1 Review What are autosomes Explain What determines whether a person is male or female Propose a Solution How can you use a karyotype to identify a species 2 Review Explain how sex linked traits work Infer Why would the Y chromosome be unlikely to contain any of the genes that are absolutely necessary for survival

Ch 14 Human Heredity 14.1 Human Chromosomes

Karyotypes Shows the complete diploid set of chromosomes grouped together in pairs, arranged in order of decreasing size.

Genome Full set of genetic information that an organism carries.

Sex Chromosomes Two of the 46 chromosomes determine sex Females are XX Males XY.

X chromosome contains 1200 genes Y chromosome contains 140 genes Most are associated with male development.

Autosomal Chromosomes Remaining 44 human chromosomes.

Transmission of Human Traits Many traits have a pattern of simple dominance Many are also codominant.

Dominant and Recessive Alleles Rhesus, or Rh blood group Rh+ and Rh- Rh+ is dominant so heterozygous individual is Rh+ Rh- individuals need to have both negatives.

Codominant and Multiple Alleles Human blood types Determined by a gene with three alleles: IA, IB, and i.

Codominant and Multiple Alleles Alleles IA and IB are codominant Produce molecules known as antigens on the surface of red blood cells Individuals with alleles IA and IB produce both A and B antigens Blood type AB The i allele is recessive Homozygous for the i allele (ii) produce no antigen and are type O.

Sex Linked Gene Gene located on a sex chromosome Genes on Y chromosomes only pass from father to son Genes on X chromosome are found in both sexes Remember males only have one.

Sex-Linked Inheritance Three genes responsible for color vision all are on the X chromosome Males only have one X so if they have one recessive allele they will have some form of color blindness, 1 in 12 Females have 2 X chromosomes so they would need both copies of a recessive allele, 1 in 200.

X-Chromosome Inactivation Females really only need to use 1 X chromosome (males make it work) The second X chromosome is turned off Barr Body Inactivated x chromosome that gets shoved off to the side.

X-Chromosome Inactivation Also occurs in other mammals like cats One X chromosome has an allele for orange spots Other X chromosome has an allele for black spots Some cells has one X chromosome switched off other cells turns off the other.

Pedigree Shows the presence or absence of a trait according to the relationships between parents, siblings, and offspring.

This pedigree shows how a white lock of hair just above the forehead passes through three generations of a family White lock is dominant.

Grandfather has trait Two of his three children inherited the trait Three grandchildren have the trait, but two do not.

All family members lacking this trait must have homozygous recessive alleles One of the grandfather’s children lacks the white forelock trait, so the grandfather must be heterozygous.