and other mammals, there are two varieties of sex chromosomes, designated X and Y.
- In both testes nd ovaries, the two sex chromosomes segregate during meiosis, and each gamete receives one.
- In humans, the anatomical signs of sex begin to emerge when the embryo is about 2 months old.
- The inactive X in each cell of a female condenses into a compact object called a Barr body, which lies along the inside of the nuclear envelope.
Diagram:
The tortoiseshell gene is on the X chromosome, and the tortoiseshell phenotype requires the presence of two differnt alleles, one for orange fur and one for black fur. Normally, only females can have both alleles, because only they have two X chromosomes. If a female is heterozygous for the tortoiseshell gene, she is tortoiseshell. Orange patches are formed by populations of cells in which the X chromosome with the orange allele is active; black patches have cells in which the X chromosome with the black allele is active.
Summary:
Gregor Mendel's "hereditory factors" were purely an abstract concept when he proposed their existence. At that time, no cellular structure were known that could house these imaginary units. Today, we can show that genes Mendel's factors are located along chromosomes.
Whether we are male or female is one of our more obvious phenotypic characters. Although the anatomical and physiological differnces between woman and men are numerous, the chromosomal basis for determining sex is rather simple.
Video:
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