14.1 Human Chromosomes What makes us human? What makes us different from other animals such as a chimpanzee? About 1% of our DNA differs from a chimp The number of chromosomes and the genes found on those chromosomes.

14.1 Human Chromosomes Karyotype –photograph of chromosomes taken during mitosis, then arranged in decreasing size Where did these chromosomes come from? 23 from mom 23 from dad 5,000

14.1 Human Chromosomes Chromosome pairs 1 - 22 = autosomes Chromosome pair 23 = sex chromosomes (XX or XY) Females are written as 46XX; males are written as 46XY.

Sex Chromosomes Males and females born in 50:50 ratio X chromosome carries about 1,200 genes. Y carries only about 140.

Transmission of Human Traits - Recessive Alleles Cystic Fibrosis Autosomal recessive disorder on chromosome 7 People with cystic fibrosis lack one amino acid in the 1,480 amino acid sequence that makes up the CFTR protein CFTR protein is a transport protein located in the cell membrane – absence causes a thick mucus that clogs the lungs and makes patient susceptible to infection.

Transmission of Human Traits - Dominant Alleles Huntington disease, achondroplastic dwarfism, and polydactyly If a genetic disorder is dominant, it is expressed even if the individual is heterozygous.

Codominant Alleles Both alleles contribute to the phenotype of the organism. Sickle Cell Disease Characterize by “sickle” shaped red blood cells, cause blockage and severe pain in limbs and organs

Sex-Linked Genes Sex-linked Genes – genes located on the X chromosome More than 100 sex-linked genetic disorders have been linked to the X chromosome Y chromosome is much smaller and contains only a few genes Males have only 1 X chromosome All alleles on the X chromosome are expressed in males, even if they are recessive

X Chromosome Disorder Colorblindness 3 genes associated with colorblindness are found on the X chromosome 1/10 males are colorblind 1/100 females are colorblind Why is colorblindness more common in males? Males need only one allele to be colorblind. Females need two alleles to be colorblind.

Human Pedigrees How does one trace an inherited trait through generations? How does one predict who in the next generation will show that trait? The Pedigree Chart – show the relationships within a family

Human Pedigrees Circle represent female Square represents male Horizontal line represents marriage Vertical line represents children

Human Pedigrees Unshaded circle or square indicates that the person does not express the trait Half shaded circle or square indicates the person is a carrier for the trait. Completely shaded circle or square indicates that the person expresses the trait. How many generations are shown? 3

14-2 Human Genetic Disorders Genome – all the DNA contained in an organism. 3.2 billion letters of coding in the human genome. Genetic disorders result from: Changes in the DNA sequence that alter amino acids and could alter phenotype (cystic fibrosis) Chromosomal disorders – errors during meiosis that affect the number of chromosomes present in an individual (Down Syndrome)

Chromosomal Disorders Nondisjunction – homologous chromosomes fail to separate during meiosis Abnormal number of chromosomes find their way into gametes

Chromosomal Disorder Trisomy – having three copies of a chromosome Trisomy in chromosome 21 – Down Syndrome 1/800 births, causes mild to severe mental retardation

Chromosomal Disorder Turner Syndrome Females are born with only one X chromosome Females are sterile because sex organs do not develop at puberty. Klinefelter’s Syndrome Males born with an extra X chromosome Male is sterile

Autosomal Dominant Traits Appear with equal frequency in both sexes Are not likely to skip generations Both sexes can transmit the trait to the offspring Affected people must have affected parents

Autosomal Recessive Traits Appear with equal frequency in both sexes (unless penetrance differs in males and females) Appear only when two recessive alleles are inherited These traits seem to skip generations If trait is uncommon most parents carrying the allele are heterozygous (carriers)

X-linked Recessive Traits X-linked traits are more readily inherited by males Because males tend to inherit the trait from unaffected females, these traits tend to skip generations Sons can only inherit the trait from their mothers not their fathers All daughters will inherit an affected allele from affected fathers

X-linked Dominant Traits Appear in males and females (often more females than males) Each child with an X-linked dominant trait must have an affected parent Do not skip generations Affected men pass the trait to all of their daughters but none of their sons Affected women pass the trait on to about ½ of their daughters if heterozygous

Red-green color blindness is the inability to distinguish the colors red and green. The gene for this trait is located on the X-chromosome. The allele for normal color vision(XB) is dominant and the allele for color blindness (Xb) is recessive. A color blind woman and a man with normal vision plan to have their first child. Complete a punnet square for the couple.