Karyotypes Pedigrees Sex-Linked Traits Genetic Disorders

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1 Karyotypes Pedigrees Sex-Linked Traits Genetic Disorders

2 Consists of 23 pairs of chromosomes. Images are taken from diploid cells during mitosis. Chromosomes 1 through 22 are called autosomes. The X and Y chromosomes are the sex chromosomes. Males are XY. Females are XX. The Human Genome

3 Karyotyping Explained A karyotype is an organized profile of an organisms chromosomes. This arrangement helps scientists quickly identify chromosomal alterations that may result in a genetic disorder. To create a karyotype, scientists take a picture of the chromosomes from one cell, cut them out, and arrange them using size, banding pattern, and centromere position as guides. This is karyotype from a human male. How do we know??? Karyotyping 1

4 Karyotyping Can you identify the chromosome abnormality in this karyotype? Is this individual a male or a female?

5 Pedigrees All of the conclusions regarding gene action (dominant/recessive) we have discussed so far have been obtained from analyzing the results of controlled crosses (Punnett Squares). In some situations, we do not have the opportunity to perform controlled crosses. Instead, we need to analysis an existing population. Scientists have devised another approach, called pedigree analysis, to study the inheritance of genes in humans. In the simplest pedigrees, a trait is considered either present or absent, such as with the expression of a disease.

6 Pedigrees Basic Symbols

7 Pedigrees The offspring are depicted below the parents. Shading the symbol indicates the expression of the studied trait.

8 Analyzing Pedigrees: Human Genetic Disorders Boxes represent males. Circles represent females. Diamond represents an individual of unspecified gender. Shading represents affected individuals. This example: -Autosomal dominant disorder -Single gene disorder

9 Factors to Consider in Pedigrees Is the trait located on a sex chromosome or an autosome? Autosomal not on a sex chromosome Sex Linkage located on one of the sex chromosomes Y-linked - only males carry the trait. X-linked (recessive) - sons inherit the disease from normal parents How is the trait expressed? Dominant - the trait is expressed in every generation Recessive - expression of the trait may skip generations

10 Albinism: Genotype the Affected Individuals Assign codes for the alleles. Code A for the dominant normal allele. Code a for the recessive allele for albinism. Affected individuals must be homozygous for a. First generation parents must be Aa because they have normal phenotypes, but affected offspring.

11 Albinism: Genotype the Affected Individuals Normal individuals must have at least one A.

12 Albinism: Parent- Offspring Relationships #1 must transmit a to each offspring. The A in the offspring must come from the father. Normal father could be either heterozygous or homozygous for an A. **

13 Sex Determination Sex chromosomes determine an individual s gender.

14 Sex-Linked Traits In sex-linked traits, the gene for the trait is found on the X chromosome, a sex chromosome, not an autosome. Sex-linked traits affect primarily males, since they have only one copy of the X chromosome (male genotype: XY). Females, who have two copies of the X chromosome, are affected only if they are homozygous for the trait. Females can, however, be carriers for sex-linked traits, passing their X chromosomes on to their sons.

15 Sex-linked inheritance works as follows: if a female carrier and a normal male give birth to a daughter, she has a 1 in 2 chance of being a carrier of the trait (like her mother). If the child is a son, he has a 1 in 2 chance of being colorblind. If a female carrier and an affected male give birth to a daughter, she will either be not affected or be a carrier.

16 Another example of a sexlinked trait is hemophilia, made famous by the "Queen Victoria pedigree" of the European nobility. Beginning with Queen Victoria of England (in whom it was probably a spontaneous mutation), the hemophilia gene spread quickly throughout the European rulers (who intermarried). The disease, which prevents blood from clotting properly and renders a minor injury a life-threatening event, claimed several in the royal line.

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18 Hairy Ears: A Rare Y- linked Trait? Only males are affected. Sons of an affected father have hairy ears. Genetic studies have determined this is NOT a sex-linked trait, BUT we are going to use it for practice with pedigrees!

19 Hairy Ears: Female Sex Determination All females are XX.

20 Hairy Ears: Male Sex Determination All males are XY.

21 Hairy Ears: Gene on the Y Chromosome Code H indicates the allele on the Y chromosome for hairy ears.

22 Hairy Ears: Normal Allele for Normal Ears Code + indicates the allele on the Y chromosome for normal ears. + is Normal H is Hairy

23 Calico Cats #1 Black

24 Black Calico Cats #2

25 Genetic Testing Used for diagnostic, carrier, prenatal, or presymptomatic testing. Knowing physical traits can determine what genes an individual is most likely to have. Record keeping helps scientists use pedigree analysis to study inheritance patterns, determine phenotypes, and ascertain genotypes. Concerns for discrimination and privacy will need to be addressed by society before medical genetics can reach its full potential to prevent or treat disease.

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27 Complex Inheritance and Human Heredity

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29 Identify the disease characterized by the absence of melanin. A. albinism B. cystic fibrosis C. galactosemia D. Tay-Sachs

30 Under what circumstances will a recessive trait be expressed? A. A recessive allele is passed on by both parents. B. One parent passes on the recessive allele. C. The individual is heterozygous for the trait. D. There is a mutation in the dominant gene.

31 Which is the genotype of a person who is a carrier for a recessive genetic disorder? A. DD B. Dd C. dd D. de

32 Complex Inheritance and Human Heredity Albinism is a recessive condition. If an albino squirrel is born to parents that both have normal fur color, what can you conclude about the genotype of the parents? A. at least one parent is a carrier B. both parents are carriers C. both parents are homozygous recessive D. at least one parent is homozygous dominant

33 Of the 23 pairs of chromosomes in human cells, one pair is considered to be the. A. autosomes B. Barr bodies C. monosomes D. sex chromosomes

34 What does a karyotype show? A. The blood type of an individual. B. The locations of nitrogen bases on a chromosome. C. The cell s chromosomes arranged in order. D. The phenotype of individuals in a pedigree.

35 If a genetic disorder is caused by a dominant allele, what is the genotype of those who do not have the disorder? A. heterozygous B. homozygous dominant C. homozygous recessive

36 Why are males affected by recessive sexlinked traits more often than are females? A. Males have only one X chromosome. B. Males have two X chromosomes. C. Males have only one Y chromosome. D. The traits are located on the Y chromosomes.

37 Complete Genetics Practice Problems 2 Worksheet!