Chapter 9

Fundamentals of Genetics

Page 164

• Look at the photo and answer the following questions in complete sentences!

• How is this alligator different from other alligators you have seen?

Background Vocab

• Genetics:– Field of biology to understand how

characteristics are given from parents to their children

• Heredity:– The sending of characteristics

from parents to children

• Gregor Mendel:– Person who did much of the work

to create genetics as a topic to study

Mendel’s Peas

• Mendel looked at 7 characteristics.

• Each characteristic had 2 options.– Height—tall or short– Seed color—yellow or green– Texture—smooth or wrinkled– Flower color—purple or white

• He collected seeds from his pea plants and planted them the next year.

• Seeds from a purple flower plant…

Purple Flower & White Flower Plants

• Seeds from a tall plant…

Tall & Short Plants

• P1 Generation:

– Parents

• F1 Generation:

– 1st set of children

• F2 Generation:

– 2nd set of children

For Example…

P1 F1 F2

Tall X Short All Tall Most Tall

Some Short

Purple X White

All Purple Most Purple

Some White

Mendel’s Conclusions

• A pair of factors must control each trait (ex. Tall vs. Short).

• One factor must prevent the other from being seen. (In F1 only saw tall plants.)

• Dominant:– Trait that is seen

• Recessive:– Trait that does NOT appear

• Law of Segregation:– A pair of factors is separated when eggs and

sperm are made

• Example—Sperm tall factor Egg short factor

Baby is…tall or short

WHY?????

• Law of Independent Assortment:– Factors are given to the gametes (?)

independently

• Allele:– New name for forms of a gene (Mendel’s

factors)– Use letters– CAPITAL LETTERS = dominant alleles– Lowercase letters = recessive alleles

For Example…

• Seed Color

• Green is dominant– G

• Yellow is recessive– g

• Genotype:– Genetic make-up– Ex: Gg

• Phenotype:– Appearance of an organism– Ex: Green

9.2

Genetic Crosses

• Homozygous:– Both alleles are alike– Homozygous dominant = TT = tall– Homozygous recessive = tt = short

• Heterozygous:– The two alleles are different– Tt = tall

• Probability:– How likely it is for something to occur– Often written in the form of a fraction

• Monohybrid cross:– A cross using one pair of traits– Ex: cross between a pure purple flowering

plant and a pure white flowering plant

How do you show a cross?

• Punnett Square:– A diagram to predict

how traits are inherited

P

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