Human GeneticsHuman Genetics

Linkage & Gene MapsLinkage & Gene Maps Some traits almost always appear together Some traits almost always appear together

(red hair & freckles)(red hair & freckles) Each chromosome is a group of linked Each chromosome is a group of linked

genes. The chromosomes sort genes. The chromosomes sort independently, not the individual genesindependently, not the individual genes

Two genes found on the same Two genes found on the same chromosome are not linked forever due to chromosome are not linked forever due to crossing-over. (Genetic diversity!)crossing-over. (Genetic diversity!)

The farther apart the genes, the more The farther apart the genes, the more likely they are to be separated during likely they are to be separated during crossing-overcrossing-over

Gene mapGene map: relative location of each : relative location of each known gene on one chromosomeknown gene on one chromosome

Human GeneticsHuman Genetics Karyotype: Set of Karyotype: Set of

photographs of photographs of chromosomes grouped in chromosomes grouped in order in pairsorder in pairs

Sex Chromosomes- Sex Chromosomes- females have two X females have two X chromosomes, males chromosomes, males have one X & one Yhave one X & one Y

Autosome: the Autosome: the remaining 44 remaining 44 chromosomes (non sex chromosomes (non sex chromosomes)chromosomes)

Male vs. FemaleMale vs. Female

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

Human ChromosomesHuman Chromosomes Human Human

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

Sex-Linked TraitsSex-Linked Traits

Sex-linked Traits:Sex-linked Traits: Traits that are Traits that are controlled by a gene on a sex controlled by a gene on a sex chromosome.chromosome.

Ex. – Eye color in fruit fliesEx. – Eye color in fruit flies

R – RedR – Red

r - Whiter - White

Sex-Linked Traits in HumansSex-Linked Traits in Humans

Several “defective” alleles are sex-linked. Several “defective” alleles are sex-linked. Few females suffer from sex-linked traits, Few females suffer from sex-linked traits, they are most often the carriers rather they are most often the carriers rather than affected by the disorder.than affected by the disorder.

Ex – Colorblindness, hemophilia, muscular Ex – Colorblindness, hemophilia, muscular dystrophy, night blindness.dystrophy, night blindness.

• Since the father can contribute only a Y, Since the father can contribute only a Y, the mother determines if the son will have the mother determines if the son will have the defective alleles.the defective alleles.

Multiple Gene Inheritance Multiple Gene Inheritance (Polygenic Inheritance)(Polygenic Inheritance)

Many traits (in both plant and animals) Many traits (in both plant and animals) do not appear in two contrasting forms.do not appear in two contrasting forms.

Ex: Height, skin colorEx: Height, skin color

Traits that vary between 2 extremes, Traits that vary between 2 extremes, are controlled by alleles of a single are controlled by alleles of a single gene, but by alleles of two or more gene, but by alleles of two or more genes.genes.

MisconceptionsMisconceptions

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

Inherited TraitsInherited Traits

Tongue RollingTongue Rolling DimplesDimples

Inherited TraitsInherited Traits

Detached/Attached Detached/Attached EarlobesEarlobes

FrecklesFreckles

Inherited TraitsInherited Traits

Cleft ChinCleft Chin HairlineHairline

Other Inherited TraitsOther Inherited Traits

Taste PTC paperTaste PTC paper Right handedRight handed Curly hairCurly hair AllergiesAllergies