1. Introduction to Genetics
Chapter 11

2. The Work of Gregor Mendel

3. Genetics
The scientific study of heredity.

4. Vocabulary to Know
Trait: a specific characteristic varying among individuals
ex: eye color
Gene: a portion of DNA determining a trait; found on the chromosomes
ex: the gene for eye color

5. Vocabulary (continued)
Hybrid: the offspring of two parents with different traits
Gametes: reproductive cells (aka: sex cells; sperm & egg)

6. Allele: the form of a gene
Allele: the different forms of a gene
* Represented by a letter.
ex: Widow’s Peak = W
* Organisms have two alleles for each trait, one inherited from the mother and one from the father.
ex: WW

7. Forms of Alleles
Dominant Allele: trait will be expressed with only one copy present
* Represented with capital letters.
ex: W (Widow’s peak)
Recessive Allele: trait will only be expressed when no dominant alleles are present
* Represented with lower case letters.
ex: w (No widow’s peak)

8. Gregor Mendel Considered the father of genetics. Mid-1800s
Monk who experimented with pea plants in the monastery garden.

9. Mendel’s Conclusions
Inheritance is determined by factors passed from one generation to the next.
2. Principle of dominance: Some alleles are dominant and others are recessive.

10. Mendel’s Conclusions
3. Segregation: A gamete carries only one copy of each gene. 4. Principle of independent assortment: Genes for different traits segregate independently from one another.

11. Applying Mendel’s Principles

12. Allele Combinations Homozygous: both alleles are the same ex: WW or ww
Heterozygous: alleles are different
ex: Ww (capital letter is always 1st!)

13. Genotype: the actual allele combination; what the genes say
ex: WW, Ww, ww
Phenotype: the trait observed
ex: Widow’s Peak

14. Punnett Squares
Used to predict the genotypes of offspring when the genotypes of both parents is known.

15. Other Patterns of Inheritance

16. Incomplete Dominance
The heterozygous phenotype (Ww) is somewhere between both homozygous phenotypes (WW & ww).
Ex: pink flowers

17. Codominance
Both alleles contribute to the phenotype; neither allele is dominant .
Ex: roan cattle

18. Multiple Alleles
More than two allele possibilities.
Ex: blood type

19. Polygenic Traits Traits controlled by more than one gene.
Ex: skin color

20. Meiosis

21. Words to Know
Haploid: “one set”; cells that contain one set of each chromosome (gametes); 1n
Example: in humans n=23, so human haploid cells (gametes) have 1(23) or 23 total chromosomes
Diploid: “two sets”; cells that contain two sets of each chromosome ; 2n
Example: in humans n=23, so human diploid cells have 2(23) or 46 total chromosomes

22. Homologous Chromosomes
The pair of chromosomes that have the genes for the same traits.
A copy is inherited from each parent.

23. Meiosis
A type of cell division that produces gametes containing half the number of chromosomes as a body cell.
Contains two separate rounds of division, called Meiosis I & Meiosis II.
For example, during meiosis in humans, diploid cells with 46 chromosomes are divided into 4 haploid sex cells (gametes) with 23 chromosomes each.
Animation/

24. Interphase: cell grows, replicates its chromosomes and prepares to divide.
Prophase I: chromosomes take shape; homologous chromosomes pair up, forming a tetrad
Crossing over can occur! Chromosomes touch & exchange genes. This can mix up linked genes. (ones found on the same chromosome that occur together).
Phases of Meiosis

25. Metaphase I, Anaphase I, Telophase I
Nuclear membrane reforms & cytokinesis occurs.
Homologous chromosome pairs separate.
Chromosomes line up across the cell’s center.

26. Similar to Mitosis, except 4 haploid daughter cells are created.
Meiosis II
Similar to Mitosis, except 4 haploid daughter cells are created.
Prophase II:
No Replication occurs!
Metaphase II:
Chromosomes line up across the cell’s center.

27. Meiosis II (continued)
Telophase II:
Nuclear membrane reforms & cytokinesis occurs.
Anaphase II:
Chromosomes separate.

28. The end result: In males, all 4 of the daughter cells become sperm.
In females, the division of the cytoplasm is uneven, so only 1 egg is produced. The other three cells, called polar bodies are not used for reproduction.

29. Genetic Recombination
The reassortment of chromosomes and the genetic information that they carry by segregation and crossing over.
For example:
In humans, n = 23, so the number of different gametes that can be produced is 223 (more than 8 million).
When fertilization occurs, 223 x 223, or 70 trillion different zygotes are possible and this is without accounting for crossing over!
Zygote: the fertilized egg

30. Mitosis vs. Meiosis Mitosis Meiosis
Two identical daughter cells are formed.
Each daughter cell has one complete set of chromosomes. (diploid)
Four different gamete cells are created (although in females, only 1 is viable).
Each gamete cell has half of the total number of chromosomes. (haploid)

31. Linked genes
Genes that are located on the same chromosome & thus, tend to be inherited together.

32. Human Heredity

33. Things You May Not Know About DNA
Genome: the full set of genetic information carried in an organism’s DNA
Humans have 46 chromosomes in their genome.
Karyotype: a picture of all
diploid pairs of
chromosomes, arranged in
order of decreasing size

34. Chromosome Types
Autosomes: the remaining 44 human chromosomes other than
the sex chromosomes
Sex chromosomes: the pair of chromosomes determining gender
Males have XY.
Females have XX.
In female cells, most of the genes in 1 X are randomly switched off (called Barr bodies).
Ex: female calico cats

35. Sex-linked genes A gene located on a sex chromosome.
Genes on the Y chromosome are only found in males.
Genes on the X chromosome are found in both genders.
For recessive traits on the X, they are more common in males than females.
Ex: color-blindedness, hemophilia

36. Pedigree
A chart used to show the presence or absence of a trait within a family.

37. Human Genetic Disorders

38. Nondisjunction
When homologous chromosomes fail to separate during meiosis.
Creates monosomy and trisomy.

39.
When a Mistake is made…