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 species2 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 HEREDITY14.1 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.