1. Genetics
Chapter 11

2. Heredity
Passing of traits from parent to offspring

3. Genetics The study of heredity
Gregor Mendel- Austrian monk known as the “father of genetics”

4. Mendel’s Four Hypotheses
For each inherited trait, an individual has a copy of that gene from each parent.
There are alternate versions of genes, called alleles. (ex: freckles or no freckles)

5. Hypothesis continued
When 2 different alleles occur together, one of them may be completely expressed (dominant), while the other may not be observed (recessive).
4. Alleles separate independently, so that each gamete only carries 1 allele for that trait.

6. Monohybrid cross Mendel began with 1 trait (monohybrid) crosses
He bred pea plants to produce several generations
P- the parent generation
F1 - the first filial generation
F2 - second filial generation

8. Mendel concluded that each parent has two separate “factors” for a particular trait
“Factors” are now called genes.

9. Mendel’s Laws of Heredity
Law of Segregation- two alleles separate when gametes are formed
Law of Independent Assortment- alleles of different genes separate independently of one another during gamete formation

10. Mendel’s Law of Segregation
Homozygous dominant parent
Homozygous recessive parent
Mendel’s Law of Segregation
(chromosomes duplicated before meiosis)
meiosis I
meiosis II
(gametes)
(gametes)
fertilization produces heterozygous offspring
Fig. 11-5, p.172

11. Independent Assortment
Nucleus of a
diploid (2n)
reproductive cell
with two pairs of
homologous
chromosomes
Possible alignments
of the two homologous
chromosomes during
metaphase I of meiosis
The resulting alignments
at metaphase II
Allelic combinations
possible in gametes
1/4 AB
1/4 ab
1/4 Ab
1/4 aB
Fig. 11-8, p.174

12. Some modern genetic terms
Alleles are represented by letters
Dominant allele is a capital letter
Recessive allele is a lower case letter

13. Homozygous- identical alleles for a specific trait (BB, FF, rr, tt)
Heterozygous- alleles are different for a specific trait (Bb, Ff, Rr, Tt) (aka “hybrid”)
Genotype- the set of alleles an individual inherits for a trait (i.e.- Rr, Ww, ff)
Phenotype- the physical expression of a trait (i.e. blue eyes, freckles, dimples)

14. Punnett Square Predicts possible outcomes of traits
Shows all possible outcomes of a genetic cross

15. Probability (likelihood that an event will occur) of a genetic outcome can be predicted
Ex: cross two heterozygous individuals Aa x Aa
predict ratios of
3:1 for phenotype and
1:2:1 for genotype

16. Practice
Curly hair is dominant over straight hair. A man with straight hair and a woman who is heterozygous for curly hair have a child. What is the probability that this child will have straight hair?

17. Incomplete Dominance- when an individual shows a combination of the inherited alleles.
Ex: red snapdragon x white snapdragon will produce a pink snapdragon
straight hair x curly hair = wavy hair

18. Codominance- 2 dominant alleles are expressed at the same time
Ex: Roan horses show both red and white hairs in equal numbers

19. Patterns of heredity can be very complex
Sex-linked trait- a trait whose alleles is located on the X chromosome (most are recessive)
Polygenic trait- trait where several genes influence the outcome (eye color, hair color, skin color, height, weight)

20. Multiple Alleles- genes with 3 or more alleles
- Blood type is an example of multiple alleles because we have A, B and O alleles and 4 possible blood type outcomes
(A, B, AB and O)

21. ABO Blood Type Range of genotypes: IAIA IBIB or or IAi IAIB IBi ii
Fig a, p.176

22. Diploid
Number of chromosomes found in the body or somatic cells of an organism
“2n”

23. Haploid
Number of chromosomes found in the gametes of an organism
“n”

24. Meiosis The type of cell division that produces gametes
Gametes = sex cells
female gamete = egg or ovum (plural = ova)
male gamete = sperm

25. Meiosis

26. Formation of sperm and egg