1. Human Inheritance & Pedigree

2. Patterns of Human Inheritance
Human traits are controlled by:
single genes with two alleles
others by single genes with multiple alleles.
Still other traits are controlled by many genes that act together
All genes are made up of the DNA sequences on your chromosomes.

3. A Single Gene with Two Alleles
Have 1 dominant and 1 recessive allele
Have 2 distinctly different phenotypes
Examples:
Widow’s Peak and straight hair line
Smile dimples and no dimples

4. Hybrids=Heterozygous- Have two different alleles for a gene: Rr
Hybrid vs. Purebred
Hybrids=Heterozygous- Have two different alleles for a gene: Rr
Purebreds=Homozygous- Have the same allele for a gene:
RR or rr

5. Incomplete Dominance
When the offspring of two homozygous parents show an “in-between” phenotype.
Example:
Purebred white flowers
Purebred red flowers
Makes “in-between”
color pink flowers

6. Any trait that is controlled by many alleles.
Multiple Alleles
Any trait that is controlled by many alleles.
Example:
Blood Type

7. Single Genes with Multiple Alleles
Some traits have more than 2 alleles even though a person can have only 2 of those alleles (because chromosomes exist in pairs!)
Each chromosome in a pair carries only 1 allele for each gene
Ex: Human blood type
3 alleles (A, B, O)
A and B are codominant
O is recessive

9. Polygenic Inheritance
When many genes act to control a trait.
Poly=many
Examples:
hair color
eye color
skin color

10. Traits Controlled by Many Genes
Produce a large
variety of phenotypes
Genes act together as a group to produce a single trait
Examples:
Height –
at least 4 genes
Skin color –
at least 3 genes

11. The Sex Chromosomes
One of the 23 pairs of chromosomes that carries the genes that determine whether a person is male or female
Also carries genes that determine other traits

12. Girl or Boy? Sperm cells carry either an X or a Y
Egg cell always carries an X chromosome
Girl – two sex chromosomes match (X,X)
Boy –don’t match (X,Y)
(The Y chromosome is smaller
than the X!!)

13. Sex-Linked Genes
Sex-linked genes can have dominant and recessive alleles
In females a dominant allele on one x will mask a recessive on the other X
In males, there is no matching allele on the Y to mask a recessive allele on the X
Any trait on the X chromosome in males (even a recessive trait) will produce the trait in a male who inherits it.
Example: Red-green colorblindness

14. Inheritance of Colorblindness
Colorblindness is a trait controlled by a recessive allele on the X chromosome
More males have colorblindness than females.
Females can be carriers. If they have one dominant trait for normal color vision and one recessive trait for colorblindness. They have normal color vision.

15. Red-Green Colorblindness

16. Inheritance of Colorblindness
If the mother passes on the X chromosome to a son, he will be colorblind
If she passes it onto a daughter, she will also have an X chromosome from her father.
If her father has normal color vision, then she will inherit the dominant allele for normal color vision from him and she will have normal color vision

17. Inheritance of Colorblindness
Father XCY XC Y XC
XCXC
XCY
Mother
XCXc
XCXc
XcY Xc

18. The Effect of Environment
Many of a person’s characteristics are determined by an interaction between genes and the environment.
Several genes work together to determine height.
Environment affects height – a poor diet can prevent a person from reaching their potential.
Environmental factors can also affect human skills – Ex: Playing a musical instrument – need instruction to play well

19. Pedigree
One important tool that geneticists use to trace the inheritance of traits in humans is a pedigree.
A pedigree is a chart or “family tree” that tracks which members of a family have a particular trait.

20. Pedigree Chart A circle represents a female A square represents a male
A completely shaded square or circle indicates that the person has the trait.
A circle or square that is NOT shaded indicates that a person neither has the trait nor is a carrier.
A half-shaded square
indicates that a person is a
carrier.