Chromosomes and Gene Expression. Exceptions to the Rule other than sex linked traits

Transcription

1 Chromosomes and Gene Expression Exceptions to the Rule other than sex linked traits

2 Chromosome Inactivation If girls have two X chromosomes, do they produce more proteins than boys with only one X chromosome??? No One of the X chromosomes from the female pair turns off, or becomes inactive. The inactivated chromosome becomes called the BARR BODY.

3 Barr Body The inactivation of the X chromosome in different cells is random. So different cells may have a different X chromosome activated. This is responsible for producing the tortoiseshell coat color in female cats.

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5 Polygenic Inheritance Literally Many genes control the one product. Ex. The ear length of corn, height and skin color of humans. Where multiple genes are contributing to the final product we arrive at a continuous variation.

6 Modifier Genes These are extra genes that work with other genes to influence the final product. Ex. Eye color in humans. Arguably there should be only two colors, Brown (dominant) and Blue (recessive), but because of the various modifier genes acting on the final product we get a range of various colors.

7 Major Changes Other than crossing over, changes can occur in the actual chromosomes code that can have profound affects on the possible outcomes!!! Changes will usually occur spontaneously when a cell becomes irradiated or exposed to certain chemicals. There are four main types of changes: - deletion - duplication - inversion -translocation

8 Deletion is when a portion of the chromosome is lost or removed due to irradiation, viruses or various chemicals. These pieces coded for genes, so when they are lost so is the genetic trait it coded for. Example when a piece of chromosome #5 is lost, the child is born with a mentally handicapped and a different facial appearance.

9 Inversion occurs when a piece of the chromosome becomes free momentarily before being reinserted in the reverse order. This completely changes the genes that this chromosome coded for. Example - Autism is believed to be linked to a chromosomal inversion.

10 Duplication is when multiple copies of a gene sequence occur. For the most part this can have no affect on a human, but in some cases to many repeats can be detrimental.

11 Example Duplication on the X chromosome may become too excessive and lead to a condition known as fragile X syndrome. Most people have about 29 repeats of this particular region, but a person with fragile X syndrome will have around 700 repeats.

12 Translocation occurs when part of one chromosome changes places with part of a nonhomologous chromosome.

13 Example If part of chromosome 14 exchanges places with #8 then cancer can occur. Down syndrome linked to translocation between chromosome 14 & 21. A type of Leukemia has been traced to translocation between #22 and #9.

14 Many other defects occur due to Nondisjunction Nondisjunction is the result of chromosomes not separating during meiosis. As a result the chromosomes will either have too many or not enough chromosomes. inheriting an extra chromosome is referred to as trisomy inheriting only one chromosome is referred to as monosomy

15 Human embryos with either condition rarely survive to birth. Many miscarriages can be linked to these conditions. Down Syndrome is probably one of the most common nondisjunction syndromes. It occurs when an individual receives 3 copies of chromosome 21.

16 -Symptoms include: mild to moderate mental impairment and a thick tongue that can create speech defects. Skeleton may not develop properly resulting in a short stocky body type.

17 Turner Syndrome results when a person only has one X sex chromosome. The woman will have external female genitalia, but will lack ovaries. They are therefore infertile and not mature sexually. Other defects include heart, kidney and skeletal defects. A single Y chromosome individual is not possible. This embryo would not survive where they would be lacking vital genetic information.

18 Klinefelter syndrome occurs when an extra X chromosome occurs in a male (XXY). This individual will have immature sex organs and will not grow facial hair. They are also likely to develop some breasts. XXX females do not show any at all symptoms.

19 Jacobs syndrome occurs in males with an extra Y (XYY). These individuals show speech and reading problems and have persistent acne. A study once found that there seemed to be an extremely high occurrence of this condition amongst prisoners compared to the rest of society.

20 Do page # 1,2,3, and 9