1. Chapter 7: Extending Mendelian Genetics

2. Section 1: Chromosomes & Phenotype

3. Autosomal Genes & Phenotype
Phenotype is determined by 2 copies of each autosomal gene
Mendel studied autosomal characteristics
Most traits in humans are determined by autosomal genes

4. Autosomal Disorders
Many genetic disorders are caused by recessive alleles on autosomes
NN: healthy
Nn: healthy; carrier for the disorder
nn: has disorder
Less genetic disorders are caused by dominant alleles on autosomes
NN and Nn: has disorder
nn: healthy

5. Sex-Linked Traits
Genes located on the sex chromosomes (X or Y) are called sex-linked genes
Genes on the Y chromosome are responsible for male characteristics only
X chromosome has many more genes that affect many traits
In males, all sex-linked traits are expressed
they only have one copy of each chromosome, so all alleles are expressed even if they’re recessive

6. X Chromosome Inactivation
Since females have 2 X chromosomes, one of them is randomly turned off in each cell
Because it is random, a female will have some cells with one X turned off, and others with the other X turned off

7. Section 2: Complex Patterns of Heredity

8. Complex Patterns
Incomplete dominance - heterozygous individual shows a blending of the two homozygous phenotypes
Ex. Four o’clock plants
RR = red flowers
rr = white flowers
Rr = pink flowers

9. Ex. Human ABO blood type - has multiple alleles (IA, IB, & i)
Codominance - both alleles are dominant, so both are fully and separately expressed
Ex. Human ABO blood type - has multiple alleles (IA, IB, & i)
IAIA or IAi = type A blood
IBIB or IBi = type B blood
IAIB = type AB blood
ii = type O blood

10. Ex. human skin tone, human eye color
Polygenic traits - traits produced by two or more genes, leading to a range of phenotypes
Ex. human skin tone, human eye color
In a polygenic trait, one gene may be epistatic, meaning it can interfere with the expression of the other genes
Ex. albinism in mammals

11. Genes & the Environment
Phenotype is usually a mixture of genes & the environment
Ex. genes determine your underlying skin tone & hair color, but sunlight can cause your skin to become darker and hair to become lighter

12. Section 4: Human Genetics & Pedigrees

13. Human Genetics Humans follow the same basic patterns of heredity
The inheritance of many human traits can be very complex
Polygenic traits, the environment, etc…
Some human traits are single-gene traits that follow simple dominant and recessive patterns like Mendel’s peas
Ex. widow’s peak, Huntington’s disease

14. X and Y Chromosomes
X chromosome is 3x larger than the Y & has many more genes
Since females have 2 X chromosomes, they can be carriers for sex-linked traits
Sex-linked disorders are more common in males since they only have one X chromosome

15. Pedigree Circle = female Square = male Shaded = person with trait
Unshaded = person without trait
Half shaded = carrier for a genetic disorder
Horizontal line = marriage
Vertical line & bracket = offspring
For some individuals in a pedigree, you can determine genotypes based on their phenotypes

16. Pedigrees: Tracing Autosomal Traits
If trait is recessive, shaded individuals would be nn, unshaded would be NN or Nn, carriers would be Nn
If trait is dominant, unshaded would be nn, shaded would be either NN or Nn

17. Pedigrees for sex-linked traits
Shaded females must be homozygous recessive XnXn
Unshaded females could be XNXN or XNXn - carrier
Shaded males must have the recessive allele XnY
Unshaded males must have the dominant allele XNY

18. Karyotype Picture of all the chromosomes in a cell (see pg. 217)
Can show gender as well as any chromosomal abnormalities
Down syndrome: extra chromosome #21
Turner’s syndrome: female only has 1 X
Klinefelter’s syndrome: male has XXY
Caused by non-disjunction, which is when chromosomes fail to separate during meiosis