biology study guide

what did gregor mendel experiment with

garden peas

2 hypotheses as to how traits were passed through generations

Blending inheritance and Inheritance of acquired characteristics

blending inheritance

children are a blend of their parents traits

Inheritance of acquired characteristics

traits are modified in the parents and passed to the children in modified form

trait

characteristic of an individual

heredity

transmission of traits from parents to offspring

genetics

inheritance of traits passed through generations

can peas self pollinate

yes

phenotype

visible characteristics

how many phenotypes does each trait have

2

hybrid

a mix of 2 different pure lines

why did mendel choose a common pea

• easy to grow

• produces lots of offspring

• short reproductive cycle

• he could control matings

• easily recognizable traits

how could mendel prevent self fertilization

by removing the male reproductive organs from the flower to allow cross fertilization using pollen from a different plant

Mendel chose 7 easily recognizable traits

1. Seed shape

2. Seed color

3. Pod shape

4. Pod color

5. Flower color

6. Flower and pod position

7. Stem length

adults

parental generation

offspring

F1 (first fillial)

genetic determinant for wrinkled seeds

recessive

genetic determinant for round seeds

dominant

particulate hypothesis

hereditary determinants maintain their integrity from generation to generation

what does the particular hypothesis contradict

blending inheritance and inherently acquired characteristics

does it matter which parent has the recessive trait

no

in a cross between round seeds and wrinkled seeds

the F1 generation was round seeds

what happened when mendel allowed the seeds to self pollinate

the wrinkled seed trait reappeared in the F2 generation in ¼ of the plants

ratio of dominant vs recessive in F2 generation

3:1

gene

hereditary determinants

allele

different versions of a gene

genotype

alleles in an individual

uppercase A

dominant trait

lowercase a

recessive trait

homozygous

2 copies of the same allele (AA or aa)

heterozygous

2 different copies of different alleles (Aa)

monohybrid cross

mating between parents that are both heterozygous

punnet square

predicts the genotype and phenotype of the offspring from a cross

Mendel's genetic model

hypotheses explaining how a trait is inherited. Explains the results if a cross between 2 pure lines

dihybrid cross

matings between parents that are both heterozygous for 2 traits

why did mendel use dihybrid crosses

to see if the principle of segregation is true if parents differ in more than 1 trait

Principle of independent assortment

alleles of different genes are transmitted independently of each other

does mendels results support the principle of independent assortment

yes with phenotypes of f2 offspring from dihybrid cross

Pleiotropic

a single gene that influences many traits rather than just one

Phenotypic affects of marfan syndrome

1. Increased height

2. Disproportionately long limbs and fingers

3. Abnormally shaped chest

4. Heart problems

why did mendel control the physical environment of his plants

to be sure that it did not affect phenotype when he studied plant height

what are phenotypes influenced by

physical environment

Phenylketonuria (PKU)

phenylalanine accumulates in the body and results in poor development of the nervous system and mental retardation. should be on a low phenylalanine diet

Epistasis

one gene affects the action of another gene by masking or reducing the affects of alleles

how are mitochondrial and chloroplast genomes typically transmitted to offspring

by the mother

Polygenic inheritance

each gene adds a small amount to the value of the phenotype

Quantitative traits

Traits that are not discrete but fall into a continuum

what type of traits did mendel work with

discrete traits

are there intermediate phenotypes in garden peas

no. only yellow and green

what do the frequencies of different values for a quantitative trait form

a bell curve

what are quantitative traits produced by

the actions of many genes

pedigree

family trees used to analyze the human crosses that already exist

To analyze the inheritance of a trait that shows discrete variation, biologists assume the simplest case

1. That a simple autosomal gene is involved

2. The alleles present in the population have a simple dominant recessive relationship

If a phenotype results from an autosomal recessive allele...

the individuals with the trait must be homozygous and the parents are heterozygous carriers

If a trait is autosomal dominant...

individuals who are homozygous or heterozygous for the trait will display the dominant phenotype

huntingtons disease

dominant defect, people whos parents have it will definitely get it

Autosomal trait

appears equally often in males and females

x linked dominant traits

• rarely skip generations

• affected male has affected daughters and unaffected sons

• Hypophosphatemia (vitamin d-resistant rickets)

X linked recessive diseases

• skip generations

• more in males than females

another example of an x linked trait resulting from a recessive allele

hemophilia

theory of inheritance

mendels rules can be explained by independent alignment and separation of homologous chromosomes at meiosis 1

Who founded the chromosome theory of inheritance

sutton and boveri

Principle of segregation

alleles encoding a specific trait segregate randomly into different daughter cells during meiosis

Why do genes for different traits assort independently

they are located on different nonhomologous chromosomes

model organism for genetic research

fruit flies

why are fruit flies the model organism

• short generation time (2 weeks)

• many of their genes have more than 1 version

• easily identifiable phenotypes

wild type

individuals with most common phenotypes

mutations

some gene has changed and become different from the wild type

what color eyes does the wild type fruit fly have

red

what color does the mutant type fruit fly have

white

What was the association of fruit flies

sex of the fly and eye color

What does the small y chromosome pair with

large X

female beetles

diploid cells contain 20 large chromosomes (xx)

male beetles

diploid cells have 19 large chromosomes and 1 small one (xy)

female

xx

male

xy

Hypothesis of x linked inheritance

the gene for white eyes resides on the x chromosome, and the y chromosome does not carry an allele for this gene

Sex linked inheritance

various inheritance patterns occur when genes are carried on the sex chromosomes (females and males have different numbers of alleles of that gene)

autosomes

non sex chromosomes

What do the genes on autosomes show

autosomal inheritance

linkage

the physical association of genes on the same chromosome

if chromsomes are sex linked

it makes up part of a sex chromosome

recombination

when the combination of alleles of the chromosome of progeny is different from the combinations of alleles present in the parental generation

Can the location of genes be mapped

yes

independent genes

genes that are 50+ map units apart on the same chromosome, can assort independently

multiple allelism

genes with more than 2 alleles

beta globin

component of hemoglobin that contains 500+ alleles

incomplete dominance

heterozygotes have an intermediate phenotype

codominance

heterozygous organism that has the phenotype of both alleles of a single gene. Neither allele is dominant or recessive to the other

fitness

the ability to produce offspring in a particular environment

Do dominance relationships have anything to do with fitness

no

what violates the principle of assortment?

linked genes

result of incomplete dominance

polymorphism

polymorphism

heterozygotes have unique phenotype. more than 2 phenotypes associated with a single gene are present

codominance

heterozygotes have phenotype of both alleles

gene by gene interaction

phenotype associated with an allele depends on which alleles are present at another gene

gene by environment interaction

phenotype influenced by environment experienced by an individual

example of autosomal recessive trait

sickle cell diseases

Hypothesis of the 20th century

genes were made of proteins