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Getting Organized

Getting Organized. How genetic material is arranged. Organization Overview. http://www.accessexcellence.org/RC/VL/GG/chromosome.php. Homologous Chromosomes. These have the same traits on them (not always the same alleles however). Gene Linkage. Homologous chromosomes.

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Getting Organized

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  1. Getting Organized How genetic material is arranged

  2. Organization Overview http://www.accessexcellence.org/RC/VL/GG/chromosome.php

  3. Homologous Chromosomes These have the same traits on them (not always the same alleles however)

  4. Gene Linkage Homologous chromosomes During gamete formation (meiosis) homologous chromosomes segregate into individual gametes Genes on the same chromosome are LINKED That means they’re inherited together Like red hair and freckles. Image from: http://anthro.palomar.edu/biobasis/images/linked_genes.gif

  5. Homologous Chromosomes

  6. Looking at Chromosomes Withdrawing some amniotic fluid from around the fetus for analysis Determined in babies through amniocentesis and karyotyping Taking a look at the cell going through mitosis and taking a picture of the chromosomes. The chromosomes are counted and examined

  7. Sex Determination The first 22 homologous pairs are referred to as the body chromosomes or autosomes. The last pair are the sex chromosomes and determine gender Individuals with two X chromosomes are female and those with an X and a Y are male This is a ….?

  8. Sex Determination Since we now know that it isn’t individual alleles that segregate but whole chromosomes, we can use a Punnett square to show the chances of a child being male or female X Y 50% male 50% female X X X X Y X X X X Y

  9. Sex Determination • This chromosomal difference between boys and girls, boys being XY and girls XX means that boys’ chromosomes do NOT all come in pairs. • There are actually different traits coded on the X and Y chromosomes. • In dudes, the sex chromosomes are NOT homologous

  10. Sex-linked traits • We’ve already discussed how alleles on the same chromosome tend to be inherited together showing the pattern of inheritance known as Gene Linkage. • Alleles on the X or Y chromosome are said to be Sex-linked and show another unusual pattern of inheritance.

  11. Y-linked traits • Since the Y chromosome is the smallest chromosome, it actually has very few genes on it. • Question: can girls show Y-linked traits? Why/whynot? • Answer: No, they can’t. Girls don’t have a Y chromosome

  12. X-linked traits • Traits on the X chromosome are X-linked. • Boys and girls both have X chromosomes (boys have one while girls have two). • Question: Who would show recessive, X-linked traits more often? Girls or boys? • Answer: Though it would be tempting to say girls because they have two chances to have the alleles, it’s actually boys.

  13. X-linked traits and Punnett Squares • The classic example of an X-linked trait is color-blindness. It is recessive. XB Xb The X shows it is X-linked The superscript letter represents the allele

  14. X-linked traits and Punnett Squares • Here’s a Punnett Square for color-blindness XB Y Dad = normal vision: XB Y Mom = “carrier”: XB Xb 50% chance of color-blindness in boys. No chance of color-blindness in girls. (50% chance the girls will be carriers though) XB Xb

  15. X-linked traits and Punnett Squares • Because girls have two X chromosomes they have a chance to be heterozygous carriers and not show the trait. Guys do not have this chance. • Dad’s cannot pass X-linked traits to sons because they pass Y chromosomes to sons. If they pass their X chromosome to their offspring, it will be a girl (not a son).

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