Chapter 14 Flashcards
Why did Mendel choose to study inheritance using the pea plant model system?
- There are many varieties with distinct heritable features, or characters (such as flower color); character variants (such as purple or white flowers) are called traits.
- Mating can be controlled. This enabled Mendel to isolate and control variables and to produce observable results that he and others could duplicate.
- Each flower has a sperm-producing organs (stamens) and an egg-producing organ (carpel). Cross-pollination (fertilization between different plants) involves dusting one plant with pollen from another.
- Pea plants grow quickly and reproduce in about 90 days, which allowed him to quickly repeat the experiment as many times as he wants.
Explain the terms trait and variant.
a. Trait
i. Characteristic/character
ii. Ex: flower color
b. Variety
i. Variant/phenotype
ii. Ex: red flowers OR white flowers
What is the difference between self-pollination and cross-pollination?
a. self-pollinate: typical
i. if they SELF POLLINATE, only ever see ONE VARIETY for every trait
Mendel disproved the blending model of inheritance by obtaining data that supported a particulate model. If inheritance DID work by blending, what variants would one expect in the monohybrid crosses that followed seed shape and flower color traits, in the F1 and F2 generation pea plants?
• If inheritance did work by blending, the F1 and F2 generation pea plants would have flowers that are light purple in color. In regards to seed shape, the seeds would be wrinkled and round.
Explain the terms genotype and phenotype.
a. Phenotype
i. physical appearance of organism
ii. color variation
iii. result of genotype and environment
b. genotype
i. genetic makeup
ii. Dominant: two purple alleles, PP
iii. Recessive: two white alleles, pp
When is a genotype homozygous or heterozygous?
a. homozygous
i. having IDENTICAL alleles for a gene pair
ii. TRUE BREADING PARENTS
b. heterozygous
i. having DIFFERENT alleles for a gene pair
ii. HYBRID
What are alleles of a gene?
a. Alleles
i. Alternate versions
ii. Come from mutations
What is a dominant allele and what is a recessive allele?
a. DOMINANT ALLELES affect phenotype
i. Makes functional proteins
ii. Does not mean most common.
b. Recessive alleles encode defective proteins
How many alleles do most genes have?
most genes have more than 2 alleles
i. Ex: Blood Group Trait
1. 4 phenotypes: A, B, AB, O
2. 3 alleles: IA, IB, i
3. 6 genotypes
Incomplete Dominance
i. When heterozygotes shown an INTERMEDIATE phenotype between the homozygous genotypes.
ii. If genotypic ratio = phenotypic ratio then ID.
iii. Ex: flower color trait in snap dragons
Complete Dominance
occurs when phenotypes of the heterozygote and dominant homozygote are identical.
Explain how the heterozygotes of complete dominance are different from the heterozygotes of incomplete dominance.
In the heterozygotes of complete dominance, the trait expressed is the dominant allele. However, in heterozygotes of incomplete dominance, the result is a blend of the traits expressed from the alleles
How many alleles are present in the human population for the ABO blood group trait? Write out all of the possible genotypes and phenotypes. Then identify which allele is dominant and which allele is recessive, for every PAIR of alleles.
a. Blood group phenotypes
i. A,B,AB,O = sugar, oligosaccharide
b. THREE ALLELES
1. IA, IB, i alleles
c. Dominant v recessive
i. Type A
1. DOMIANT
ii. Type B
1. Dominant
iii. Type AB
1. Codominance
iv. Type O
1. Recessive
- What is meant by polygenic inheritance?
Polygenic inheritance is an additive effect of two or more genes on a single phenotypic character. Examples of human polygenic inheritance are height, skin color, eye color, and weight.
