Gene Linkage, Karyotypes & Chromosomal Mutations

1. Gene Linkage, Karyotypes & Chromosomal Mutations

2. Mendel's Flawed Principle • In fact not all genes independently assort! • An early example was found in sweet peas. • Flower color and pollen length did not yield the expected 9:3:3:1 ratio in the F2. Instead a 23:1:1:9 was observed.

3. Gene Linkage • An exception to independent assortment develops when genes appear near one another on the same chromosome. • When genes occur on the same chromosome, they are usually inherited as a single unit. Genes inherited in this way are said to be linked, and are referred to as "linkage groups." • For example, in fruit flies the genes affecting eye color and wing length are inherited together because they appear on the same chromosome.

4. Gene Linkage • Gene linkage - The tendency of genes located on the same chromosome to be inherited together.

5. Gene Linkage • Crossing Over

6. Gene Linkage • Multiple Cross Overs

7. Gene Linkage

8. Gene Linkage • Animations • http://www.execulink.com/~ekimmel/crossing_over.htm • http://www.biostudio.com/d_%20Meiotic%20Recombination%20Between%20Linked%20Genes.htm

9. Chromosomal Mutations

10. Chromosomal Mutations • One well known example of mutation is non-disjunction. • Non-disjunction is when the spindle fibers fail to separate during meiosis, resulting in gametes with one extra chromosome and other gametes lacking a chromosome.

11. Chromosomal Mutations

12. Chromosomes and Cell Reproduction CHROMOSOME NUMBER AND STRUCTURE AFFECT DEVELOPMENT • Karyotype – array of the chromosomes found in an individual’s cells arranged in order of size and shape.

13. Chromosomes and Cell Reproduction CHROMOSOME NUMBER AND STRUCTURE AFFECT DEVELOPMENT • Autosomes – chromosomes that are not directly involved in determining sex. • Sex Chromosomes - chromosomes that are involved in determining the sex of an individual. In humans the 23rd pair. XX (female) XY (male).

14. Karyotypes • Normal Female

15. Karyotypes • Normal Male

16. Karyotypes • Bands depict where identified genes are located.

17. Karyotypes • Most embryos with trisomy 13 (patau syndrome) do not survive gestation and are spontaneously aborted. • Of those embryos that do survive to gestation and subsequent birth, common anomalies seen include mental & motor retardation, polydactyly (extra digits), microcephaly and cleft palate/lip. • There have been 5 cases reported in the medical history of patients living beyond 10 years of age.

18. Karyotypes • The survival rate for Edwards Syndrome is very low. • About half die in utero. Of liveborn infants, only 50% live to 2 months, and only 5 - 10% will survive their first year of life. • This results in characteristic physical abnormalities such as low birth weight; a small, abnormally shaped head; small jaw; small mouth; low-set ears; and clenched fists with overlapping fingers. • Babies with Edwards syndrome also have heart defects, and other organ malformations such that most systems of the body are affected

19. Karyotypes Individuals with Down syndrome may have some or all of the following physical characteristics: oblique eye fissures with epicanthic skin folds on the inner corner of the eyes, muscle hypotonia (poor muscle tone), a flat nasal bridge, a single palmar fold (also known as a simian crease), a protruding tongue (due to small oral cavity, and an enlarged tongue near the tonsils), a short neck, white spots on the iris known as Brushfield spots, excessive flexibility in joints, congenital heart defects, excessive space between large toe and second toe, a single flexion furrow of the fifth finger, and a higher number of ulnar loop dermatoglyphs.

20. Karyotypes • Most individuals with Down syndrome have mentalretardation in the mild (IQ 50–70) to moderate (IQ 35–50) range, with scores of children having Mosaic Down syndrome (explained below) typically 10–30 points higher. • In addition, individuals with Down syndrome can have serious abnormalities affecting any body system.

21. Karyotypes • Affected males are almost always effectively sterile. • In adults, possible characteristics vary widely and include little to no signs of affectedness, a lanky, youthful build and facial appearance, or a rounded body type with some degree of gynecomastia (increased breast tissue).

22. Karyotypes • Decreased testicular hormone/endocrine function. • Because of this hypogonadism, patients will often have a low serum testosterone level but high serum follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels Despite this misunderstanding of the term, however, it is true that XXY men often also have "microorchidism" (i.e. small testicles).

23. Karyotpes • XYY syndrome is an aneuploidy (specifically a trisomy) of the sex chromosomes in which a human male receives an extra Y chromosome, producing a 47,XYY karyotype. • 47,XYY boys and men are usually taller than average and several centimeters taller than their parents and siblings. • Severe acne was noted in a very few early case reports, but dermatologists specializing in acne now doubt the existence of a relationship with 47,XYY.

24. Karyotpes • 47,XYY boys have an increased risk of learning difficulties (in up to 50%) and delayed speech and language skills • Aggression is not seen more frequently in 47,XYY males

25. Karyotpes Turner Syndrome Symptoms • Short stature • Lymphoedema (swelling) of the hands and feet • Broad chest (shield chest) and widely-spaced nipples • Low hairline • Low-set ears • Reproductive sterility • Amenorrhea, or the absence of a menstrual period • increased weight, obesity

26. Karyotpes Turner Syndrome • Other symptoms may include a small lower jaw (micrognathia), cubitus valgus (turned-in elbows), a webbed neck, soft upturned nails, Simian crease and drooping eyelids. • Less common are pigmented moles, hearing loss, and a high-arch palate (narrow maxilla). • Turner syndrome manifests itself differently in each female affected by the condition, and no two individuals will share the same symptoms.

27. Chromosomal Mutations • The fundamental structure of a chromosome is subject to mutation, which will most likely occur during crossing over at meiosis. • There are a number of ways in which the chromosome structure can change, which will detrimentally change the genotype and phenotype of the organism. • If the chromosome mutation effects an essential part of DNA, it is possible that the mutation will abort the offspring before it has the chance of being born.

28. Chromosomal Mutations Deletion of a Gene • As the name implies, genes of a chromosome are permanently lost as they become unattached to the centromere and are lost forever. • 1 is Normal chromosome before mutation. • 2Genes not attached to centromere become loose and lost forever. • 3 New chromosome lacks certain genes which may prove fatal depending on how important these genes are.

29. Chromosomal Mutations Duplication of Genes • In this mutation, the mutants genes are displayed twice on the same chromosome due to duplication of these genes. This can prove to be an advantageous mutation as no genetic information is lost or altered and new genes are gained. • 1 Normal chromosome before mutation. • 2 Genes from the homologous chromosome are copied and inserted into the genetic sequence. • 3 New chromosome possesses all its initial genes plus a duplicated one, which is usually harmless. • These chromosome mutations and mutations that happen within genes that can prove to be more harmful to the organism at hand.

30. Chromosomal Mutations Inversion of Genes • This is where the order of a particular order of genes are reversed as seen below. • 1 Normal chromosome un-altered. • 2 The connection between genes break and the sequence of these genes are reversed. • 3 The new sequence may not be viable to produce an organism, depending on which genes are reversed. • Advantageous characteristics from this mutation are also possible.

31. Chromosomal Mutations Translocation of Genes • This is where information from one of two homologous chromosomes breaks and binds to the other. • Usually this sort of mutation is lethal. • 1 An un-altered pair of homologous chromosomes. • 2 Translocation of genes has resulted in some genes from one of the chromosomes attaching to the opposing chromosome.

32. Chromosomal Mutations • Humans are diploid creatures, meaning for every chromosome in our body, there is another one to match it. • Haploid creatures have one of each chromosome. • Diploid creatures have two of each chromosome. • Triploid creatures have three of each chromosome. • Polyploid creatures have three or more of each chromosome. • They can be represented by n where n equals haploid, 2n equals diploid and so on.

33. Chromosomal Mutations • It is possible for a species, particularly plant species, to produce offspring that contains more chromosomes than its parent. • This can be a result of non-disjunction, where normally a diploid parent would produce diploid offspring, but in the case of non-disjunction in one of the parents, produces a polyploid.

34. Chromosomal Mutations • In the case of triploids, although the creation of particular triploids in species is possible, they cannot reproduce themselves because of the inability to pair homologous chromosomes at meiosis, therefore preventing the formation of gametes. • Polyploidy is responsible for the creation of thousands of species on earth, and will continue to do so. • It is also responsible for increasing genetic diversity and producing species showing an increase in size, vigor and an increased resistance to disease.

35. Chromosomal Mutations