Human Genetics

Linkage & Gene Maps Some traits almost always appear together (red hair & freckles) Some traits almost always appear together (red hair & freckles) Each chromosome is a group of linked genes. The chromosomes sort independently, not the individual genes Each chromosome is a group of linked genes. The chromosomes sort independently, not the individual genes Two genes found on the same chromosome are not linked forever due to crossing-over. (Genetic diversity!) Two genes found on the same chromosome are not linked forever due to crossing-over. (Genetic diversity!) The farther apart the genes, the more likely they are to be separated during crossing-over The farther apart the genes, the more likely they are to be separated during crossing-over Gene map: relative location of each known gene on one chromosome Gene map: relative location of each known gene on one chromosome

Human Genetics Karyotype: Set of photographs of chromosomes grouped in order in pairs Karyotype: Set of photographs of chromosomes grouped in order in pairs Sex Chromosomes- females have two X chromosomes, males have one X & one Y Sex Chromosomes- females have two X chromosomes, males have one X & one Y Autosome: the remaining 44 chromosomes (non sex chromosomes) Autosome: the remaining 44 chromosomes (non sex chromosomes)

Male vs. Female Males and females are born in an almost 50:50 ratio. This is because all egg cells carry a single X chromosome and half of all sperm carry an X chromosome and half carry a Y chromosome Males and females are born in an almost 50:50 ratio. This is because all egg cells carry a single X chromosome and half of all sperm carry an X chromosome and half carry a Y chromosome

Human Chromosomes Human chromosomes contain both DNA and protein. Each chromosome contains a single, double- stranded DNA molecule. Human genes are coded directly in the sequences of nucleotides in DNA Human chromosomes contain both DNA and protein. Each chromosome contains a single, double- stranded DNA molecule. Human genes are coded directly in the sequences of nucleotides in DNA

Sex-Linked Traits Sex-linked Traits: Traits that are controlled by a gene on a sex chromosome. Sex-linked Traits: Traits that are controlled by a gene on a sex chromosome. Ex. – Eye color in fruit flies R – Red r - White

Sex-Linked Traits in Humans Several “defective” alleles are sex-linked. Few females suffer from sex-linked traits, they are most often the carriers rather than affected by the disorder. Several “defective” alleles are sex-linked. Few females suffer from sex-linked traits, they are most often the carriers rather than affected by the disorder.  Ex – Colorblindness, hemophilia, muscular dystrophy, night blindness. Since the father can contribute only a Y, the mother determines if the son will have the defective alleles. Since the father can contribute only a Y, the mother determines if the son will have the defective alleles.

Multiple Gene Inheritance (Polygenic Inheritance) Many traits (in both plant and animals) do not appear in two contrasting forms. Many traits (in both plant and animals) do not appear in two contrasting forms. Ex: Height, skin color Traits that vary between 2 extremes, are controlled by alleles of a single gene, but by alleles of two or more genes. Traits that vary between 2 extremes, are controlled by alleles of a single gene, but by alleles of two or more genes.

Misconceptions A widespread misconception is that traits due to dominant alleles are the most common in the population. While this is sometimes true, it is not always the case. For example, the allele for Huntington’s Disease is dominant, while the allele for not developing this disorder is recessive. At most, only 1 in 20,000 people will get Huntington’s; most people have two recessive, normal alleles. A widespread misconception is that traits due to dominant alleles are the most common in the population. While this is sometimes true, it is not always the case. For example, the allele for Huntington’s Disease is dominant, while the allele for not developing this disorder is recessive. At most, only 1 in 20,000 people will get Huntington’s; most people have two recessive, normal alleles.

Inherited Traits Tongue Rolling Tongue Rolling Dimples Dimples

Inherited Traits Detached/Attached Earlobes Detached/Attached Earlobes Freckles Freckles

Inherited Traits Cleft Chin Cleft Chin Hairline Hairline

Other Inherited Traits Taste PTC paper Taste PTC paper Right handed Right handed Curly hair Curly hair Allergies Allergies