1. Genetics
The Study of Heredity

2. Gregor Mendel Discovered many of the principles of modern genetics
Mendel studied the inheritance of traits using pea plants
Principles of basic inheritance are called Mendelian genetics

3. Genes
Genes are segments of chromosomes that determine the traits of an organism (ex. Eye color)
There may be several hundred to several thousand genes on a chromosome
We inherit 50% of our genes from our mothers and 50% from our fathers

5. 50% of your genes
from dad
50% of your genes
from mom

6. Alleles Three people with different alleles for a gene involved in
Every gene comes in different variations called alleles
Most genes have two different alleles while some have more than two
One person can have no more than two different alleles for the same gene (we get one from each parent)
Three people with different
alleles for a gene involved in
eye color

7. Dominant vs. Recessive Alleles
Alleles interact to produce traits (eye color, shape of skeleton, blood type, etc.)
Dominant alleles “overpower” recessive alleles (see diagram)
Brown
eyes
Brown
eyes
Blue
eyes

8. (picture of all 46 chromosomes) Each pair is called a homologous pair
Human Karyotype
(picture of all 46 chromosomes)
Each pair is called a homologous pair

9. Homologous Chromosomes
Mother
Father
Chromosomes that are very similar (size, shape, same type of genes) except that they come from two different individuals (see diagram)
A pair of homologous chromosomes
from one individual

10. Using probability to determine the likely inheritance of a trait
Monohybrid Crosses
Using probability to determine the likely inheritance of a trait

11. ALBINISM
Lack of pigment in skin, hair, and eyes

12. Example problem a= albino
The allele for normal skin pigment (A) is dominant over the allele for albinism (a). If a heterozygous normal pigmented man (Aa) marries a homozygous albino woman (aa), will they have any albino children?
A= normal pigmentation
a= albino

13. Punnett Square A a a Aa aa a aa Aa DAD’s possible
gametes
MOM’s possible gametes A a a Aa aa a aa Aa
Possible gene combinations (genotypes) of children

14. What percentage of their children have normal skin pigment?
50%
WHY?
The allele for normal pigment (A) is dominant over the allele for albinism (a).

15. Genotype vs. Phenotype
Genotype is the genetic make-up of an organism (its genes)
Phenotype refers to the actual physical traits an organism has as a result of its genes
The genotype determines the phenotype (see picture)
The genes of the fly give it its
unique characteristics

16. Heterozygous & Homozygous
Homozygous - having the same alleles for a given trait
Heterozygous - having different alleles for a trait

17. Meiosis Formation of gametes (sperm and egg)
Happens in testes (males) and ovaries (females)
Reduces the chromosome number by half
Meiosis produces 4 genetically different cells from the original cell

19. Why are the cells produced in meiosis different?
When gametes are made, they receive only one chromosome from each homologous pair, making haploid cells (have half the number of chromosomes as the original cell)
Chromosomes are distributed to gametes randomly resulting in different combinations of chromosomes (called independent assortment)
Independent assortment - random
distribution of chromosomes into the gametes
during meiosis

20. Why are the cells produced in meiosis different? (continued)
Chromosome shuffling (independent assortment)
Crossing over - homologous chromosomes exchange genetic information forming new combinations of genes (see diagram)
Mutations - a change in the DNA (genes) of an organism
Crossing over during prophase I
of meiosis

21. Mitosis vs. Meiosis One cell division
Results in 2 diploid cells (full set of chromosomes
Daughter cells are identical
Happens in body cells (somatic cells)
For growth and repair
Two cell divisions
Results in 4 haploid cells (half # of chromosomes)
Daughter cells are different
Happens in sex cells (gametes)
For maintaining the chromosome # of the species

22. Mendel’s Law of Segregation
Alleles for the same trait separate from each other during the formation of gametes
(see Punnett square diagram)

23. Mendel’s Law of Independent Assortment
Alleles for different traits are randomly
distributed to gametes (unless they are very closely linked)

24. Predicting Genetic Crosses with Punnett Squares
Monohybrid crosses (shows segregation)
Dihybrid crosses
(shows segregation and independent assortment)
Example of a dihybrid cross

25. Dihybrid cross (example)
A heterozygous guinea pig for black, rough fur mates with another heterozygous guinea pig for black, rough fur. What will the genotypes and phenotypes of their offspring be given the information below:
B = black fur
b = white fur
R = rough fur
r = smooth fur

26. Answer to Problem Black, rough fur (B__R__) Black, smooth fur (B__rr)
White, rough fur (bbR__)
White, smooth fur (bbrr) 9 3 3 1
A 9:3:3:1 ratio occurs when two heterozygous parents
have offspring in a dihybrid cross

27. Human Inheritance
Chapter 12

28. Patterns of Inheritance
Complete dominance
Incomplete dominance
Codominance
Polygenic Inheritance
Sex-linked inheritance

29. Incomplete Dominance
Neither allele of a pair is dominant over the other
A blend of both traits results
Genotypes and phenotypes of flowers showing incomplete dominance for
petal color (R= red and W=white)

30. Codominance Both alleles show dominance causing
both traits to be expressed in the phenotype of the organism
Examples:
1. Coat color in animals
2. Blood type in humans
Example of black roan coat
showing codominance

31. Blood type 3 different alleles for blood type exist:
IA and IB are codominant to each other
IA and IB are both dominant to i
Genotypes of the 4 blood types:
IAIA or IAi = type A
IBIB or IBi = type B
IAIB = type AB
ii = type O
Possible outcomes of children of
dad with type AB blood and mom with type O blood

32. Polygenic Traits
Traits that are controlled by the combined action of many genes
Show a diverse range of phenotypes
Most traits are polygenic
Ex. Skin color, hair color, eye color, height, risk for heart disease, etc.

33. Sex-linked traits Any trait that is carried on the X or Y chromosome
If allele is on the X chromosome, females will have two copies (XX) but males only one (XY)
Example: Hemophilia (blood does not clot properly)
Independent assortment of
sex chromosomes

34. Symbolizing Sex-Linked Traits
Hemophilia is a sex-linked recessive trait that is carried
on the X chromosome.
XH = normal
Xh = hemophilia
* Y chromosome has no gene for hemophilia

35. XH XH XH Xh Xh Xh XH Y Xh Y Possible genotypes and phenotypes
= normal woman XH Xh
= carrier (does not have disorder but carries the allele) Xh Xh
= hemophiliac female XH Y
= normal man Xh Y
= hemophiliac male