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Sex Linked Traits. What do you think sex linked means??? Traits that are controlled by genes located on the sex chromosomes. What are the sex chromosomes? XX for female, and XY for males. Chromosomes and Sex Linked Traits. The chromosomal theory of inheritance:
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Sex Linked Traits • What do you think sex linked means??? • Traits that are controlled by genes located on the sex chromosomes. • What are the sex chromosomes? • XX for female, and XY for males
Chromosomes and Sex Linked Traits • The chromosomal theory of inheritance: • Chromosomes carry ______ (the units of heredity) • Each chromosome contains many different genes • Paired chromosomes segregate during _______. Each sex cell or gamete has ____ the number of chromosomes found in a somatic cell • Chromosomes assort __________ during meiosis. This means that each gamete receives one member from each pair of chromosomes, and that each chromosome pair has no influence on the movement of any other chromosome pair.
Chromosomes and Sex Linked Traits cont. • Females have two __ chromosomes, while males have one __ and one __ chromosome • Sex linked traits are controlled by genes located on the sex chromosomes. A recessive trait located on the X chromosome is more likely to express itself in males than in females since males need only one copy of the recessive allele while females need two
Sex Linked Traits Info • Genes found on X chromosome, but not on Y chromosome • Females (XX) with one recessive and one dominant trait will display the dominant trait • Males (XY) with one recessive trait will display the recessive trait because they do not have a dominant trait to display
Sex Linked Traits in Humans 1. Hemophilia: the defective allele prevents the synthesis of a factor needed for blood clotting. 2. Colour Blindness: A condition where not all colours in the spectrum are visible. 3. Duchenne’s muscular dystrophy: A condition where muscles begin to degenerate in childhood.
Sample Problem A man with hemophilia maries a homozygous normal woman. Predict the possible genotypes and phenotypes of their children. XH X chromosome with normal dominant allele (non-hemophilia) Xh X chromosome with recessive hemophilia allele Y Y chromosome (does not contain comparable gene)
Sample Problem Step 1: Determine the genotypes of the parents Step 2: Determine the gamete genotypes produced by each parent Step 3: Set up a Punnett square using the gamete genotypes Step 4: Combine the gamete genotypes of one parent with those of the other parent to show all possible offspring genotypes Step 5: State the genotype and phenotype ratios of the offspring
Human Pedigrees • The tool we would use to demonstrate the passing on of traits within a family from generation to generation. • The pedigree uses different symbols and numbers that we need to be aware of in order for us to read it.
