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Chromosomes and Genetics

Chromosomes and Genetics. Chromosomes are long pieces of DNA, with supporting proteins. Genes are short regions of this DNA that hold the information needed to build and maintain the body Genes have fixed locations: each gene is in a particular place on a particular chromosome

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Chromosomes and Genetics

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  1. Chromosomes and Genetics • Chromosomes are long pieces of DNA, with supporting proteins. • Genes are short regions of this DNA that hold the information needed to build and maintain the body • Genes have fixed locations: each gene is in a particular place on a particular chromosome • Diploids have 2 copies of each chromosome, one from each parent. This means 2 copies of each gene. • The interactions between the 2 copies of each gene give rise to the various forms of dominance.

  2. Human Chromosomes • We have 46 chromosomes, or 23 pairs. • 44 of them are called autosomes and are numbered 1 through 22. Chromosome 1 is the longest, 22 is the shortest. • The other 2 chromosomes are the sex chromosomes: the X chromosome and the Y chromosome. • Males have and X and a Y; females have 2 X’s: XY vs. XX.

  3. The basic rule: if the Y chromosome is present, the person is male. If absent, the person is female. In meiosis, the X and Y chromosomes separate and go into different sperm cells. All eggs have one of the mother’s X chromosomes. The Y chromosome has the main sex-determining gene on it, called SRY. Sex Determination

  4. Sex-Influenced Traits • Such a trait is called sex-influenced. More specifically, a trait that is dominant in one sex but recessive in the other is a sex-influenced trait. • The best human example is male pattern baldness. • Baldness is dominant in males: heterozygote and homozygote both become bald. In females, baldness is recessive: only homozygote become bald. Also, females tend to lose hair more evenly than men, giving a sparse hair pattern rather than completely baldness.

  5. Words learned to know • Chromosome • Diploid • Haploid • Traits • Genes • DNA • Mitosis • Meiosis

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