1. Mendel & Heredity

2. Gregor Mendel “Father of Genetics”
Austrian monk who completed breeding experiments with the garden pea plant, Pisum sativum
Wanted to learn more about how traits were passed from one generation to the next
Terms to know:
Character ~ physical features inherited (Ex: color)
Trait ~ several possible forms of character (Ex: purple, white)
Hybrid ~ results from crossing different traits (Ex: purple with a white)
Generation ~ a group of offspring from a given group of parents (P= parental, F= filial)

3. More Terms to Know
Allele: one of the alternative forms of a gene that governs a characteristic
Homozygous: Having identical alleles for a trait
Heterozygous: Having different alleles for a trait

4. And Even More Terms
Genotype: Combination of genes for one or more specific traits
Phenotype: organism’s appearance or other detectable characteristic that results from the organism’s genotype and environment

5. Mendel’s results

6. Mendel’s Theory
Why did that happen? Purple one generation, purple and white for another generation
ALLELES
Diff. versions of traits (Ex: White trait represented by “p” allele & Purple trait represented by “P” allele)
Get one from each parent
Dominant ~ always fully expressed (P)
Recessive ~ only expressed when there is no dominant (p)

7. Mendel’s Laws
Law of segregation ~ each pair of alleles is separated (meiosis) & each gamete has equal chance receiving either allele (GENETIC VARIATION)
Combination of alleles for a character = genotype (Ex: PP or Pp or pp)
Combination of alleles for a trait = phenotype “physical” (Ex: PP or Pp = purple, pp = white)
Two of same alleles = homozygous (Ex: PP or pp)
Two diff alleles = heterozygous (Ex: Pp)

8. Mendel’s Laws con’t Law of Independent Assortment
The allele of each gene segregate independently
One trait won’t affect another
If traits are not located close to 1 another on chromosome

9. Good ol’ Mendel Punnett squares ~ Predict the likely ratio of the
Why are Mendel’s Laws and work so important?
Monohybrid homozygous ~ always result in 0:4:0 genotype & 4:0 phenotype offspring (Yy dominant trait expressed)
Monohybrid heterozygous ~ will result in 1:2:1 genotype (1=YY, 2=Yy, 1=yy) & 3:1 phenotype (3 dominant trait expressed, 1 recessive trait expressed)
Punnett squares ~ Predict the likely ratio of the
genotype of a given cross

10. Punnett Practice
A plant has two alleles of a gene for stem length, long (L) and short (l). Two plants that are both heterozygous for the gene are crossed. Use a Punnett square to estimate the chances of getting heterozygous offspring.

11. Punnett Practice
A plant has two alleles of a gene for stem length, long (L) and short (l). Two plants that are both heterozygous for the gene are crossed. Use a Punnett square to estimate the chances of getting heterozygous offspring.

12. Punnett Practice
A plant has two alleles of a gene for stem length, long (L) and short (l). Two plants that are both heterozygous for the gene are crossed. Use a Punnett square to estimate the chances of getting heterozygous offspring.

13. Punnett Practice L l L L L l L l l l
A plant has two alleles of a gene for stem length, long (L) and short (l). Two plants that are both heterozygous for the gene are crossed. Use a Punnett square to estimate the chances of getting heterozygous offspring.
Parents are “Ll” L l
1 LL : 2 Ll : 1 ll
2/4 are Ll (heterozygous)
50% chance
L L
L l
L l
l l

14. Punnett Practice
A cat is heterozygous for long hair (Hh), and its mate is homozygous recessive, giving it short hair (hh). If they mated and had a litter of eight kittens, how many short hair kittens would you expect to find?

15. Punnett Practice H h H h h h H h h h
A cat is heterozygous for long hair (Hh), and its mate is homozygous recessive, giving it short hair (hh). If they mated and had a litter of eight kittens, how many short hair kittens would you expect to find?
Looking for “hh” H h
2 Hh : 2 hh
2/4 are hh (homozygous recessive)
½ * 8 = 4
H h
h h
H h
h h