King Henry VIII and his six wives
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King Henry VIII and his six wives
King Henry VIII of England married six times in an attempt to have a legitimate male heir to the English throne. Henry VIII blamed his wives for their inability to produce a son.
Was Henry correct in blaming his wives? Explain.
Sex Determination in Humans:
Phenotype: 50% female , 50% male
Genotype: 50% XX , 50% XY
Prince William and Kate Middleton
The firstborn of Prince William and Kate Middleton will be heir to the throne, whether it’s a boy or a girlunder the new successionrules.
Sex-Linked Inheritance• Sex linked traits: Occur in humans, for which genes are on the X
chromosome.
• Each X-chromosome in the female will have one allele for a gene for a total of 2 alleles per gene
• Because Males have only one X-chromosome they will only have one allele for a particular gene.
Female Male
Sex-Linked Inheritance
• Types of inheritance: X-linked Dominant: dominant allele carried on one or both of the X-
chromosomes will cause expression of the phenotype
X-linked Recessive: recessive alleles must be present on both X-chromosomes for a woman in order for the phenotype to be expressed, whereas a man only needs one recessive allele
Dominant alleleRecessive allele
Sex- Linked Disorders• There are various disorders that arise from sex-linked inheritance.
(Note: the disorder is considered to be the phenotype).
Severe Combined Immunodeficiency Haemophilia
Colour Blindness
The gene that causes colour blindness is on the X chromosome.
Sex-linked Inheritance Problem:• Color blindness is an sex-linked recessive disorder. Suppose a
heterozygous female (carrier) is crossed with a normal male. What would be the genotype and phenotype proportions of the F1 generation?
X H Xh
XH
Y
X H X H Xh X H
X H Y Xh Y
Phenotype: 2 normal females 1 normal male 1 color blind male (Xh Y)
Genotype: 25% XHXH
25% XH Y 25% Xh XH
25% Xh Y
Defective allele