Presentation on theme: "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."— Presentation transcript:
1 14.1 Human ChromosomesWhat makes us human? What makes us different from other animals such as a chimpanzee?About 1% of our DNA differs from a chimpThe number of chromosomes and the genes found on those chromosomes.
2 14.1 Human ChromosomesKaryotype –photograph of chromosomes taken during mitosis, then arranged in decreasing sizeWhere did these chromosomes come from?23 from mom23 from dad5,000
3 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.
4 Sex Chromosomes Males and females born in 50:50 ratio X chromosome carries about 1,200 genes. Y carries only about 140.
5 Transmission of Human Traits - Recessive Alleles Cystic FibrosisAutosomal recessive disorder on chromosome 7People with cystic fibrosis lack one amino acid in the 1,480 amino acid sequence that makes up the CFTR proteinCFTR 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.
6 Transmission of Human Traits - Dominant Alleles Huntington disease, achondroplastic dwarfism, and polydactylyIf a genetic disorder is dominant, it is expressed even if the individual is heterozygous.
7 Codominant AllelesBoth alleles contribute to the phenotype of the organism.Sickle Cell DiseaseCharacterize by “sickle” shaped red blood cells, cause blockage and severe pain in limbs and organs
8 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 chromosomeY chromosome is much smaller and contains only a few genesMales have only 1 X chromosomeAll alleles on the X chromosome are expressed in males, even if they are recessive
9 X Chromosome Disorder Colorblindness 3 genes associated with colorblindness are found on the X chromosome1/10 males are colorblind1/100 females are colorblindWhy is colorblindness more common in males?Males need only one allele to be colorblind. Females need two alleles to be colorblind.
10 Human PedigreesHow 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
11 Human Pedigrees Circle represent female Square represents male Horizontal line represents marriageVertical line represents children
12 Human PedigreesUnshaded circle or square indicates that the person does not express the traitHalf 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
13 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)
14 Chromosomal Disorders Nondisjunction – homologous chromosomes fail to separate during meiosisAbnormal number of chromosomes find their way into gametes
15 Chromosomal Disorder Trisomy – having three copies of a chromosome Trisomy in chromosome 21 – Down Syndrome1/800 births, causes mild to severe mental retardation
16 Chromosomal Disorder Turner Syndrome Females are born with only one X chromosomeFemales are sterile because sex organs do not develop at puberty.Klinefelter’s SyndromeMales born with an extra X chromosomeMale is sterile
17 Autosomal Dominant Traits Appear with equal frequency in both sexesAre not likely to skip generationsBoth sexes can transmit the trait to the offspringAffected people must have affected parents
18 Autosomal Recessive Traits Appear with equal frequency in both sexes (unless penetrance differs in males and females)Appear only when two recessive alleles are inheritedThese traits seem to skip generationsIf trait is uncommon most parents carrying the allele are heterozygous (carriers)
19 X-linked Recessive Traits X-linked traits are more readily inherited by malesBecause males tend to inherit the trait from unaffected females, these traits tend to skip generationsSons can only inherit the trait from their mothers not their fathersAll daughters will inherit an affected allele from affected fathers
20 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 parentDo not skip generationsAffected men pass the trait to all of their daughters but none of their sonsAffected women pass the trait on to about ½ of their daughters if heterozygous
21 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.