CHAPTER 9

Question 1

How did Gregor Mendel use the scientific method to study inheritance in pea plants?

Answer 1

SCIENTIFIC METHOD
-Observe the variations of plants
-Experiment → controlled matings with two different “true-breeding”(plant only makes one type of flower; also known as homozygous) varieties
-Looked at the results of the offsprings (F1 generation)
-Let the F1 plants cross or self fertilize
-Then he looked at the results of the F2 generation
-Results of what we called mendel’s MONOhybrid cross (one trait; true breeding: parents are homozygous) → results always ended up being the same
-P generation: cross a plant that only make purple flowers with a plant that only make white flowers
-Produces F1 generation which only made purple flowers
-After F1 cross/self fertilize the F2 generation had 3 purple flowers for every 1 white flowers
-Conclusions → the purple trait is dominant (meaning that’s the on you see the most of) and the white trait is recessive
-He got this result of every trait he did this experiment for

Question 2

What were Mendel’s four hypotheses?

Answer 2

1. Alternate forms of the same gene = alleles
2. For each trait, inherit 2 alleles, one from each parent
3. If 2 different alleles are inherited, dominant one, shows physical appearance
4. Allele pair separate during production of gametes = meisois

Question 3

What are alleles?

Answer 3

Different forms of the same gene

Question 4

What are homologous chromosomes?

Answer 4

Matching pair of chromosomes, one from each parent, carrying different versions of the same genes (meaning one might be dominant one might be recessive)

Question 5

What is homozygous dominant?

Answer 5

Two identical dominant pairs of alleles

Question 6

What is homozygous recessive?

Answer 6

Two identical recessive pairs of alleles

Question 7

What is heterozygous?

Answer 7

Two different alleles

Question 8

Mendel’s Law of Independent Assortment (a dihybrid cross): describe predicted results of Punnett square as a phenotypic ratio

Answer 8

9:3:3:1 ratio

Question 9

Define Incomplete Dominance

Answer 9

Mixing of traits through the offspring of a heterozygous (Aa) intermediate trait

Question 10

Describe incomplete dominance: red and white snapdragons

Answer 10

If offspring is heterozygous (Aa), it shows an intermediate trait (blending of colors)
-pink snapdragon

Question 11

Describe co-dominance: human blood types

Answer 11

Gene controlling ABO blood has 3 alleles
- 2 alleles are codominant (IA, IB), 3rd allele is recessive (i)
genotypes: (IA, IB, i)
Phenotypes: blood types -> A, B, AB, O

Question 12

Describe polygenic inheritance and give examples.

Answer 12

Traits controlled by many genes, the phenotype is determined by the genotype and environmental factors
EX: Skin color -> at least 3 genes that are all incomplete dominance

Question 13

How may environmental factors influence phenotype in polygenic traits?

Answer 13

Nature vs Nurture

Question 14

How is sex determined in humans (XX, XY sex chromosomes)?

Answer 14

-X chromosome is very large vs. Y chromosome
- Most genes on X chromosome are not found in Y chromosome
XY -> male
XX -> female

Question 15

Know how to use Punnett squares for sex-linked traits: red-green colorblindness and hemophilia in humans.