1. Mendelian VS. Non-Mendelian Genetics
GENETICS UNIT 2015
Mendelian VS.
Non-Mendelian Genetics

2. GENE Gene = section of DNA that codes for a particular protein.
Locus = specific position on a pair of homologous chromosomes.

3. ALLELE Allele = alternative form of a gene.
Each parent donates one for every gene
Homozygous = two alleles are that are the same
Heterozygous = two alleles that are different.

4. TRAIT
Trait = genetically determined characteristic of a person.

5. Genotype = makeup of a specific set of genes.
Phenotype = physical expression of a trait.

6. Dominant vs. Recessive
Dominant = expressed when at least one allele is dominant.
Represented by uppercase letters
Recessive = expressed only when two copies are present.
Represented by lowercase letters

7. PUNNETT SQUARES
Punnett square = grid system for predicting possible genotypes from a cross.
Axes = possible gametes from each parent
Boxes = possible genotypes of offspring.

8. Mendel Gregor Mendel was born in 1822.
Called the “Father of Genetics” & worked on Pea Plants.
Late 1800 chromosomes and the process of meiosis were unknown.
Mendel’s work was considered obscure and unimportant until 1900.

9. Gregor Mendel’s Findings
Principle of Dominance
When contrasting traits are crossed, the offspring will express the dominant trait.
Principle of Segregation
The pair of homologous chromosomes separate during meiosis so that only one chromosome is in each gamete.
Principle of Independent Assortment
Genes separate independently of one another in meiosis.

10. MONOHYBRID CROSS
Monohybrid = examines a specific trait.

11. PROBABILITY
Probability = likelihood that something will happen.

12. TESTCROSS
Testcross = cross between an organism with the unknown genotype and an organism with the recessive phenotype.

13. DIHYBRID CROSS Dihybrid = cross that involves two traits.
Cross with two heterozygous traits will always yield a 9:3:3:1 phenotypic ratio.

14. Non-Mendelian Inheritance
Exception to the Rules

15. Let’s Review Mendelian GeneticsB b
Blue(B) is dominant to green(b).
Alien Body Color BB bb Bb

16. INCOMPLETE DOMINANCE
Incomplete dominance = neither allele is completely dominant nor completely recessive.
Result = The phenotype of the heterozygous is a blend of the two homozygous phenotypes.
R r R r RR Rr rr
RR Rr rr

17. CODOMINANCE Codominance = alleles are neither dominant or recessive.
Result = both alleles will be completely expressed.
Ex: Blood types of humans.
Type B is dominant to Type O
Type O
is recessive
Type AB is
co-dominant
Type A is dominant to Type O

18. Codominance W w Ww W w WW Ww Ww ww
Both alleles are expressed equally

19. POLYGENIC Polygenic traits = produced by two or more genes
Genes may be located on the same chromosome or on different chromosomes
Order of dominance: brown > green > blue.

20. SEX-LINKED GENES Sex-linked genes = genes on sex chromosomes..
Y chromosome genes in mammals are responsible for male characteristics.
X chromosome genes in mammals affect many traits.

21. SEX-LINKED GENES Male mammals have XY genotype
All sex-linked genes are expressed
Have no second copies of the genes
XX XY

22. SEX-LINKED GENES
Genes found only on the X chromosomes
Female mammals have XX genotype
Expression similar to autosomal genes
One X chromosome is randomly turned off
Colorblindness and Baldness are examples of sex-linked traits.

23. SEX-LINKED GENETIC DISORDERS
Females can be carriers of sex-linked disorders
Males express all of their sex-linked genes.

24. PEDIGREE
Pedigree = chart for tracing genes in a family

25. PEDIGREES