ch. 14 and 15: mendelian genetics

Blending inheritance

traits from the mother and from the father literally mix together in the offspring, perhaps from the semen of the father mixing with the blood of the mother to form the blood of the offspring

What did people believe about genetics before Mendel’s discovery?

blending inheritance

What does “P” symbolize?

parental generation

Parental generation

the original parents of a genetic cross

What does “F1” symbolize?

filial one

Filial one

the first generation of offspring in a genetics cross

What does “F2” symbolize?

filial two

Filial two

the second generation of offspring in a genetics cross

Is the blending theory true or false?

false

Why is the blending theory false?

genes are particulate (solids not liquids) and that particle is DNA

Alleles

versions of a gene

How many copies of each gene do organisms inherit from their parents?

two copies of each gene, one from each parent

Genotype

the genetic makeup of a cell or organism

Phenotype

the physical makeup of a cell or organism

Homozygous

a cell or organism with two identical alleles for a particular trait

Heterozygous

a cell or organism with two different alleles for a particular trait

Is Bb an example of a genotype or phenotype?

genotype

Is dark brown an example of a genotype or phenotype?

phenotype

Law of segregation

a heterozygote will pass on either allele with an equal 50/50 chance

How was Mendel able to make his discoveries?

Used pure-breeding and self-fertilizing peas with contrasting traits

What was the importance of using pure-breeding peas?

peas of one phenotype that always gave that same phenotype in their offspring when bred together

What was the importance of having contrasting pea traits?

each pea plant was one of two phenotypes with no “in between” types

What was the importance of using self-fertilizing peas?

mendel could cross one plant with itself instead of needing two plants to breed together

Dominant allele

expressed in the phenotype of a heterozygote

How are dominant alleles represented?

an upper case letter

Recessive allele

not expressed in the phenotype of a heterozygote

How are recessive alleles represented?

a lower case letter

What did Mendel use for his first genetics cross?

yellow peas x green peas

What phenotype did Mendel observe from F1 of his first genetics cross?

all yellow peas

What phenotype did Mendel observe from F2 of his first genetics cross?

6,022 yellow peas and 2,001 green peas

True or false: Dominant allele does not mean it is more common.

true

True or false: Dominant allele means it is better or healthier.

false

True or false: Dominant allele does not mean it is more likely to be inherited.

true

Incomplete dominance

the phenotype of a heterozygote is inbetween the phenotypes of the two homozygotes

Multiple alleles

many genes have more than two alleles in a population

What are the 3 alleles of the human blood group?

A=I^a, B=I^B, O=i

What are the 4 blood types and their genotypes?

Type A (AA or AO), Type B (BB or BO), Type AB (AB), and Type O (OO)

X-linked/sex-linked traits

genes found on the X chromosome

How many copies of x-linked/sex-linked traits do females have?

two copies of these genes (XX)

How many copies of x-linked/sex-linked traits do males have?

one copy of these genes (XY)

Law of Independent Assortment

inheritance of alleles from one gene does not affect the inheritance of alleles from other genes

What is an exception to the law of independent assortment?

linked genes

Linked genes

two genes close together on the same chromosome will usually be inherited together

Polygenic traits

traits with many genes effecting the same phenotype

Epistasis

expression of one gene effects the expression of a second gene

Complex traits

traits that are affected by many genes and many environmental influences and sometimes development influences

How did a trait come about if it is complicated to answer nature or nurture?

both nature and nurture, complex trait

What 5 things did Mendel conclude from his genetic cross experiments?

genes are particulate, blending theory of inheritance is false, organisms inherit one copy of each gene from each parent, law of segregation, law of independent assortment